全文获取类型
收费全文 | 7469篇 |
免费 | 392篇 |
国内免费 | 3篇 |
出版年
2022年 | 91篇 |
2021年 | 157篇 |
2020年 | 100篇 |
2019年 | 106篇 |
2018年 | 151篇 |
2017年 | 127篇 |
2016年 | 207篇 |
2015年 | 266篇 |
2014年 | 315篇 |
2013年 | 430篇 |
2012年 | 492篇 |
2011年 | 426篇 |
2010年 | 287篇 |
2009年 | 226篇 |
2008年 | 310篇 |
2007年 | 310篇 |
2006年 | 242篇 |
2005年 | 273篇 |
2004年 | 208篇 |
2003年 | 230篇 |
2002年 | 202篇 |
2001年 | 190篇 |
2000年 | 156篇 |
1999年 | 144篇 |
1998年 | 76篇 |
1997年 | 57篇 |
1996年 | 47篇 |
1995年 | 51篇 |
1994年 | 48篇 |
1992年 | 119篇 |
1991年 | 89篇 |
1990年 | 130篇 |
1989年 | 100篇 |
1988年 | 105篇 |
1987年 | 95篇 |
1986年 | 79篇 |
1985年 | 92篇 |
1984年 | 82篇 |
1983年 | 63篇 |
1982年 | 65篇 |
1981年 | 87篇 |
1980年 | 66篇 |
1979年 | 94篇 |
1978年 | 63篇 |
1977年 | 66篇 |
1976年 | 47篇 |
1975年 | 60篇 |
1974年 | 57篇 |
1973年 | 50篇 |
1972年 | 47篇 |
排序方式: 共有7864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.
J Shobha B Bhattacharyya D Balasubramanian 《Journal of biochemical and biophysical methods》1989,18(4):287-295
Enhancement of the fluorescence intensity of colchicine occurs in media of low polarity and appreciable viscosity; this is suggested to be the basis of the intensification of its fluorescence when it is bound to and immobilized in tubulin. We show here that the tubulin-bound fluorescence features of colchicine are largely reconstructed upon solubilizing it in chosen micellar aggregates that offer optimal polarities and microviscosities. Triton X-100 and bile salt micelles intensify the colchicine emission but the maximal effects are obtained with tetrameric aggregates of the peptide melittin. Estimates of the polarity, microviscosity and binding-site dimensions of colchicine are obtained using this mimetic approach. Our results suggest that well chosen micellar systems act as good models to reconstruct and analyze the spectral properties of molecules immobilized in their binding sites. 相似文献
5.
6.
7.
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
8.
M F Ahmad N Nasrin M K Bagchi I Chakravarty N K Gupta 《The Journal of biological chemistry》1985,260(11):6960-6965
The characteristics of yeast eukaryotic initiation factor 2 (eIF-2) and Co-eIF-2A have been studied and compared with those of the corresponding factors from rabbit reticulocytes. 1) Unlike eIF-2r, purified eIF-2y did not contain bound GDP. 2) Purified eIF-2y preparation contained GTPase activity and dephosphorylated GTP to GDP. 3) An anti-eIF-2r preparation which predominantly precipitated the gamma-subunit (Mr 54,000) of eIF-2r also precipitated the larger subunit (Mr 54,000) of eIF-2y. 4) Unlike eIF-2r, ternary complex formation by eIF-2y was not inhibited by Mg2+. 5) Both Co-eIF-2A20y and Co-eIF-2r significantly enhanced Met-tRNAf binding to eIF-2y and, again, Mg2+ did not have any effect on this stimulated Met-tRNAf binding to eIF-2y. 6) Both Co-eIF-2A20y and Co-eIF-2r were similarly effective in stimulating Met-tRNAf binding to eIF-2r in the absence of Mg2+. However, in the presence of Mg2+, Co-eIF-2A20y was significantly less effective than Co-eIF-2r as Co-eIF-2A20y did not promote displacement of GDP from eIF-2r X GDP. 7) eIF-2y bound [3H]GDP and this binding was significantly enhanced in the presence of Mg2+. Also, [3H]GDP in the preformed eIF-2y X [3H]GDP complex was rapidly exchanged with exogenously added unlabeled GDP in the presence of Mg2+. Co-eIF-2A20y had no effect on GDP binding to eIF-2y nor on GDP exchange reactions. 8) Reticulocyte heme-regulated protein synthesis inhibitor, which phosphorylated almost completely (in excess of 80%) the alpha-subunit (Mr 38,000) of eIF-2r, also phosphorylated similarly the smaller subunit (Mr 36,000) of eIF-2y. However, such phosphorylation had no significant effect on ternary complex formation, GDP binding, and GDP exchange reactions. 相似文献
9.
10.