全文获取类型
收费全文 | 9456篇 |
免费 | 954篇 |
国内免费 | 4篇 |
出版年
2022年 | 64篇 |
2021年 | 157篇 |
2020年 | 81篇 |
2019年 | 85篇 |
2018年 | 112篇 |
2017年 | 86篇 |
2016年 | 209篇 |
2015年 | 325篇 |
2014年 | 381篇 |
2013年 | 475篇 |
2012年 | 582篇 |
2011年 | 609篇 |
2010年 | 359篇 |
2009年 | 324篇 |
2008年 | 387篇 |
2007年 | 478篇 |
2006年 | 450篇 |
2005年 | 391篇 |
2004年 | 390篇 |
2003年 | 396篇 |
2002年 | 355篇 |
2001年 | 264篇 |
2000年 | 215篇 |
1999年 | 185篇 |
1998年 | 129篇 |
1997年 | 100篇 |
1996年 | 106篇 |
1995年 | 114篇 |
1994年 | 86篇 |
1993年 | 95篇 |
1992年 | 137篇 |
1991年 | 135篇 |
1990年 | 132篇 |
1989年 | 102篇 |
1988年 | 121篇 |
1987年 | 113篇 |
1986年 | 87篇 |
1985年 | 108篇 |
1984年 | 93篇 |
1983年 | 85篇 |
1982年 | 74篇 |
1981年 | 65篇 |
1980年 | 62篇 |
1979年 | 86篇 |
1978年 | 85篇 |
1976年 | 66篇 |
1975年 | 73篇 |
1974年 | 64篇 |
1973年 | 67篇 |
1972年 | 72篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
Wendy A. Douglass Robert H. Hyland Christopher D. Buckley Aymen Al-Shamkhani Jacqueline M. Shaw Sarah L. Scarth David L. Simmons S.K.Alex Law 《FEBS letters》1998,440(3):125
The cysteine-rich region (CRR) of the β2 integrin subunit was replaced by that of β1 to give the chimera β2NV1. β2NV1 can combine with αL to form a variant leukocyte-function-associated antigen (LFA)-1 on COS cell surface, suggesting that the specificity of the β2 interaction with αL does not lie in the CRR. Unlike those expressing wild-type LFA-1, COS cells expressing αLβ2NV1 are constitutively active in intercellular adhesion molecule (ICAM)-1 adhesion. These results suggest that activation of LFA-1 involves the release of an intramolecular constraint, which is maintained, in part, by the authentic β2 CRR. 相似文献
2.
Internode length in Pisum. I. The effect of the Le/le gene difference on endogenous gibberellin-like substances 总被引:2,自引:0,他引:2
The allelopathic potential of the dry fruits of Washingtonia filifera (L. Linden) H. Wendl. was investigated. Leachates from fruits inhibited the germination of lettuce, wheat, red cabbage and cucumber seeds. The inhibitory effect was partly neutralized by kinetin (20 mg 1−1 ) and gibberellic acid (50 mg 1−1 ). The effect of kinetin was more pronounced at 25°C than at 20°C. Substances inhibiting germination were localized in the pericarp of the fruit and were resistant to high temperature. 相似文献
3.
The RAINFOR database: monitoring forest biomass and dynamics 总被引:1,自引:0,他引:1
Problem: Data from over 100 permanent sample plots which have been studied for 10–20 years need a suitable system for storage which allows simple data manipulation and retrieval for analysis. Methods: A relational database linking tree records, taxonomic nomenclature and corresponding environmental data has been built in MS Access as part of the RAINFOR project. Conclusion: The database allows flexible and long‐term use of a large amount of data: more than 100 tree plots across Amazonia, incorporating over 80 000 records of individual trees and over 300 000 total records of tree diameter measurements from successive censuses. The database is designed to enable linkages to existing soil, floristic or plant‐trait databases. This database will be a useful tool for exploring the impact of environmental factors on forest structure and dynamics at local to continental scales, and long term changes in forest ecology. As an early example of its potential, we explore the impact of different methodological assumptions on estimates of tropical forest biomass and carbon storage. 相似文献
4.
5.
6.
Contrary to results published recently, we observe three, rather than two, phenotypes for the enzyme glucosephosphate isomerase (EC 5.3.1.9) from sheep. The phenotypic electrophoretic patterns conform to the patterns observed for this dimeric enzyme in other species. Genotype frequencies in a flock of Southdowns do not deviate significantly from those predicted under the assumption of the Hardy-Weinberg equilibrium. A remarkable observation is that the electrophoretically distinct phenotypes of GPI are largely or entirely obliterated by the addition of 1-10 mmol/l MgCl2 to the electrophoretic buffers. Modification of the usual staining recipe for GPI result in greater resolution and shorter staining times. 相似文献
7.
8.
9.
M A Taylor K A Pratt D F Revell K C Baker I G Sumner P W Goodenough 《Protein engineering》1992,5(5):455-459
For the first time the pro-form of a recombinant cysteine proteinase has been expressed at a high level in Escherichia coli. This inactive precursor can subsequently be processed to yield active enzyme. Sufficient protein can be produced using this system for X-ray crystallographic structure studies of engineered proteinases. A cDNA clone encoding propapain, a precursor of the papaya proteinase, papain, was expressed in E. coli using a T7 polymerase expression system. Insoluble recombinant protein was solubilized in 6 M guanidine hydrochloride and 10 mM dithiothreitol, at pH 8.6. A protein-glutathione mixed disulphide was formed by dilution into oxidized glutathione and 6 M GuHCl, also at pH 8.6. Final refolding and disulphide bond formation was induced by dilution into 3 mM cysteine at pH 8.6. Renatured propapain was processed to active papain at pH 4.0 in the presence of excess cysteine. Final processing could be inhibited by the specific cysteine proteinase inhibitors E64 and leupeptin, but not by pepstatin, PMSF or EDTA. This indicates that final processing was due to a cysteine proteinase and suggests that an autocatalytic event is required for papain maturation. 相似文献
10.
Wendy M Milne 《Australian Journal of Entomology》1999,38(2):145-147
The aphid parasitoid Aphidius ervi was released in the major lucerne-growing areas of New South Wales (NSW), Australia, between 1978 and 1981. With the collaboration of district agronomists of the New South Wales Department of Agriculture, five State-wide surveys were conducted in 1982–1983 to determine the success of the release program. In each survey, the distribution of the parasitoid was checked in relation to populations of the aphids Acyrthosiphon kondoi Shinji and Acyrthosiphon pisum (Harris) (Hemiptera: Aphididae). The surveys confirmed the successful dispersal and establishment of A. ervi in the major lucerne-growing areas of NSW. They demonstrated its ability to survive and recover rapidly after a severe and widespread drought. 相似文献