全文获取类型
收费全文 | 10271篇 |
免费 | 25篇 |
国内免费 | 38篇 |
专业分类
系统科学 | 30篇 |
丛书文集 | 48篇 |
教育与普及 | 30篇 |
理论与方法论 | 24篇 |
现状及发展 | 3979篇 |
研究方法 | 535篇 |
综合类 | 5515篇 |
自然研究 | 173篇 |
出版年
2012年 | 153篇 |
2011年 | 331篇 |
2010年 | 60篇 |
2009年 | 55篇 |
2008年 | 172篇 |
2007年 | 210篇 |
2006年 | 195篇 |
2005年 | 216篇 |
2004年 | 214篇 |
2003年 | 192篇 |
2002年 | 209篇 |
2001年 | 431篇 |
2000年 | 440篇 |
1999年 | 296篇 |
1996年 | 52篇 |
1994年 | 269篇 |
1992年 | 256篇 |
1991年 | 201篇 |
1990年 | 230篇 |
1989年 | 192篇 |
1988年 | 186篇 |
1987年 | 194篇 |
1986年 | 202篇 |
1985年 | 271篇 |
1984年 | 202篇 |
1983年 | 164篇 |
1982年 | 138篇 |
1981年 | 141篇 |
1980年 | 145篇 |
1979年 | 326篇 |
1978年 | 264篇 |
1977年 | 219篇 |
1976年 | 194篇 |
1975年 | 195篇 |
1974年 | 209篇 |
1973年 | 179篇 |
1972年 | 206篇 |
1971年 | 246篇 |
1970年 | 303篇 |
1969年 | 230篇 |
1968年 | 226篇 |
1967年 | 195篇 |
1966年 | 225篇 |
1965年 | 149篇 |
1959年 | 75篇 |
1958年 | 123篇 |
1957年 | 81篇 |
1956年 | 58篇 |
1954年 | 62篇 |
1948年 | 57篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
The levels of membrane alkaline phosphatase have been measured on different lymphocyte fractions from human peripheral blood separated on bovine serum albumin discontinuous gradients. The peak in enzyme activity was observed in a non-T-, non-B-cell fraction, rich in "null" lymphocytes; the lowest values were found in the fraction with the highest proportion of T-cells. 相似文献
92.
(3H)-Ouabain binding to liver and kidney preparations was utilized to estimate the number of Na+, K+-ATPase enzyme units in livers and kidneys from rats fed 2% corn oil supplemented or fat-free diets. The specific (3H)-ouabain binding in liver and kidney preparations from fatty acid deficient rats was increased approximately 40%, but the affinity of the binding sites for ouabain (Kd-value) remained unchanged. The increased concentration of Na+, K+-ATPase enzyme units observed in the essential fatty acid deficient rats may contribute to the reduced body fat accumulation and elevated heat production observed in these animals. 相似文献
93.
Summary A rotator culture method is described which provides a continuous flow of oxygenating gas to cultures in rotating bottles. The system maintains constant O2 and CO2 levels in the culture medium throughout the incubation period. It also provides a more stable pH than systems with sealed culture bottles.Acknowledgments. We would like to thank Mr B. Secker, Mr C. Hellon and Mr S. J. Ellis, of the Physiological Laboratory workshop, for constructing the rotator apparatus. We also thank the Medical Research Council, London, for financial support for the project. 相似文献
94.
T. Saito T. Nohno H. Yoshida H. Yokoya 《Cellular and molecular life sciences : CMLS》1979,35(5):696-699
Summary Trans-4-hydroxy-3-methoxycinnamic acid (ferulic acid, FA) antagonized the effect of exogenous androgens on the ventral prostate (VP) in castrated rats as well as the effect of endogenous androgens in intact rats. FA, however, had no effect on the seminal vesicles (SV) and levator ani muscle (LAM), nor oestrogenic effect in female rats and mice. FA did not antagonize the receptor binding of testosterone nor inhibit the conversion of testosterone into 5-dihydrotestosterone (DHT).Supported in part by the project fund (grant 53-403) of Kawasaki Medical School.The authors would like to thank the Central Laboratory, Sankyo Pharmaceutical Co., Tokyo, for supplying 19-nortestosterone-17-ferulate. 相似文献
95.
IT has been suggested that the bacterial flora of the rumen should be considered as three distinct, interacting populations-the bacteria of rumen fluid (the population which has been studied most extensively), the bacteria associated with food particles, and the bacteria adhering to the epithelial wall of the organ(1). Until now, studies of the 'epithelial' population have been restricted to examination of postmortem samples of wall tissue and its attached bacterial flora(2-5). A recently developed technique(6) for feeding young sheep for long periods solely by infusion of protein and other essential nutrients into the abomasum, and of volatile fatty acids and bicarbonate buffer into the rumen, has provided us with an opportunity to study in isolation the role of the bacterial population of the wall in the ecomicrobiology of the rumen in the living animal. Our studies show that this population can exist independently of the other two populations, that it is primarily responsible for urea digestion in the rumen and that it initiates breakdown of dead epithelial tissue. Furthermore, our results point to an inverse relationship between ammonia concentration and ureolytic activity in rumen fluid, which may account for the control which ammonia exerts over flux of urea across the rumen wall(7-9). 相似文献
96.
Summary The paper describes a hexagonal array of nuclear pores in a non-redundant region of the nuclear envelope underlying the basal surface of the rat spermatozoon head. It is concluded that intranuclear material protruding through these pores is the cause of the characteristic rows of circular bumps found in surface replicas of this region. 相似文献
97.
Summary The serum activities of aspartate aminotransferase, alanine aminotransferase, -hydroxybutyrate dehydrogenase and creatine phosphokinase have been measured in the African elephant. In general, the values were broadly comparable with those of man except that alanine aminotransferase was much lower and creatine phosphokinase higher. No variation due to age, sex, season or location was observed. 相似文献
98.
99.
The DNP fibres gamma-irradiated under aerobic condition showed a reduction of their diameter, while no remarkable changes were observed in the DNP fibres irradiated under hypoxic condition by scanning electron microscopy. 相似文献
100.
T Dalton 《Experientia》1976,32(11):1421-1423
5-Hydroxytryptamine creatinine sulphate loses its biological activity when maintained at room temperature. The loss of 5-HT activity (in stimulating sodium transport across frog skin) is greater than the loss of creatinine sulphate activity (inhibition of sodium transport). 相似文献