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   31407篇
  免费   46篇
  国内免费   68篇
系统科学   156篇
丛书文集   717篇
教育与普及   81篇
理论与方法论   200篇
现状及发展   13520篇
研究方法   1360篇
综合类   15113篇
自然研究   374篇
  2013年   174篇
  2012年   422篇
  2011年   838篇
  2010年   182篇
  2008年   555篇
  2007年   548篇
  2006年   599篇
  2005年   593篇
  2004年   523篇
  2003年   579篇
  2002年   573篇
  2001年   979篇
  2000年   902篇
  1999年   601篇
  1992年   571篇
  1991年   463篇
  1990年   486篇
  1989年   489篇
  1988年   491篇
  1987年   499篇
  1986年   490篇
  1985年   599篇
  1984年   495篇
  1983年   405篇
  1982年   346篇
  1981年   340篇
  1980年   448篇
  1979年   969篇
  1978年   855篇
  1977年   846篇
  1976年   580篇
  1975年   631篇
  1974年   931篇
  1973年   785篇
  1972年   804篇
  1971年   1017篇
  1970年   1342篇
  1969年   1007篇
  1968年   945篇
  1967年   989篇
  1966年   831篇
  1965年   609篇
  1964年   148篇
  1959年   360篇
  1958年   522篇
  1957年   443篇
  1956年   366篇
  1955年   316篇
  1954年   363篇
  1948年   193篇
排序方式: 共有10000条查询结果,搜索用时 312 毫秒
71.
72.
73.
Enzymatic control of cell division in micro-organisms   总被引:1,自引:0,他引:1  
NICKERSON WJ 《Nature》1948,162(4111):241-245
  相似文献   
74.
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   
75.
On the face of it, the directors of new large scientific projects have an impossible task. They have to make technical decisions about sciences in which they have never made a research contribution—sciences in which they have no contributory expertise. Furthermore, these decisions must be accepted and respected by the scientists who are making research contributions. The problem is discussed in two interviews conducted with two directors of large scientific projects. The paradox is resolved for the managers by their use of interactional and referred expertise. The same analysis might be applicable to management in general. An Appendix, co-authored with Jeff Shrager, compares the notion of referred expertise with contributory expertise.  相似文献   
76.
77.
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   
78.
79.
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   
80.
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