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   1377366篇
  免费   29769篇
  国内免费   7739篇
化学   693924篇
晶体学   20477篇
力学   75672篇
综合类   106篇
数学   244301篇
物理学   380394篇
  2021年   13502篇
  2020年   15966篇
  2019年   16112篇
  2018年   14029篇
  2016年   28546篇
  2015年   20934篇
  2014年   30521篇
  2013年   74478篇
  2012年   40219篇
  2011年   39172篇
  2010年   38494篇
  2009年   40461篇
  2008年   37663篇
  2007年   33800篇
  2006年   38399篇
  2005年   31469篇
  2004年   32127篇
  2003年   29877篇
  2002年   30634篇
  2001年   30762篇
  2000年   26132篇
  1999年   23143篇
  1998年   21254篇
  1997年   21148篇
  1996年   21206篇
  1995年   19266篇
  1994年   18718篇
  1993年   18299篇
  1992年   18565篇
  1991年   18778篇
  1990年   18005篇
  1989年   18034篇
  1988年   17634篇
  1987年   17563篇
  1986年   16515篇
  1985年   22870篇
  1984年   23983篇
  1983年   20097篇
  1982年   21723篇
  1981年   20959篇
  1980年   20290篇
  1979年   20599篇
  1978年   21802篇
  1977年   21425篇
  1976年   21134篇
  1975年   19844篇
  1974年   19497篇
  1973年   19905篇
  1972年   14426篇
  1967年   12654篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
971.
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   
972.
973.
974.
975.
Levoglucosenone reacts with α-aminoazoles to yield azolo[1,5-a]pyrimidine systems fused with a carbohydrate fragment. The reaction oocurs much more smoothly than in the case of other α,β-unsaturated ketones. The reactions of levoglucosenone with β-dicarbonyl compounds (dimedone, barbituric acid) in the presence of a base results in the pyran ring closure, which has never been observed earlier in reactions of β-dicarbonyl compounds with α,β-unsaturated ketones under the conditions of basic catalysis. The structures of products were established by IR and NMR spectroscopy. For Part 3, see Ref. 1. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 3, pp. 553–558, March, 1997.  相似文献   
976.
The oxime and Schiff's base of N-furoylphenylhydroxylamine form complexes with Co2+, Cu2+, Zn2+ and Fe3+. These complexes were studied by means of the UV — Vis. spectra of nujol mulls, electron spin resonance (ESR) spectra and magnetic susceptibility to determine their stereochemistry. The complexes were characterized via elemental analyses, molar conductivities and thermogravimetric analyses. Organic reagents were used for the gravimetric determination of Co2+, Cu2+ and Fe3+ through the precipitation of their complexes. The compounds were also used for separation of a binary mixture of Cu2+ and Cu2+. Interferences were studied.  相似文献   
977.
978.
Thetrans-[Pt(NC5H4C(O)NHC2H4ONO2)2Cl2] complex (2) was prepared by the reaction of nicorandyl (N-nitroethoxynicotinamide), which is widely used in cardiology, with K2PtCl4 in water. The structure of2 was established by X-ray structural analysis. It was found that complex2 exhibits high antitumor activity, in particular, antimetastatic activity, unlike the analogous CuII complex with bromine atoms. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 1672–1675, September, 1997.  相似文献   
979.
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   
980.
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