全文获取类型
收费全文 | 1612篇 |
免费 | 164篇 |
学科分类
生物科学 | 1776篇 |
出版年
2023年 | 16篇 |
2022年 | 16篇 |
2021年 | 59篇 |
2020年 | 27篇 |
2019年 | 32篇 |
2018年 | 37篇 |
2017年 | 27篇 |
2016年 | 45篇 |
2015年 | 88篇 |
2014年 | 90篇 |
2013年 | 98篇 |
2012年 | 111篇 |
2011年 | 91篇 |
2010年 | 62篇 |
2009年 | 77篇 |
2008年 | 77篇 |
2007年 | 86篇 |
2006年 | 76篇 |
2005年 | 54篇 |
2004年 | 63篇 |
2003年 | 52篇 |
2002年 | 40篇 |
2001年 | 43篇 |
2000年 | 39篇 |
1999年 | 29篇 |
1998年 | 18篇 |
1997年 | 12篇 |
1996年 | 14篇 |
1995年 | 12篇 |
1994年 | 15篇 |
1992年 | 17篇 |
1991年 | 21篇 |
1990年 | 23篇 |
1989年 | 20篇 |
1988年 | 32篇 |
1987年 | 16篇 |
1986年 | 14篇 |
1985年 | 14篇 |
1983年 | 5篇 |
1982年 | 11篇 |
1979年 | 15篇 |
1977年 | 11篇 |
1976年 | 4篇 |
1975年 | 7篇 |
1974年 | 7篇 |
1973年 | 8篇 |
1972年 | 4篇 |
1971年 | 4篇 |
1969年 | 5篇 |
1967年 | 5篇 |
排序方式: 共有1776条查询结果,搜索用时 15 毫秒
91.
92.
93.
Soil Solution Chemistry and Element Fluxes in Three European Heathlands and Their Responses to Warming and Drought 总被引:4,自引:0,他引:4
Inger K.?SchmidtEmail author Albert?Tietema Dylan?Williams Per?Gundersen Claus?Beier Bridget A.?Emmett Marc?Estiarte 《Ecosystems》2004,7(6):638-649
Soil water chemistry and element budgets were studied at three northwestern European Calluna vulgaris heathland sites in Denmark (DK), The Netherlands (NL), and Wales (UK). Responses to experimental nighttime warming and early summer drought were followed during a two-year period. Soil solution chemistry measured below the organic soil layer and below the rooting zone and water fluxes estimated with hydrological models were combined to calculate element budgets. Remarkably high N leaching was observed at the NL heath with 18 and 6.4 kg N ha–1 year–1 of NO3–N and NH4–N leached from the control plots, respectively, indicating that this site is nitrogen saturated. Increased soil temperature of +0.5°C in the heated plots almost doubled the concentrations and losses of NO3–N and DON at this site. Temperature also increased mobilization of N in the O horizon at the UK and DK heaths in the first year, but, because of high retention of N in the vegetation or mineral soil, there were no significant effects of warming on seepage water NO3–N and NH4–N. Retention of P was high at all three sites. In several cases, drought increased concentrations of elements momentarily, but element fluxes decreased because of a lower flux of water. Seepage water DOC and DON was highly significantly correlated at the UK site where losses of N were low, whereas losses of C and N were uncoupled at the NL site where atmospheric N input was greatest. Based on N budgets, calculations of the net change in the C sink or source strength in response to warming suggest no change or an increase in the C sink strength during these early years. 相似文献
94.
Strader MB Verberkmoes NC Tabb DL Connelly HM Barton JW Bruce BD Pelletier DA Davison BH Hettich RL Larimer FW Hurst GB 《Journal of proteome research》2004,3(5):965-978
We present a comprehensive mass spectrometric approach that integrates intact protein molecular mass measurement ("top-down") and proteolytic fragment identification ("bottom-up") to characterize the 70S ribosome from Rhodopseudomonas palustris. Forty-two intact protein identifications were obtained by the top-down approach and 53 out of the 54 orthologs to Escherichia coli ribosomal proteins were identified from bottom-up analysis. This integrated approach simplified the assignment of post-translational modifications by increasing the confidence of identifications, distinguishing between isoforms, and identifying the amino acid positions at which particular post-translational modifications occurred. Our combined mass spectrometry data also allowed us to check and validate the gene annotations for three ribosomal proteins predicted to possess extended C-termini. In particular, we identified a highly repetitive C-terminal "alanine tail" on L25. This type of low complexity sequence, common to eukaryotic proteins, has previously not been reported in prokaryotic proteins. To our knowledge, this is the most comprehensive protein complex analysis to date that integrates two MS techniques. 相似文献
95.
Pelletier L Ozlü N Hannak E Cowan C Habermann B Ruer M Müller-Reichert T Hyman AA 《Current biology : CB》2004,14(10):863-873
BACKGROUND: The centrosome is composed of a centriole pair and pericentriolar material (PCM). By marking the site of PCM assembly, the centrioles define the number of centrosomes present in the cell. The PCM, in turn, is responsible for the microtubule (MT) nucleation activity of centrosomes. Therefore, in order to assemble a functional bipolar mitotic spindle, a cell needs to control both centriole duplication and PCM recruitment. To date, however, the molecular mechanisms that govern these two processes still remain poorly understood. RESULTS: Here we show that SPD-2 is a novel component of the C. elegans centrosome. SPD-2 localizes to the centriole throughout the cell cycle and accumulates on the PCM during mitosis. We show that SPD-2 requires SPD-5 for its accumulation on the PCM and that in the absence of SPD-2, centrosome assembly fails. We further show that centriole duplication is also defective in spd-2(RNAi) embryos, but not in spd-5(RNAi) embryos, where PCM recruitment is efficiently blocked. CONCLUSIONS: Taken together, our results suggest that SPD-2 may link PCM recruitment and centriole duplication in C. elegans. SPD-2 shares homology with a human centrosome protein, suggesting that this key component of the C. elegans centrosome is evolutionarily conserved. 相似文献
96.
97.
HLM1, an essential signaling component in the hypersensitive response,is a member of the cyclic nucleotide-gated channel ion channel family 总被引:3,自引:0,他引:3 下载免费PDF全文
Balagué C Lin B Alcon C Flottes G Malmström S Köhler C Neuhaus G Pelletier G Gaymard F Roby D 《The Plant cell》2003,15(2):365-379
The hypersensitive response (HR) in plants is a programmed cell death that is commonly associated with disease resistance. A novel mutation in Arabidopsis, hlm1, which causes aberrant regulation of cell death, manifested by a lesion-mimic phenotype and an altered HR, segregated as a single recessive allele. Broad-spectrum defense mechanisms remained functional or were constitutive in the mutant plants, which also exhibited increased resistance to a virulent strain of Pseudomonas syringae pv tomato. In response to avirulent strains of the same pathogen, the hlm1 mutant showed differential abilities to restrict bacterial growth, depending on the avirulence gene expressed by the pathogen. The HLM1 gene encodes a cyclic nucleotide-gated channel, CNGC4. Preliminary study of the HLM1/CNGC4 gene pro-duct in Xenopus oocytes (inside-out patch-clamp technique) showed that CNGC4 is permeable to both K(+) and Na(+) and is activated by both cGMP and cAMP. HLM1 gene expression is induced in response to pathogen infection and some pathogen-related signals. Thus, HLM1 might constitute a common downstream component of the signaling pathways leading to HR/resistance. 相似文献
98.
99.
HLA-DR2 dose effect on susceptibility to multiple sclerosis and influence on disease course 总被引:7,自引:0,他引:7 下载免费PDF全文
Barcellos LF Oksenberg JR Begovich AB Martin ER Schmidt S Vittinghoff E Goodin DS Pelletier D Lincoln RR Bucher P Swerdlin A Pericak-Vance MA Haines JL Hauser SL;Multiple Sclerosis Genetics Group 《American journal of human genetics》2003,72(3):710-716
Models of disease susceptibility in multiple sclerosis (MS) often assume a dominant action for the HLA-DRB1*1501 allele and its associated haplotype (DRB1*1501-DQB1*0602 or DR2). A robust and phenotypically well-characterized MS data set was used to explore this model in more detail. A dose effect of HLA-DR2 haplotypes on MS susceptibility was revealed. This observation suggests that, in addition to the role of HLA-DR2 in MS, two copies of a susceptibility haplotype further increase disease risk. Second, we report that DR2 haplotypes modify disease expression. There is a paucity of benign MS and an increase of severe MS in individuals homozygous for DR2. Concepts of the molecular mechanisms that underlie linkage and association of the human leukocyte antigen (HLA) region to MS need to be revised to accommodate these data. 相似文献
100.