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   212601篇
  免费   4005篇
  国内免费   733篇
化学   118965篇
晶体学   2663篇
力学   8998篇
综合类   7篇
数学   24709篇
物理学   61997篇
  2021年   1455篇
  2020年   1716篇
  2019年   1710篇
  2018年   2044篇
  2017年   1876篇
  2016年   3646篇
  2015年   3146篇
  2014年   3694篇
  2013年   10221篇
  2012年   9222篇
  2011年   10894篇
  2010年   6652篇
  2009年   6485篇
  2008年   9871篇
  2007年   9876篇
  2006年   9285篇
  2005年   8713篇
  2004年   7745篇
  2003年   6586篇
  2002年   6278篇
  2001年   6708篇
  2000年   5135篇
  1999年   3899篇
  1998年   2957篇
  1997年   2916篇
  1996年   2962篇
  1995年   2530篇
  1994年   2467篇
  1993年   2341篇
  1992年   2681篇
  1991年   2575篇
  1990年   2307篇
  1989年   2271篇
  1988年   2254篇
  1987年   2183篇
  1986年   2062篇
  1985年   3082篇
  1984年   3048篇
  1983年   2411篇
  1982年   2665篇
  1981年   2530篇
  1980年   2467篇
  1979年   2407篇
  1978年   2467篇
  1977年   2376篇
  1976年   2363篇
  1975年   2333篇
  1974年   2234篇
  1973年   2313篇
  1972年   1293篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
121.
ASTRASSENLAWOFTHEITERATEDLOGARITHMFORPROCESSESWITHINDEPENDENTINCREMENTWangJiagangAbstractLetX={X(t),t0}beaproceswithindep...  相似文献   
122.
123.
124.
125.
126.
Using a system based on non-dispersive infrared (NDIR) detectors, evolved gas analysis (EGA) was able to identify and quantify the principal volatiles produced by heating powdered samples of UK brick clays. From these results, atmospheric emissions likely to result from brick production can be predicted. In addition, EGA results for extruded brick clay test pieces are significantly different from those of powdered samples. Within an extruded brick clay body, evolved gases are contained within a pore system and evolved gas-solid phase reactions also occur. This EGA study provides further evidence on the nature of firing reactions within brick clay bodies. The qualitative and quantitative influence of heating rate — a key process condition in brick manufacture — on gas release is also outlined.Dedicated to Dr. Robert Mackenzie on the occasion of his 75th birthday  相似文献   
127.
2 laser of wide tunability to pump 13CD3OD we could observe 10 new far infrared laser lines ranging from 109 μm to 472 μm. The lines were generated by pumping infrared absorbing transitions of large offset appertaining to the C-O stretching Q-branch. All lines were characterised in wavelength, polarisation, optimum pressure of operation and precise offset measurements. Received: 17 September 1996/Revised version: 18 November 1996  相似文献   
128.
129.
 The effect of iodine sorption on the free volume of polycarbonate is investigated by Positron Annihilation Lifetime method. The observed results are interpreted in terms of the Charge Transfer Complex formation and precipitation of iodine at the initial and final stages of sorption, respectively. At higher levels of sorption, changes in the second lifetime and its intensity seem to suggest a conformational transformation, probably due to the net change in the amorphous-crystalline boundary regions of the polymer matrix. The free volume cavities have been predominantly occupied by I- 3 species and the diffusion process obeys Fick’s law. An exponential type correlation has been observed between fractional free volume and the diffusion coefficient. Received: 13 June 1996/Accepted: 20 September 1996  相似文献   
130.
The retention behavior of eight halomethanes and four saturated hydrocarbons was measured in gas chromatographic stationary phases consisting in tri-n-octylamine (TOA), squalane (SQ) and six TOA+SQ mixtures, at 55.0, 58.5, 62.5 and 65.0°C. Equlibrium constants for complex formation were extracted from experimental data by using a lattice model developed by Martire. The results may be interpreted in terms of the formation of weak hydrogen-bonded complexes, with sociation constants of about 0.13 L-mol–1 for haloforms and 0.07 L-mol–1 for dihalomethanes at 60°C.  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