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   228974篇
  免费   4490篇
  国内免费   878篇
化学   129422篇
晶体学   2789篇
力学   9263篇
综合类   11篇
数学   27947篇
物理学   64910篇
  2021年   1805篇
  2020年   1981篇
  2019年   2029篇
  2018年   2302篇
  2017年   2155篇
  2016年   4195篇
  2015年   3571篇
  2014年   4214篇
  2013年   11158篇
  2012年   10138篇
  2011年   11966篇
  2010年   7364篇
  2009年   7203篇
  2008年   10825篇
  2007年   10783篇
  2006年   10168篇
  2005年   9510篇
  2004年   8374篇
  2003年   7129篇
  2002年   6763篇
  2001年   7027篇
  2000年   5447篇
  1999年   4139篇
  1998年   3174篇
  1997年   3144篇
  1996年   3206篇
  1995年   2721篇
  1994年   2667篇
  1993年   2521篇
  1992年   2850篇
  1991年   2709篇
  1990年   2429篇
  1989年   2371篇
  1988年   2349篇
  1987年   2282篇
  1986年   2160篇
  1985年   3184篇
  1984年   3164篇
  1983年   2495篇
  1982年   2758篇
  1981年   2605篇
  1980年   2552篇
  1979年   2458篇
  1978年   2516篇
  1977年   2424篇
  1976年   2410篇
  1975年   2370篇
  1974年   2261篇
  1973年   2355篇
  1972年   1315篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
141.
ASTRASSENLAWOFTHEITERATEDLOGARITHMFORPROCESSESWITHINDEPENDENTINCREMENTWangJiagangAbstractLetX={X(t),t0}beaproceswithindep...  相似文献   
142.
143.
144.
145.
146.
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   
147.
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   
148.
149.
 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   
150.
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