全文获取类型
收费全文 | 2056428篇 |
免费 | 209558篇 |
国内免费 | 2021篇 |
专业分类
2268007篇 |
出版年
2018年 | 20856篇 |
2017年 | 19534篇 |
2016年 | 30727篇 |
2015年 | 44754篇 |
2014年 | 53076篇 |
2013年 | 79432篇 |
2012年 | 62768篇 |
2011年 | 56967篇 |
2010年 | 52337篇 |
2009年 | 50954篇 |
2008年 | 51585篇 |
2007年 | 51548篇 |
2006年 | 51859篇 |
2005年 | 52417篇 |
2004年 | 51464篇 |
2003年 | 48442篇 |
2002年 | 46085篇 |
2001年 | 72078篇 |
2000年 | 70690篇 |
1999年 | 60197篇 |
1998年 | 30497篇 |
1997年 | 30364篇 |
1996年 | 29088篇 |
1995年 | 27259篇 |
1994年 | 26796篇 |
1993年 | 26460篇 |
1992年 | 51049篇 |
1991年 | 49147篇 |
1990年 | 47786篇 |
1989年 | 47641篇 |
1988年 | 44040篇 |
1987年 | 42200篇 |
1986年 | 39547篇 |
1985年 | 40807篇 |
1984年 | 36414篇 |
1983年 | 31707篇 |
1982年 | 27832篇 |
1981年 | 26016篇 |
1980年 | 24407篇 |
1979年 | 33522篇 |
1978年 | 28269篇 |
1977年 | 26371篇 |
1976年 | 24934篇 |
1975年 | 25994篇 |
1974年 | 27771篇 |
1973年 | 27748篇 |
1972年 | 24487篇 |
1971年 | 22625篇 |
1970年 | 19697篇 |
1969年 | 19177篇 |
排序方式: 共有10000条查询结果,搜索用时 62 毫秒
981.
Progesterone metabolism in T47Dco human breast cancer cells--II. Intracellular metabolic path of progesterone and synthetic progestins 总被引:1,自引:0,他引:1
K B Horwitz A W Pike C Gonzalez-Aller P V Fennessey 《Journal of steroid biochemistry》1986,25(6):911-916
We show here that progesterone added to the medium of proliferating T47Dco human breast cancer cells is metabolized with a half life of 2-4h. The final metabolic product, 5 alpha-pregnan-3 beta,6 alpha-diol-20-one, (P-metabolite) is released into the medium. This structure suggested that the intracellular metabolism of progesterone involves the enzymes 5 alpha-reductase, 3 beta-hydroxysteroid dehydrogenase, and 6 alpha-hydroxylase. To investigate this pathway, the cells were incubated with a variety of potential substrates. In addition to progesterone, only precursors with the 5 alpha-configuration served as substrates for the enzymes leading to P-metabolite formation. Some precursors with a 5 beta-configuration were also metabolized by T47Dco cells. This metabolism reflected activity by either 3 beta-hydroxysteroid dehydrogenase and/or 6 alpha-hydroxylase but, in contrast to progesterone metabolism, the rates were different and the products were often mixtures. In T47Dco and MCF-7 human breast tumor cells, the reduction at C-3 followed by 6 alpha-hydroxylation, appear to be the major, and possibly only, route of progesterone metabolism. In contrast, preliminary data suggest that in normal human breast epithelial cells, this is not an exclusive route. Androgens are partially subject to the same metabolic enzymes, but synthetic progestins are not metabolized by T47Dco during an 18 h incubation. 相似文献
982.
N A Voskanian E K Dzhikidze M A Pochkhura 《Zhurnal mikrobiologii, epidemiologii, i immunobiologii》1986,(3):62-65
The work presents the results of investigations, carried out in different monkey species, on the physiological norms as regards the bactericidal factors of neutrophilic polymorphonuclear leukocytes in the blood, nonenzymatic lysosomal cationic proteins and myeloperoxidase, as well as on changes in these characteristics in monkeys at different periods of their acclimatization at the Institute of Experimental Pathology and Therapy, Sukhumi. The possibility of correcting the characteristics under study by means of the immunostimulating agent levamisole is shown. 相似文献
983.
Steven C. Wiest 《Physiologia plantarum》1986,66(3):527-535
Kinetic parameters of 3-(3, 4-dichlorophenyl)-1, 1-dimethyl urea (DCMU)-induced inhibition of electron transport in chloroplast thylakoids isolated from Phaseolus vulgaris L. cv. Oregon 1604 were determined from analysis of a convergent, parallel electrical circuit. Through this analogue, the apparent affinity of the purported binding site for DCMU (K1 ) and the relative amount of DCMU-insensitive electron transport (vmax 1 /vo ) were obtained using a reiterative non-linear least squares curve-fitting procedure. Exposure of thylakoids to heat caused a gradual increase in K1 (or decrease in the affinity of the thylakoid for DCMU) with an apparent activation energy of 134 kJ mol−1 . Tryptic susceptibility of a protein region regulating K1 also decreased gradually with exposure to 45°C, suggesting that the heat-induced increase in K1 might be due to a protein conformational change. On the other hand, thylakoid exposure to 45°C resulted in a rapid (<5 min) irreversible increase in vmax I /vo , which was also the apparent result of a conformational change in a region of the protein which regulates this function. These results are suggestive of the existence of differential thermal sensitivities of proteins within the thylakoids and, perhaps, of different regions within a single membrane protein. 相似文献
984.
985.
986.
987.
C Chong-Cerrillo M E Selsted E M Peterson L M de la Maza 《The journal of peptide research》2003,61(5):237-242
Four antimicrobial peptides, protegrin-1, RTD-1, cryptdin-4, and indolicidin, were tested for their ability to inhibit the in vitro growth of Chlamydia trachomatis serovars E, L2, and mouse pneumonitis (MoPn). In general, protegrin-1 was found to have the strongest anti-chlamydial activity. Overall, of the three serovars tested, L2 was the most susceptible while MoPn was the most resistant to these peptides. 相似文献
988.
989.
The activity of cAMP-dependent protein kinases, cAMP binding and the spectrum of cAMP-binding proteins in renal papillary cytosol of intact rats and of rats kept on a water-deprived diet for 24 hours were investigated. It was found that the stimulation of protein kinases by 10(-6) M cAMP in the experimental group was significantly higher than in the control one. On DEAE-cellulose chromatography, the position of peaks of the specific cAMP binding corresponded to those of the regulatory cAMP-dependent protein kinases type I and II. Under these conditions, more than 80% of the binding activity in intact animals was localized in peak II, whereas in rats kept on a water-deprived diet over 60% of the binding activity was localized in peak I. The total binding activity of cytosol in experimental animals remained unchanged is compared to intact rats. It is suggested that in renal papilla dehydration is accompanied by the induction of synthesis of regulatory subunits of cAMP-dependent protein kinase type I. 相似文献
990.