全文获取类型
收费全文 | 215118篇 |
免费 | 10791篇 |
国内免费 | 12785篇 |
专业分类
238694篇 |
出版年
2024年 | 326篇 |
2023年 | 1768篇 |
2022年 | 3918篇 |
2021年 | 6485篇 |
2020年 | 4520篇 |
2019年 | 5612篇 |
2018年 | 15811篇 |
2017年 | 13538篇 |
2016年 | 12214篇 |
2015年 | 8450篇 |
2014年 | 9626篇 |
2013年 | 10124篇 |
2012年 | 15707篇 |
2011年 | 22628篇 |
2010年 | 17954篇 |
2009年 | 13846篇 |
2008年 | 16308篇 |
2007年 | 17126篇 |
2006年 | 5735篇 |
2005年 | 4850篇 |
2004年 | 4734篇 |
2003年 | 4539篇 |
2002年 | 3766篇 |
2001年 | 2623篇 |
2000年 | 2274篇 |
1999年 | 2040篇 |
1998年 | 1306篇 |
1997年 | 1188篇 |
1996年 | 1108篇 |
1995年 | 916篇 |
1994年 | 924篇 |
1993年 | 729篇 |
1992年 | 928篇 |
1991年 | 731篇 |
1990年 | 538篇 |
1989年 | 494篇 |
1988年 | 398篇 |
1987年 | 399篇 |
1986年 | 288篇 |
1985年 | 317篇 |
1984年 | 172篇 |
1983年 | 189篇 |
1982年 | 111篇 |
1981年 | 94篇 |
1980年 | 64篇 |
1979年 | 82篇 |
1977年 | 60篇 |
1975年 | 62篇 |
1972年 | 299篇 |
1971年 | 295篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
31.
32.
33.
34.
David Skelly 《BMC biology》2010,8(1):136
A new study of divergence in freshwater fish provides strong evidence of rapid, temperature-mediated adaptation. This study
is particularly important in the ongoing debate over the extent and significance of evolutionary response to climate change
because divergence has occurred in relatively few generations in spite of ongoing gene flow and in the aftermath of a significant
genetic bottleneck, factors that have previously been considered obstacles to evolution. Climate change may thus be more likely
to foster contemporary evolutionary responses than has been anticipated, and I argue here for the importance of investigating
their possible occurrence. 相似文献
35.
36.
Li Zhang Mark Morrison Páraic ó Cuív Paul Evans Claire M. Rickard 《Journal of bacteriology》2012,194(23):6639
In recent years, Staphylococcus epidermidis has become a major nosocomial pathogen and the most common cause of intravascular catheter-related bacteremia, which can increase morbidity and mortality and significantly affect patient recovery. We report a draft genome sequence of Staphylococcus epidermidis AU12-03, isolated from an intravascular catheter tip. 相似文献
37.
Transcriptional regulatory network triggered by oxidative signals configures the early response mechanisms of japonica rice to chilling stress 总被引:3,自引:0,他引:3
38.
Jianxi Xiao Rayna M. Addabbo Janelle L. Lauer Gregg B. Fields Jean Baum 《The Journal of biological chemistry》2010,285(44):34181-34190
The mechanism by which enzymes recognize the “uniform” collagen triple helix is not well understood. Matrix metalloproteinases (MMPs) cleave collagen after the Gly residue of the triplet sequence Gly∼[Ile/Leu]-[Ala/Leu] at a single, unique, position along the peptide chain. Sequence analysis of types I-III collagen has revealed a 5-triplet sequence pattern in which the natural cleavage triplets are always flanked by a specific distribution of imino acids. NMR and MMP kinetic studies of a series of homotrimer peptides that model type III collagen have been performed to correlate conformation and dynamics at, and near, the cleavage site to collagenolytic activity. A peptide that models the natural cleavage site is significantly more active than a peptide that models a potential but non-cleavable site just 2-triplets away and NMR studies show clearly that the Ile in the leading chain of the cleavage peptide is more exposed to solvent and less locally stable than the Ile in the middle and lagging chains. We propose that the unique local instability of Ile at the cleavage site in part arises from the placement of the conserved Pro at the P3 subsite. NMR studies of peptides with Pro substitutions indicate that the local dynamics of the three chains are directly modulated by their proximity to Pro. Correlation of peptide activity to NMR data shows that a single locally unstable chain at the cleavage site, rather than two or three labile chains, is more favorable for cleavage by MMP-1 and may be the determining factor for collagen recognition. 相似文献
39.
Recent studies have revealed an unexpected synergism between two seemingly unrelated protein families: CCN matricellular proteins
and the tumor necrosis factor (TNF) family of cytokines. CCN proteins are dynamically expressed at sites of injury repair
and inflammation, where TNF cytokines are also expressed. Although TNFα is an apoptotic inducer in some cancer cells, it activates
NFκB to promote survival and proliferation in normal cells, and its cytotoxicity requires inhibition of de novo protein synthesis
or NFκB signaling. The presence of CCN1, CCN2, or CCN3 overrides this requirement and unmasks the apoptotic potential of TNFα,
thus converting TNFα from a proliferation-promoting protein into an apoptotic inducer. These CCN proteins also enhance the
cytotoxicity of other TNF cytokines, including LTα, FasL, and TRAIL. Mechanistically, CCNs function through integrin α6β1 and the heparan sulfate proteoglycan (HSPG) syndecan-4 to induce reactive oxygen species (ROS) accumulation, which is essential
for apoptotic synergism. Mutant CCN1 proteins defective for binding α6β1-HSPGs are unable to induce ROS or apoptotic synergism with TNF cytokines. Further, knockin mice that express an α6β1-HSPG-binding defective CCN1 are blunted in TNFα- and Fas-mediated apoptosis, indicating that CCN1 is a physiologic regulator
of these processes. These findings implicate CCN proteins as contextual regulators of the inflammatory response by dictating
or enhancing the cytotoxicity of TNFα and related cytokines. 相似文献
40.