全文获取类型
收费全文 | 1057篇 |
免费 | 78篇 |
国内免费 | 23篇 |
专业分类
1158篇 |
出版年
2023年 | 7篇 |
2022年 | 18篇 |
2021年 | 22篇 |
2020年 | 11篇 |
2019年 | 23篇 |
2018年 | 31篇 |
2017年 | 29篇 |
2016年 | 31篇 |
2015年 | 61篇 |
2014年 | 66篇 |
2013年 | 80篇 |
2012年 | 115篇 |
2011年 | 88篇 |
2010年 | 53篇 |
2009年 | 35篇 |
2008年 | 58篇 |
2007年 | 55篇 |
2006年 | 53篇 |
2005年 | 40篇 |
2004年 | 28篇 |
2003年 | 41篇 |
2002年 | 37篇 |
2001年 | 19篇 |
2000年 | 26篇 |
1999年 | 10篇 |
1998年 | 6篇 |
1997年 | 7篇 |
1996年 | 7篇 |
1994年 | 3篇 |
1992年 | 8篇 |
1991年 | 11篇 |
1990年 | 7篇 |
1989年 | 3篇 |
1985年 | 4篇 |
1984年 | 3篇 |
1983年 | 3篇 |
1981年 | 3篇 |
1980年 | 3篇 |
1978年 | 7篇 |
1976年 | 2篇 |
1974年 | 2篇 |
1973年 | 4篇 |
1972年 | 2篇 |
1971年 | 5篇 |
1967年 | 2篇 |
1966年 | 3篇 |
1965年 | 3篇 |
1961年 | 2篇 |
1909年 | 2篇 |
1907年 | 2篇 |
排序方式: 共有1158条查询结果,搜索用时 15 毫秒
1.
Xiuling Li Songbai Yang Zhonglin Tang Kui Li Max F. Rothschild Bang Liu Bin Fan 《Animal genetics》2014,45(3):329-339
Due to the direction, intensity, duration and consistency of genetic selection, especially recent artificial selection, the production performance of domestic pigs has been greatly changed. Therefore, we reasoned that there must be footprints or selection signatures that had been left during domestication. In this study, with porcine 60K BeadChip genotyping data from both commercial Large White and local Chinese Tongcheng pigs, we calculated the extended haplotype homozygosity values of the two breeds using the long‐range haplotype method to detect selection signatures. We found 34 candidate regions, including 61 known genes, from Large White pigs and 25 regions comprising 57 known genes from Tongcheng pigs. Many selection signatures were found on SSC1, SSC4, SSC7 and SSC14 regions in both populations. According to quantitative trait loci and network pathway analyses, most of the regions and genes were linked to growth, reproduction and immune responses. In addition, the average genetic differentiation coefficient FST was 0.254, which means that there had already been a significant differentiation between the breeds. The findings from this study can contribute to further research on molecular mechanisms of pig evolution and domestication and also provide valuable references for improvement of their breeding and cultivation. 相似文献
2.
3.
The cis/trans interconversion of Glt-Ala-Ala-Pro-Phe-4-nitroanilide and Glt-Ala-Gly-Pro-Phe-4-nitroanilide was studied both enzymatically and nonenzymatically by measuring kinetic β-deuterium isotope effects. The hydrogen atom at the α-carbon atom of the Xaa residue within the Xaa-Pro moiety was substituted by deuterium. In the nonenzymatic case the transition state of rotation is reflected by kH/kD > 1. When catalysed by 17 kDa PPIase the same bond rotation is characterized by kH/kD < 1. This suggests a covalent mechanism of catalysis which involves an approximately tetravalent carbon of the prolyl imidic bond for the transition state of reaction. 相似文献
4.
Streptomycetes possess peptidyl-prolyl cis-trans isomerases that strongly resemble cyclophilins from eukaryotic organisms 总被引:2,自引:0,他引:2
Andreas Pahl Monika Ühlein Holger Bang Wilhelm Schlumbohm Ullrich Keller 《Molecular microbiology》1992,6(23):3551-3558
A functionally active 17.5 kDa peptidyl-prolyl cis-trans isomerase was purified to homogeneity from Streptomyces chrysomallus, a Gram-positive filamentous bacterium. Characterization of the enzyme revealed inhibition and binding characteristics, against the immunsuppressive drug cyclosporin A, which were similar to cyclophilins from eukaryotes such as mammals, plants, fungi and yeasts, but different from those of cyclophilins from enterobacteria such as Escherichia coli. The amino acid sequence of the S. chrysomallus cyclophilin, as deduced from the gene sequence, revealed a striking degree of amino acid sequence identity with the corresponding 17 kDa proteins of humans (66%), Neurospora (70%) and yeast (69%). Comparison with cyclophilin sequences from the Gram-negative enterobacteria revealed much less homology (25% identity with E. coli b, 23% identity with E. coli a). Cyclophilin was detected in each of the four other Streptomyces species tested. The cyclophilins from the various streptomycetes differed in size, varying between 17 and 20.5 kDa. The cyclophilins were abundant in the Streptomyces cells, and present throughout growth. 相似文献
5.
Ultrastructural analysis of ineffective alfalfa nodules formed by nif::Tn5 mutants of Rhizobium meliloti. 总被引:24,自引:12,他引:12
Ineffective alfalfa nodules formed by Rhizobium meliloti nif::Tn5 mutants were examined by light and electron microscopy. R. meliloti nifH::Tn5 mutants formed nodules that were similar in structure to wild-type nodules except that nifH- bacteroids accumulated a compact, electron-dense body. In contrast to nodules induced by wild type and nifH mutants, nifDK- R. meliloti mutants induced nodules which contained numerous starch grains and prematurely senescent bacteroids. In addition, meristematic activity in nifDK- nodules ceased significantly earlier than in nifH- nodules. All mutant nodules exhibited elevated levels of rough endoplasmic reticulum and Golgi membranes compared to wild-type nodule cells. These elevated levels may reflect either a response to nitrogen starvation in the ineffective nodules or an abnormal synthesis and export of nodule-specific proteins during later developmental stages. 相似文献
6.
Continuous production of L-tryptophan from indole and L-serine by immobilized Escherichia coli cells 总被引:1,自引:0,他引:1
Escherichia coli B 10, which has high activity of tryptophan synthetase, was grown in a 50-L batch culture in order to determine in which growth phase the cells have the highest specific tryptophan productivity. Accordingly, whole cells of the stationary phase were used for immobilization in polyacrylamide beads. After immobilization, these immobilized cells had 56% activity of tryptophan synthetase compared with that of free cells. First, the properties of immobilized cells were investigated. Next, discontinuous productions of L-tryptophan were carried out by using immobilized cells. In discontinuous production of L-tryptophan by the batch, the activity remaining of immobilized cells was 76-79% after 30 times batchwise use. In continuous production of L-tryptophan with a continuous stirred tank reactor (CSTR), the activity remaining of the immobilized cells was 80% after continuous use for 50 days. The maximum productivity of L-tryptophan in this CSTR system was 0.12 g tryptophan L(-1) h(-1). 相似文献
7.
ELECTRON MICROSCOPY OF VIRUS-INFECTED YEAST CELLS 总被引:1,自引:0,他引:1
8.
9.
Internal pH crisis, lysine decarboxylase and the acid tolerance response of Salmonella typhimurium 总被引:10,自引:3,他引:7
Yong-Keun Park Bradley Bearson Seong Ho Bang Iel Soo Bang & John W. Foster 《Molecular microbiology》1996,20(3):605-611
Salmonella typhimurium possesses an adaptive response to acid that increases survival during exposure to extremely low pH values. The acid tolerance response (ATR) includes both log-phase and stationary-phase systems. The log-phase ATR appears to require two components for maximum acid tolerance, namely an inducible pH homeostasis system, and a series of acid-shock proteins. We have discovered one of what appears to be a series of inducible exigency pH homeostasis systems that contribute to acid tolerance in extreme acid environments. The low pH-inducible lysine decarboxylase was shown to contribute significantly to pH homeostasis in environments as low as pH 3.0. Under the conditions tested, both lysine decarboxylase and σs -dependent acid-shock proteins were required for acid tolerance but only lysine decarboxylase contributed to pH homeostasis. The cadBA operon encoding lysine decarboxylase and a lysine/cadaverine antiporter were cloned from S. typhimurium and were found to be 79% homologous to the cadBA operon from Escherichia coli . The results suggest that S. typhimurium has a variety of means of fulfilling the pH homeostasis requirement of the ATR in the form of inducible amino acid decarboxylases. 相似文献
10.
Uffe Bang Olsen 《Prostaglandins & other lipid mediators》1978,15(4):645-649
Isolated rabbit kidneys were perfused with 37°C Krebs-Henseleit solution aerated with 95% O2 + 5% CO2. Perfusion rate was varied from 1 to 10 ml/min. This was accompanied by parallel changes of perfusion pressure, prostaglandin excretion and release of radioactivity from kidneys with 14C-arachidonic acid incorporated into the tissue lipid pool. It is suggested that enhancement of perfusion rate raises the intrarenal pressure which increases renal prostaglandin release due to increased substrate availability. 相似文献