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   41338篇
  免费   153篇
  国内免费   117篇
系统科学   297篇
丛书文集   782篇
教育与普及   101篇
理论与方法论   257篇
现状及发展   17843篇
研究方法   1551篇
综合类   20270篇
自然研究   507篇
  2013年   266篇
  2012年   640篇
  2011年   1184篇
  2010年   233篇
  2008年   651篇
  2007年   675篇
  2006年   714篇
  2005年   912篇
  2004年   1123篇
  2003年   1143篇
  2002年   796篇
  2001年   1200篇
  2000年   1191篇
  1999年   791篇
  1992年   714篇
  1991年   570篇
  1990年   616篇
  1989年   611篇
  1988年   616篇
  1987年   619篇
  1986年   591篇
  1985年   750篇
  1984年   598篇
  1983年   506篇
  1982年   447篇
  1981年   437篇
  1980年   580篇
  1979年   1244篇
  1978年   1051篇
  1977年   1033篇
  1976年   778篇
  1975年   843篇
  1974年   1158篇
  1973年   1035篇
  1972年   1104篇
  1971年   1304篇
  1970年   1664篇
  1969年   1294篇
  1968年   1244篇
  1967年   1270篇
  1966年   1088篇
  1965年   782篇
  1964年   197篇
  1959年   446篇
  1958年   682篇
  1957年   541篇
  1956年   455篇
  1955年   396篇
  1954年   424篇
  1948年   269篇
排序方式: 共有10000条查询结果,搜索用时 731 毫秒
101.
Image-based gait analysis as a means of biometric identification has attracted much research attention. Most of the existing methods focus on human identification, posture analysis and movement tracking. There have been few investigations on measuring the carried load based on the carrier's gait characteristics by automatic image processing. Nevertheless, this measurement is very useful in a number of applications, such as the study of the carried load on the postural development of children and adolescence. In this paper, we investigate how to automatically estimate the carried weight from a sequence of images. We present a method to extract human gait silhouette based on an observation that humans tend to minimize the energy during motion. We compute several angles of body leaning and determine the relationship of the carried weight, the leaning angles and the centroid location according to a human kinetic study. Our weight determination method has been verified successfully by experiments.  相似文献   
102.
103.
104.
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   
105.
106.
107.
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   
108.
一种改进的实信号IFFT算法   总被引:1,自引:0,他引:1  
由于重量轻、体积小、功耗低、功能强的小卫星工作在无人干预的低温 ,高辐射的空间环境中 ,因此星上计算机系统必须满足集成度高、寿命长、可靠性高、抗辐射能力强的要求。针对立体测绘小卫星的特点 ,我们设计了满足上述要求的集集中控制与分布控制优点于一身的星上计算机系统 ,对其可靠性进行了分析 ,并对提高其可靠性应采取的关键技术进行了简要的论述。  相似文献   
109.
110.
Descartes is always concerned about knowledge. However, the Galileo affair in 1633, the reactions to his Discourse on method, and later his need to reply to objections to his Meditations provoked crises in Descartes’s intellectual development the import of which has not been sufficiently recognized. These events are the major reasons why Descartes’s philosophical position concerning how we know and what we may know is radically different at the end of his life from what it was when he began. We call this later position Descartes’s epistemic stance and contrast it with his earlier methodological, metaphysical realism. Yet Descartes’s epistemic views cannot be separated from other aspects of his work, for example, his views concerning God, causality, metaphysics, and the nature of science. A further meta-implication is that serious errors await any scholar who cites early Cartesian texts in support of late Cartesian positions, or who uses later texts in conjunction with early ones to support a reading of Descartes’s philosophy.  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