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   1390914篇
  免费   29700篇
  国内免费   7716篇
化学   697107篇
晶体学   20927篇
力学   76200篇
综合类   113篇
数学   246779篇
物理学   387204篇
  2021年   13498篇
  2020年   15937篇
  2019年   16073篇
  2018年   15850篇
  2017年   14505篇
  2016年   29273篇
  2015年   21082篇
  2014年   30415篇
  2013年   74362篇
  2012年   40882篇
  2011年   40960篇
  2010年   39850篇
  2009年   41841篇
  2008年   39482篇
  2007年   36256篇
  2006年   38345篇
  2005年   33322篇
  2004年   33110篇
  2003年   30499篇
  2002年   30827篇
  2001年   29767篇
  2000年   25536篇
  1999年   22925篇
  1998年   21211篇
  1997年   21118篇
  1996年   21210篇
  1995年   19225篇
  1994年   18701篇
  1993年   18236篇
  1992年   18280篇
  1991年   18532篇
  1990年   17733篇
  1989年   17837篇
  1988年   17456篇
  1987年   17353篇
  1986年   16244篇
  1985年   22666篇
  1984年   23909篇
  1983年   20091篇
  1982年   21706篇
  1981年   20938篇
  1980年   20264篇
  1979年   20499篇
  1978年   21784篇
  1977年   21401篇
  1976年   21089篇
  1975年   19800篇
  1974年   19452篇
  1973年   19931篇
  1972年   14406篇
排序方式: 共有10000条查询结果,搜索用时 46 毫秒
971.
972.
973.
974.
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   
975.
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   
976.
977.
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   
978.
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   
979.
980.
The concentration and chemical state of copper in the subsurface region of Cu/SiO2 composite films obtained by simultaneous magnetron sputtering from two sources (Cu and SiO2) are determined by x-ray photoelectron spectroscopy (XPS). It is established that copper in the as-grown film is primarily in the form of unoxidized atoms dispersed in a SiO2 matrix. Annealing of the film results in practically no oxidation, but about 70% of the copper atoms condense into metallic clusters with sizes below 10 Å in the subsurface region and about 50 Å in the bulk of the film. The changes in the binding energy of core electrons, and especially in the energies of Auger electrons, are so large in this situation that photoelectron and Auger spectroscopy are efficient methods for monitoring the chemical state of this composite material.  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