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   11576篇
  免费   18篇
  国内免费   40篇
系统科学   60篇
丛书文集   205篇
教育与普及   45篇
理论与方法论   55篇
现状及发展   5270篇
研究方法   545篇
综合类   5286篇
自然研究   168篇
  2013年   110篇
  2012年   187篇
  2011年   364篇
  2010年   80篇
  2008年   227篇
  2007年   237篇
  2006年   233篇
  2005年   250篇
  2004年   224篇
  2003年   219篇
  2002年   229篇
  2001年   294篇
  2000年   296篇
  1999年   194篇
  1992年   186篇
  1991年   152篇
  1990年   154篇
  1989年   164篇
  1988年   169篇
  1987年   160篇
  1986年   174篇
  1985年   235篇
  1984年   146篇
  1983年   146篇
  1982年   104篇
  1981年   117篇
  1980年   153篇
  1979年   382篇
  1978年   287篇
  1977年   306篇
  1976年   223篇
  1975年   224篇
  1974年   342篇
  1973年   280篇
  1972年   301篇
  1971年   310篇
  1970年   426篇
  1969年   366篇
  1968年   367篇
  1967年   337篇
  1966年   294篇
  1965年   215篇
  1964年   69篇
  1959年   117篇
  1958年   212篇
  1957年   169篇
  1956年   160篇
  1955年   132篇
  1954年   132篇
  1948年   104篇
排序方式: 共有10000条查询结果,搜索用时 140 毫秒
1.
Introduction3D garment CAD tools are increasingly required byclothing industries to assist the cloth design andmanufacturing process for quick response when faced withrapidly changing in style and fabrics with variable materialproperties. In the context of virtual prototyping, modelingand simulation of garment fitting to mannequin areattracting more and more people from both research andindustrial communities.Different approaches and techniques can be used…  相似文献   
2.
Summary A study was undertaken on the variations of the redox potential level produced by streptomycinin vitro andin vivo. We have been able to show that, owing to an oxidative effect, streptomycin produces an increase of the redox potential level. This oxidative effect varies in degree according to the condition of the patient.We also found that in the blood and in the spinal fluid of patients suffering from tubercular meningitis factors are present which inhibit the action of streptomycin.The results of our findings lead to the conclusion that the dose of streptomycin must be varied according to the condition of the patient if the constant level required for an efficient therapy is to be maintained in the blood and in the spinal fluid.  相似文献   
3.
4.
Summary By condensing 2:4:5-triamino-6-hydroxy-pyrimidine with dihydroxyacetone (diacetate), diaminoacetone or acetone-1,3-di (p-formylaminobenzoic acid) not the expected 8- or 9-oxymethyl resp. -aminomethyl-pteridines but 8-or 9-methyl-pteridines were obtained. With p-tolyl-d-isoglucosamine not a tetrahydroxybutyl-pteridine but a trihydroxybutyl-pteridine was formed. For an explanation of these results it is supposed that from the dihydro-pteridines formed at first by intramolecular splitting off of H2O or R·NH2 aromatization takes place.  相似文献   
5.
Summary Intravenous or subcutaneous administration of pyribenzamine and other antihistaminics is able to decrease, and to delay the appearance of chemosis produced by mustard oils in the eye of the rabbit. Simultaneously occurring vascular reactions, on the other hand, are but slightly affected by antihistaminics. Intravenous or subcutaneous administration of rutin has no clear-cut effect on chemosis; it is however able to inhibit the vascular reaction.  相似文献   
6.
7.
8.
9.
10.
F Bogner  T Eisner 《Experientia》1992,48(1):97-102
The moth Utetheisa ornatrix derives protection against predation from systemic pyrrolizidine alkaloids (PAs) that it sequesters as a larva from its foodplants (Leguminosae, Crotalaria spp.). We here show, in laboratory tests, that Utetheisa deficient in body PA can make up for the chemical shortfall by cannibalizing pupae. We present evidence indicating that cannibalism in larvae is elicited not by hunger, but possibly by PA deficiency itself, and that in making cannibalistic choices larvae prefer PA-containing over PA-free pupae. PAs themselves, either in crystalline form or as additives to food items, proved phagostimulatory to larvae. In nature Utetheisa tend to pupate away from their foodplant, essentially out of reach of larval attack. The threat of cannibalism may have contributed to the evolution of this pupation behavior.  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