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   37616篇
  免费   1844篇
  国内免费   2379篇
化学   25847篇
晶体学   201篇
力学   454篇
综合类   639篇
数学   6482篇
物理学   8216篇
  2023年   297篇
  2022年   1632篇
  2021年   1388篇
  2020年   678篇
  2019年   805篇
  2018年   600篇
  2017年   633篇
  2016年   760篇
  2015年   831篇
  2014年   1123篇
  2013年   2241篇
  2012年   1322篇
  2011年   1539篇
  2010年   1448篇
  2009年   1874篇
  2008年   1998篇
  2007年   2206篇
  2006年   1715篇
  2005年   1132篇
  2004年   1074篇
  2003年   1081篇
  2002年   3542篇
  2001年   1235篇
  2000年   801篇
  1999年   652篇
  1998年   628篇
  1997年   461篇
  1996年   556篇
  1995年   487篇
  1994年   507篇
  1993年   548篇
  1992年   539篇
  1991年   340篇
  1990年   298篇
  1989年   271篇
  1988年   286篇
  1987年   195篇
  1986年   221篇
  1985年   317篇
  1984年   229篇
  1983年   159篇
  1982年   292篇
  1981年   476篇
  1980年   441篇
  1979年   481篇
  1978年   380篇
  1977年   286篇
  1976年   242篇
  1974年   110篇
  1973年   190篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
111.
Let p be a real number greater than one. In this paper we study the vanishing and nonvanishing of the first L p -cohomology space of some groups that have one end. We also make a connection between the first L p -cohomolgy space and the Floyd boundary of the Cayley graph of a group. We apply the result about Floyd boundaries to show that there exists a real number p such that the first L p -cohomology space of a nonelementary hyperbolic group does not vanish. Received: 4 August 2006 Revised: 2 November 2006  相似文献   
112.
The solubility of carbon dioxide in aqueous solutions of sodium chloride was measured in the temperature range from 40 to 160°C, up to 6 mol-kg salt solutions and total pressures up to 10 MPa. Pitzer's(1) equations as well as the Chen and Evans(2) model were used to correlate the new data. Results are reported and compared to literature data and correlations.  相似文献   
113.
Perfluoro-1-octene was used as a model for developing a method for the preparative ozonolysis of perfluoro-1-alkenes to the corresponding perfluoro-nor-alkenals. Perfluoroheptanal was synthesized.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 6, pp. 1146–1147, June, 1994.  相似文献   
114.
Reactions of acetone, cyclohexanone, and adamantanone oximes withN,N-dibromo-tert-butylamine result in the correspondingC-bromo-diazene-N-oxides. In the case of benzophenone oxime,O, O'-(diphenylmethylene)-bis-benzophenone oxime has been obtained.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 1, pp. 176–177, January, 1994.  相似文献   
115.
The dependence of the variations in the differential molar free energy of sorption of polyfluorocarboxamides RFC(O)NR2 (RF = CF3(CF2) i ,i=0 to 5, R=H or Me) on capillary columns on the molecular structure of the amides, the temperature of analysis, and the nature of the stationary phases (OV-101, XE-60, and PEG-40M) were investigated by GLC. The peculiarities of the variation of the sorption characteristics of amides in XE-60 and PEG-40M polar phases, which cause the inversion of the order of retention of the members of pseudohomologous series, were found.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 868–871, May, 1994.We are grateful to R. V. Golovnya and D. N. Grigor'eva (Institute of Food Substances of the RAS, Moscow) for their participation in the discussion of the results obtained.  相似文献   
116.
The effect of the parameters of the electric arc (helium pressure, current and voltage, clearance between electrodes) and of the peculiarities of the setup design (arrangement of electrodes, distance between the arc and the cooling surface, temperature of the soot condensation surface) on the yield of fullerenes has been studied. Conditions for producing soot with a C60 and C70 content up to 43% (toluene extract) have been found.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 805–809, May, 1994.The authors are grateful to N. G. Spitsyna and A. V. Dubovitskii for the determination of the content of C60 and C70 fullerenes in the extract.The work was financially supported by the Russian Foundation for Basic Research (Project 93-03-18705).  相似文献   
117.
Regiochemistry and stereochemistry of the addition of mercury salts to benzobarrelene and tetrafluorobenzobarrelene have been studied in acetic acid and methanol. The effect of the substrate structure on the regiochemistry of the reaction is discussed.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 6, pp. 1105–1108, June, 1994.  相似文献   
118.
The interaction of ditoluenetitanium with CO{in2} has been studied. Based on hydrolysis, thermolysis, and IR spectral data, the conclusion is drawn that a low-valent titanium oxalate is formed.This study was financially supported by the Russian Foundation for Basic Research (Project No. 93-03-5538).Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 12, pp. 2241–2242, December, 1994.  相似文献   
119.
The results of comparative thermal analysis (TG-DTG-DTA-DSC) of the thermal decomposition of hexamminecobalt(III) chloride in air atmosphere are reported. The kinetics and mechanism of the thermal decomposition, the process enthalpy and the variation in specific thermal capacity of the solid product reaction with temperature were determined.  相似文献   
120.
D.P. Woodruff 《Surface science》2002,500(1-3):147-171
The range of surface structural problems of interest in understanding the physics and chemistry of solid surfaces is reviewed with reference to the available methods and their strengths and limitations. Key challenges being addressed currently concern the achievable precision of measurements and their physical and chemical significance, and the complexity of the problems which may be solved. Past progress and future problems are illustrated with a series of examples ranging from the relaxation of simple clean metal surfaces through complex semiconductor reconstructions to large molecular adsorption and coadsorption systems and complex adsorbate-induced reconstructions. The strengths and limitations of scanning tunnelling microscopy as a complement to true quantitative structural methods are discussed, as is the role of chemical state specificity and elemental specificity in solving complex molecular adsorbate systems.  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