全文获取类型
收费全文 | 2419篇 |
免费 | 314篇 |
学科分类
生物科学 | 2733篇 |
出版年
2023年 | 31篇 |
2022年 | 35篇 |
2021年 | 71篇 |
2020年 | 66篇 |
2019年 | 63篇 |
2018年 | 119篇 |
2017年 | 132篇 |
2016年 | 113篇 |
2015年 | 146篇 |
2014年 | 148篇 |
2013年 | 266篇 |
2012年 | 261篇 |
2011年 | 261篇 |
2010年 | 214篇 |
2009年 | 133篇 |
2008年 | 80篇 |
2007年 | 55篇 |
2006年 | 51篇 |
2005年 | 29篇 |
2004年 | 33篇 |
2003年 | 23篇 |
2002年 | 25篇 |
2001年 | 19篇 |
2000年 | 25篇 |
1999年 | 19篇 |
1998年 | 12篇 |
1997年 | 12篇 |
1996年 | 14篇 |
1995年 | 13篇 |
1994年 | 13篇 |
1993年 | 20篇 |
1992年 | 20篇 |
1991年 | 15篇 |
1990年 | 12篇 |
1989年 | 24篇 |
1988年 | 15篇 |
1987年 | 8篇 |
1986年 | 13篇 |
1985年 | 6篇 |
1984年 | 11篇 |
1983年 | 5篇 |
1981年 | 7篇 |
1980年 | 8篇 |
1978年 | 7篇 |
1977年 | 7篇 |
1976年 | 6篇 |
1973年 | 10篇 |
1971年 | 4篇 |
1962年 | 8篇 |
1959年 | 4篇 |
排序方式: 共有2733条查询结果,搜索用时 31 毫秒
991.
Brenda Jessica Arriaga‐Osnaya Jorge Contreras‐Garduño Francisco Javier Espinosa‐García Yolanda Magdalena García‐Rodríguez Miguel Moreno‐García Humberto Lanz‐Mendoza Héctor Godínez‐Álvarez Raúl Cueva del Castillo 《Ecology and evolution》2017,7(9):3037-3045
Secondary sexual traits may convey reliable information about males’ ability to resist pathogens and that females may prefer those traits because their genes for resistance would be passed on to their offspring. In many insect species, large males have high mating success and can canalize more resources to the immune function than smaller males. In other species, males use pheromones to identify and attract conspecific mates, and thus, they might function as an honest indicator of a male's condition. The males of orchid bees do not produce pheromones. They collect and store flower volatiles, which are mixed with the volatile blends from other sources, like fungi, sap and resins. These blends are displayed as perfumes during the courtship. In this study, we explored the relationship between inter‐individual variation in body size and blend composition with the males’ phenoloxidase (PO) content in Euglossa imperialis. PO content is a common measure of insect immune response because melanine, its derived molecule, encapsulates parasites and pathogens. Body size and blend composition were related to bees’ phenolic PO content. The inter‐individual variation in body size and tibial contents could indicate differences among males in their skills to gain access to some compounds. The females may evaluate their potential mates through these compounds because some of them are reliable indicators of the males’ capacity to resist infections and parasites. 相似文献
992.
An Internet‐based platform for the estimation of outcrossing potential between cultivated and Chilean vascular plants 下载免费PDF全文
Pablo Cid Carlos Aguirre Miguel Ángel Sánchez Daniel Zamorano Maritza Mihoc Erika Salazar Gustavo Chacón Humberto Navarrete Marcelo Rosas Humberto Prieto 《Ecology and evolution》2017,7(8):2480-2488
A national‐scale study of outcrossing potential within Chilean vascular flora was conducted using an upgraded algorithm, which adds parameters such as pollinator agents, climate, and geographic conditions. Datasets were organized and linked in a Web platform ( www.flujogenico.cl ), in which the development of a total outcrossing potential (TOP) predictor was formulated. The TOP predictor is the engine in the Web platform, which models the effect of a type of agricultural practice on others (coexistence calculation mode) and on the environment (biodiversity calculation mode). The scale for TOP results uses quintiles in order to define outcrossing potential between species as “very low,” “low,” “medium,” “high,” or “very high.” In a coexistence analysis considering 256 species (207 genera), the 10 highest TOP values were for genera Citrus, Prunus, Trifolium, Brassica, Allium, Eucalyptus, Cucurbita, Solanum, Lollium, and Lotus. The highest TOP for species in this analysis fell at “high” potential, 4.9% of the determined values. In biodiversity mode, seven out of 256 cultivated species (2.7%) were native, and 249 (97.3%) corresponded to introduced species. The highest TOP was obtained in the genera Senecio, Calceolaria, Viola, Solanum, Poa, Alstroemeria, Valeriana, Vicia, Atriplex, and Campanula, showing “high” potential in 4.9% of the values. On the other hand, 137 genetically modified species, including the commercial and pre‐commercial developments, were included and represented 100 genera. Among these, 22 genera had relatives (i.e., members of the same genus) in the native/introduced group. The genera with the highest number of native/introduced relatives ranged from one (Ipomea, Limonium, Carica, Potentilla, Lotus, Castanea, and Daucus) to 66 species (Solanum). The highest TOP was obtained when the same species were coincident in both groups, such as for Carica chilensis, Prosopis tamarugo, and Solanum tuberosum. Results are discussed from the perspective of assessing the possible impact of cultivated species on Chilean flora biodiversity. The TOP predictor ( http://epc.agroinformatica.cl/ ) is useful in the context of environmental risk assessment. 相似文献
993.
Association of the Production of Phenylpropanoid Compounds at the Infection Sites of Corynespora cassiicola with Soybean Resistance against Target Spot 下载免费PDF全文
Alessandro Antônio Fortunato Leonardo Araujo Fabrício Ávila Rodrigues 《Journal of Phytopathology》2017,165(2):131-142
This study investigated, at the microscopic level, whether the differential defence responses of soybean cultivars that are resistant (Fundacep 59) and susceptible (TMG 132) to target spot, caused by Corynespora cassiicola, could be associated with an increase in the production of phenolics, flavonoids and lignin at the infection sites. Many larger necrotic lesions with yellow halos were noticed on the leaves of plants from cultivar TMG 132, in contrast to the leaves of plants from cultivar Fundacep 59. Necrotic lesions also developed on the petioles of leaves of plants from cultivar TMG 132, while on the petioles and veins of leaves of plants from cultivar Fundacep 59, the lesions were of purple colour. The growth of fungal hyphae was reduced on the leaves of plants from cultivar Fundacep 59, and an apparently high density of trichomes was found in comparison with the leaves of plants from cultivar TMG 132. An appressorium‐like structure was produced at one or both extremities of the conidium of C. cassiicola, preferentially at the major and minor veins on the adaxial leaf surface of plants from both cultivars. Most cells on the leaves of plants from cultivar Fundacep 59 reacted against C. cassiicola infection by accumulating phenolic‐like compounds, which contributed to the death of many fungal hyphae and a greater maintenance of cell integrity. In contrast, fungal hyphae grew without any impedance in the leaf cells of plants from cultivar TMG 132, which was associated with signs of intense leaf tissue disorganization. Stronger autofluorescence and deposition of lignin and flavonoids were found in the cells of leaves of plants from cultivar Fundacep 59, in contrast to cultivar TMG 132. It can be concluded that soybean resistance to target spot is probably dependent on the activation of the phenylpropanoid pathway. 相似文献
994.
J. Alcalá-Gómez M. Fernández-Ruvalcaba C. Ángel-Sahagún I. Vitela-Mendoza M. Ramos-Parra 《Biocontrol Science and Technology》2017,27(8):931-939
The aim of the study was to assess the virulence of five Metarhizium anisopliae (Ma) and three of Beauveria bassiana (Bb) isolates, and the effect of the fungal infection to the reproduction of engorged females from two colonies of Rhiphicephalus microplus; one colony was collected from naturally infested cattle (Native) and the other one from a laboratory colony (Media Joya). Virulence was evaluated using the immersion technique at a concentration of 1?×?108 conidia/ml; control groups received a water suspension with Tween 80 (0.1%). The Reproductive Efficiency Index ‘REI’ (eggs laid/engorged female weight) and the Reproductive Aptitude Index ‘RAI’ (eggs hatched as larvae/engorged female weight) were calculated for both groups. This experiment shows that two entomopathogenic fungal isolates, Bb115 and Ma136, caused high mortality from 5 days post-treatment (PT), reaching mortality rates of 99–100% at 15 days PT in both R. microplus colonies. The Bb115 isolate caused 98 and 79% reduction in egg oviposition in the field and laboratory colonies, respectively, while the reduction in egg hatchability was 98 and 89% in the field and laboratories colonies, respectively. In the case of Ma136, the egg oviposition was reduced in 73% in the field colony and 64% in laboratory colony, while in the field and laboratory colonies, with a reduction in egg hatchability of 73% and 86%, respectively. These results indicate the potential of Bb115 and Ma136 isolates as possible biological control agents of R. microplus. 相似文献
995.
Sonia Martínez González Sonsoles Rodríguez-Arístegui Ana Isabel Hernández Carmen Varela Esther González Cantalapiedra Rosa María Álvarez Antonio Rodríguez Hergueta James R. Bischoff María Isabel Albarrán Antonio Cebriá Elena Cendón David Cebrián Patricia Alfonso Joaquín Pastor 《Bioorganic & medicinal chemistry letters》2017,27(11):2536-2543
996.
Oligomerization domains in the glycan‐binding receptors DC‐SIGN and DC‐SIGNR: Sequence variation and stability differences 下载免费PDF全文
Ália dos Santos Andreas Hadjivasiliou Felipe Ossa Novandy K. Lim Aylin Turgut Maureen E. Taylor Kurt Drickamer 《Protein science : a publication of the Protein Society》2017,26(2):306-316
Human dendritic cell‐specific intercellular adhesion molecule‐1 grabbing nonintegrin, DC‐SIGN, and the sinusoidal endothelial cell receptor DC‐SIGNR or L‐SIGN, are closely related sugar‐binding receptors. DC‐SIGN acts both as a pathogen‐binding endocytic receptor and as a cell adhesion molecule, while DC‐SIGNR has only the pathogen‐binding function. In addition to differences in the sugar‐binding properties of the carbohydrate‐recognition domains in the two receptors, there are sequence differences in the adjacent neck domains, which are coiled‐coil tetramerization domains comprised largely of 23‐amino acid repeat units. A series of model polypeptides consisting of uniform repeat units have been characterized by gel filtration, differential scanning calorimetry and circular dichroism. The results demonstrate that two features characterize repeat units which form more stable tetramers: a leucine reside in the first position of the heptad pattern of hydrophobic residues that pack on the inside of the coiled coil and an arginine residue on the surface of the coiled coil that forms a salt bridge with a glutamic acid residue in the same polypeptide chain. In DC‐SIGNR from all primates, very stable repeat units predominate, so the carbohydrate‐recognition domains must be held relatively closely together. In contrast, stable repeat units are found only near the membrane in DC‐SIGN. The presence of residues that disrupt tetramer formation in repeat units near the carbohydrate‐recognition domains of DC‐SIGN would allow these domains to splay further apart. Thus, the neck domains of DC‐SIGN and DC‐SIGNR can contribute to the different functions of these receptors by presenting the sugar‐binding sites in different contexts. 相似文献
997.
Plant traits determine the phylogenetic structure of arbuscular mycorrhizal fungal communities 总被引:1,自引:0,他引:1 下载免费PDF全文
Álvaro López‐García Sara Varela‐Cervero Martti Vasar Maarja Öpik José M. Barea Concepción Azcón‐Aguilar 《Molecular ecology》2017,26(24):6948-6959
Functional diversity in ecosystems has traditionally been studied using aboveground plant traits. Despite the known effect of plant traits on the microbial community composition, their effects on the microbial functional diversity are only starting to be assessed. In this study, the phylogenetic structure of arbuscular mycorrhizal (AM) fungal communities associated with plant species differing in life cycle and growth form, that is, plant life forms, was determined to unravel the effect of plant traits on the functional diversity of this fungal group. The results of the 454 pyrosequencing showed that the AM fungal community composition differed across plant life forms and this effect was dependent on the soil collection date. Plants with ruderal characteristics tended to associate with phylogenetically clustered AM fungal communities. By contrast, plants with resource‐conservative traits associated with phylogenetically overdispersed AM fungal communities. Additionally, the soil collected in different seasons yielded AM fungal communities with different phylogenetic dispersion. In summary, we found that the phylogenetic structure, and hence the functional diversity, of AM fungal communities is dependent on plant traits. This finding adds value to the use of plant traits for the evaluation of belowground ecosystem diversity, functions and processes. 相似文献
998.
Genetic favouring of pheomelanin‐based pigmentation limits physiological benefits of coloniality in lesser kestrels Falco naumanni 下载免费PDF全文
Ismael Galván Virginia Moraleda Ignacio Otero Ernesto Álvarez Ângela Inácio 《Molecular ecology》2017,26(20):5594-5602
Pheomelanin contributes to the pigmentation phenotype of animals by producing orange and light brown colours in the integument. However, pheomelanin synthesis in melanocytes requires consumption of glutathione (GSH), the most important intracellular antioxidant. Therefore, a genetic control favouring the production of large amounts of pheomelanin for pigmentation may lead to physiological costs under environmental conditions that promote oxidative stress. We investigated this possibility in the context of breeding coloniality, a reproductive strategy that may affect oxidative stress. We found in lesser kestrel Falco naumanni nestlings that the GSH:GSSG ratio, which decreases with systemic oxidative stress, increased with the size of the colony where they were reared, but the expression in feather melanocytes of five genes involved in pheomelanin synthesis (Slc7a11, Slc45a2, CTNS, MC1R and AGRP) did not vary with colony size. The antioxidant capacity (TEAC) of lesser kestrel nestlings also increased with colony size, but in a manner that depended on Slc7a11 expression and not on the expression of the other genes. Thus, antioxidant capacity increased with colony size only in nestlings least expressing Slc7a11, a gene with a known role in mediating cysteine (a constituent amino acid of GSH) consumption for pheomelanin production. The main predictor of the intensity of pheomelanin‐based feather colour was Slc45a2 expression followed in importance by Slc7a11 expression, hence suggesting that the genetic regulation of the pigmentation phenotype mediated by Slc7a11 and a lack of epigenetic lability in this gene limits birds from benefiting from the physiological benefits of coloniality. 相似文献
999.
Phenotypic characteristics of aged CD4+ CD28null T lymphocytes are determined by changes in the whole‐genome DNA methylation pattern 下载免费PDF全文
Beatriz Suarez‐Álvarez Ramón M. Rodríguez Karin Schlangen Aroa Baragaño Raneros Leonardo Márquez‐Kisinousky Agustín F. Fernández Carmen Díaz‐Corte Ana M. Aransay Carlos López‐Larrea 《Aging cell》2017,16(2):293-303
Aging is associated with a progressive loss of the CD28 costimulatory molecule in CD4+ lymphocytes (CD28null T cells), which is accompanied by the acquisition of new biological and functional properties that give rise to an impaired immune response. The regulatory mechanisms that govern the appearance and function of this cell subset during aging and in several associated inflammatory disorders remain controversial. Here, we present the whole‐genome DNA methylation and gene expression profiles of CD28null T cells and its CD28+ counterpart. A comparative analysis revealed that 296 genes are differentially methylated between the two cell subsets. A total of 160 genes associated with cytotoxicity (e.g. GRZB, TYROBP, and RUNX3) and cytokine/chemokine signaling (e.g. CX3CR1, CD27, and IL‐1R) are demethylated in CD28null T cells, while 136 de novo‐methylated genes matched defects in the TCR signaling pathway (e.g. ITK, TXK, CD3G, and LCK). TCR‐landscape analysis confirmed that CD28null T cells have an oligo/monoclonal expansion over the polyclonal background of CD28+ T cells, but feature a Vβ family repertoire specific to each individual. We reported that CD28null T cells show a preactivation state characterized by a higher level of expression of inflammasome‐related genes that leads to the release of IL‐1β when activated. Overall, our results demonstrate that CD28null T cells have a unique DNA methylation landscape, which is associated with differences in gene expression, contributing to the functionality of these cells. Understanding these epigenetic regulatory mechanisms could suggest novel therapeutic strategies to prevent the accumulation and activation of these cells during aging. 相似文献
1000.
C. Corral-Vázquez R. Aguilar-Quesada P. Catalina G. Lucena-Aguilar G. Ligero B. Miranda J. A. Carrillo-Ávila 《Cell and tissue banking》2017,18(2):271-280
Establishment of continuous cell lines from human normal and tumor tissues is an extended and useful methodology for molecular characterization of cancer pathophysiology and drug development in research laboratories. The exchange of these cell lines between different labs is a common practice that can compromise assays reliability due to contamination with microorganism such as mycoplasma or cells from different flasks that compromise experiment reproducibility and reliability. Great proportions of cell lines are contaminated with mycoplasma and/or are replaced by cells derived for a different origin during processing or distribution process. The scientific community has underestimated this problem and thousand of research experiment has been done with cell lines that are incorrectly identified and wrong scientific conclusions have been published. Regular contamination and authentication tests are necessary in order to avoid negative consequences of widespread misidentified and contaminated cell lines. Cell banks generate, store and distribute cell lines for research, being mandatory a consistent and continuous quality program. Methods implementation for guaranteeing both, the absence of mycoplasma and authentication in the supplied cell lines, has been performed in the Andalusian Health System Biobank. Specifically, precise results were obtained using real time PCR detection for mycoplasma and 10 STRs identification by capillary electrophoresis for cell line authentication. Advantages and disadvantages of these protocols are discussed. 相似文献