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   35841篇
  免费   126篇
  国内免费   171篇
系统科学   173篇
丛书文集   478篇
教育与普及   55篇
理论与方法论   115篇
现状及发展   16344篇
研究方法   1507篇
综合类   16889篇
自然研究   577篇
  2013年   240篇
  2012年   539篇
  2011年   1094篇
  2010年   227篇
  2008年   611篇
  2007年   750篇
  2006年   697篇
  2005年   714篇
  2004年   775篇
  2003年   641篇
  2002年   710篇
  2001年   1083篇
  2000年   1034篇
  1999年   728篇
  1992年   700篇
  1991年   529篇
  1990年   554篇
  1989年   522篇
  1988年   525篇
  1987年   555篇
  1986年   586篇
  1985年   736篇
  1984年   557篇
  1983年   449篇
  1982年   434篇
  1981年   450篇
  1980年   487篇
  1979年   1161篇
  1978年   953篇
  1977年   837篇
  1976年   740篇
  1975年   731篇
  1974年   983篇
  1973年   823篇
  1972年   912篇
  1971年   1008篇
  1970年   1343篇
  1969年   1039篇
  1968年   961篇
  1967年   985篇
  1966年   907篇
  1965年   677篇
  1964年   255篇
  1959年   337篇
  1958年   667篇
  1957年   437篇
  1956年   348篇
  1955年   323篇
  1954年   355篇
  1948年   242篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
72.
73.
1 Results Strongly disordered metals with the high chemical and catalytic activity are often called as skeletal metals.Usually for their preparation the metallides of d-metal (which afterwards will be left in the “skeleton“) and chemically active component(s) are firstly synthesized.Then the last one(s) is (are) removed by the leaching with aqueous solutions of alkalis or carbonates.However,this method sometime fails,first of all,for the reactions,which should be realized in non-aqueous conditions.In th...  相似文献   
74.
1 Results Simultaneous micro-and nanostructuring was prepared on polyolefin surfaces by injection molding.The molds were made of electropolished aluminum foil where the micropatterns were structured with a custom made robot.Nanopatterns were subsequently created on the molds by oxidizing the aluminum surface electrochemically in polyprotic acid.The preparation technique allowed simultaneous control of the dimensions of the micro-and nanostructures.Structuring has a remarkable effect on the contact angle...  相似文献   
75.
In this paper, we introduce a new class of generalized convex function, namely, a-pseudounivex function, by combining the concepts of pseudo-univex and α-invex functions. Further, we establish some relationships between vector variational-like inequality problems and vector optimization problems under the assumptions of α-pseudo-univex functions. Results obtained in this paper present a refinement and improvement of previously known results.  相似文献   
76.
77.
78.
79.
The effects of alcohol consumption, cigarette smoking and age on sister chromatid exchange (SCE) frequency in human lymphocytes were assessed by means of multiple linear regression. An increase in SCE rates was associated with alcohol consumption (p = 0.0001), smoking (p = 0.0231), and, to a small extent (p = 0.057), age. These three confounding factors explain 48% of the inter-personal variation in SCE rates among subjects studied.  相似文献   
80.
After a brief recall of the Sidelobe Canceler (SLC) working principle, including the derivation of a general formula for the Cancellation Ratio (CR), the effects of channel mismatching are investigated. In particular, curves providing CRvalues as a function of amplitude and phase channel mismatching, radar bandwidth, and jammer direction of arrival (JDOA) are provided for the cases of one and two auxiliary antennas. Subsequently, a time -space processor for performance restoration is analyzed in detail. In addition to the above mentioned quantities, the attainable CR value is expressed as a function of the space-time processor parameters. The contribution of the paper is related to the derivation of a number of mathematical equations of CR for several cases of practical interest for the radar engineer. In addition, several curves are presented to assist design of SLC systems.  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