全文获取类型
收费全文 | 1238873篇 |
免费 | 99993篇 |
国内免费 | 1373篇 |
专业分类
1340239篇 |
出版年
2021年 | 17720篇 |
2020年 | 12584篇 |
2019年 | 16128篇 |
2018年 | 17576篇 |
2017年 | 16361篇 |
2016年 | 27903篇 |
2015年 | 42075篇 |
2014年 | 50053篇 |
2013年 | 76268篇 |
2012年 | 33261篇 |
2011年 | 21336篇 |
2010年 | 42874篇 |
2009年 | 44441篇 |
2008年 | 20619篇 |
2007年 | 18296篇 |
2006年 | 23878篇 |
2005年 | 25259篇 |
2004年 | 24469篇 |
2003年 | 22073篇 |
2002年 | 20184篇 |
2001年 | 25952篇 |
2000年 | 23214篇 |
1999年 | 25304篇 |
1998年 | 24480篇 |
1997年 | 24150篇 |
1996年 | 23814篇 |
1995年 | 21951篇 |
1994年 | 21771篇 |
1993年 | 20822篇 |
1992年 | 22473篇 |
1991年 | 21172篇 |
1990年 | 19791篇 |
1989年 | 20986篇 |
1988年 | 19246篇 |
1987年 | 18192篇 |
1986年 | 17301篇 |
1985年 | 19472篇 |
1984年 | 20094篇 |
1983年 | 17817篇 |
1982年 | 19099篇 |
1981年 | 18500篇 |
1980年 | 17322篇 |
1979年 | 15980篇 |
1978年 | 15886篇 |
1977年 | 15310篇 |
1976年 | 14589篇 |
1975年 | 13954篇 |
1974年 | 14350篇 |
1973年 | 14750篇 |
1972年 | 12437篇 |
排序方式: 共有10000条查询结果,搜索用时 7 毫秒
211.
212.
213.
214.
Gregory L. Dilworth 《Archives of biochemistry and biophysics》1982,219(1):30-38
The nicotinic acid hydroxylase from Clostridium barkeri is a selenoenzyme, as evidenced by the copurification of selenium with enzyme activity. This conclusion is supported by data showing a 23-fold increase in nicotinic acid hydroxylase activity when C. barkeri was cultured in media supplemented with selenium. A labile, selenium-containing compound was released from the native protein by treatment with either chaotropic agents and heat or by heating alone. A stable selenium compound was formed when the enzyme was alkylated prior to denaturation. This compound had the same chromatographic properties as dialykyl selenide in a number of systems. The formation of dialkyl selenide upon alkylation is not consistent with the selenium moiety being selenocysteine. Thus, nicotinic acid hydroxylase represents a new type of selenoenzyme. 相似文献
215.
216.
P. G. LADD S. W. CONNELL 《Botanical journal of the Linnean Society. Linnean Society of London》1994,116(1):77-88
It has been suggested by some authors that the low fruit to flower ratio in some Proteaceae is due to andromonoecy, while others, looking particularly at Banksia , have not been able to find evidence for male flowers in the inflorescences. Stirlingia latifolia, Xylomelum occidentals and X. angustifolium are clearly andromonoecous, while no evidence for this condition could be found in Brabejum stellatifoliutn. Production of fertile fruit is related to andromonoecy in Xylomelum and S. latifolia but not in Brabejum. It is unlikely that all-encompassing solutions will be found to what initially seem to be widespread traits in the family, especially in regard to pollination biology, as the genera in the family occupy widely different environments and have very diverse ecological ranges. 相似文献
217.
M. Rhr 《Biometrical journal. Biometrische Zeitschrift》1985,27(1):89-95
Some points of CLIFF /KRUS 's important rotation procedure are criticized. This result in the definition of simple structure of canonical solutions, the use of STEWART /LOVE 's redundancy index as a measure of common variance, and two new rotation procedures (HAKSTIAN 's modified varimax rotation, separate rotation of both sets). The objects of rotation should be the (intraset) loadings. 相似文献
218.
Bodil Kjær Yean-Sung Jung Lian Yu John H. Golbeck Henrik Vibe Scheller 《Photosynthesis research》1994,41(1):105-114
The photosynthetic reaction center complex from the green sulfur bacteriumChlorobium vibrioforme has been isolated under anaerobic conditions. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis reveals polypeptides with apparent molecular masses of 80, 40, 30, 18, 15, and 9 kDa. The 80- and 18-kDa polypeptides are identified as the reaction center polypeptide and the secondary donor cytochromec
551 encoded by thepscA andpscC genes, respectively. N-terminal amino acid sequences identify the 40-kDa polypeptide as the bacteriochlorophylla-protein of the baseplate (the Fenna-Matthews-Olson protein) and the 30-kDa polypeptide as the putative 2[4Fe-4S] protein encoded bypscB. Electron paramagnetic resonance (EPR) analysis shows the presence of an iron-sulfur cluster which is irreversibly photoreduced at 9K. Photoaccumulation at higher temperature shows the presence of an additional photoreduced cluster. The EPR spectra of the two iron-sulfur clusters resemble those of FA and FB of Photosystem I, but also show significantly differentg-values, lineshapes, and temperature and power dependencies. We suggest that the two centers are designated Center I (with calculatedg-values of 2.085, 1.898, 1.841), and Center II (with calculatedg-values of 2.083, 1.941, 1.878). The data suggest that Centers I and II are bound to thepscB polypeptide. 相似文献
219.
The effects on a cloned DNA fragment carrying an actinomycin resistance determinant on physiological processes in strains of streptomycetes with various potencies in producing this antibiotic, their inactive mutants, and the model strain ofStreptomyces lividans66 were studied. This fragment was shown to modulate bacterial resistance to actinomycin and biosynthesis of antibiotics. 相似文献
220.