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   1344篇
  免费   11篇
  国内免费   6篇
化学   616篇
晶体学   13篇
力学   91篇
数学   195篇
物理学   446篇
  2022年   15篇
  2021年   16篇
  2020年   29篇
  2019年   24篇
  2018年   29篇
  2017年   36篇
  2016年   46篇
  2015年   13篇
  2014年   36篇
  2013年   38篇
  2012年   51篇
  2011年   67篇
  2010年   57篇
  2009年   42篇
  2008年   54篇
  2007年   51篇
  2006年   45篇
  2005年   35篇
  2004年   45篇
  2003年   30篇
  2002年   20篇
  2001年   39篇
  2000年   28篇
  1999年   12篇
  1998年   13篇
  1997年   24篇
  1996年   16篇
  1994年   19篇
  1993年   12篇
  1992年   12篇
  1991年   19篇
  1990年   15篇
  1989年   24篇
  1988年   15篇
  1987年   21篇
  1986年   14篇
  1985年   26篇
  1984年   13篇
  1983年   11篇
  1982年   15篇
  1981年   15篇
  1979年   12篇
  1978年   16篇
  1976年   21篇
  1975年   16篇
  1974年   11篇
  1973年   11篇
  1972年   11篇
  1969年   14篇
  1968年   17篇
排序方式: 共有1361条查询结果,搜索用时 15 毫秒
11.
12.
The parameters of fuel oil pyrolysis initiated by propane-butane-oxygen flame were studied as influenced by the temperature in the pyrolysis zone, time of the fuel oil contact with the initiating flame, and fuel oil feed rate. The experimental data on thermal and flame-initiated fuel oil pyrolysis were compared.  相似文献   
13.
14.
Highly polarized enediamines of the a, -diamino--cyano--nitroethylene type have been obtained by the hydrolysis of 4-chloro-5-nitropyrimidines. Several chemical conversions of the enamines obtained have been studied, particularly leading to derivatives of 2-(cyanonitromethylene)imidazoline and -hexahydropyrimidine, and also to derivatives of N, N-bisvinylpiperazine and 7 methylene-1, 4-diazabicyclo(2.2. 1 ]heptane.Center for Drug Chemistry, All-Russian Chemical and Pharmaceutical Research Institute, Moscow 119815. Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 6, pp. 811–820, June, 1996. Original article submitted February 6, 1996.For Part 1, see [1].  相似文献   
15.
The EPR method was used to study the structure of spin adducts of silyl and phosphonyl radicals with higher internal perfluoroalkenes. The capacity for spin adducts to split off hydrogen atoms is determined by the degree of steric screening of the free radical center. The preparative photochemical reaction of hydrosilanes and dialkyl phosphites with perfluoro-4-methylpent-2-ene leads to regiospecific hydrosilylation and hydrophosphorylation products with yields up to 80%.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 5, pp. 1018–1023, May, 1991.  相似文献   
16.
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   
17.
Conclusions The electron density on the-cyclopentadienyl ligand in cyclopentadienylmanganese tricarbonyl derivatives is higher than in the corresponding cyclopentadienylrhenium tricarbonyl derivatives.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 9, pp. 2142–2143, September, 1973.  相似文献   
18.
Catalytic oxidation of N,N'-dimethylthiourea and thiourea by dioxygen in water using a new cobalt(II) complex of octasulfophenyltetrapyrazinoporphyrazine was performed under mild conditions. The reaction is shown to include the formation of an intermediate anionic five-coordinate complex followed by an unusual two-electron oxidation to produce the corresponding urea and elemental sulfur (S8). Kinetic and thermodynamic parameters for the different reaction steps of the process were determined. Drastic differences in catalytic activity of cobalt and iron octasulfophenyltetrapyrazinoporphyrazines were observed.  相似文献   
19.
The catalytic activity of composites constituted by a porous metallic or ceramic support, intermediate layers of oxide nature, and perovskite coatings, including those doped with silver, was studied in reactions of deep oxidation of CO and organic compounds of various classes. The relationship between the catalytic activity of a composite and its composition and nature of substances being oxidized was analyzed.  相似文献   
20.
The primary and final products arising from the pyrolysis of perfluoro-2,4-dimethyl-3-ethylpentane, perfluoro-3-isopropyl-4-methyl-2-pentene, perfluoro-2-methyl-3-isopropyl-2-pentene, perfluoro-2,4-dimethyl-3-heptene, and perfluoro-4-methyl-2-pentene have been studied using low-energy mass spectrometry and chromatography-mass spectrometry. Thermal decomposition of hexafluoropropene oligomers, containing perfluoroisopropyl groups attached to a double bond, occurs via loss of a radical pair to form perfluorodienes, as well as via abstraction of a hexafluoropropene molecule from the iso-C3F7 group. A correlation between the principal fragmentation pathway observed under electron impact and the primary process in the main thermolysis pathway was detected only in the case of perfluoro-4-methyl-2-pentene and perfluoro-2,4-dimethyl-3-heptene, which are capable of cleavage of.CF3 and.C2F5 radicals, respectively, to give a single possible allyl radical structure.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 5, pp. 1037–1041, May, 1990.  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