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   50617篇
  免费   311篇
  国内免费   573篇
系统科学   1271篇
丛书文集   167篇
教育与普及   286篇
理论与方法论   524篇
现状及发展   30499篇
研究方法   653篇
综合类   15904篇
自然研究   2197篇
  2014年   428篇
  2013年   821篇
  2012年   574篇
  2011年   2629篇
  2010年   431篇
  2009年   622篇
  2008年   819篇
  2007年   914篇
  2006年   966篇
  2005年   1124篇
  2004年   2351篇
  2003年   1888篇
  2002年   1563篇
  2001年   1169篇
  2000年   708篇
  1999年   847篇
  1998年   644篇
  1997年   773篇
  1996年   532篇
  1994年   682篇
  1993年   692篇
  1992年   745篇
  1991年   672篇
  1990年   726篇
  1989年   550篇
  1988年   526篇
  1987年   529篇
  1986年   617篇
  1985年   757篇
  1984年   686篇
  1983年   590篇
  1982年   741篇
  1981年   784篇
  1980年   851篇
  1979年   1209篇
  1978年   1120篇
  1977年   1112篇
  1976年   985篇
  1975年   962篇
  1974年   763篇
  1973年   1046篇
  1972年   1131篇
  1971年   1096篇
  1970年   1124篇
  1969年   1053篇
  1968年   1000篇
  1967年   884篇
  1966年   725篇
  1965年   607篇
  1964年   465篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
141.
142.
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   
143.
144.
Karyotypes of seven species of bats from Thailand (Chiroptera,Mammalia)   总被引:2,自引:0,他引:2  
Summary Karyotypes ofMyotis siligorensis, Myotis mystacinus, Pipistrellus pulveratus, Tylonycteris robustula, Miniopterus schreibersi fuliginosus, Hipposideros fulvus andAselliscus stoliczkanus from Thailand are investigated.Acknowledgment. The authors are very grateful to Dr N. Ratanawarabhan, Mrs S. Sittilert, P. Noonpakdee and S. Kuanchalern of Thailand Institute of Scientific and Technological Research for their valuable advice and assistance during our field survey in Thailand.  相似文献   
145.
146.
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   
147.
本文给出了基于扰动单位根的Hermite插值对As(|z|<1)中函数f(z)及其导数的同时一致及平均逼近阶。  相似文献   
148.
The systemic effect of the immunosuppressive drug cyclosporine (CS) on formation of new blood vessels was studied quantitatively in rats using the mesenteric-window assay. Angiogenesis was induced by i.p. injection of saline. CS at a s.c. dose of 4 mg/kg/day, which is in the range used clinically, suppressed angiogenesis (inhibiting branching or tortuosity more than spatial expansion), and appeared to be non-toxic. This is the first report on an apparently selective angiostatic effect of CS. The finding is likely to have implications for the clinical use of CS, not only in certain types of organ transplantation but possibly also in psoriasis and other angiogenesis-dependent diseases.  相似文献   
149.
The study of metabolic fuel provision and its regulation has reached an exciting stage where specific molecular events can be correlated with parameters of the organism's ecology. This paper examines substrate supply pathways from storage sites to locomotory muscle mitochondria and discusses ecological implications of the limits for maximal flux through these pathways. The relative importance of the different oxidative fuels is shown to depend on aerobic capacity. Very aerobic, endurance-adapted animals such as long distance migrants favor the use of lipids and intramuscular fuels over carbohydrates and circulatory fuels. The hypothesis of functional co-adaptation between oxygen and metabolic fuel supply systems allows us to predict that the capacity of several biochemical processes should be scaled with maximal oxygen consumption. Key enzymes, transmembrane transporter proteins, glucose precursor supply and soluble fatty acid transport proteins must all be geared to support higher maximal glucose and fatty acid fluxes in aerobic than in sedentary species.  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