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   197754篇
  免费   2394篇
  国内免费   983篇
化学   101569篇
晶体学   2711篇
力学   8927篇
综合类   19篇
数学   26467篇
物理学   61438篇
  2021年   1015篇
  2020年   1136篇
  2019年   1149篇
  2018年   2330篇
  2017年   2591篇
  2016年   3010篇
  2015年   2453篇
  2014年   2944篇
  2013年   8320篇
  2012年   9223篇
  2011年   10131篇
  2010年   6507篇
  2009年   6431篇
  2008年   7820篇
  2007年   7852篇
  2006年   7562篇
  2005年   10771篇
  2004年   9588篇
  2003年   7228篇
  2002年   5404篇
  2001年   6247篇
  2000年   4636篇
  1999年   3622篇
  1998年   2722篇
  1997年   2677篇
  1996年   2606篇
  1995年   2310篇
  1994年   2201篇
  1993年   2047篇
  1992年   2489篇
  1991年   2435篇
  1990年   2132篇
  1989年   2091篇
  1988年   2103篇
  1987年   2008篇
  1986年   1907篇
  1985年   2806篇
  1984年   2777篇
  1983年   2226篇
  1982年   2406篇
  1981年   2286篇
  1980年   2239篇
  1979年   2200篇
  1978年   2263篇
  1977年   2216篇
  1976年   2206篇
  1975年   2150篇
  1974年   2061篇
  1973年   2150篇
  1972年   1235篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
ASTRASSENLAWOFTHEITERATEDLOGARITHMFORPROCESSESWITHINDEPENDENTINCREMENTWangJiagangAbstractLetX={X(t),t0}beaproceswithindep...  相似文献   
82.
83.
84.
85.
86.
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   
87.
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   
88.
89.
 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   
90.
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