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   404篇
  免费   3篇
化学   308篇
晶体学   1篇
力学   8篇
数学   14篇
物理学   76篇
  2021年   3篇
  2019年   7篇
  2018年   5篇
  2017年   7篇
  2016年   7篇
  2015年   5篇
  2014年   14篇
  2013年   25篇
  2012年   27篇
  2011年   19篇
  2010年   21篇
  2009年   34篇
  2008年   20篇
  2007年   26篇
  2006年   24篇
  2005年   16篇
  2004年   12篇
  2003年   14篇
  2002年   13篇
  2001年   7篇
  2000年   12篇
  1999年   4篇
  1998年   2篇
  1997年   5篇
  1996年   9篇
  1995年   2篇
  1993年   3篇
  1991年   3篇
  1990年   1篇
  1989年   7篇
  1988年   1篇
  1987年   3篇
  1986年   1篇
  1985年   1篇
  1984年   1篇
  1983年   3篇
  1982年   5篇
  1981年   3篇
  1980年   7篇
  1979年   1篇
  1978年   2篇
  1977年   1篇
  1975年   4篇
  1974年   4篇
  1973年   2篇
  1972年   3篇
  1971年   1篇
  1967年   2篇
  1966年   1篇
  1957年   3篇
排序方式: 共有407条查询结果,搜索用时 31 毫秒
61.
62.
The germanium atom is penta‐coordinated and adopts a trigonal bipyramidal geometry. The 2‐furfuryl group and the nitrogen atom each occupy an apical position with a transannular N→Ge bond distance of 2.173(3) Å. Copyright © 2004 John Wiley & Sons, Ltd.  相似文献   
63.
A convenient method was developed for the synthesis of derivatives of 6H-pyrazolo[1,5-c]pyrimidine-7-thione and 7-aminopyrazolo[1,5-c]pyrimidine from difluoroboron chelate complexes of aroylacetones, amide acetals, and thiosemicarbazide or aminoguanidine. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 992–994, May, 2007.  相似文献   
64.
The reaction of furan, thiophene, pyridine, and also furylacryloyl aldehydes with 2-trifluoromethylanilines has been studied in the presence of molecular sieves and a series of new heterocyclic aldimines has been synthesized. The molecular and crystalline structure of some of them were determined by X-ray structural analysis.  相似文献   
65.
The results of X-ray diffraction investigations of compounds containing selenophene and tellurophene fragments are reviewed and analyzed. The structural features of unsubstituted selenophene and tellurophene and their mono-, di-, tri-, and tetrasubstituted derivatives and also the structure of the complexes of selenophenes and tellurophenes with transition metals are discussed.  相似文献   
66.
The adiabatic calorimetry method is used to measure the isochoric heat capacity and the dew-bubble curves for the methane-normal pentane mixtures in bulk for three different mixture compositions of n-pentane. The near-critical behavior of the mixture heat capacity indicates that at low n-pentane concentrations, this system is close to the special point of the critical locus. The effect of porous medium has been investigated for one of the mixtures studied in bulk. It has been shown that in porous medium the essential shift of the dew-bubble curve takes place. In our opinion this shift is caused by the formation of wetting film on the surface of porous medium. The estimation of film thickness resulting from the data obtained yields the value 7–8 nm.  相似文献   
67.
The mechanism of the unexpected formation of 3-methyl derivatives of imidazo[2,1-b]thiazoles in the system 2-mercaptoimidazole–1,3-dichloroacetone–solid K2CO3–solid KI–18-crown-6–toluene has been studied. The structure of 3-methyl[1,3]thiazolo[3,2-a]benzimidazole has been confirmed using X-ray structural analysis.  相似文献   
68.
In the title compound, germanium is penta‐coordinated and adopts a trigonal bipyramidal geometry. The (2‐thienyl)phenyl group and the nitrogen atom each occupy an apical position with a transannular N→Ge bond distances of 2.247(4) and 2.219(4) Å for the two independent molecules. Copyright © 2005 John Wiley & Sons, Ltd.  相似文献   
69.
A theoretical analysis is presented of the possibilities of satisfying the conditions of phase matching (PM) in the coherent inelastic Mössbauer scattering (CIMS, which is scattering accompanied by the creation or annihilation of phonons) of synchrotron radiation (SR) and the conditions under which the maximum intensity of CIMS obtains are studied. Of the two types of CIMS — 1) participation of phonons in a scattering event only in the stage of absorption or only during re-emission of a photon, and 2) participation of phonons in both stages of scattering — PM is possible only in the first. The process in which phonons participate only at the photon absorption stage leads to efficient conversion of the SR from a wide spectral line into a narrow line, determined by the width of the Mössbauer transition. Photons of this type of CIMS effectively possess a higher penetrating power than the standard Mössbauer radiation, and their spectral distribution is shifted somewhat in the direction of low frequencies.  相似文献   
70.
Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 4, pp. 973–974, April, 1991.  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