首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   40717篇
  免费   183篇
  国内免费   332篇
系统科学   492篇
丛书文集   794篇
教育与普及   105篇
理论与方法论   136篇
现状及发展   16606篇
研究方法   1582篇
综合类   20608篇
自然研究   909篇
  2013年   474篇
  2012年   773篇
  2011年   1709篇
  2010年   498篇
  2009年   447篇
  2008年   894篇
  2007年   1081篇
  2006年   1028篇
  2005年   997篇
  2004年   900篇
  2003年   709篇
  2002年   742篇
  2001年   1154篇
  2000年   1176篇
  1999年   818篇
  1992年   722篇
  1991年   546篇
  1990年   580篇
  1989年   542篇
  1988年   536篇
  1987年   542篇
  1986年   555篇
  1985年   714篇
  1984年   552篇
  1983年   429篇
  1982年   398篇
  1981年   427篇
  1980年   508篇
  1979年   1169篇
  1978年   898篇
  1977年   919篇
  1976年   699篇
  1975年   745篇
  1974年   1078篇
  1973年   909篇
  1972年   985篇
  1971年   1082篇
  1970年   1410篇
  1969年   1147篇
  1968年   1029篇
  1967年   1077篇
  1966年   1002篇
  1965年   737篇
  1959年   387篇
  1958年   715篇
  1957年   508篇
  1956年   399篇
  1955年   375篇
  1954年   405篇
  1948年   257篇
排序方式: 共有10000条查询结果,搜索用时 11 毫秒
171.
Crosses between two classes of Drosophila melanogaster strains (reactive and inducer) may lead to partially sterile F1 females. This sterility, called S.F. sterility, can be characterized by its physiological features. It appears to be the result of an interaction between two factors: "R" brought into the initial croos by the reactive mother and "I" by chromosomes of the inducer father. Except for chromosome 4, each chromosome of the well known inducer strains may carry the I factor (inducer chromosomes). The present results provide evidence for the presence of an inducer fourth chromosome in the inducer strain Nagasaki.  相似文献   
172.
The use of the stable isotopes 6 and 7 of lithium, and detection with the ionic analyser, allow the measurement of unidirectional transepithelial Li-fluxes, between "external" and "internal" solutions which both contain 80% Na and 20% Li. Efflux was found to be bigger than influx. An important lag-phase on the curve, reveals the interference of a Li-compartment, with a high capacity, in the epithelium itself.  相似文献   
173.
174.
Summary The binding of coumarin to serum proteins of the rat has been demonstrated. Of the total bound coumarin (37% of injected dose), 36% was bound to the slow and fast 1 globulins, 11% to the post albumins, 10% to globulin and 9% to albumin.  相似文献   
175.
Summary The male antifertility agent 1-amino-3-chloropropan-2-ol (ACP,I) has been shown to be metabolized to-chlorohydrin (III) and metabolites of-chlorohydrin. This accounts for the similar antifertility and renal toxicity effects of both compounds.  相似文献   
176.
Summary Abnormal-8-tetrahydrocannabidiol (ABN-8-THC) failed to elicit central nervous system and cardiovascular effects in laboratory animals. Abnormal-cannabidiol (ABN-CBD) was also devoid of overt behavioral effects but produced marked hypotension with only slight bradycardia in anesthesized dogs.Acknowledgment. This work was supported by NIDA (grant No. DA-00574-01 and DA-00490) and Virginia Heart Society (grant No. RR-05697)  相似文献   
177.
178.
Summary Using the Fell technique of organ culture of cartilage in a chemically defined medium, it has been shown that prostaglandin A1 at a concentration of 25 g/ml caused chondrocyte death in chick embryonic limb rudiments. An equimolar concentration of PGE2 was not toxic to the cells.Acknowledgments. We are grateful for the support of C. J. K. by the Medical Research Council and of D. L. G. by the Arthritis and Rheumatism Council for Research. Our thanks are due to Dame Honor Fell, F. R. S. for invaluable advice and guidance, to Dr J. Pike (Upjohn Co.) for supplies of prostaglandin A1, and to Dr Sylvia Fitton-Jackson for the gift of culture medium.  相似文献   
179.
180.
Summary On the basis of comparative spectral data, the structures of 3 novel steroidal glycosides from the Mediterranean starfishHacelia attenuata have been elucidated as3, 4 and5. These are further examples of a novel group of 24-O-glycosidated steroids recently encountered in the same species and in the Pacific speciesProtoreaster nodosus.Part 9. L. Minale, C. Pizza, R. Riccio and F. Zollo, Experientia39 (1983) 567. This contribution is part of the Progetto Finalizzato Chimica fine e secondaria del C.N.R., Roma.Acknowledgments. We thank Prof. K. Nakanishi, Columbia University, New York, for FD-mass spectral analyses, the Centro Interfacoltà di Metodologie Chimico-Fisiche for 270 MHz NMR facilities, and Miss R. Aquino for part of the experimental work.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号