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   1422369篇
  免费   29928篇
  国内免费   7824篇
化学   721966篇
晶体学   20745篇
力学   76596篇
综合类   112篇
数学   248600篇
物理学   392102篇
  2021年   13581篇
  2020年   16065篇
  2019年   16192篇
  2018年   15256篇
  2017年   13594篇
  2016年   29260篇
  2015年   21247篇
  2014年   30779篇
  2013年   75008篇
  2012年   42569篇
  2011年   43272篇
  2010年   40110篇
  2009年   41709篇
  2008年   41154篇
  2007年   37923篇
  2006年   40865篇
  2005年   34893篇
  2004年   34534篇
  2003年   31791篇
  2002年   32243篇
  2001年   32511篇
  2000年   27359篇
  1999年   23706篇
  1998年   21514篇
  1997年   21413篇
  1996年   21380篇
  1995年   19411篇
  1994年   18879篇
  1993年   18483篇
  1992年   18926篇
  1991年   19118篇
  1990年   18276篇
  1989年   18295篇
  1988年   17920篇
  1987年   17820篇
  1986年   16769篇
  1985年   23121篇
  1984年   24199篇
  1983年   20250篇
  1982年   21843篇
  1981年   21082篇
  1980年   20440篇
  1979年   20808篇
  1978年   21964篇
  1977年   21599篇
  1976年   21379篇
  1975年   20069篇
  1974年   19759篇
  1973年   20148篇
  1972年   14644篇
排序方式: 共有10000条查询结果,搜索用时 296 毫秒
981.
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   
982.
983.
984.
985.
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   
986.
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   
987.
988.
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   
989.
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   
990.
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