全文获取类型
收费全文 | 196959篇 |
免费 | 15665篇 |
国内免费 | 13370篇 |
专业分类
225994篇 |
出版年
2024年 | 363篇 |
2023年 | 2255篇 |
2022年 | 5100篇 |
2021年 | 8858篇 |
2020年 | 5760篇 |
2019年 | 7275篇 |
2018年 | 7291篇 |
2017年 | 5418篇 |
2016年 | 7743篇 |
2015年 | 11210篇 |
2014年 | 13290篇 |
2013年 | 14390篇 |
2012年 | 17257篇 |
2011年 | 15836篇 |
2010年 | 9795篇 |
2009年 | 8705篇 |
2008年 | 10302篇 |
2007年 | 9285篇 |
2006年 | 8280篇 |
2005年 | 6874篇 |
2004年 | 5900篇 |
2003年 | 5083篇 |
2002年 | 4484篇 |
2001年 | 4111篇 |
2000年 | 3710篇 |
1999年 | 3721篇 |
1998年 | 2081篇 |
1997年 | 2225篇 |
1996年 | 2103篇 |
1995年 | 1896篇 |
1994年 | 1911篇 |
1993年 | 1391篇 |
1992年 | 1965篇 |
1991年 | 1683篇 |
1990年 | 1320篇 |
1989年 | 1163篇 |
1988年 | 934篇 |
1987年 | 801篇 |
1986年 | 680篇 |
1985年 | 720篇 |
1984年 | 429篇 |
1983年 | 370篇 |
1982年 | 273篇 |
1981年 | 200篇 |
1980年 | 180篇 |
1979年 | 199篇 |
1978年 | 145篇 |
1977年 | 106篇 |
1974年 | 105篇 |
1973年 | 103篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
Yi-Hua Wu Chia-Pei Chang Chin-I Chien Yi-Kuan Tseng Chien-Chia Wang 《Molecular and cellular biology》2013,33(17):3515-3523
The yeast Saccharomyces cerevisiae possesses two distinct glycyl-tRNA synthetase (GlyRS) genes: GRS1 and GRS2. GRS1 is dually functional, encoding both cytoplasmic and mitochondrial activities, while GRS2 is dysfunctional and not required for growth. The protein products of these two genes, GlyRS1 and GlyRS2, are much alike but are distinguished by an insertion peptide of GlyRS1, which is absent from GlyRS2 and other eukaryotic homologues. We show that deletion or mutation of the insertion peptide modestly impaired the enzyme''s catalytic efficiency in vitro (with a 2- to 3-fold increase in Km and a 5- to 8-fold decrease in kcat). Consistently, GRS2 can be conveniently converted to a functional gene via codon optimization, and the insertion peptide is dispensable for protein stability and the rescue activity of GRS1 at 30°C in vivo. A phylogenetic analysis further showed that GRS1 and GRS2 are paralogues that arose from a gene duplication event relatively recently, with GRS1 being the predecessor. These results indicate that GlyRS2 is an active enzyme essentially resembling the insertion peptide-deleted form of GlyRS1. Our study suggests that the insertion peptide represents a novel auxiliary domain, which facilitates both productive docking and catalysis of cognate tRNAs. 相似文献
2.
3.
4.
5.
6.
Involvement of the galactosyl-1-phosphate transferase encoded by the Salmonella enterica rfbP gene in O-antigen subunit processing. 总被引:11,自引:5,他引:6 下载免费PDF全文
rfbT of Salmonella enterica LT2 was previously thought, together with rfaL, to be involved in the ligation of polymerized O antigen to core-lipid A, and three mutants were known. We report the mapping of the mutations to rfbP, the galactosyl-1-phosphate transferase gene, which is now shown to encode a bifunctional protein. The mutations which have the former rfbT phenotype are referred to as rfbP(T). We also show that rfbP(T) mutants are not blocked in the ligation step as previously believed but in an earlier step, possibly in flipping the O-antigen subunit on undecaprenyl pyrophosphate from the cytoplasmic to periplasmic face of the cytoplasmic membrane. 相似文献
7.
8.
Food availability is important to the dynamics of animal social organizations or populations. However, the role of winter
food availability in animal population dynamics is still controversial. We carried out an experimental study to test Lack’s
hypothesis that reduced food in winter limits survival and spring numbers of breeding individuals of social groups, using
the Mongolian gerbil (Meriones unguiculatus) as model species. We established 24 gerbil social groups in 24, 10 × 10 m, pens in September 2008. We provided wheat seeds
as supplemental food in 12 enclosures from September 2008 to March 2009; the other 12 enclosures, not provided with supplemental
food, served as controls. We live-trapped gerbils at a 2-week interval from September to April. Supplemental food during winter
increased biweekly survival by 10% relative to that in control groups. Only four control social groups survived to the end
of our study whereas all 12 food-supplemented social groups survived through our study period. Supplemental food also increased
cumulative numbers of recruits and group sizes of gerbils. We conclude that winter food availability limits winter survival
and spring social groups or population sizes of Mongolian gerbils. 相似文献
9.
10.