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   54687篇
  免费   257篇
  国内免费   556篇
系统科学   1239篇
丛书文集   249篇
教育与普及   286篇
理论与方法论   525篇
现状及发展   31468篇
研究方法   788篇
综合类   18758篇
自然研究   2187篇
  2013年   816篇
  2012年   619篇
  2011年   2647篇
  2009年   618篇
  2008年   834篇
  2007年   904篇
  2006年   1002篇
  2005年   1173篇
  2004年   2296篇
  2003年   1888篇
  2002年   1527篇
  2001年   1308篇
  2000年   830篇
  1999年   934篇
  1998年   648篇
  1997年   778篇
  1996年   537篇
  1994年   684篇
  1993年   701篇
  1992年   871篇
  1991年   741篇
  1990年   819篇
  1989年   644篇
  1988年   623篇
  1987年   611篇
  1986年   678篇
  1985年   847篇
  1984年   752篇
  1983年   632篇
  1982年   780篇
  1981年   813篇
  1980年   893篇
  1979年   1325篇
  1978年   1200篇
  1977年   1200篇
  1976年   1083篇
  1975年   1071篇
  1974年   913篇
  1973年   1173篇
  1972年   1249篇
  1971年   1257篇
  1970年   1346篇
  1969年   1247篇
  1968年   1202篇
  1967年   1061篇
  1966年   888篇
  1965年   720篇
  1964年   481篇
  1958年   562篇
  1957年   472篇
排序方式: 共有10000条查询结果,搜索用时 8 毫秒
141.
This paper is concerned with the development of ‘Systems Thinking.’ In particular, it considers and critiques ‘traditional Systems Thinking’ within the framework of Critical Systems Thinking. Before embarking on such a venture it is necessary to derive a base context from which to develop argument and analysis. Therefore the outline of this paper is as follows: A contextual setting for Systems Thinking, Theoretical Considerations, Soft Systems Thinking and Methodology, and A Critical Systems Thinking (CST) approach. The account of the development of Systems Thinking is followed by a synopsis of a theoretical framework for Systems Thinking which will allow us to gain an understanding of contemporary views. The paper then goes on to review SSM and CST in order to provide a platform for a critique of traditional forms of Systems Thinking. The final section briefly discusses the applicability of CST to the ‘real-world’ context by outlining some current studies being undertaken by the author.  相似文献   
142.
This paper introduces the conception of open complex giant system and the methodology for dealing with the system, with stress on its profound significance in development of science and technology. The authors conclude that the reductionism underlying the exact science is not suitable to open complex giant system, and the only feasible alternative is the meta-synthetic engineering from the qualitative to the quantitative.  相似文献   
143.
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   
144.
等截面垂直管道中气粉流的临界管长   总被引:2,自引:1,他引:1  
考虑重力和摩擦力的影响,建立了描述垂直管道中气粉流行为的数学模型,采用马赫数检验法,确定了产生摩擦壅塞时的临界管长,计算表明,当气粉流以不同方式喷入相同的冶金熔池时,底吹垂直管道比顶吹垂直管道需要更大的临界管长。  相似文献   
145.
146.
147.
148.
149.
During the past few years, several methods have been developed for the detection of specific nucleic acid sequences by in situ hybridization using non-radioactive labels such as fluorochromes, cytochemically detectable enzymes and electron-dense markers. These methods are preferable to autoradiography in terms of speed of performance and topological resolution. Their limited sensitivity, however, has so far restricted their use to the detection of repeated sequences. Here we report single gene detection with a procedure using 2-acetylaminofluorene (AAF)-modified probes, immunoperoxidase cytochemistry and reflection-contrast microscopy. We confirmed the autoradiographic data on the localization of the human thyroglobulin (Tg) gene to the distal end of the long arm of chromosome 8. A mixture of cosmid cHT2-derived subclones of the 3' part of the Tg gene, 22.3 kilobase pairs (kbp) in total, was used as a hybridization probe. This procedure can be used to map other unique sequences, if genomic clones are available from which clones with an appropriate amount of inserts can be isolated.  相似文献   
150.
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