全文获取类型
收费全文 | 13542篇 |
免费 | 969篇 |
国内免费 | 9篇 |
专业分类
14520篇 |
出版年
2022年 | 148篇 |
2021年 | 258篇 |
2020年 | 164篇 |
2019年 | 207篇 |
2018年 | 242篇 |
2017年 | 219篇 |
2016年 | 362篇 |
2015年 | 565篇 |
2014年 | 630篇 |
2013年 | 759篇 |
2012年 | 946篇 |
2011年 | 850篇 |
2010年 | 545篇 |
2009年 | 487篇 |
2008年 | 672篇 |
2007年 | 688篇 |
2006年 | 600篇 |
2005年 | 643篇 |
2004年 | 547篇 |
2003年 | 531篇 |
2002年 | 493篇 |
2001年 | 266篇 |
2000年 | 200篇 |
1999年 | 217篇 |
1998年 | 145篇 |
1997年 | 113篇 |
1996年 | 92篇 |
1995年 | 108篇 |
1994年 | 96篇 |
1993年 | 84篇 |
1992年 | 155篇 |
1991年 | 123篇 |
1990年 | 170篇 |
1989年 | 126篇 |
1988年 | 130篇 |
1987年 | 137篇 |
1986年 | 99篇 |
1985年 | 118篇 |
1984年 | 120篇 |
1983年 | 90篇 |
1982年 | 101篇 |
1981年 | 120篇 |
1980年 | 90篇 |
1979年 | 118篇 |
1978年 | 90篇 |
1977年 | 81篇 |
1976年 | 69篇 |
1975年 | 74篇 |
1974年 | 77篇 |
1973年 | 75篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
The effect of waveguiding property (i.e., the intensity distribution) of the photoreceptor on the number of photons absorbed in a photoreceptor has been studied. It has been found that the effect is significant only for large values of the exposure and the maximum effect is less than 11% in the case of human rod photoreceptor. In the analysis, the funnelling effect, which follows from the coupling between the interior and exterior fields, has not been considered.Work partially supported by the Department of Science and Technology (India)B. D. Gupta is associated with the School of Bioscience Studies 相似文献
2.
Páraic ó Cuív Rajesh Gupta Hareshwar P. Goswami Mark Morrison 《Applied and environmental microbiology》2013,79(19):6173-6175
Clostridium thermocellum encodes a cellulosomal, modular, and thermostable serine protease inhibitor (serpin), PinA. PinA stability but not inhibitory activity is affected by the Fn(III) and Doc(I) domains, and PinA is a broad inhibitor of subtilisin-like proteases and may play a key role in protecting the cellulosome from protease attack. 相似文献
3.
4.
5.
6.
Summary The physicochemical properties of the interactions of RNA polymerase (RPase) with promoter and nonspecific DNA sequences have been investigated. These show that nonspecific binding is principally an ionic interaction and that promoter binding is more complex, involving nonionic interactions. Nonspecific binding has been shown to be very important in the promoter search, and one-dimensional diffusion can account for the rate at which RPase finds the promoter. Significant differences have been reported in the binding process for various promoters and in the effects of regulatory proteins. Further investigation of these differences will lead to a better understanding of the selectivity and regulation of the initiation process.The pathways of the initiation process have been outlined, by recent studies and considerable progress has been made in determining the rates of interconversion of the intermediate states. A number of questions remain about the detail of initiation and the effects of various parameters on the reactions. Of particular importance is the identification of the point at which the enzyme becomes truly processive. In addition, the step which is rate limiting has not been identified in either the productive or nonproductive process. The mechanistic features of the steps after bond formation are just beginning to yield to investigation.Use of substrate analogs with RPase has led to a picture of the polymerization site according to the ability of the enzyme to incorporate analogs. Base specificity appears to be determined primarily by interaction with the template rather than the enzyme, but the ribose moiety must interact with the site quite specifically. The orientation of the phosphate residues has been determined by NMR, which has also proved to be a valuable probe of the initiation site. At this site base specificity is resident in the enzyme and expressed through the interaction of the base and intrinsic metal, as shown by studies with the Cobalt substituted enzyme. In both initiation and polymerization, the reaction has been shown to proceed by inversion of configuration. Techniques similar to those used for initiation will probably be applied to the polymerization reaction as well, which has not recently received as much attention with respect to mechanism. Functional phenomena such as pausing make the polymerization process particularly promising for producing insight into RPase reactions. 相似文献
7.
8.
Studies with substrate analogues and the pH optimum indicated the involvement of carboxyl group in the active site of goat
carboxypeptidase A. Chemical modification of the enzyme with 1-cyclohexyl-3-(2-morpholinoethyl) carbodiimide methoI -p-toluene sulphonate, a carboxyl specific reagent, led to loss of both esterase and peptidase activities. Protection studies
showed that this carboxyl group was in the active site and was protected by Βp-phenylpropionic acid and glycyl-L-tyrosine. Kinetic studies also confirmed the involvement of carboxylic group because the
enzyme modification with water soluble carbodiimide was a two step reaction which excluded the possibility of tyrosine or
lysine which are known to give a one step reaction with this reagent 相似文献
9.
10.