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   7930篇
  免费   86篇
  国内免费   26篇
系统科学   235篇
丛书文集   27篇
教育与普及   8篇
理论与方法论   52篇
现状及发展   3606篇
研究方法   232篇
综合类   3764篇
自然研究   118篇
  2017年   48篇
  2016年   78篇
  2015年   95篇
  2014年   51篇
  2013年   56篇
  2012年   226篇
  2011年   301篇
  2008年   100篇
  2007年   102篇
  2006年   119篇
  2005年   300篇
  2004年   615篇
  2003年   560篇
  2002年   231篇
  2001年   205篇
  2000年   251篇
  1999年   159篇
  1992年   133篇
  1991年   83篇
  1990年   78篇
  1989年   74篇
  1988年   59篇
  1987年   65篇
  1986年   82篇
  1985年   98篇
  1984年   103篇
  1983年   69篇
  1982年   63篇
  1981年   58篇
  1980年   66篇
  1979年   186篇
  1978年   126篇
  1977年   146篇
  1976年   111篇
  1975年   115篇
  1974年   188篇
  1973年   176篇
  1972年   159篇
  1971年   181篇
  1970年   223篇
  1969年   216篇
  1968年   236篇
  1967年   194篇
  1966年   204篇
  1965年   157篇
  1964年   82篇
  1959年   42篇
  1958年   61篇
  1957年   50篇
  1956年   54篇
排序方式: 共有8042条查询结果,搜索用时 15 毫秒
41.
Summary N-methanesulfonyl 16-phenoxy--tetranor PGE2 is a prostaglandin analog which is markedly more tissue selective than PGE2. This compound is 10–30 times more potent than PGE2 in animal models which are considered relevant to antifertility effects in humans. In pharmacological tests which are believed to be predictive for side effects in humans, the compound has potency either equal to or less than that of PGE2.  相似文献   
42.
Summary A dissociation between inhibition of RNA synthesis and cell lysis was observed when thymocytes of adrenalectomized rats were incubated with high concentrations of pregn-4-ene-11-ol-3, 20-dione and pregna-1,4-diene-11-ol-3,20-dione. In contrast, no dissociation of these effects was found with the typical glucocorticoids cortisol and corticosterone, nor with their 1,4-diene analogs under the same conditions.Acknowledgments. This work was supported by grants from the Consejo Nacional de Investigaciones Científicas y Técnicas de la República Argentina to the Instituto de Biologia y Medicina Experimental and the Programa de Regulación Hormonal y Metabólica as well as by financial help from the Secretaría de Ciencia y Tecnología.  相似文献   
43.
Summary Daily evening injections of isoproterenol extended the period of high pineal N-acetyltransferase activity and retarded the growth of testes, seminal vesicles and prostate in rats treated neonatally with testosterone propionate.The authors are grateful to Mrs Marie Svobodová for her skillful technical assistance.  相似文献   
44.
45.
Summary The biochemical changes in the hemolymph and tissues were followed during regeneration of the optic tentacles of the snailCryptozona ligulata (Pulmonata-Stylommatophora). There is a remarkable increase in total carbohydrates in hemolymph and tissues and glycogen in tissues at the expense of free amino acids and fatty acids. It is clear that ablation of the optic tentacles stimulates carbohydrate synthesis through glyconeogenic routes. The optic tentacles regenerate completely in 18–21 days.  相似文献   
46.
In 10 sibships of haemophilic A patients, every one including 1 haemophilic brother with an antibody to factor VIII and 1 haemophilic brother without antibody, pattern of HLA segregation was analysed. All sibships were HLA haploidentical or different and not HLA identical. This fact suggested a linkage between the major histocompatibility complex and an "Ir" gene to factor VIII.  相似文献   
47.
J R Martinez  O H Petersen 《Experientia》1979,35(10):1343-1345
Using an automated system for the analysis of amylase, the release of this enzyme was compared in superfused parotid gland segments from control and reserpine treated rats. Stimulant-evoked amylase release was delayed and of smaller magnitude in the glands of the treated animals and a reduction of the transmembrane K+ gradient caused a smaller and short lasting reduction in Ach-evoked release of amylase in the glands from these animals.  相似文献   
48.
Three acidic polysaccharide (AP) fractions and the prostaglandin-like substances (PLS) isolated from P. acnes were investigated regarding their chemotactic activities on polymorphonuclear leukocytes. Both AP's and PLS induced a significant chemotatic response, which suggests their involvement in inflammatory acne vulgaris.  相似文献   
49.
It was shown that, in physiological concentrations, insulin enhances, in vitro, the immunological phagocytosis of sensitized sheep erythrocytes by cultured mouse peritoneal macrophages. Insulin seems to stimulate macrophage phagocytosis as a cholinomimetic agonist by increasing the intracellular levels of cyclic GMP.  相似文献   
50.
Hogg DC  Guiraud FO 《Nature》1979,279(5712):408-409
MEASUREMENT of the absolute value of absorption by water vapour at microwave frequencies is difficult because the effect is so small. Far in the wings of the absorption lines, in the so-called 'windows' of the spectrum, it is especially difficult to achieve high accuracy in the free atmosphere. But it is in these windows that the behaviour of the absorption is important from both applied and scientific points of view. Satellite communications, remote sensing of the atmosphere, and radioastronomy, are all influenced by this behaviour. Measurements on an Earth-space path are reported here; the results indicate a nonlinear relationship between absorption and water-vapour content.  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