全文获取类型
收费全文 | 5626篇 |
免费 | 374篇 |
国内免费 | 566篇 |
出版年
2024年 | 17篇 |
2023年 | 108篇 |
2022年 | 143篇 |
2021年 | 193篇 |
2020年 | 182篇 |
2019年 | 188篇 |
2018年 | 184篇 |
2017年 | 179篇 |
2016年 | 182篇 |
2015年 | 170篇 |
2014年 | 222篇 |
2013年 | 472篇 |
2012年 | 175篇 |
2011年 | 195篇 |
2010年 | 153篇 |
2009年 | 264篇 |
2008年 | 302篇 |
2007年 | 313篇 |
2006年 | 250篇 |
2005年 | 220篇 |
2004年 | 228篇 |
2003年 | 182篇 |
2002年 | 160篇 |
2001年 | 165篇 |
2000年 | 101篇 |
1999年 | 116篇 |
1998年 | 114篇 |
1997年 | 88篇 |
1996年 | 95篇 |
1995年 | 93篇 |
1994年 | 83篇 |
1993年 | 75篇 |
1992年 | 80篇 |
1991年 | 70篇 |
1990年 | 56篇 |
1989年 | 68篇 |
1988年 | 65篇 |
1987年 | 49篇 |
1986年 | 45篇 |
1985年 | 71篇 |
1984年 | 89篇 |
1983年 | 45篇 |
1982年 | 64篇 |
1981年 | 41篇 |
1980年 | 44篇 |
1979年 | 39篇 |
1978年 | 36篇 |
1977年 | 28篇 |
1976年 | 19篇 |
1974年 | 15篇 |
排序方式: 共有6566条查询结果,搜索用时 15 毫秒
1.
Robert C. Tait Byron E. Froman Debbie L. Laudencia-Chingcuanco Leslie D. Gottlieb 《Plant molecular biology》1988,11(4):381-388
Nuclear genes that appear to encode both cytosolic and plastid isozymes of phosphoglucose isomerase (PGI), an essential glycolytic enzyme, have been isolated from three diploid species of the annual wild flower genus Clarkia (Onagraceae). The genes do not contain introns and are expressed to varying degrees in Escherichia coli when cloned in either Charon 35 phage or pUC plasmid vectors. The PGI proteins synthesized in E. coli form dimers, are catalytically active, and their electrophoretic mobilities are similar to those of appropriate Clarkia PGIs. The nucleotide sequence of a gene encoding a plastid isozyme of C. unguiculata is described. 相似文献
2.
The influence of hypomagnesemia on erythrocyte antioxidant enzyme defence system in mice 总被引:2,自引:1,他引:1
Andrzej Kuzniar Przemyslaw Mitura Piotr Kurys Stanislawa Szymonik-Lesiuk Boleslaw Florianczyk Marta Stryjecka-Zimmer 《Biometals》2003,16(2):349-357
The effect of magnesium deficiency on antioxidant defence system was studied in RBC of mice suffering from hypomagnesemia. The animals were kept for 8, 15 and 22 days on magnesium-deficient diet with consequent reduction of magnesium level in plasma by 38% at the first 8 days and by 64% after 22 days of experiment. The activities of the most important antioxidant enzymes, catalase, glutathione peroxidase, superoxide dismutase, glutathione reductase, glutahione S-transferase were assayed in hemolysates. The level of reduced glutathione in erythrocytes was measured as well. Apart from catalase, the activities of antioxidant enzymes were decreasing. The activity of superoxide dismutase decreased gradually during the experiment and on the 15th and 22nd day of experiment was significantly (P<0,05) lowered by 30 and 32% respectively. The catalase activity was increased on each point of the experiment with the peak value up to 149% on 15th day, and by 32% on 22nd day. Glutathione peroxidase activity was insignificantly reduced. The reduction of Glutatione reductase and Glutathione S-transferase activities by 24 and 21%, respectively, were observed after 8 days of the experiment with a further downward tendency. The reduced glutathione was significantly depleted after 8 days by 33% and was kept on that level in the course of the study. These findings support previous reports on the hypomagnesemia – induced alteration in endogenous enzyme antioxidant defences and glutathione redox cycle of mice. 相似文献
3.
Free radical mechanisms in enzyme reactions 总被引:1,自引:0,他引:1
Isao Yamazaki 《Free radical biology & medicine》1987,3(6):397-404
Free radicals are formed in prosthetic groups or amino acid residues of certain enzymes. These free radicals are closely related to the activation process in enzyme catalysis, but their formation does not always result in the formation of substrate free radicals as a product of the enzyme reactions. The role of free radicals in enzyme catalysis is discussed. 相似文献
4.
Lawrence Que Jr. 《Journal of biological inorganic chemistry》2004,9(6):684-690
The oxygen activation mechanisms proposed for nonheme iron systems generally follow the heme paradigm in invoking the involvement of iron-peroxo and iron-oxo species in their catalytic cycles. However, the nonheme ligand environments allow for end-on and side-on dioxygen coordination and impart greater flexibility in the modes of dioxygen activation. The currently available evidence for nonheme iron-peroxo and iron-oxo intermediates is summarized and discussed in light of the ongoing discussion on the nature of the oxidant(s) in heme enzymes. 相似文献
5.
6.
Preparation of chloroplast DNA from pea plastids isolated in a medium of high ionic strength 总被引:8,自引:0,他引:8
A simple, rapid, and inexpensive method for the preparation and purification of chloroplast DNA (cpDNA) from pea has been developed. The crucial step is the isolation of chloroplasts in a medium of high ionic strength (I congruent equal to 1.40 M). CpDNA from pea prepared according to this method has successfully been used for restriction enzyme mapping, Southern transfers, and cloning. 相似文献
7.
《Fungal biology》2020,124(1):65-72
This review deals with characteristics of peptidases of fungi whose life cycles are associated with insects to varying degrees. The review examines the characteristic features of the extracellular peptidases of entomopathogenic fungi, the dependence of the specificity of these peptidases on the ecological characteristics of the fungi, and the role of peptidases in the development of the pathogenesis. Data on the properties and physiological role of hydrolytic enzymes of symbiotic fungi in “fungal gardens” are also considered in detail. For the development of representations about mechanisms of control over populations of insect pests, special attention is given to analysis of possibilities of genetic engineering for the creation of entomopathogens with enhanced virulence. Clarification of the role of fungi and their secreted enzymes and careful environmental studies are still required to explain their significance in the composition of the biota and to ensure widespread adoption of these organisms as effective biological control agents. The systematization and comparative analysis of the existing data on extracellular peptidases of insect-associated fungi will help in the planning of further work and the search for markers of pathogenesis and symbiosis. 相似文献
8.
9.
Summary Using an aeroscope, airborne fungal spores were sampled for two years, 1987–1988 at Tiruchirapalli, Tamil Nadu, India. The aerospora components, their seasonal and annual variations in incidence in the air are discussed and a spore calendar for Tiruchirapalli is presented. 相似文献
10.