全文获取类型
收费全文 | 11848篇 |
免费 | 1365篇 |
国内免费 | 6篇 |
出版年
2022年 | 143篇 |
2021年 | 299篇 |
2020年 | 131篇 |
2019年 | 181篇 |
2018年 | 198篇 |
2017年 | 151篇 |
2016年 | 293篇 |
2015年 | 491篇 |
2014年 | 495篇 |
2013年 | 620篇 |
2012年 | 838篇 |
2011年 | 764篇 |
2010年 | 466篇 |
2009年 | 395篇 |
2008年 | 575篇 |
2007年 | 559篇 |
2006年 | 530篇 |
2005年 | 478篇 |
2004年 | 497篇 |
2003年 | 392篇 |
2002年 | 406篇 |
2001年 | 221篇 |
2000年 | 217篇 |
1999年 | 211篇 |
1998年 | 156篇 |
1997年 | 84篇 |
1996年 | 99篇 |
1995年 | 106篇 |
1994年 | 108篇 |
1993年 | 103篇 |
1992年 | 163篇 |
1991年 | 168篇 |
1990年 | 140篇 |
1989年 | 158篇 |
1988年 | 147篇 |
1987年 | 130篇 |
1986年 | 117篇 |
1985年 | 109篇 |
1984年 | 106篇 |
1983年 | 103篇 |
1981年 | 77篇 |
1979年 | 106篇 |
1978年 | 82篇 |
1977年 | 88篇 |
1976年 | 76篇 |
1975年 | 84篇 |
1974年 | 100篇 |
1973年 | 77篇 |
1972年 | 84篇 |
1971年 | 78篇 |
排序方式: 共有10000条查询结果,搜索用时 140 毫秒
1.
Demonstration that a chemically synthesized BPV1 oncoprotein and its C-terminal domain function to induce cellular DNA synthesis 总被引:17,自引:0,他引:17
Bovine papillomavirus type 1 contains the smallest known oncogene (ORF E5), encoding a hydrophobic 44 amino acid protein. To study the biochemical functions of the E5 oncoprotein, we have chemically synthesized it and several deletion mutant peptides. We demonstrate induction of cellular DNA synthesis in growth-arrested cells by microinjection of E5 oncoprotein. This activity can be broken down into two functionally distinguishable domains. Remarkably, the first domain, which alone is sufficient to induce cellular DNA synthesis, contains only the C-terminal 13 amino acids. This is the smallest known protein fragment that can autonomously activate cellular DNA synthesis. The second domain is the hydrophobic middle region, which by itself fails to induce cellular DNA synthesis but confers a 1000-fold increase in specific activity. The N-terminal one-third of the molecule is dispensable for induction of DNA synthesis. 相似文献
2.
Scott P. Lawrence Nicholas A. Bright J. Paul Luzio Katherine Bowers 《Molecular biology of the cell》2010,21(20):3540-3551
The pH and lumenal environment of intracellular organelles is considered essential for protein sorting and trafficking through the cell. We provide the first evidence that a mammalian NHE sodium (potassium)/proton exchanger, NHE8, plays a key role in the control of protein trafficking and endosome morphology. At steady state, the majority of epitope-tagged NHE8 was found in the trans-Golgi network of HeLa M-cells, but a proportion was also localized to multivesicular bodies (MVBs). Depletion of NHE8 in HeLa M-cells with siRNA resulted in the perturbation of MVB protein sorting, as shown by an increase in epidermal growth factor degradation. Additionally, NHE8-depleted cells displayed striking perinuclear clustering of endosomes and lysosomes, and there was a ninefold increase in the cellular volume taken up by LAMP1/LBPA-positive, dense MVBs. Our data points to a role for the ion exchange activity of NHE8 being required to maintain endosome morphology, as overexpression of a nonfunctional point mutant protein (NHE8 E225Q) resulted in phenotypes similar to those seen after siRNA depletion of endogenous NHE8. Interestingly, we found that depletion of NHE8, despite its function as a sodium (potassium)/proton antiporter, did not affect the overall pH inside dense MVBs. 相似文献
3.
4.
5.
John G. Neuhoff Katherine L. Long Rebecca C. Worthington 《Evolution and human behavior》2012,33(4):318-322
Listeners consistently perceive approaching sounds to be closer than they actually are and perceptually underestimate the time to arrival of looming sound sources. In a natural environment, this underestimation results in more time than expected to evade or engage the source and affords a “margin of safety” that may provide a selective advantage. However, a key component in the proposed evolutionary origins of the perceptual bias is the appropriate timing of anticipatory motor behaviors. Here we show that listeners with poorer physical fitness respond sooner to looming sounds and with a larger margin of safety than listeners with better physical fitness. The anticipatory perceptual bias for looming sounds is negatively correlated with physical strength and positively correlated with recovery heart rate (a measure of aerobic fitness). The results suggest that the auditory perception of looming sounds may be modulated by the response capacity of the motor system. 相似文献
6.
A method is described for the subcellular fractionation of goldfish xanthophores. The procedure produces relatively pure fractions of caroteniod droplets, pterinosomes, cytosol and what appears to be plasma membrane. The presence of a distinct pattern of proteins is shown to be associated with the carotenoid droplets. Treatment of the xanthophores with ACTH affects the buoyant density of some carotenoid droplets and stimulates the phosphorylation of a polypeptide associated with the carotenoid droplets. 相似文献
7.
8.
9.
A conceptual framework for comparing species assemblages in native and exotic habitats 总被引:4,自引:0,他引:4
Exotic (nonnative) species are known to have a wide variety of impacts on native biota. One potential set of impacts that have been poorly studied are the effects of replacing native habitat-providing species with exotic ones, e.g. when native trees that compose a woodland are replaced by an exotic tree plantation. Here we develop a graphical model that can be used to explore how multiple taxonomic components (such as birds, mammals and plants) respond to such changes. We suggest that four categorical responses are possible, with respect to changes in species richness (or other quantitative measures) of taxonomic groups within species assemblages. First, that each taxonomic group compared between habitats will be relatively unchanged, e.g. have equivalent values of species richness. Second, that a decrease (for example in species richness) of one group will be compensated for by an increase (in species richness) of another group. Third, that one or more groups will decrease without any compensated increases in other groups. Fourth, that one or more groups will increase without any compensated decreases in other groups. We provide empirical support for 3 of these 4 responses, with respect to measures of species richness, with much evidence for equivalency between habitats. These types of comparisons should provide a valuable tool for evaluating 1) the efficacy of environmental mitigation efforts that artificially create or restore habitats and 2) the types of changes that have occurred over time or across space as native habitat-producing species are replaced by exotic ones. Finally, this conceptual framework should help to broaden the range of possible changes considered by ecologists who study the impacts of exotic species. 相似文献
10.
Primate microbiome research is a quickly growing field with exciting potential for informing our understanding of primate biology, ecology, and evolution as well as host‐microbe interactions more broadly. This introductory essay to a special section of the American Journal of Primatology provides a cross‐sectional snapshot of current activity in these areas by briefly summarizing the diversity of contributed papers and their relationships to key themes in host‐associated microbiome research. It then uses this survey as a foundation for consolidating a set of key research questions to broadly guide future research. It also argues for the importance of methods standardization to facilitate comparative analyses and the identification of generalizable patterns and relationships. While primatology will benefit greatly from the integration of microbial datasets, it is uniquely positioned to address important questions regarding microbiology and macro‐ecology and evolution more generally. We are eager to see where the primate microbiome leads us. 相似文献