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   26866篇
  免费   80篇
  国内免费   112篇
系统科学   139篇
丛书文集   140篇
教育与普及   74篇
理论与方法论   113篇
现状及发展   11194篇
研究方法   1169篇
综合类   13771篇
自然研究   458篇
  2013年   204篇
  2012年   398篇
  2011年   858篇
  2010年   171篇
  2008年   476篇
  2007年   543篇
  2006年   541篇
  2005年   557篇
  2004年   562篇
  2003年   521篇
  2002年   482篇
  2001年   868篇
  2000年   866篇
  1999年   538篇
  1994年   354篇
  1992年   530篇
  1991年   393篇
  1990年   461篇
  1989年   422篇
  1988年   392篇
  1987年   457篇
  1986年   444篇
  1985年   583篇
  1984年   427篇
  1983年   373篇
  1982年   334篇
  1981年   320篇
  1980年   337篇
  1979年   862篇
  1978年   645篇
  1977年   595篇
  1976年   538篇
  1975年   560篇
  1974年   695篇
  1973年   622篇
  1972年   566篇
  1971年   708篇
  1970年   981篇
  1969年   716篇
  1968年   719篇
  1967年   690篇
  1966年   697篇
  1965年   488篇
  1959年   245篇
  1958年   433篇
  1957年   259篇
  1956年   264篇
  1955年   231篇
  1954年   214篇
  1948年   241篇
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
251.
252.
Chlordiazepoxide selectively augments GABA action in spinal cord cell cultures   总被引:24,自引:0,他引:24  
D W Choh  D H Farb  G D Fischbach 《Nature》1977,269(5626):342-344
  相似文献   
253.
254.
Summary A one-step synthesis of hexahydrocannabinoid analogs (HHC) is described making use of the condensation of phenolic ketones and aldehydes with citronellal in the presence of pyridine.Grateful thanks are accorded to Drs L. Chopard and S. Selvavinayakam for spectral measurements and Dr I. Fleming for useful discussion.R. Mechoulam and Y. Gaoni, Recent advances in the chemistry of Hashish, in: Progress in the Chemistry of Organic natural products, vol. 25, p. 175. Ed. L. Zechmeister. Springer Verlag, Wien 1967; R. Mechoulam, Marijuana Chemistry and Pharmacology, metabolism and clinical effects. Academic Press, New York 1973; R. Mechoulam, N. K. McCallum and S. Burstein, Chem. Rev.76, 75 (1976).  相似文献   
255.
256.
Summary Wound trauma-induced survival from radiation may be related to increased mitosis in hematopoietic cells. This is supported by the cell cycle-dependent drug hydroxyurea, which 1. blocked survival of wounded mice injected 2 or 3 days after 900 rad and 2. reduced the number of endogenous CFU-s in wounded mice injected shortly before 700 rad.Supported by the Armed Forces Radiobiology Research Institute, Defense Nuclear Agency, under Research Work Unit MJ00018. Views presented in this paper are those of the authors; no endorsement by the Defense Nuclear Agency has been given or should be inferred.Research was conducted according to the principles enunciated in the Guide for the Care and Use of Laboratory Animals prepared by the Institute of Laboratory Research, National Research Council.  相似文献   
257.
Summary Basal and insulin-stimulated transport of 2-deoxy glucose and of -aminoisobutyric acid in mouse 3T3 fibroblasts were modulated by increasing the lipid microviscosity of the cell plasma membrane. The kinetics indicate that the insulin effect is induced either by recruitment of new transport carriers or by reduction of the translocation activation energy.This investigation was supported by grant No.5-R01-CA-27471-02, awarded by the National Cancer Institute, Department of Health, Education and Welfare.  相似文献   
258.
Summary The effect of cholesterol and fatty acid treatment in vitro was tested on rat liver plasma membrane-bound enzymes and lipid fluidity. The observed alterations of membrane fluidity affect both (Na+–K+)-ATPase and Mg2+-ATPase activities but not 5-nucleotidase; basal adenylate cyclase as well as its hormonal sensitivity were differentially affected by changes of membrane microenvironment.This investigation was partially supported by the Italian National Research Council.  相似文献   
259.
Summary The activity of D-lactate dehydrogenase in the foot of the snail,Helix pomatia, is closely correlated with time of year and mean daily temperature, and increases strikingly after the animals have been exposed to a nitrogen atmosphere for 24 h.I thank U. Platzer for technical assistance and D. Frank for help with the statistics. The investigation was supported by the Fonds zur Förderung der wissenschaftlichen Forschung in Österreich, project No. 1257 and 2919.  相似文献   
260.
Summary The transmitter substance released by nigro-thalamic fibres is proposed to be -aminobutyric acid, since picrotoxin blocked nigra-evoked monosynaptic inhibition of thalamic neurons.Supported by grants Nos 212009 and 311410 from Ministry of Education of Japan.The authors wish to thank Dr Marjorie Anderson, University of Washington, Seattle, for improving the English.  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