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   66171篇
  免费   1341篇
  国内免费   2106篇
系统科学   1897篇
丛书文集   2021篇
教育与普及   2094篇
理论与方法论   277篇
现状及发展   7851篇
研究方法   814篇
综合类   54496篇
自然研究   168篇
  2023年   666篇
  2022年   848篇
  2021年   1003篇
  2020年   614篇
  2018年   420篇
  2017年   578篇
  2016年   514篇
  2015年   1090篇
  2014年   1577篇
  2013年   1462篇
  2012年   1777篇
  2011年   2183篇
  2010年   1810篇
  2009年   2203篇
  2008年   2688篇
  2007年   2552篇
  2006年   2016篇
  2005年   2029篇
  2004年   1562篇
  2003年   1339篇
  2002年   1321篇
  2001年   1695篇
  2000年   1892篇
  1999年   2962篇
  1998年   2517篇
  1997年   2617篇
  1996年   2450篇
  1995年   2125篇
  1994年   2218篇
  1993年   1743篇
  1992年   1701篇
  1991年   1459篇
  1990年   1368篇
  1989年   1226篇
  1988年   1054篇
  1987年   795篇
  1986年   578篇
  1985年   442篇
  1979年   509篇
  1978年   434篇
  1977年   392篇
  1974年   479篇
  1973年   424篇
  1972年   431篇
  1971年   563篇
  1970年   612篇
  1969年   531篇
  1968年   535篇
  1967年   460篇
  1966年   410篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
61.
62.
Summary The depressor action of small doses of adrenaline on the blood pressure (B.P.) of the decapitated cat may be abolished by pretreatment with pilocarpine; atropine restores the original depressor action. The fall in B.P. due to adrenaline after ergotamine once more becomes an increase when pilocarpine has been given earlier. After atropine a fall in B.P. again occurs. This effect of pilocarpine and atropine on a depressor response has already been described in the case of Aludrine (N-isopropyl-noradrenaline) byFromherz.  相似文献   
63.
Summary (1) By precipitation with ammonium sulfate, streptomycin, or calcium salts, we obtained from the pulp of tomatoes a substance containing carotinoids. The behaviour of this substance was analogous to that of chloroplst-substance and to that of animal cytoplasmatic nucleoproteins. Like these it contains proteins, lipids, and very probably nucleic acids. We regard this substance as achromoplastine.(2) Experiments with slices of green tomatoes show that the changing over of the chlorophyll content into the carotinoid content is inhibited by the presence of streptomycin.(3) Streptomycin inhibits the formation of chlorophyll in etiolated separated cabbage leafs, just as this drug inhibits the formation of chlorophyll in growing seeds.(4) The development of anthocyanides is not influenced by streptomycin.  相似文献   
64.
65.
66.
67.
68.
69.
Study Objective: To compare and analyze the changes of the pulmonary-artery pressure of the migrants coming from different elevation in the hypoxic environment of 4636 - 4907 m extreme altitude. To explore the susceptibility to hypoxic pulmonary-artery hypertension (PH) in the subjects from different altitude and profession. Methods: By using Color Doppler Ultmsonography (CDU), measuring the pulmonary-artery pressure of 207 healthy men, who had continuously being lived and worked at the extreme altitude for more than six months, and then were divided into three groups according to their profession and the altitude of original living place. Results: There was a significant difference in the outcomes of pulmonary-artery pressure from the 3 groups. Conclusions: Altitude of original living place, labor intensity are some of factors that impact the pulmonary-artery pressure of the people who exposure to a hypoxic environment. The pulmonary- artery pressure of person without strenuously physical work experience was more sensitive to hypoxic surroundings than that of labor workers. It was not always the fact at an extreme altitude that the moderate altitude mountaineers were superior to other migrants from a lower altitude or plain. The higher PH was found in the groups of the moderate altitude mountaineers and labor workers. It is unlikely certain that one with PH would surfer from HAPE.  相似文献   
70.
反渗透作为一种重要的水处理技术,越来越广泛地应用到各种领域,其处理水源也变得复杂多样化,因此要求在反渗透系统和反渗透预处理设计时予以高度关注。本文主要讨论针对不同水源时反渗透系统的设计思路。  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