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   93474篇
  免费   2999篇
  国内免费   5047篇
系统科学   4047篇
丛书文集   3024篇
教育与普及   2606篇
理论与方法论   434篇
现状及发展   587篇
研究方法   250篇
综合类   90556篇
自然研究   16篇
  2024年   536篇
  2023年   1011篇
  2022年   1697篇
  2021年   1911篇
  2020年   1346篇
  2019年   707篇
  2018年   965篇
  2017年   1208篇
  2016年   1286篇
  2015年   2529篇
  2014年   3548篇
  2013年   3418篇
  2012年   4040篇
  2011年   4441篇
  2010年   4295篇
  2009年   4669篇
  2008年   5284篇
  2007年   5346篇
  2006年   4287篇
  2005年   4117篇
  2004年   2959篇
  2003年   2541篇
  2002年   2980篇
  2001年   3077篇
  2000年   2827篇
  1999年   4107篇
  1998年   3432篇
  1997年   3467篇
  1996年   3124篇
  1995年   2769篇
  1994年   2494篇
  1993年   2134篇
  1992年   1861篇
  1991年   1713篇
  1990年   1507篇
  1989年   1346篇
  1988年   1100篇
  1987年   718篇
  1986年   383篇
  1985年   154篇
  1984年   29篇
  1983年   14篇
  1982年   13篇
  1981年   13篇
  1980年   15篇
  1979年   12篇
  1973年   10篇
  1972年   12篇
  1970年   11篇
  1969年   8篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
421.
Discovery and character of the Kunlun-Yellow River Movement   总被引:2,自引:0,他引:2  
Based on geomorphological, tectonic and sedimentary data, a Kunlun Yellow River Tectonic Movement has been recognized in 1 10-0 60 Ma B.P. This tectonic movement, which leads to uplift of the Qinghai_Xizang (Tibet) Plateau from 1 500 to 3 000-3 500 m, is periodic, abrupt and changeable in the movement rate of uplifting and slide slipping.  相似文献   
422.
A new interpretation of the Himalayan orogenic belt   总被引:2,自引:0,他引:2  
  相似文献   
423.
Discovery of eclogite at northern margin of Qaidam Basin, NW China   总被引:19,自引:0,他引:19  
Eclogite was first discovered at the northern margin of the Qaidam Basin in this study. It occurs as pods in the gneiss sequence of Middle to Upper Proterozoic age and is mainly composed of garnet, omphacite, phengite and rutile. The garnets contain 44%-62% of almandine, 15%-33% of grossular and 12%-30% of pyrope molecules, and the omphacites contain 40%-46% of jadeite. Applying garnet_clinopyroxene thermometry and jadeite geobarometry, the peak conditions of eclogite facies metamorphism occurred at about (722±123)℃ and at the pressure of up to c. 22 ×10 8 Pa.  相似文献   
424.
425.
The range and the nonextinction property of a supercritical superdiffusion and solutions of its corresponding differential equation are studied. It is pruved that under a suitable condition, the conditioned superprocess of the supercritical superdiffusion is a subcritical superdiffusion.  相似文献   
426.
The Matuyama/Brunhes polarity boundary (MBPB) is recorded in Chinese loess L8, which is associated with the glacial period. It is proved that loess L8 is capable of recording earth’s secular variation, and the lock-in depth in Chinese loess is no more than that of marine sediments. Comparison with the location of MBPB in Chinese loess and marine sediments, it is put forward that there is a recording phase lag between ocean and continent climate changes.  相似文献   
427.
The development of stamen is an important stage during the sexual reproduction in higher plants. Studying the genes that predominantly or even specifically expressed in stamens will aid in undestanding the molecular mechanism of stamen development. The structure of a rice CHS-like gene (D5) which predominantly expressed in anthers has been analysised, showing high structural similarity with two other anther-specific genes (A1 and BA42) fromBrassica napus. Northern analysis also reveals that the three genes share a similar expression pattern and that the expression of D5 may relate to the early development of pollens. It is concluded that D5, A1 and BA42 represent a group of diverged CHS-like genes which are related to stamen development.  相似文献   
428.
The smectite to illite transformation in active geothermal systems of New Zealand can be simulated by a first-order reaction kinetic model, which provides direct estimates about the minumum ages of active geothermal systems themselves. The derived kinetic values show that the smectite to illite transformation is sensitive to both temperature and time.  相似文献   
429.
430.
The effect of lanthanum ions on the structural and conformational change of yeast tRNA Phe was studied by 1H NMR. The results suggest that the tertiary base pair (G-15)(C-48), which was located in the terminal in the augmented dihydrouridine helix (D-helix), was markedly affected by adding La 3+ and shifted 0.33 downfield. Based pair (U-8)(A-14), which is associated with a tertiary interaction, links the base of the acceptor stem to the D-stem and anchors the elbow of the L structure, shifted 0.20 upfield. Another imino proton that may be affected by La 3+ in tRNA Phe is the tertiary base pair (G-19)(C-56). The assignment of this resonance is tentative since it is located in the region of highly overlapping resonances between 12.6 and 12.2. This base pair helps to anchor the D-loop to the TΨC loop.  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