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   1274142篇
  免费   31294篇
  国内免费   8999篇
化学   628308篇
晶体学   20067篇
力学   73959篇
综合类   222篇
数学   237742篇
物理学   354137篇
  2021年   13863篇
  2020年   16300篇
  2019年   16441篇
  2016年   27316篇
  2015年   20940篇
  2014年   30795篇
  2013年   74664篇
  2012年   34983篇
  2011年   28979篇
  2010年   35229篇
  2009年   38258篇
  2008年   29087篇
  2007年   23823篇
  2006年   32180篇
  2005年   23349篇
  2004年   25853篇
  2003年   25079篇
  2002年   26655篇
  2001年   24828篇
  2000年   22582篇
  1999年   21545篇
  1998年   20726篇
  1997年   20774篇
  1996年   20936篇
  1995年   19054篇
  1994年   18473篇
  1993年   18001篇
  1992年   17507篇
  1991年   17859篇
  1990年   17096篇
  1989年   17191篇
  1988年   16705篇
  1987年   16755篇
  1986年   15641篇
  1985年   22114篇
  1984年   23487篇
  1983年   19748篇
  1982年   21498篇
  1981年   20751篇
  1980年   20081篇
  1979年   20083篇
  1978年   21507篇
  1977年   21056篇
  1976年   20717篇
  1975年   19380篇
  1974年   19011篇
  1973年   19489篇
  1972年   14014篇
  1968年   11890篇
  1967年   12270篇
排序方式: 共有10000条查询结果,搜索用时 15 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