全文获取类型
收费全文 | 13432篇 |
免费 | 2349篇 |
国内免费 | 1615篇 |
专业分类
化学 | 16964篇 |
晶体学 | 34篇 |
力学 | 7篇 |
综合类 | 31篇 |
数学 | 2篇 |
物理学 | 358篇 |
出版年
2024年 | 31篇 |
2023年 | 253篇 |
2022年 | 358篇 |
2021年 | 514篇 |
2020年 | 973篇 |
2019年 | 686篇 |
2018年 | 657篇 |
2017年 | 465篇 |
2016年 | 827篇 |
2015年 | 926篇 |
2014年 | 1020篇 |
2013年 | 1180篇 |
2012年 | 917篇 |
2011年 | 956篇 |
2010年 | 756篇 |
2009年 | 799篇 |
2008年 | 839篇 |
2007年 | 691篇 |
2006年 | 675篇 |
2005年 | 636篇 |
2004年 | 638篇 |
2003年 | 517篇 |
2002年 | 397篇 |
2001年 | 218篇 |
2000年 | 177篇 |
1999年 | 196篇 |
1998年 | 181篇 |
1997年 | 175篇 |
1996年 | 140篇 |
1995年 | 142篇 |
1994年 | 98篇 |
1993年 | 65篇 |
1992年 | 67篇 |
1991年 | 30篇 |
1990年 | 29篇 |
1989年 | 36篇 |
1988年 | 32篇 |
1987年 | 19篇 |
1986年 | 15篇 |
1985年 | 17篇 |
1984年 | 10篇 |
1983年 | 13篇 |
1982年 | 8篇 |
1980年 | 3篇 |
1979年 | 2篇 |
1977年 | 4篇 |
1974年 | 3篇 |
1973年 | 3篇 |
1972年 | 1篇 |
1971年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
11.
The first MCM-41-supported bidentate phosphine palladium(0) complex has been prepared. This complex is a highly efficient catalyst for Sonogashira reaction and can be reused at least 10 times without any decrease in activity. 相似文献
12.
Characteristic features of reactions involving esters of phosphorus-containing acids in highly organized media (micelles, liquid crystals, vesicles, and emulsions) are surveyed.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 2, pp. 298–312, February, 1996. 相似文献
13.
The key factors influencing the Diels—Alder reaction rate at ambient and elevated pressures were elucidated using data on the reactivity of various diene—dienophile systems in usual and Lewis acid-catalyzed Diels—Alder reactions, the reaction enthalpy, complex formation, dissolution, and solvation, and the donor-acceptor properties of the reactants. It was found that taking account of both the orbital interaction energy and the balance of bond rupture and formation energies allows correct prediction of the reaction rate in the absence or in the presence of Lewis acids. 相似文献
14.
U. M. Dzhemilev F. A. Selimov R. A. Khusnutdinov A. A. Fatykhov E. I. Andreikov G. A. Obanin 《Russian Chemical Bulletin》1992,41(5):895-902
Liquid-phase condensation of 3-, 4-, and 8-aminoquinolines with aliphatic and aromatic aldehydes catalyzed by transition and rare-earth metal complexes is an efficient method for synthesis of substituted 1,7- and 1,6-naphthyridines and 1,10-phenanthrolines.Institute of Organic Chemistry, Ural Branch, Russian Academy of Sciences, 450054 Ufa; Eastern Scientific-Research Institute of Coal Chemistry, 620219 Sverdlovsk. Translated from Izvestiya Akademii Nauk, Seriya Khimicheskaya, No. 5, pp. 1139–1148, May, 1992. 相似文献
15.
We report the first enzyme-catalysed kinetic resolution of epoxy enol esters. The lipase-promoted hydrolysis of these compounds provided α-hydroxyketones or α-hydroxyaldehydes (arising from the spontaneous rearrangement of the epoxy enols) and the residual esters with moderate to good enantioselectivity (E up to 100). 相似文献
16.
《Tetrahedron letters》2004,45(11):2377-2380
The β-substituted captodative olefins methyl 2-aryloxy-3-dimethylaminopropenoates 4a-h were synthesized, via aminomethylenation of the corresponding 2-phenoxyacetic esters 9a-h. Lewis acid promoted intramolecular cyclization of alkenes 4 led to benzofurans 7a-h, in an efficient synthetic approach to the benzofuran frame. 相似文献
17.
Trost BM Shen HC Horne DB Toste FD Steinmetz BG Koradin C 《Chemistry (Weinheim an der Bergstrasse, Germany)》2005,11(8):2577-2590
The Ru-catalyzed intramolecular [5+2] cycloaddition of cyclopropylenynes is investigated with respect to the regio- and diastereoselectivity as well as the functional group compatibility of the reaction. Evidence for the mechanism as occurring through a ruthenacyclopentene intermediate is elucidated from 1) the study of the diastereoselectivity of the cycloaddition; 2) the effect of variation of substituents on the regioselectivity of cyclopropyl bond cleavage in 1,2-trans- and 1,2-cis-disubstituted cyclopropanes and 3) examples that clearly do not involve ruthenacyclohexene as intermediates as products still incorporate the cyclopropyl moiety. The scope and limitations of the Ru-catalyzed cycloaddition are discussed and compared with the Rh-catalyzed reaction. The potential power of this methodology towards natural product total synthesis is demonstrated by the formation of several polycyclic systems with the chosen reaction conditions and readily available cyclopropylenyne substrates. 相似文献
18.
Michael W. Fennie 《Tetrahedron》2005,61(26):6249-6265
Metal complexes of C2-symmetric Lewis acid/Lewis base salen ligands provide bifunctional activation resulting in rapid rates in the enantioselective addition of diethylzinc to aldehydes (up to 92% ee). Further experiments probed the reactivity of the individual Lewis acid and Lewis base components of the catalyst and established that both moieties are essential for asymmetric catalysis. These catalysts are also effective in the asymmetric addition of diethylzinc to α-ketoesters. This finding is significant because α-ketoesters alone serve as their own ligands to accelerate racemic 1,2-carbonyl addition of Et2Zn and racemic carbonyl reduction. The latter proceeds via a metalloene pathway, and often accounts for the predominant product. Singular Lewis acid catalysts do not accelerate enantioselective 1,2-addition over these two competing paths. The bifunctional amino salen catalysts, however, rapidly provide enantioenriched 1,2-addition products in excellent yield, complete chemoselectivity, and good enantioselectivity (up to 88% ee). A library of the bifunctional amino salens was synthesized and evaluated in this reaction. The utility of the α-ketoester method has been demonstrated in the synthesis of an opiate antagonist. 相似文献
19.
徐肖邢 《理化检验(化学分册)》2004,40(12):697-699
制备了普鲁士蓝修饰的丝网印刷过氧化氢传感器,研究了过氧化氢在该修饰电极上的电催化还原特性,考察了有关修饰膜制备和试验条件对传感器性能的影响。结果表明,pH4.0的0.2mol·L-1KH2PO4 K2HPO4缓冲溶液(PBS)中,修饰电极对过氧化氢显示出快速的电化学响应,较高的稳定性、重现性和催化活性,测定的线性范围为1.0×10-5~1.0×10-3mol·L-1,相关系数为0.999,检出限为6.0×10-6mol·L-1(3σ)。电极制作方法简便,可用于实际样品的测定。 相似文献
20.
Fátima Nunes Serralha José Madeira Lopes Francisco Lemos Duarte Prazeres Maria Aires-Barros Joo Rocha Joaquim Cabral Fernando Ramôa Ribeiro 《Reaction Kinetics and Catalysis Letters》2000,69(2):217-222
Novel [CrIII(amp)(bipy)(Cl)] (1) (H2amp = N-(hydroxyphenyl)salicyldimine; bipy = 2,2-bipyridyl) and [CrIII(app)(bipy)(Cl)]+ (2) (H2app = N-(hydroxyphenyl)pyridine-2-carboxaldimine; bipy = 2,2-bipyridyl) complexes have been synthesized and characterized by physico-chemical methods. Complexes 1 and 2 have been employed as catalysts in the oxidation of both saturated and unsaturated hydrocarbons using tert-butylhydroperoxide (t-BuOOH). The significance of the results with respect to oxo-functionalization of C-H bonds both in unsaturated and saturated hydrocarbons is noted. 相似文献