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   688篇
  免费   2篇
化学   455篇
晶体学   7篇
力学   30篇
数学   21篇
物理学   177篇
  2021年   11篇
  2020年   9篇
  2019年   13篇
  2018年   30篇
  2017年   20篇
  2016年   27篇
  2015年   6篇
  2014年   20篇
  2013年   22篇
  2012年   21篇
  2011年   20篇
  2010年   25篇
  2009年   19篇
  2008年   19篇
  2007年   23篇
  2006年   26篇
  2005年   29篇
  2004年   23篇
  2003年   14篇
  2002年   20篇
  2001年   28篇
  2000年   17篇
  1999年   14篇
  1998年   14篇
  1997年   14篇
  1996年   13篇
  1995年   8篇
  1994年   8篇
  1992年   5篇
  1988年   5篇
  1987年   6篇
  1986年   5篇
  1985年   5篇
  1984年   7篇
  1983年   4篇
  1982年   4篇
  1980年   7篇
  1979年   7篇
  1978年   5篇
  1977年   6篇
  1976年   7篇
  1975年   11篇
  1974年   10篇
  1973年   7篇
  1972年   8篇
  1966年   6篇
  1965年   7篇
  1963年   4篇
  1961年   4篇
  1960年   5篇
排序方式: 共有690条查询结果,搜索用时 0 毫秒
1.
The design of new solid-state proton-conducting materials is a great challenge for chemistry and materials science. Herein, a new anionic porphyrinylphosphonate-based MOF ( IPCE-1Ni ), which involves dimethylammonium (DMA) cations for charge compensation, is reported. As a result of its unique structure, IPCE-1Ni exhibits one of the highest value of the proton conductivity among reported proton-conducting MOF materials based on porphyrins (1.55×10−3 S cm−1 at 75 °C and 80 % relative humidity).  相似文献   
2.
Liquid-phase chlorination of a number of chloro(chlorovinyl)methylsilanes was investigated. A number of novelC-chlorosilanes were characterized by IR and1H NMR spectra. Some regularities of these reactions were determined; correlations between the structure of chloro(chlorovinyl)methylsilanes and their reactivities were identified.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 11, pp. 2256–2260, November, 1995.  相似文献   
3.
It has been shown that the alkylation of 2-methyl-9-hydroxy-4H-pyrido[1,2-a]pyrimidin-4-one takes place at the oxygen atom, but electrophilic substitution takes place mainly at position 8 of the molecule (the ortho position relative to the hydroxy group).Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 12, pp. 1660–1666, December, 1992.  相似文献   
4.
Unlike rheumycin and fervenulin, isofervenulin and 3-methylisofervenulin are hydrolyzed by aqueous alkalies at the N(5)-C(6) bond. On acidification of the reaction mixture, the N-carboxy-N-methylcarbamoyltriazines formed are reconverted into the starting isofervenulins, and on basification (pH>10) into methylaminotriazinecarboxamides. A by-product of the alkaline hydrolysis of isofervenulin is a product of the contraction of the uracil ring, namely imidazotriazinone-7a-carboxylic acid.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 11, pp. 1555–1559, November, 1987.  相似文献   
5.
6.
7.
The dependence of the rate of a photochemical reaction of XeO4with H2on the concentrations of H2and the diluent gases He and CO2is studied at room temperature. The results are compared with the data for the dark reaction. A mechanism with the elementary energetic branched-chain reaction OH (v) + XeO4OH + O + XeO3is proposed to explain the results of the study.  相似文献   
8.
9.
The mixtures of mono-and dihalothiophenesulfonyl chlorides, formed in the sulfochlorination reaction of 2,5-dichlorothiophene and 2,5-dibromothiophene, were treated with aqueous ammonia and thus converted into mixtures of the corresponding stable thiophenesulfonamides. The structure and composition of the latter were studied by physicochemical methods: GC-MS and 1H, 13C, 1H-13C HSQC, 1H-13C HMBC, and NOESY NMR spectroscopy. As a result of the above chemical transformations, 2,5-dichlorothiophene afforded a mixture of 5-chlorothiophene-2-sulfonamide and 4,5-dichlorothiophene-3-sulfonamide in a roughly 70:30 ratio. In the case of 2,5-dibromothiophene, a mixture of 5-bromothiophene-2-sulfonamide, 4,5-dibromothiophene-3-sulfonamide, and 3,5-dibromothiophene-2-sulfonamide (3:54:43) was formed. Original Russian Text I.B. Rozentsveig, Yu.A. Aizina, K.A. Chernyshev, L.V. Klyba, E.R. Zhanchipova, E.N. Sukhomazova, L.B. Krivdin, G.G. Levkovskaya, 2007, published in Zhurnal Obshchei Khimii, 2007, Vol. 77, No. 5, pp. 831–836.  相似文献   
10.
Novel dialkylaminocarbenium salts with metallocomplex counter ions were prepared by the reaction of phosgene with either DMF or tetramethylurea in the presence of metal chlorides. Reactions of organosilicon amides with phosgene gave corresponding carbenium salts, while organosilicon ureas yielded aminoiminocarbenium salts. Dialkylaminochlorocarbenium salts were reduced with hydrosilanes to give dialkylaminocarbenium, salts and can be easily hydrolyzed to afford either amides or ureas. Pathways of the reaction with water and alcohols depend on the nature of reagent and the reaction conditions. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 1035–1040, May 1997.  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