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   29957篇
  免费   62篇
  国内免费   107篇
系统科学   188篇
丛书文集   387篇
教育与普及   65篇
理论与方法论   111篇
现状及发展   12194篇
研究方法   1330篇
综合类   15301篇
自然研究   550篇
  2013年   268篇
  2012年   446篇
  2011年   1012篇
  2010年   180篇
  2009年   131篇
  2008年   501篇
  2007年   616篇
  2006年   625篇
  2005年   593篇
  2004年   594篇
  2003年   536篇
  2002年   540篇
  2001年   1074篇
  2000年   1034篇
  1999年   627篇
  1992年   571篇
  1991年   463篇
  1990年   508篇
  1989年   493篇
  1988年   457篇
  1987年   476篇
  1986年   509篇
  1985年   547篇
  1984年   474篇
  1983年   420篇
  1982年   344篇
  1981年   351篇
  1980年   406篇
  1979年   957篇
  1978年   753篇
  1977年   725篇
  1976年   560篇
  1975年   628篇
  1974年   916篇
  1973年   755篇
  1972年   734篇
  1971年   932篇
  1970年   1192篇
  1969年   817篇
  1968年   788篇
  1967年   801篇
  1966年   725篇
  1965年   508篇
  1959年   278篇
  1958年   464篇
  1957年   349篇
  1956年   275篇
  1955年   242篇
  1954年   247篇
  1948年   204篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
181.
Summary Claviceps purpurea 275 F.I. fed with -aminobutyric acid produces ergostine with the corresponding -hydroxy--aminoacid undiluted by endogenous aminoacid. Almost all the -aminobutyric acid not incorporated into the ergostine remains unchanged in the medium. The significance of these results in the biosynthesis of ergot alkaloids is discussed.  相似文献   
182.
Summary A simple device is described, which permits us to quantify several parameters of spontaneous behaviour of small animals. Using this device with mice we obtained statistically satisfactory results, showing a strong genetic influence on the behavioural characteristics tested.We wish to thank Mr R. Laplace for technical help, Mr J. P. Arnould for electronic work as well as I.N.S.E.R.M.-SCR 3.  相似文献   
183.
D S McDevitt  S K Brahma 《Experientia》1977,33(8):1087-1089
The ontogeny and localization of the gamma crystallins in Discoglossus pictus lens development has been determined. Using antibody specific for amphibian gamma crystallins in the immunofluorescence technique, it was found that gamma crystallins first appear in primary lens fibre cells in the lens rudiment, and continue to be restricted to the fibre area as lens development progresses. Thus the role of gamma crystallins as indicators of a differentiated state remains constant in amphibian evolution, having been demonstrated in the most archaic anuran superfamily, as well as in others more recently evolved.  相似文献   
184.
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   
185.
Summary Aldosterone (15 g BID) and methylprednisolone (8 mg QD) administration to female guinea-pigs augmented both the total and the specific activity of NaK-ATPase but not the activity of adenylate cyclase in the cardiac sarcolemma. The rise in NaK-ATPase was due to increase in the number of enzyme molecules; catalytic activity and ouabain-sensitivity of individual molecules did not change.Acknowledgments. This work was supported by grant 1 R01 HL16611 from the National Heart and Lung Institute of the National Institutes of Health, United States Public Health Service. I thank Mr Kooil Kang for his excellent technical assistance.  相似文献   
186.
Summary Mouse foetuses were treated by Thalidomide on days 11–12 in order to verify whether the drug would induce blood abnormalities leading to circulatory troubles. About 18% of the treated foetuses showed both severe limb haemorrhages on day 14, and obvious alterations of the nucleated red blood cells of vitelline origin. These blood abnormalities, occurring suddenly during the well-known critical stage of foetal development, could be responsible for circulatory blocks leading to necrosis.  相似文献   
187.
    
Summary Unambiguous assignment of the1H-NMR. resonances due to the hydrogen atoms in the -position of homoserine indicates that the hydrogen which is exchanged and removed in the cystathionine--synthase catalyzed reactions holds the pro-R configuration.  相似文献   
188.
Summary The present results show that the sensitivity of the chick myocardium to the positive motropic effect of Ca++ decreases during development and that the Ca++ concentration of the physiological solution used must be lowered below normal to study the effects of positive inotropic agents in preparations from younger embryos. Isoproterenol elicits positive inotropic responses in 7–9-day embryonic ventricle and in newborn chick atria; however, the 4-day embryonic myocardium is unresponsive to isoproterenol.This work was supported by Grant No. HL-15995 from the National Heart Institute (USPHS).The authors would like to thank Dr.F. E. Shideman for the isolated tissue baths used in these experiments.  相似文献   
189.
Summary RIA of ecdysones are made on nymphal extracts ofPisaura mirabilis during the intermoulting cycle. The hormone level is low during exuviation and the greatest part of the intermoulting period but increases notably before and after ecdysis. The main hormonal peak or pre-ecdysial peak is due to -ecdysone, characterized by combined TLC/RIA.Acknowledgment. We wish to thank Dr M. Hirn for his help during the manipulations and J. Britton who has translated the text into English.  相似文献   
190.
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   
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