全文获取类型
收费全文 | 6650篇 |
免费 | 488篇 |
国内免费 | 1篇 |
学科分类
生物科学 | 7139篇 |
出版年
2023年 | 41篇 |
2022年 | 59篇 |
2021年 | 195篇 |
2020年 | 111篇 |
2019年 | 138篇 |
2018年 | 187篇 |
2017年 | 157篇 |
2016年 | 259篇 |
2015年 | 353篇 |
2014年 | 380篇 |
2013年 | 494篇 |
2012年 | 560篇 |
2011年 | 582篇 |
2010年 | 377篇 |
2009年 | 311篇 |
2008年 | 385篇 |
2007年 | 424篇 |
2006年 | 340篇 |
2005年 | 297篇 |
2004年 | 306篇 |
2003年 | 279篇 |
2002年 | 223篇 |
2001年 | 58篇 |
2000年 | 53篇 |
1999年 | 61篇 |
1998年 | 65篇 |
1997年 | 49篇 |
1996年 | 48篇 |
1995年 | 37篇 |
1994年 | 25篇 |
1993年 | 22篇 |
1992年 | 27篇 |
1991年 | 24篇 |
1990年 | 22篇 |
1989年 | 17篇 |
1988年 | 15篇 |
1987年 | 9篇 |
1986年 | 7篇 |
1985年 | 9篇 |
1984年 | 13篇 |
1983年 | 12篇 |
1982年 | 8篇 |
1981年 | 12篇 |
1979年 | 6篇 |
1978年 | 9篇 |
1976年 | 5篇 |
1973年 | 7篇 |
1971年 | 7篇 |
1969年 | 4篇 |
1935年 | 4篇 |
排序方式: 共有7139条查询结果,搜索用时 483 毫秒
41.
Over a period of 7 years the biology and phenotypic variability of Chusquea culeou were studied at 5 locations in cool temperate forests of southern Argentina. Excavated rhizomes had an average of 1.1 successful rhizome buds, and an average of 2.1 years elapsed between successive generations of rhizomes. Rhizome buds usually develop within the first four years after a rhizome forms. Height, volume and weight of a culm can be calculated from its diameter 1 m above the ground. Culm size, length of foliage leaf blades, and pattern of secondary branching differed among study sites. Dead culms were numerous and commonly remained erect for more than 7 years after dying. New culm shoots appear in spring and reach full size within a few months. Shoots can grow more than 9 cm/day. Less than half of the shoots survived a year; most were killed by moth larvae. Multiple primary branch buds emerge through the culm leaf sheaths in the second spring. The mean number of branch buds at mid-culm nodes varied between 34.8 and 81.5, and the mean number of primary branches was between 22.8 and 40.8. Number and length of branches, and number and length of foliage leaf blades at each node is related to the position of the node on a culm. Most branches grow about 3 cm and produce 1 to 3 foliage leaves annually. Foliage leaf blades generally live 2 years or more; few survive 6 years. Relative lengths of foliage leaf blades and their spacing along a branch permit recognition of annual cohorts.Both gregarious and sporadic flowering have been reported, and every year a few isolated plants flower and die. Length of the life cycle is unknown. Seedlings require up to 15 years to produce culms of mature size. Foliage branches may live more than 23 years, and culms may survive 33 years. Extensive loss of new shoots to predation suggests that gregarious flowering may be driven by a need to escape parasitism. C. culeou clumps expand slowly. Average annual rate of increase of the number of live culms in a clump was 4.6%. Methods of seed dispersal are undocumented. A dense stand of Chusquea culeou had an estimated phytomass of 179 tons/hectare (dry weight), 28% of which was underground. Net annual production was about 16 t/ha dry weight. 相似文献
42.
Luisa F. Fanjul Isabel Marrero F. Estevez J. Gonzalez J. Quintana Pino Santana C. M. Ruiz De Galarreta 《Journal of cellular physiology》1993,155(2):273-281
In the present investigation, a hCG sensitive glycosyl-phosphatidylinositol (GPI) was isolated from cultured rat granulosa cells obtained from the ovaries of diethylstilbestrol (DES) implanted immature rats. The inositol-phosphoglycan (IPG) moiety of the GPI-lipid contains galactose, glucosamine, and myoinositol as demonstrated by metabolic labelling of granulosa cells for different time periods (5–96 h) with [3H]galactose, [3H]glucosamine, or [3H]myoinositol and treatment of the purified [3H]GPI with phosphatidylinositol-specific phospholipase C. Labelling equilibrium of the GPI-lipid was achieved after 24 h ([3H]galactose and [3H]myoinositol) or 72 h ([3H]glucosamine) incubation, whereas incorporation of other labelled carbohydrates tested ([3H]galactosamine, [3H]mannose, and [3H]sorbitol) was negligible throughout the time period studied. The glucosamine C-1 appears to be linked through a glycosidic bond to the myoinositol molecule of the IPG moiety as revealed by the generation of phosphatidylinositol (PtdIns) after nitrous acid deamination of dual labelled ([3H]glucosamine/[14C]palmitate or [3H]glucosamine/[14C]myristate) glycosyl-phosphatidylinositol. To investigate the fatty acid composition of the diacylglycerol (DAG) backbone of the GPI, granulosa cells were also labelled (5–72 hr) with [14C]linoleate, [3H]myristate, [3H]-oleate, [3H]palmitate, or [3H]stearate and the radioactivity associated with the purified glycosyl-phosphatidylinositol determined. Incorporation of [3H]palmitate and [3H]myristate into the GPI-lipid peaked after 8 h and 24 h of labelling, respectively, and both fatty acids were partially released after PLA2 treatment of the dual labelled ([3H]glucosamine/[14C]palmitate or [3H]glucosamine/[14C]myristate) GPI. In parallel experiments no significant incorporation of labelled stearate, oleate, or linoleic acid into the DAG backbone of the glycosylphosphatidylinositol could be detected. Granulosa cells were also labelled with [3H]glucosamine in the presence of FSH (30 ng/ml), cholera toxin (1 μg/ml), or the membrane permeable cAMP analog (but)2 cAMP (1 mM). Time related increases in GPI-labelling were apparent after 48 h and reached a maximum level (3-, 5-, and 7-fold for FSH, CT, and (but)2 cAMP, respectively) after 72 h in culture. In another set of experiments, granulosa cells were labelled for 72 h with [3H]glucosamine in the presence of (but)2cAMP (1 mM), TPA (10?7 M), or combination thereof. The effect of treatment with the membrane permeable cAMP analog on GPI labelling was prevented in the presence of TPA, whereas no differences in [3H]GPI content could be observed in untreated granulosa cells or cells cultured in the presence of the protein kinase C-activating phorbol ester alone. In cells differentiated with FSH (30 ng/ml for 3 days) to induce LH receptors, treatment with hCG (100 ng/ml) induced a rapid (60 sec) and transient (5 min) decrease in the GPI content, whereas no efect of the hormone on undifferentiated granulosa cells could be observed. The rapid effect elicited by hCG on GPI content and turnover may be an early transduction mechanism involved in the biological effects of LH/hCG in differentiated granulosa cells. © 1993 Wiley-Liss, Inc. 相似文献
43.
Update on proliferation-associated antibodies applicable to formalin-fixed paraffin-embedded tissue and their clinical applications 总被引:8,自引:0,他引:8
Summary This review provides an update on proliferation-associated antibodies applicable to immunohistochemical techniques in formalin-fixed
paraffin-embedded tissue. New insights into proliferating cell nuclear antigen (PCNA) and antibodies to PCNA are presented.
The characterization of the protein recognized by the Ki-67 antibody has enabled production of a new range of antibodies (monoclonal
and polyclonal) which have immunostaining profiles similar to those of the original antibody. A new proliferation-associated
antibody, KiS1, is described. The clinical applications of antibodies to PCNA in human material are summarized, and the limitations
of these studies are discussed. 相似文献
44.
Estaras Matias Ortiz-Placin Candido Castillejo-Rufo Alba Fernandez-Bermejo Miguel Blanco Gerardo Mateos Jose M. Vara Daniel Gonzalez-Cordero Pedro L. Chamizo Sandra Lopez Diego Rojas Adela Jaen Isabel de Armas Noelia Salido Gines M. Iovanna Juan L. Santofimia-Castaño Patricia Gonzalez Antonio 《Journal of physiology and biochemistry》2023,79(1):235-249
Journal of Physiology and Biochemistry - We have investigated the effects of melatonin on major pathways related with cellular proliferation and energetic metabolism in pancreatic stellate cells.... 相似文献
45.
Andrew F. Feldman Daniel J. Short Gianotti Jianzhi Dong Isabel F. Trigo Guido D. Salvucci Dara Entekhabi 《Global Change Biology》2023,29(1):110-125
Vegetation cover creates competing effects on land surface temperature: it typically cools through enhancing energy dissipation and warms via decreasing surface albedo. Global vegetation has been previously found to overall net cool land surfaces with cooling contributions from temperate and tropical vegetation and warming contributions from boreal vegetation. Recent studies suggest that dryland vegetation across the tropics strongly contributes to this global net cooling feedback. However, observation-based vegetation-temperature interaction studies have been limited in the tropics, especially in their widespread drylands. Theoretical considerations also call into question the ability of dryland vegetation to strongly cool the surface under low water availability. Here, we use satellite observations to investigate how tropical vegetation cover influences the surface energy balance. We find that while increased vegetation cover would impart net cooling feedbacks across the tropics, net vegetal cooling effects are subdued in drylands. Using observations, we determine that dryland plants have less ability to cool the surface due to their cooling pathways being reduced by aridity, overall less efficient dissipation of turbulent energy, and their tendency to strongly increase solar radiation absorption. As a result, while proportional greening across the tropics would create an overall biophysical cooling feedback, dryland tropical vegetation reduces the overall tropical surface cooling magnitude by at least 14%, instead of enhancing cooling as suggested by previous global studies. 相似文献
46.
Opale Coutant Céline Jézéquel Karel Mokany Isabel Cantera Raphaël Covain Alice Valentini Tony Dejean Sébastien Brosse Jérôme Murienne 《Global Change Biology》2023,29(7):1741-1758
Freshwater ecosystems are among the most endangered ecosystem in the world. Understanding how human activities affect these ecosystems requires disentangling and quantifying the contribution of the factors driving community assembly. While it has been largely studied in temperate freshwaters, tropical ecosystems remain challenging to study due to the high species richness and the lack of knowledge on species distribution. Here, the use of eDNA-based fish inventories combined to a community-level modelling approach allowed depicting of assembly rules and quantifying the relative contribution of geographic, environmental and anthropic factors to fish assembly. We then used the model predictions to map spatial biodiversity and assess the representativity of sites surveyed in French Guiana within the EU Water Framework Directive (WFD) and highlighted areas that should host unique freshwater fish assemblages. We demonstrated a mismatch between the taxonomic and functional diversity. Taxonomic assemblages between but also within basins were mainly the results of dispersal limitation resulting from basin isolation and natural river barriers. Contrastingly, functional assemblages were ruled by environmental and anthropic factors. The regional mapping of fish diversity indicated that the sites surveyed within the EU WFD had a better representativity of the regional functional diversity than taxonomic diversity. Importantly, we also showed that the assemblages expected to be the most altered by anthropic factors were the most poorly represented in terms of functional diversity in the surveyed sites. The predictions of unique functional and taxonomic assemblages could, therefore, guide the establishment of new survey sites to increase fish diversity representativity and improve this monitoring program. 相似文献
47.
48.
Sabine Nöbel Antoine Jacquet Guillaume Isabel Arnaud Pocheville Paul Seabright Etienne Danchin 《Biological reviews of the Cambridge Philosophical Society》2023,98(1):132-149
Although conformity as a major driver for human cultural evolution is a well-accepted and intensely studied phenomenon, its importance for non-human animal culture has been largely overlooked until recently. This limited for decades the possibility of studying the roots of human culture. Here, we provide a historical review of the study of conformity in both humans and non-human animals. We identify gaps in knowledge and propose an evolutionary route towards the sophisticated cultural processes that characterize humanity. A landmark in the study of conformity is Solomon Asch's famous experiment on humans in 1955. By contrast, interest in conformity among evolutionary biologists has only become salient since the turn of the new millennium. A striking result of our review is that, although studies of conformity have examined many biological contexts, only one looked at mate choice. This is surprising because mate choice is probably the only context in which conformity has self-reinforcing advantages across generations. Within a metapopulation, i.e. a group of subpopulations connected by dispersing individuals, dispersers able to conform to the local preference for a given type of mate have a strong and multigenerational fitness advantage. This is because once females within one subpopulation locally show a bias for one type of males, immigrant females who do not conform to the local trend have sons, grandsons, etc. of the non-preferred phenotype, which negatively and cumulatively affects fitness over generations in a process reminiscent of the Fisher runaway process. This led us to suggest a sex-driven origin of conformity, indicating a possible evolutionary route towards animal and human culture that is rooted in the basic, and thus ancient, social constraints acting on mating preferences within a metapopulation. In a generic model, we show that dispersal among subpopulations within a metapopulation can effectively maintain independent Fisher runaway processes within subpopulations, while favouring the evolution of social learning and conformity at the metapopulation scale; both being essential for the evolution of long-lasting local traditions. The proposed evolutionary route to social learning and conformity casts surprising light on one of the major processes that much later participated in making us human. We further highlight several research avenues to define the spectrum of conformity better, and to account for its complexity. Future studies of conformity should incorporate experimental manipulation of group majority. We also encourage the study of potential links between conformity and mate copying, animal aggregations, and collective actions. Moreover, validation of the sex-driven origin of conformity will rest on the capacity of human and evolutionary sciences to investigate jointly the origin of social learning and conformity. This constitutes a stimulating common agenda and militates for a rapprochement between these two currently largely independent research areas. 相似文献
49.
Douglas Maciel Reisla Oliveira Paulo Enrique Cardoso Peixoto 《Ethology : formerly Zeitschrift fur Tierpsychologie》2023,129(2):99-106
Sexually selected traits, such as male weapons, are highly variable in shape and size across species. However, little is known about the mechanisms that may govern this variation. Because males with greater investment in weapon size tend to win more fights, but also pay higher costs related to weapon development and maintenance, larger weapons should be expected only in species in which victory in male–male fights generate reproductive benefits that outweigh investment costs. Here, we hypothesized that the reproductive characteristics that increase the chances of winners to access females or to fertilize eggs will favor the evolution of larger weapons. To evaluate this hypothesis, we conducted a meta-analysis using arthropods as model organisms. To measure investment in weapon size, we gathered both Pearson correlation coefficient and the standardized (but non centralized) slope values for the relationship between weapon size and body size. We found that none of the reproductive characteristics we investigated was related to male weapon size. Thus, it seems that greater certainty of accessing a female or fertilizing female eggs with a victory does not modulate the investment in male weapon size. Perhaps the cost–benefit ratio between weapon size investment and reproductive success is not the main factor driving the variation in weapon size. 相似文献
50.
Davide Scaccini Davide Bramuzzo Cengiz Bostancı Massimo Faccoli Isabel Martinez-Sañudo Alexey Matov Alberto Zilli Alberto Pozzebon 《Journal of Applied Entomology》2023,147(3):239-243
The Asian walnut moth, Garella musculana (Erschov, 1874) (Lepidoptera: Nolidae), is a major pest of walnut. Native to Central Asia, it was found to be invasive in 2008 in Sevastopol (Crimea) and nowadays widespread in Turkey, Bulgaria, Romania and Russia. Here, we account for the finding of G. musculana in NE Italy (Veneto region) in 2021, where adults were found in a light lamp, representing the first record of the Asian walnut moth for this country and Western Europe. Adult specimens were identified morphologically on both external characters and genitalia features. G. musculana larvae and damage were also observed on a plantation of Juglans regia L. (Fagales: Juglandaceae) located in Veneto in October 2021. A COI-barcoding analysis was performed to attain a molecular characterization of our specimens and probate our morphological identification. However, because no sequence of G. musculana was present in major gene databases and the similarity of our sequences with those attributed to Garella ruficirra (Hampson, 1905) (Lepidoptera: Nolidae) made clear that these taxa deserved further scrutiny regarding their specific distinction. Some subtle differences in the male terminalia could be found between them and their vast geographic distributions, but the strong similarity in most features calls for further morphological and genetical insights on a broad set of samples to assess whether they represent two closely related, substantially parapatric species, or a unique, geographically varying entity. Solving this issue may turn out crucial in the identification and proper management of walnut moths of the genus Garella. 相似文献