全文获取类型
收费全文 | 7631篇 |
免费 | 292篇 |
国内免费 | 271篇 |
专业分类
化学 | 4013篇 |
晶体学 | 119篇 |
力学 | 165篇 |
综合类 | 31篇 |
数学 | 2476篇 |
物理学 | 1390篇 |
出版年
2023年 | 23篇 |
2022年 | 34篇 |
2021年 | 51篇 |
2020年 | 113篇 |
2019年 | 146篇 |
2018年 | 132篇 |
2017年 | 142篇 |
2016年 | 139篇 |
2015年 | 117篇 |
2014年 | 166篇 |
2013年 | 249篇 |
2012年 | 175篇 |
2011年 | 350篇 |
2010年 | 271篇 |
2009年 | 466篇 |
2008年 | 357篇 |
2007年 | 401篇 |
2006年 | 351篇 |
2005年 | 380篇 |
2004年 | 512篇 |
2003年 | 434篇 |
2002年 | 391篇 |
2001年 | 306篇 |
2000年 | 265篇 |
1999年 | 195篇 |
1998年 | 161篇 |
1997年 | 170篇 |
1996年 | 195篇 |
1995年 | 157篇 |
1994年 | 197篇 |
1993年 | 152篇 |
1992年 | 132篇 |
1991年 | 77篇 |
1990年 | 60篇 |
1989年 | 60篇 |
1988年 | 53篇 |
1987年 | 70篇 |
1986年 | 56篇 |
1985年 | 47篇 |
1984年 | 44篇 |
1983年 | 13篇 |
1982年 | 38篇 |
1981年 | 41篇 |
1980年 | 48篇 |
1979年 | 67篇 |
1978年 | 52篇 |
1977年 | 52篇 |
1976年 | 37篇 |
1974年 | 13篇 |
1973年 | 17篇 |
排序方式: 共有8194条查询结果,搜索用时 515 毫秒
51.
T. Katsuki 《Russian Chemical Bulletin》2004,53(9):1859-1870
The recent development of asymmetric Baeyer014;Villiger oxidation of prochiral and racemic ketones is briefly summarized, focusing on the regio- and stereocontrol of the oxidation attained by regulating the stereoelectronic demand in the step of rearrangement of the Criegee intermediate.Based on the report presented at the International Conference 0.gif" alt="ldquo" align="MIDDLE" BORDER="0">Modern Trends in Organoelement and Polymer Chemistry0"> dedicated to the 50th anniversary of the A. N. Nesmeyanov Institute of Organoelement Compounds of the Russian Academy of Sciences (Moscow, May 30013;June 4, 2004).Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 1784013;1794, September, 2004. 相似文献
52.
Hans-Georg Henning Giedrius Mazunaitis 《Monatshefte für Chemie / Chemical Monthly》1992,123(1-2):93-98
Summary Irradiation of solutions of excess cyclohexene and 2-acetyl-5,5-dimethyl-1,3-cyclohexanedione (1), and 3-acetyl-1,5,5-trimethyl-2,4-pyrrolidinedione (4) results mainly in the formation of 1,5-diones2 and5. These originate from intermediate cycloadducts of cyclohexene and theexo-enols of the cyclic 1,3-diketones. The yields decrease with increasing polarity of the solvent. In solution2 and5 are in equilibrium with the cyclic hemiacetales3 and6. 相似文献
53.
54.
The reaction of W(CO)6 with pyOSNa (C5-H4NOSNa) and Et4NCl in MeCN affords a new tungsten(0) complex [Et4N][W(pyS)(CO)4] 1 (Mr.= 536.29).The crystal and molecular structures have been determined by X-ray single-crystal diffraction.Complex 1 crystallizes in the orthorhombic system,space group P212121 with a = 8.2429(5),b = 9.1045(4),c =26.8851(14) (A),β = 90.00°,V= 2017.66(18) (A)3,Z = 4,Dc.= 1.765 g/cm3,μ = 58.51 cm-1,F(000) =1048,the final R = 0.0204 and wR = 0.0400 for 4432 observed reflections with I > 2σ(I).X-ray structure analysis revealed that the molecule is acentric and has large first-order hyperpolarizability (7.2 × 10-30 esu),so it could be an IR second-order nonlinear optical candidate material. 相似文献
55.
N. K. Gusarova B. A. Trofimov T. N. Rakhmatulina S. F. Malysheva S. N. Arbuzova S. I. Shaikhudinova A. I. Albanov 《Russian Chemical Bulletin》1994,43(9):1591-1592
The reaction of styrene and 0">-methylstyrene with P in aprotic polar solvents in the presence of KOH affords diorganylphosphinous acids.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 1680013;1681, September, 1994. 相似文献
56.
U. M. Dzhemilev O. S. Vostrikova R. M. Sultanov I. N. Batalina 《Russian Chemical Bulletin》1992,41(5):936-944
The reaction of organomagnesium compounds (OMC) containing alkyl radicals of normal structure with 0w7/xxlarge945.gif" alt="agr" align="BASELINE" BORDER="0">-olefins, resulting in the formation of alkenylorganomagnesium compounds and accompanied by hydride transfer was discovered and systematically investigated. A scheme providing for the formation of zirconacyclopentane complexes was proposed for the mechanism of the reaction.Institute of Organic Chemistry, Ural Branch, Russian Academy of Sciences, 450054 Ufa. Translated from Izvestiya Akademii Nauk, Seriya Khimicheskaya, No. 5, pp. 1187013;1196, May, 1992. 相似文献
57.
A series of ethyl(phenyl) 6-amino-2,3,6-trideoxy-0">-D-glucopyranosides (amino=piperidino (Pip), pyrrolidino (Pyr), azetidino (Az), Bu2N) have been prepared from tri-O-acetyl-D-glucal to obtain catalysts for asymmetric synthesis and the starting compounds for the syntheses of other bidentate ligands.Published in Khimiya Geterotsiklicheskikh Soedinenii, No. 1, pp. 45013;52, January, 2000. 相似文献
58.
Summary The capillary gas chromatographic retention behavior of 078x7x25010h0186/xxlarge945.gif" alt="agr" align="BASELINE" BORDER="0">-pinene and tricyclene has been investigated on stationary phases of different polarities. On all but one of the columns employed, tricyclene eluted before 078x7x25010h0186/xxlarge945.gif" alt="agr" align="BASELINE" BORDER="0">-pinene; only permethylated 078x7x25010h0186/xxlarge946.gif" alt="beta" align="MIDDLE" BORDER="0">-cyclodextrins dissolved in moderately polar polisiloxanes gave a reversed elution order. The intermolecular interactions which caused the unexpected retention behavior were investigated in detail, applying methods of computer simulation. To achieve this, we have developed a calculation algorithm on the basis of molecular mechanical optimizations and programmed it in a macro. This makes it possible to systematically investigate a given configuration space in which all the possible interactions can take place. It was shown that permethylated 078x7x25010h0186/xxlarge946.gif" alt="beta" align="MIDDLE" BORDER="0">-cyclodextrin as host molecule for both guest molecules offers an optimum cavity size. As a result the number of energetically favorable contacts between host and guest molecules as well as the strength of the interactions in this stationary phase were larger. As a consequence the elution order, normally only influenced by the vapor pressure of the compounds at a given temperature, was changed. Nonspecific interactions played an especially important role for these kinds of substances. 相似文献
59.
The reaction of B2H4 with acetylene has been studied by the MNDO method. It is shown that the reaction is exothermic and proceeds in two steps. The first step is the formation of a three-center 0.gif" alt="pgr" align="BASELINE" BORDER="0">-complex and this is the rate-determining step of the reaction. The second step is the rearrangement of the 0.gif" alt="pgr" align="BASELINE" BORDER="0">-complex to the product and this step requires a very small amount of activation energy. The activation barrier for the diboration reaction is 12.8 kcal/mol.The proposed mechanism is significantly different from those proposed earlier and explains all experimental data relating to this reaction. 相似文献
60.