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   1491篇
  免费   47篇
  国内免费   69篇
系统科学   58篇
丛书文集   52篇
教育与普及   21篇
理论与方法论   13篇
现状及发展   260篇
研究方法   46篇
综合类   1150篇
自然研究   7篇
  2023年   11篇
  2022年   29篇
  2021年   44篇
  2020年   37篇
  2019年   20篇
  2018年   19篇
  2017年   25篇
  2016年   32篇
  2015年   55篇
  2014年   64篇
  2013年   77篇
  2012年   92篇
  2011年   94篇
  2010年   83篇
  2009年   72篇
  2008年   87篇
  2007年   95篇
  2006年   67篇
  2005年   37篇
  2004年   34篇
  2003年   40篇
  2002年   39篇
  2001年   40篇
  2000年   38篇
  1999年   24篇
  1998年   16篇
  1997年   7篇
  1996年   8篇
  1995年   8篇
  1994年   8篇
  1993年   12篇
  1992年   9篇
  1990年   13篇
  1989年   9篇
  1987年   8篇
  1985年   7篇
  1980年   7篇
  1979年   16篇
  1978年   7篇
  1977年   13篇
  1974年   16篇
  1973年   19篇
  1972年   18篇
  1971年   25篇
  1970年   13篇
  1969年   18篇
  1968年   22篇
  1967年   14篇
  1966年   13篇
  1965年   10篇
排序方式: 共有1607条查询结果,搜索用时 15 毫秒
131.
In fed geese, plasma levels of glucose and alanine were 1.9 g.l-1 and 560 mumol.l-1, respectively. During a long fast (40 days), plasma glucose and alanine were maintained at a high level (1.5-1.8 g.l-1 and 370-540 mumol.l-1, respectively). Plasma level of acetoacetate was very low (40 mumol.l-1); by contrast, plasma level of beta hydroxybutyrate reached very high values (20 mmol.l-1) after about 20 days of fasting, then it decreased. Plasma levels of lactate and pyruvate decreased along the course of the fast, from 2 500 to 2 000 mumol.l-1 and 220 to 170 mumol.l-1, respectively.  相似文献   
132.
Araneus cornutus spiderling activities recorded from hatching to scattering show a particular distribution of the general motor activity over a 24-hour period. More motor activity is first observed during the light sequence, while at a nocturnal activity distribution appears after the 2nd nymphean ecdysis.  相似文献   
133.
When animals are exposed to cigarette smoke, the concentration of carbon monoxide in blood is rapidly increased, so that intensive inhalation tests cannot be carried out. A simple apparatus is described to expose Rats alternatively to cigarette smoke and to oxygen in order to reduce the concentration of carbon monoxide in the blood. This method makes it possible to increase the daily administration of smoke considerably; nevertheless, under such conditions, lung tumors were not observed.  相似文献   
134.
本文提出了人口经济区域规划中的资源和经济发展分析模型.此模型由两个模型组成,第一个是采用AHP 决策方法的区域发展战略决策模型,第二个是在第一个模型基础上,引入可能度、满意度概念的经济发展平衡优化模型.通过这两个模型的计算,农业可以为地区未来人口、经济规划提供资源经济分析基础.本文最后给出了勉县,发展分析的实例.  相似文献   
135.
Summary A decrease in the number of binding sites (Bmax) for [3H]ouabain was observed in the heart (37%) and the brain (22%) of spontaneously hypertensive rats (SHR) when compared with age-matched control Wistar Kyoto rats. No variation was detected in the affinity constant (KD).  相似文献   
136.
RNA-fragments U2 obtained by mild degradation with RNase U2 of ribosomal RNA containing A and G nucleotides in excess are capable of exhibiting either a stimulatory effect on the induction of Crown-gall tumors or an inhibitory action on their subsequent development. These different effects are dependent on the moment at which RNA-fragments were introduced into wounded Pea seedlings infected by Agrobacterium tumefaciens B6. The results obtained in vitro and in vivo suggest that an interaction between auxin and RNA-fragments U2 may take place, either increasing the tumor induction or inhibiting the proliferation of tumourous cells.  相似文献   
137.
The role of platelet-activating factor in platelet aggregation.   总被引:21,自引:0,他引:21  
  相似文献   
138.
139.
140.
Evidence for two distinct c-src loci on human chromosomes 1 and 20   总被引:1,自引:0,他引:1  
A number of proto-oncogenes have recently been localized to the chromosomal segments that are the breakpoints in the specific rearrangements noted in human malignant diseases. Moreover, rearranged forms of several proto-oncogenes have been identified in malignant cells; in several instances, the proto-oncogene has undergone an alteration as a result of a nonrandom chromosomal rearrangement. One proto-oncogene that has yet to be associated with human neoplastic disease is c-src, the cellular homologue of the transforming sequence of Rous sarcoma virus (RSV). By somatic cell hybridization, c-src has been mapped to chromosome 20, but its precise location was not determined. We have now mapped this gene by using in situ hybridization of the cloned human c-src probe to human mitotic chromosomes. We report here that the human genome contains two loci with strong homology to the coding regions of this oncogene, at 1p34-p36 and 20q12-q13. It is noteworthy that these chromosomal regions are frequently involved in the structural rearrangements observed in haematological malignant diseases.  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