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   29443篇
  免费   136篇
  国内免费   118篇
系统科学   289篇
丛书文集   451篇
教育与普及   42篇
理论与方法论   199篇
现状及发展   12818篇
研究方法   1343篇
综合类   14040篇
自然研究   515篇
  2018年   206篇
  2017年   253篇
  2013年   234篇
  2012年   474篇
  2011年   1097篇
  2010年   234篇
  2008年   586篇
  2007年   858篇
  2006年   613篇
  2005年   686篇
  2004年   732篇
  2003年   682篇
  2002年   664篇
  2001年   869篇
  2000年   831篇
  1999年   594篇
  1992年   564篇
  1991年   390篇
  1990年   425篇
  1989年   412篇
  1988年   407篇
  1987年   417篇
  1986年   455篇
  1985年   585篇
  1984年   405篇
  1983年   337篇
  1982年   294篇
  1981年   321篇
  1980年   371篇
  1979年   870篇
  1978年   680篇
  1977年   654篇
  1976年   521篇
  1975年   517篇
  1974年   773篇
  1973年   642篇
  1972年   705篇
  1971年   766篇
  1970年   1079篇
  1969年   846篇
  1968年   723篇
  1967年   750篇
  1966年   711篇
  1965年   530篇
  1959年   268篇
  1958年   525篇
  1957年   361篇
  1956年   279篇
  1955年   255篇
  1954年   298篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
61.
62.
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   
63.
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   
64.
It is well known that considering a non-Euclidean Minkowski metric in Multidimensional Scaling, either for the distance model or for the loss function, increases the computational problem of local minima considerably. In this paper, we propose an algorithm in which both the loss function and the composition rule can be considered in any Minkowski metric, using a multivariate randomly alternating Simulated Annealing procedure with permutation and translation phases. The algorithm has been implemented in Fortran and tested over classical and simulated data matrices with sizes up to 200 objects. A study has been carried out with some of the common loss functions to determine the most suitable values for the main parameters. The experimental results confirm the theoretical expectation that Simulated Annealing is a suitable strategy to deal by itself with the optimization problems in Multidimensional Scaling, in particular for City-Block, Euclidean and Infinity metrics.  相似文献   
65.
66.
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   
67.
68.
69.
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   
70.
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