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   38859篇
  免费   67篇
  国内免费   106篇
系统科学   185篇
丛书文集   779篇
教育与普及   100篇
理论与方法论   233篇
现状及发展   17193篇
研究方法   1543篇
综合类   18500篇
自然研究   499篇
  2013年   245篇
  2012年   524篇
  2011年   1047篇
  2010年   232篇
  2008年   648篇
  2007年   670篇
  2006年   703篇
  2005年   717篇
  2004年   637篇
  2003年   691篇
  2002年   665篇
  2001年   1149篇
  2000年   1056篇
  1999年   732篇
  1992年   697篇
  1991年   557篇
  1990年   603篇
  1989年   595篇
  1988年   599篇
  1987年   612篇
  1986年   580篇
  1985年   737篇
  1984年   584篇
  1983年   494篇
  1982年   444篇
  1981年   434篇
  1980年   572篇
  1979年   1214篇
  1978年   1031篇
  1977年   1020篇
  1976年   757篇
  1975年   823篇
  1974年   1128篇
  1973年   1009篇
  1972年   1066篇
  1971年   1256篇
  1970年   1634篇
  1969年   1260篇
  1968年   1211篇
  1967年   1239篇
  1966年   1061篇
  1965年   754篇
  1964年   191篇
  1959年   446篇
  1958年   682篇
  1957年   541篇
  1956年   455篇
  1955年   396篇
  1954年   424篇
  1948年   269篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
281.
Summary Growth-promoting alpha-globulin (GPAG), a specific serum protein complex which induces mitotic activity in continually replicating metazoan cells in vitro, was shown in this study to support growth of astrocytes and mesenchymal cells as well as process formation of nerve cells isolated from cerebral hemispheres of chick embryos.  相似文献   
282.
Summary Subdermal injections of PGE2 (5 g) in the rat foot lead to increases in the potentials evoked in sensory nerve branches by the mechanical stimulation of the skin. This sensitization of both A and C fibres complements the previously described hyperalgesic effects of prostaglandins of the E series.  相似文献   
283.
    
Summary -Galactosidase activity in intact cells of 21 species ofStreptomyces was measured using ONPG hydrolysis, without addition of a permeabilizing agent. Differences in the induction efficiency of ONPG-hydrolytic activity by lactose or galactose, which could have taxonomic implications, were observed among the species.  相似文献   
284.
Summary Adult spontaneously hypertensive rats (SHR) are less sensitive to painful stimuli than their normotensive controls, Wistar-Kyoto (WKY) rats. This difference can be eliminated by the specific opiate antagonist, naloxone, and by the -adrenergic blocking agent, propranol.Acknowledgment. The author wishes to thank Miss R. L. Holcomb for her editorial assistance.  相似文献   
285.
In vivo studies indicated that the primary effects of E. coli endotoxin on hepatic clearance of sulfobromophthalein were at the excretory level. Newborns were more sensitive to the LPS than older animals.  相似文献   
286.
287.
J J?rhult  J J Holst 《Experientia》1977,33(2):236-237
The influence from carotid baroreceptors on portal immuno-reactive glucagon and insulin levels and on arterial plasma glucose concentration was studied in vagotomized cats by sectioning of the sinus nerves. Such a complete elimination of the afferent baroreceptor discharge caused a prompt and pronounced increase in the glucose and glucagon levels, whereas the insulin concentration significantly decreased. The role of vascular barorecptors in the hyperglycemic response to hemorrhage is discussed.  相似文献   
288.
Summary Goat placental lactogen was partially purified from a medium collected after placental tissue incubation. The data obtained by disc electrophoresis and isoelectric focusing experiments, as well as by means of radioreceptor assay methods, provide evidence of the similarity between the goat and ovine placental lactogen.The careful technical assistance of L. Tichovská is gratefuly acknowledged.  相似文献   
289.
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   
290.
Summary Neurohypophyseal blood flow increases in water-deprived rats. This increase is independent of vasopressin release, since it occurs even in rats with hereditary defect of hypothalamic vasopressin synthesis.Acknowledgment. The technical assistance of D. Vilimovská is acknowledged.  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