全文获取类型
收费全文 | 10738篇 |
免费 | 993篇 |
国内免费 | 12篇 |
出版年
2023年 | 34篇 |
2022年 | 87篇 |
2021年 | 225篇 |
2020年 | 115篇 |
2019年 | 155篇 |
2018年 | 200篇 |
2017年 | 192篇 |
2016年 | 284篇 |
2015年 | 522篇 |
2014年 | 551篇 |
2013年 | 728篇 |
2012年 | 874篇 |
2011年 | 854篇 |
2010年 | 542篇 |
2009年 | 466篇 |
2008年 | 729篇 |
2007年 | 666篇 |
2006年 | 635篇 |
2005年 | 599篇 |
2004年 | 536篇 |
2003年 | 508篇 |
2002年 | 488篇 |
2001年 | 148篇 |
2000年 | 114篇 |
1999年 | 131篇 |
1998年 | 129篇 |
1997年 | 86篇 |
1996年 | 74篇 |
1995年 | 54篇 |
1994年 | 75篇 |
1993年 | 61篇 |
1992年 | 57篇 |
1991年 | 53篇 |
1990年 | 69篇 |
1989年 | 52篇 |
1988年 | 55篇 |
1987年 | 46篇 |
1986年 | 42篇 |
1985年 | 36篇 |
1984年 | 44篇 |
1983年 | 29篇 |
1982年 | 39篇 |
1981年 | 38篇 |
1980年 | 28篇 |
1979年 | 46篇 |
1978年 | 32篇 |
1977年 | 29篇 |
1974年 | 29篇 |
1973年 | 21篇 |
1972年 | 24篇 |
排序方式: 共有10000条查询结果,搜索用时 171 毫秒
951.
The gastric pathogen Helicobacter pylori must combat chronic acid and oxidative stress. It does so via many mechanisms, including macromolecule repair and gene regulation. Mitomycin C-sensitive clones from a transposon mutagenesis library were screened. One sensitive strain contained the insertion element at the locus of hp119, a hypothetical gene. No homologous gene exists in any (non-H. pylori) organism. Nevertheless, the predicted protein has some features characteristic of histone-like proteins, and we showed that purified HP119 protein is a DNA-binding protein. A Δhp119 strain was markedly more sensitive (viability loss) to acid or to air exposure, and these phenotypes were restored to wild-type (WT) attributes upon complementation of the mutant with the wild-type version of hp119 at a separate chromosomal locus. The mutant strain was approximately10-fold more sensitive to macrophage-mediated killing than the parent or the complemented strain. Of 12 mice inoculated with the wild type, all contained H. pylori, whereas 5 of 12 mice contained the mutant strain; the mean colonization numbers were 158-fold less for the mutant strain. A proteomic (two-dimensional PAGE with mass spectrometric analysis) comparison between the Δhp119 mutant and the WT strain under oxidative stress conditions revealed a number of important antioxidant protein differences; SodB, Tpx, TrxR, and NapA, as well as the peptidoglycan deacetylase PgdA, were significantly less expressed in the Δhp119 mutant than in the WT strain. This study identified HP119 as a putative histone-like DNA-binding protein and showed that it plays an important role in Helicobacter pylori stress tolerance and survival in the host. 相似文献
952.
953.
Melissa Richard-Greenblatt Horacio Bach John Adamson Sandra Pe?a-Diaz Wu Li Adrie J. C. Steyn Yossef Av-Gay 《The Journal of biological chemistry》2015,290(38):23064-23076
Ergothioneine (EGT) is synthesized in mycobacteria, but limited knowledge exists regarding its synthesis, physiological role, and regulation. We have identified Rv3701c from Mycobacterium tuberculosis to encode for EgtD, a required histidine methyltransferase that catalyzes first biosynthesis step in EGT biosynthesis. EgtD was found to be phosphorylated by the serine/threonine protein kinase PknD. PknD phosphorylates EgtD both in vitro and in a cell-based system on Thr213. The phosphomimetic (T213E) but not the phosphoablative (T213A) mutant of EgtD failed to restore EGT synthesis in a ΔegtD mutant. The findings together with observed elevated levels of EGT in a pknD transposon mutant during in vitro growth suggests that EgtD phosphorylation by PknD negatively regulates EGT biosynthesis. We further showed that EGT is required in a nutrient-starved model of persistence and is needed for long term infection of murine macrophages. 相似文献
954.
955.
956.
957.
958.
959.
Sandra Lavorel Matthew J. Colloff Sue Mcintyre Michael D. Doherty Helen T. Murphy Daniel J. Metcalfe Michael Dunlop Richard J. Williams Russell M. Wise Kristen J. Williams 《Global Change Biology》2015,21(1):12-31
Ecosystem services are typically valued for their immediate material or cultural benefits to human wellbeing, supported by regulating and supporting services. Under climate change, with more frequent stresses and novel shocks, 'climate adaptation services', are defined as the benefits to people from increased social ability to respond to change, provided by the capability of ecosystems to moderate and adapt to climate change and variability. They broaden the ecosystem services framework to assist decision makers in planning for an uncertain future with new choices and options. We present a generic framework for operationalising the adaptation services concept. Four steps guide the identification of intrinsic ecological mechanisms that facilitate the maintenance and emergence of ecosystem services during periods of change, and so materialise as adaptation services. We applied this framework for four contrasted Australian ecosystems. Comparative analyses enabled by the operational framework suggest that adaptation services that emerge during trajectories of ecological change are supported by common mechanisms: vegetation structural diversity, the role of keystone species or functional groups, response diversity and landscape connectivity, which underpin the persistence of function and the reassembly of ecological communities under severe climate change and variability. Such understanding should guide ecosystem management towards adaptation planning. 相似文献
960.