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   1421550篇
  免费   31906篇
  国内免费   9410篇
化学   724534篇
晶体学   20713篇
力学   76956篇
综合类   180篇
数学   247706篇
物理学   392777篇
  2021年   13978篇
  2020年   16435篇
  2019年   16678篇
  2018年   14827篇
  2017年   13053篇
  2016年   29358篇
  2015年   21617篇
  2014年   31388篇
  2013年   75687篇
  2012年   42917篇
  2011年   42876篇
  2010年   40110篇
  2009年   41676篇
  2008年   40626篇
  2007年   37032篇
  2006年   41012篇
  2005年   34097篇
  2004年   34262篇
  2003年   31588篇
  2002年   32213篇
  2001年   32972篇
  2000年   27628篇
  1999年   23947篇
  1998年   21723篇
  1997年   21539篇
  1996年   21493篇
  1995年   19488篇
  1994年   19002篇
  1993年   18532篇
  1992年   19078篇
  1991年   19215篇
  1990年   18476篇
  1989年   18455篇
  1988年   18022篇
  1987年   17895篇
  1986年   16892篇
  1985年   23214篇
  1984年   24235篇
  1983年   20268篇
  1982年   21834篇
  1981年   21071篇
  1980年   20395篇
  1979年   20849篇
  1978年   21947篇
  1977年   21643篇
  1976年   21382篇
  1975年   20128篇
  1974年   19781篇
  1973年   20194篇
  1972年   14692篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
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   
992.
993.
994.
995.
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   
996.
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   
997.
998.
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   
999.
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   
1000.
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