全文获取类型
收费全文 | 185132篇 |
免费 | 10014篇 |
国内免费 | 89篇 |
专业分类
195235篇 |
出版年
2021年 | 1756篇 |
2020年 | 1476篇 |
2019年 | 1493篇 |
2018年 | 3661篇 |
2017年 | 3530篇 |
2016年 | 6058篇 |
2015年 | 10173篇 |
2014年 | 9915篇 |
2013年 | 11197篇 |
2012年 | 11678篇 |
2011年 | 8690篇 |
2010年 | 6220篇 |
2009年 | 5510篇 |
2008年 | 5785篇 |
2007年 | 5529篇 |
2006年 | 5240篇 |
2005年 | 10490篇 |
2004年 | 9163篇 |
2003年 | 6999篇 |
2002年 | 4412篇 |
2001年 | 3762篇 |
2000年 | 2966篇 |
1999年 | 3585篇 |
1998年 | 1274篇 |
1997年 | 993篇 |
1996年 | 994篇 |
1992年 | 3265篇 |
1991年 | 3175篇 |
1990年 | 3155篇 |
1989年 | 3082篇 |
1988年 | 3017篇 |
1987年 | 2782篇 |
1986年 | 2538篇 |
1985年 | 2569篇 |
1984年 | 1952篇 |
1983年 | 1462篇 |
1982年 | 994篇 |
1979年 | 1684篇 |
1978年 | 1301篇 |
1977年 | 1033篇 |
1976年 | 971篇 |
1975年 | 1342篇 |
1974年 | 1481篇 |
1973年 | 1500篇 |
1972年 | 1336篇 |
1971年 | 1260篇 |
1970年 | 1115篇 |
1969年 | 1155篇 |
1968年 | 1029篇 |
1967年 | 991篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
101.
102.
Effect of precursors on biosynthesis of monensins A and B 总被引:1,自引:0,他引:1
Precursors of monensins (acetate, propionate, butyrate, isobutyrate) affect the total production and the relative proportion of monensins A and B. Addition of propionate into the fermentation medium causes a prevalence of monensin B whereas butyrate and isobutyrate stimulate the production of monensin A and suppress the production of monensin B. 相似文献
103.
E E Vasar L K Riago A Kh Soosaar A M Nurk M O Ma?mets 《Biulleten' eksperimental'no? biologii i meditsiny》1985,100(12):711-713
Subcutaneous administration of caerulein (100-500 micrograms/kg) significantly reduced the development of picrotoxin (8 mg/kg) seizures in male mice. The same doses of caerulein inhibited 3H-flunitrazepam binding in in vivo experiments. Proglumide, an antagonist of cholecystokinin receptors, in low dose (5 mg/kg) potentiated the effects of caerulein (100 micrograms/kg), whereas the administration of proglumide in high dose (25 mg/kg) reduced the action of caerulein on 3H-flunitrazepam binding and picrotoxin seizures. Caerulein (5-1000 nM) decreased 3H-flunitrazepam binding in in vitro experiments only after supplementation of the binding medium with 120 mM NaCl and 5mM KCl. The results suggest the possible interaction of caerulein with chloride ionophor. It seems probable that the direct interaction of caerulein with chloride ionophor in involved in the inhibitory effect of caerulein on picrotoxin seizures and 3H-flunitrazepam binding. 相似文献
104.
P T M?nnist? 《Medical biology》1980,58(6):310-318
The subcellular distribution of the TRH-like immunoreactivity in the rat hypothalamus and brain was studied. In differential centrifugation, the 900 g for 10 min supernatant (S1) of the hypothalamus or brain contained 61--79% of the total TRH. At 11,000 g for 20 min, 51--73% of the TRH in S1 was sedimented. When the hypothalamic S1 was fractioned under non-equilibrium conditions at 25 degrees C, two populations of TRH-containing particles were observed in several types of continuous linear density gradients. Metrizamide and sucrose gradients affected TRH-assay. TRH-particles were very light in Percol-gradients. Isotonic dextran 40,000-sucrose gradients gave the most reproducible results. In these gradients, the large TRH-particles (35%) equilibrated at 1.055--1.060 kg/l and the small ones (23%) at 1.041--1.047 kg/l. Working at 4 degrees C decreased the amount of large TRH-particles. The apparently larger particles contained cytoplasmic and mitochondrial enzymes and were sensitive to hypoosmotic shock like synaptosomes. Electron micrographs confirmed that these particles were synaptosomes. The true nature of the small particles remained unclear but morphologically a part of them were also synaptosomes. Treatment of the animals with reserpine (10 mg/kg i.p., 24 h), with 6-hydroxydopamine (100 microgram/rat i.c.v.) or with 5,7-dihydroxytryptamine (200 microgram/rat i.c.v.) did not affect significantly TRH-recovery or distribution in the hypothalamus. 相似文献
105.
106.
The present study has shown that on the level of the parasitic system the epidemic process is a biological system, wherein the host population serves as the internal regulator, the mechanism of transmission serves as the external regulator and the parasite population, as the regulated object. The biological regulating mechanisms of the epidemic process have fundamental differences in the groups of infectious with various mechanisms of transmission, and the specific nature of the mechanism of transmission determines the peculiar features of the biological mechanism which governs the self-regulation of the epidemic process. In contrast, on a higher level of the organization of the epidemic process, i. e. on the level of the socio-ecological system, the epidemic process is a biosocial system, wherein the human society serves as the regulator, the parasitic system serves as the regulated object and the mechanism of transmission plays the role of the filter which determines the scope of social factors, most important in the regulation of the epidemic process in a given infection. The spontaneous regulation of the epidemic process is the freed forward channel from the regulator to the regulated object, and the controlled regulation is the feedback channel. 相似文献
107.
Is the mitochondrial precursor protein apocytochrome c able to pass a lipid barrier? 总被引:4,自引:0,他引:4
To obtain insight into the role of lipids in the translocation of extramitochondrially synthesized proteins, we studied the ability of apocytochrome c to pass lipid bilayers. With polyacrylamide gel electrophoresis, the digestion of externally added apocytochrome c by trypsin, enclosed in lipid vesicles, was followed. The experiments demonstrate that apocytochrome c is able to pass a lipid barrier and this process shows both a lipid- and protein specificity. The most probable molecular mechanisms involved in this phenomenon are discussed. 相似文献
108.
109.
I de Hurtado A G Osler 《Proceedings of the Society for Experimental Biology and Medicine. Society for Experimental Biology and Medicine (New York, N.Y.)》1975,149(3):633-637
The anti-DNP response to DNP-BGG is substantially suppressed in guinea pigs sensitized to DNCB. The degree of antibody suppression varies with the mode of skin sensitization and with the degree of conjugation of the challenging immunogen. Suppression of the anti-HSA response was also induced by the prior injection of CFA. 相似文献
110.