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   28371篇
  免费   238篇
  国内免费   399篇
系统科学   511篇
丛书文集   689篇
教育与普及   271篇
理论与方法论   97篇
现状及发展   9541篇
研究方法   918篇
综合类   16610篇
自然研究   371篇
  2014年   293篇
  2013年   341篇
  2012年   526篇
  2011年   930篇
  2010年   367篇
  2009年   345篇
  2008年   641篇
  2007年   690篇
  2006年   624篇
  2005年   626篇
  2004年   537篇
  2003年   549篇
  2002年   518篇
  2001年   909篇
  2000年   891篇
  1999年   696篇
  1998年   259篇
  1995年   256篇
  1992年   537篇
  1991年   459篇
  1990年   486篇
  1989年   403篇
  1988年   438篇
  1987年   400篇
  1986年   359篇
  1985年   491篇
  1984年   366篇
  1983年   303篇
  1981年   258篇
  1980年   345篇
  1979年   689篇
  1978年   582篇
  1977年   551篇
  1976年   472篇
  1975年   531篇
  1974年   664篇
  1973年   580篇
  1972年   589篇
  1971年   701篇
  1970年   925篇
  1969年   727篇
  1968年   624篇
  1967年   652篇
  1966年   596篇
  1965年   433篇
  1959年   264篇
  1958年   400篇
  1957年   303篇
  1956年   269篇
  1954年   263篇
排序方式: 共有10000条查询结果,搜索用时 46 毫秒
51.
通过对国内外液压防爆绞车的技术水平及其现状的分析,探讨了液压防爆绞车的发展前景。  相似文献   
52.
冠心病患者拔牙前后的内科保障   总被引:1,自引:0,他引:1  
冠心病患者拔牙有一定的危险性,不但要严格掌握拔牙适应症,还要采取系统的内科保障,确保生命安全本报告有120例冠心病患者临床资料,介绍冠心病患者的拔牙指征和常用的内科治疗措施.  相似文献   
53.
Summary Hydrochlorothiazide, acutely injected in rats, has a weak analgesic activity per se and potentiates and prolongs the antinociceptive effect of morphine.This work was supported in part by grants from Consiglio Nazionale delle Ricerche, and by Ministero della Pubblica Istruzione, Roma.  相似文献   
54.
55.
Summary Traces of nor-adrenaline restore the vascular action of adrenaline altered in epinephrectomized dogs to the reaction of the normal animal. Therefore it is claimed that the adrenals discharge one or several substances into the blood stream, which are necessary for the usual peripheral vascular action of adrenaline. Further investigations are in progress.  相似文献   
56.
Hypertriglyceridemia is a hallmark of many disorders, including metabolic syndrome, diabetes, atherosclerosis and obesity. A well-known cause is the deficiency of lipoprotein lipase (LPL), a key enzyme in plasma triglyceride hydrolysis. Mice carrying the combined lipase deficiency (cld) mutation show severe hypertriglyceridemia owing to a decrease in the activity of LPL and a related enzyme, hepatic lipase (HL), caused by impaired maturation of nascent LPL and hepatic lipase polypeptides in the endoplasmic reticulum (ER). Here we identify the gene containing the cld mutation as Tmem112 and rename it Lmf1 (Lipase maturation factor 1). Lmf1 encodes a transmembrane protein with an evolutionarily conserved domain of unknown function that localizes to the ER. A human subject homozygous for a deleterious mutation in LMF1 also shows combined lipase deficiency with concomitant hypertriglyceridemia and associated disorders. Thus, through its profound effect on lipase activity, LMF1 emerges as an important candidate gene in hypertriglyceridemia.  相似文献   
57.
58.
Summary The application of diphenylilacetic acid has shown favorable effects on the growth of tobacco plants. Solutions containing 10 p.p.m. and 20 p.p.m. produce, in weight, an almost double growth in treated plants in comparison with the controls. Diphenylilacetic acid can be considered as a growth-promoting substance. The data are not definite.  相似文献   
59.
In econometrics, as a rule, the same data set is used to select the model and, conditional on the selected model, to forecast. However, one typically reports the properties of the (conditional) forecast, ignoring the fact that its properties are affected by the model selection (pretesting). This is wrong, and in this paper we show that the error can be substantial. We obtain explicit expressions for this error. To illustrate the theory we consider a regression approach to stock market forecasting, and show that the standard predictions ignoring pretesting are much less robust than naive econometrics might suggest. We also propose a forecast procedure based on the ‘neutral Laplace estimator’, which leads to an improvement over standard model selection procedures. Copyright © 2004 John Wiley & Sons, Ltd.  相似文献   
60.
A Kowluru  R A Kowluru 《Experientia》1992,48(5):486-488
Urinary excretion of glycated albumin was quantitated in genetically hyperglycemic mice (C57BL-Ks-J, db/db mice), a model for non-insulin-dependent diabetes mellitus, and compared with their non-diabetic littermates. The data indicated a preferential excretion of glycated albumin in non-diabetic mice. This phenomenon of 'editing' of glycated albumin is decreased significantly in diabetic mice. Quantitative measurements of overall excretion of glycated albumin suggested that the loss of editing in diabetic mice is due to the dilution of glycated albumin by the unmodified albumin which is excreted in large amounts in diabetic mice. Therefore, the loss of editing observed in this model resembled the one we characterized in insulin-dependent diabetic humans and a streptozotocin-diabetic rat model.  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