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   21044篇
  免费   34篇
  国内免费   74篇
系统科学   81篇
丛书文集   171篇
教育与普及   55篇
理论与方法论   64篇
现状及发展   8878篇
研究方法   941篇
综合类   10650篇
自然研究   312篇
  2013年   120篇
  2012年   293篇
  2011年   609篇
  2010年   135篇
  2008年   327篇
  2007年   402篇
  2006年   351篇
  2005年   404篇
  2004年   384篇
  2003年   365篇
  2002年   368篇
  2001年   694篇
  2000年   705篇
  1999年   489篇
  1994年   312篇
  1992年   447篇
  1991年   353篇
  1990年   396篇
  1989年   357篇
  1988年   358篇
  1987年   369篇
  1986年   338篇
  1985年   478篇
  1984年   345篇
  1983年   298篇
  1982年   288篇
  1981年   260篇
  1980年   290篇
  1979年   682篇
  1978年   528篇
  1977年   480篇
  1976年   417篇
  1975年   458篇
  1974年   494篇
  1973年   462篇
  1972年   531篇
  1971年   567篇
  1970年   694篇
  1969年   565篇
  1968年   581篇
  1967年   536篇
  1966年   519篇
  1965年   336篇
  1959年   174篇
  1958年   317篇
  1957年   211篇
  1956年   175篇
  1955年   152篇
  1954年   141篇
  1948年   140篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
992.
In a sensitive strain of Rat (Sprague-Dawley) a deregulation of the secretion of some pituitary hormones was noted in the female during induction of mammary tumors by dimethylbenzanthracene administration. The deregulation occurred quickly and depended on the stage of the estrous cycle. It mainly consists of hyposecretion of gonadotropins. TSH and GH and of hypersecretion of prolactin.  相似文献   
993.
The authors investigated basal levels of plasma immunoreactive growth-hormone in the rat (R-GH) after administration of 3 different anesthetic drugs: urethan, chloral hydrate and gamma-hdroxy-butyrate (GHB). Lowest R-GH concentrations (5 +/- 3 ng/ml) are observed after urethan; they are significantly higher (15 +/- 4 ng/ml) after chloral hydrate but this anesthetic also causes hyperglycemia (210 +/- 30 mg/100 ml). Normal blood glucose levels are observed under GHB narco-analgesia which elicits a clear-cut R-GH secretory episode (70 +/- 5 ng/ml); basal values (12 +/- 3 ng/ml) are maintained for several hours thereafter.  相似文献   
994.
Restoration of blood flow after 15 or 45 min. of ischemia induced an immediate recovery of phosphocreatine level and adenylate energy charge whereas ATP and total adenine nucleotides remained significantly below their normal values. These results prove that oxidative phosphorylations are not impaired but that a pool of myocardial adenine nucleotides is lost during ischemia which cannot be restored shortly after reperfusion. The significance of energy charge as a regulatory parameter in the myocardium is discussed.  相似文献   
995.
This paper reviews research that makes use of one of the most popular forecasting methods applied in accounting: time-series analysis using the Box-Jenkins methodology. It organizes the research in the area, surveys recent applications of time-series analysis in accounting, and discusses the potential for the methodology in addressing future research issues. The emphasis is on those aspects of the accounting system that possibly cause difficulties in applying time-series methods in accounting.  相似文献   
996.
Chick embryo nerve cells from the lumbo-sacral spinal cord have been isolated by trypsinisation and cultivated in Rose chambers on polylysine-L as a substrate. The cells are analysed by scanning electron microscopy. The mode of adherence of these cells to the substrate and the modifications of the surface of the neuroblasts during their transformation into neurocytes are studied.  相似文献   
997.
998.
999.
A new diagram for discriminating a forecasting technique's history with respect to the two types of turning-point errors, missed turns and false signals is presented. This diagram extends Theil's original prediction-realization (P-R) presentation so that each of the four quadrants and the axes locates a distinct type of forecasting error or correct forecast, thus reducing much of the former ambiguity. This improvement is accomplished without the loss of any information.  相似文献   
1000.
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