全文获取类型
收费全文 | 134887篇 |
免费 | 4128篇 |
国内免费 | 841篇 |
出版年
2022年 | 258篇 |
2021年 | 599篇 |
2020年 | 396篇 |
2019年 | 491篇 |
2018年 | 12355篇 |
2017年 | 11099篇 |
2016年 | 8378篇 |
2015年 | 2331篇 |
2014年 | 2153篇 |
2013年 | 2732篇 |
2012年 | 7128篇 |
2011年 | 15681篇 |
2010年 | 13763篇 |
2009年 | 9772篇 |
2008年 | 12124篇 |
2007年 | 13667篇 |
2006年 | 2517篇 |
2005年 | 2829篇 |
2004年 | 3233篇 |
2003年 | 3180篇 |
2002年 | 2890篇 |
2001年 | 760篇 |
2000年 | 566篇 |
1999年 | 537篇 |
1998年 | 618篇 |
1997年 | 482篇 |
1996年 | 421篇 |
1995年 | 393篇 |
1994年 | 363篇 |
1993年 | 378篇 |
1992年 | 413篇 |
1991年 | 369篇 |
1990年 | 280篇 |
1989年 | 280篇 |
1988年 | 297篇 |
1987年 | 266篇 |
1986年 | 235篇 |
1985年 | 303篇 |
1984年 | 331篇 |
1983年 | 276篇 |
1982年 | 354篇 |
1981年 | 275篇 |
1980年 | 258篇 |
1979年 | 192篇 |
1978年 | 223篇 |
1977年 | 212篇 |
1974年 | 191篇 |
1973年 | 194篇 |
1972年 | 374篇 |
1971年 | 375篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
181.
182.
183.
184.
Paul H. De Kruif 《The Journal of general physiology》1922,4(4):387-393
A distinct difference in acid agglutination optimum for Type D (bacillus of rabbit septicemia) and its mutant form, Type G, has been observed. The optimum for Type D lies between pH 3.5 and pH 3.0. This changes during mutation, the resulting Type G mutants having in general an optimum lying between pH 4.7 and pH 3.8. The constancy of the optimum for Type D is very strict, while that for Type G is slightly less so. The variation is never so great as to cause an overlapping of optima and consequent failure of differentiation. These acid agglutination optima are in the nature of physical constants for the two types and would imply a fundamental difference in the chemical constitution of the organisms. Animal passage, far from causing a reversion of the mutant Type G to the primordial Type D form, brings about a still greater instability in the presence of H ions. 相似文献
185.
186.
Background
Arsenic contamination is widespread throughout the world and this toxic metalloid is known to cause cancers of organs such as liver, kidney, skin, and lung in human. In spite of a recent surge in arsenic related studies, we are still far from a comprehensive understanding of arsenic uptake, detoxification, and sequestration in plants. Crambe abyssinica, commonly known as 'abyssinian mustard', is a non-food, high biomass oil seed crop that is naturally tolerant to heavy metals. Moreover, it accumulates significantly higher levels of arsenic as compared to other species of the Brassicaceae family. Thus, C. abyssinica has great potential to be utilized as an ideal inedible crop for phytoremediation of heavy metals and metalloids. However, the mechanism of arsenic metabolism in higher plants, including C. abyssinica, remains elusive. 相似文献187.
Paul C. Lauterbur 《Cell biochemistry and biophysics》1986,9(1-2):211-214
188.
189.
Different secretory pathways of renin from mouse cells transfected with the human renin gene 总被引:5,自引:0,他引:5
R E Pratt J A Flynn P M Hobart M Paul V J Dzau 《The Journal of biological chemistry》1988,263(7):3137-3141
Mammalian cells in culture, transfected with human renin gene, can provide a useful tool for studying renin biosynthesis and secretion. We transfected fibroblast cells (mouse L929 and Chinese hamster ovary cells) and pituitary tumor cells (mouse AtT-20) with the human renin gene and a selectable plasmid (pSV2Neo). Transfected fibroblasts synthesize prorenin only. Prorenin is secreted by fibroblasts constitutively and the secretion is not influenced by 8-bromo-cAMP. On the other hand, transfected AtT-20 cells synthesized both prorenin and mature active renin. Transfected AtT-20 cells release prorenin by constitutive secretion but mature renin is secreted by a regulated mechanism since the secretion of the former is not influenced by 8-bromo-cAMP but the release of the latter is significantly stimulated. Our studies demonstrate that human renin may be secreted by at least two cellular pathways: prorenin by a constitutive pathway and mature renin by a regulated pathway. These transfected cells may provide useful models for studies of human renin synthesis, processing, and secretion. 相似文献
190.
Using the imidate procedure, 2,3,4,6-tetra-O-benzyl-1-O-(N-methylacetimidoyl)-β-d-galactopyranose was condensed with various monosaccharides to provide, in good yield and with high stereoselectivity, α-linked disaccharides. 相似文献