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   1303992篇
  免费   29680篇
  国内免费   7685篇
化学   647591篇
晶体学   15562篇
力学   74212篇
综合类   112篇
数学   240874篇
物理学   363006篇
  2021年   13386篇
  2020年   15886篇
  2019年   16011篇
  2016年   27287篇
  2015年   20591篇
  2014年   30339篇
  2013年   74285篇
  2012年   37154篇
  2011年   32196篇
  2010年   36599篇
  2009年   39033篇
  2008年   31504篇
  2007年   26780篇
  2006年   34577篇
  2005年   26036篇
  2004年   28076篇
  2003年   26940篇
  2002年   28286篇
  2001年   27758篇
  2000年   24264篇
  1999年   22308篇
  1998年   20958篇
  1997年   20947篇
  1996年   21042篇
  1995年   19135篇
  1994年   18576篇
  1993年   18105篇
  1992年   18183篇
  1991年   18425篇
  1990年   17117篇
  1989年   17116篇
  1988年   16712篇
  1987年   16733篇
  1986年   15599篇
  1985年   22143篇
  1984年   23408篇
  1983年   19504篇
  1982年   21203篇
  1981年   20449篇
  1980年   19746篇
  1979年   20102篇
  1978年   21370篇
  1977年   21069篇
  1976年   20790篇
  1975年   19499篇
  1974年   19136篇
  1973年   19674篇
  1972年   14168篇
  1968年   12248篇
  1967年   12607篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
992.
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   
993.
994.
995.
996.
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   
997.
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   
998.
999.
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   
1000.
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   
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