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   1445347篇
  免费   29944篇
  国内免费   7812篇
化学   740740篇
晶体学   20614篇
力学   76750篇
综合类   108篇
数学   249854篇
物理学   395037篇
  2021年   13594篇
  2020年   16060篇
  2019年   16201篇
  2018年   14643篇
  2016年   29110篇
  2015年   21216篇
  2014年   30802篇
  2013年   75095篇
  2012年   44198篇
  2011年   45282篇
  2010年   40156篇
  2009年   41496篇
  2008年   42794篇
  2007年   39548篇
  2006年   43437篇
  2005年   36468篇
  2004年   36335篇
  2003年   33254篇
  2002年   33654篇
  2001年   34144篇
  2000年   28292篇
  1999年   24233篇
  1998年   21760篇
  1997年   21583篇
  1996年   21486篇
  1995年   19470篇
  1994年   18955篇
  1993年   18519篇
  1992年   19178篇
  1991年   19325篇
  1990年   18522篇
  1989年   18502篇
  1988年   18146篇
  1987年   17965篇
  1986年   16991篇
  1985年   23335篇
  1984年   24294篇
  1983年   20355篇
  1982年   21954篇
  1981年   21148篇
  1980年   20472篇
  1979年   20922篇
  1978年   22047篇
  1977年   21711篇
  1976年   21476篇
  1975年   20241篇
  1974年   19924篇
  1973年   20328篇
  1972年   14804篇
  1967年   12971篇
排序方式: 共有10000条查询结果,搜索用时 15 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