全文获取类型
收费全文 | 517篇 |
免费 | 30篇 |
国内免费 | 1篇 |
专业分类
548篇 |
出版年
2023年 | 4篇 |
2022年 | 5篇 |
2021年 | 7篇 |
2019年 | 5篇 |
2018年 | 6篇 |
2017年 | 11篇 |
2016年 | 14篇 |
2015年 | 18篇 |
2014年 | 28篇 |
2013年 | 37篇 |
2012年 | 35篇 |
2011年 | 28篇 |
2010年 | 16篇 |
2009年 | 24篇 |
2008年 | 17篇 |
2007年 | 24篇 |
2006年 | 33篇 |
2005年 | 16篇 |
2004年 | 15篇 |
2003年 | 13篇 |
2002年 | 8篇 |
2001年 | 16篇 |
2000年 | 12篇 |
1999年 | 6篇 |
1998年 | 11篇 |
1997年 | 3篇 |
1996年 | 3篇 |
1995年 | 3篇 |
1994年 | 3篇 |
1992年 | 7篇 |
1991年 | 10篇 |
1990年 | 8篇 |
1989年 | 10篇 |
1988年 | 4篇 |
1987年 | 6篇 |
1986年 | 10篇 |
1985年 | 4篇 |
1984年 | 6篇 |
1982年 | 3篇 |
1981年 | 4篇 |
1979年 | 8篇 |
1978年 | 2篇 |
1977年 | 6篇 |
1976年 | 5篇 |
1975年 | 7篇 |
1974年 | 4篇 |
1973年 | 4篇 |
1971年 | 4篇 |
1969年 | 3篇 |
1967年 | 2篇 |
排序方式: 共有548条查询结果,搜索用时 0 毫秒
521.
522.
Goldfish were exposed to three qualitatively distinct forms of respiratory stress: phenylhydrazine HCl-induced reduction in blood oxygen-carrying capacity; transient (3 h) hypoxia; and transient (1 or 2 h) temperature-forced increases in oxygen demand. Response embodied three common features: (1) the relative number of immature red cells increased, and these were 3 H-thymidine positive; (2) the abundance of apparently karyorrhectic or degenerating cells rose; (3) cells undergoing a form of division became prevalent. Neither of the latter two cell types evidenced thymidine uptake. These observations suggest that respiratory distress triggers the proliferation of new erythrocytes, and that this is accompanied by elimination of some portion of the preexisting red cell population. It is hypothesized that the latter process limits viscosity-related elevation of cardiac work costs. The significance of division by circulating erythrocytes is not clear. 相似文献
523.
Goldfish acclimated for minimum periods of 3 weeks to 5, 15, 25 and 35°C exhibited significant changes in circulating leucocyte types and numbers. Total leucocyte, lymphocyte, neutrophil and eosinophil levels increased significantly between 5 and 25°C, as did their relative contributions to the total leucocyte population. Thrombocyte and blast cell counts increased non-significantly, while variations in monocyte and basophil levels were inconsistent. Between 25 and 35° C, lymphocyte numbers fell sharply, while neutrophil concentrations remained essentially constant as did those of thrombocytes. Response to an intraperitoneally administered mitogen, phytohaemagglutinin, was delayed and reduced at 5° C compared with 25° C. 相似文献
524.
T M Murad 《Acta cytologica》1971,15(4):400-409
525.
526.
The effect of hydralazine on several parameters of collagen biosynthesis has been studied in cultured human skin fibroblasts. Cells treated with hydralazine synthesized procollagen which was severely deficient in hydroxyproline and hydroxylysine, indicating inhibition of prolyl and lysyl hydroxylase reactions in the cell. Assays of prolyl and lysyl hydroxylase activities, however, revealed markedly increased levels in hydralazine-treated cells. The stimulatory effect of hydralazine could not be simulated in cell extracts, demonstrating its requirement for intact cells. The effect occurred slowly over a period of 96 h and was dependent on hydralazine concentration between 10 and 100 microM. This phenomenon was also observed in lysyl hydroxylase-deficient mutants. In both normal and mutant cells the relative magnitude of the hydralazine effect could be modified by ascorbic acid in the culture medium. Ascorbic acid increased the response of prolyl hydroxylase to hydralazine from 1.5- to 2-fold to 3- to 7-fold, whereas it decreased the response of lysyl hydroxylase to hydralazine from 4- to 8-fold to 2- to 3-fold. Total collagen synthesis was substantially reduced in hydralazine-treated cells; the time course and the dose-response relationship were similar to those observed for the hydroxylases. alpha, alpha'-Dipyridyl, an iron chelator, mimicked these effects of hydralazine. The studies suggest the existence in cultured cells of a compensatory mechanism for overproduction of these crucial enzymes in collagen biosynthesis, a mechanism which remains functional in cells derived from patients afflicted with hydroxylysine-deficient collagen disease. 相似文献
527.
A NO synthase (NOS, EC 1.14.23) was isolated from human cerebellum by two sequential chromatography steps, that is affinity chromatography on 2'5'ADP sepharose and size exclusion chromatography on Superose 6. Human NOS migrated as a single band of 160 kDa on SDS/PAGE. The enzyme was Ca2+/calmodulin-regulated and NADPH/tetrahydrobiopterin (BH4)-dependent, which are characteristics of a type I NOS previously isolated from rat cerebellum. Antisera raised against purified rat cerebellar NOS crossreacted specifically with a 160 kDa protein in crude supernatant fraction of human cerebellum and purified human NOS but not in crude supernatant fraction of the temporal lobe. These findings provide evidence that nitrinergic signal transduction through conversion of L-arginine to L-citrulline and NO does also occur in humans and NO may function as a neurotransmitter in the human central nervous system. 相似文献
528.
T M Murad 《Acta cytologica》1973,17(5):401-409
529.
530.