全文获取类型
收费全文 | 2877篇 |
免费 | 57篇 |
国内免费 | 8篇 |
专业分类
化学 | 1855篇 |
晶体学 | 42篇 |
力学 | 99篇 |
数学 | 621篇 |
物理学 | 325篇 |
出版年
2023年 | 17篇 |
2022年 | 55篇 |
2021年 | 68篇 |
2020年 | 50篇 |
2019年 | 51篇 |
2018年 | 32篇 |
2017年 | 25篇 |
2016年 | 73篇 |
2015年 | 74篇 |
2014年 | 69篇 |
2013年 | 143篇 |
2012年 | 119篇 |
2011年 | 174篇 |
2010年 | 113篇 |
2009年 | 88篇 |
2008年 | 147篇 |
2007年 | 121篇 |
2006年 | 145篇 |
2005年 | 137篇 |
2004年 | 123篇 |
2003年 | 109篇 |
2002年 | 95篇 |
2001年 | 36篇 |
2000年 | 25篇 |
1999年 | 29篇 |
1998年 | 23篇 |
1997年 | 25篇 |
1996年 | 52篇 |
1995年 | 28篇 |
1994年 | 32篇 |
1993年 | 30篇 |
1992年 | 26篇 |
1991年 | 24篇 |
1990年 | 25篇 |
1989年 | 16篇 |
1988年 | 22篇 |
1987年 | 21篇 |
1986年 | 14篇 |
1985年 | 30篇 |
1984年 | 20篇 |
1983年 | 24篇 |
1982年 | 28篇 |
1981年 | 28篇 |
1980年 | 36篇 |
1979年 | 37篇 |
1978年 | 20篇 |
1977年 | 12篇 |
1976年 | 19篇 |
1975年 | 15篇 |
1973年 | 11篇 |
排序方式: 共有2942条查询结果,搜索用时 0 毫秒
61.
Amantini D Beleggia R Fringuelli F Pizzo F Vaccaro L 《The Journal of organic chemistry》2004,69(8):2896-2898
Tetrabutylammonium fluoride (TBAF) is an efficient catalyst in the [3 + 2] cycloaddition reaction of organic nitriles 1 with trimethylsilyl azide (TMSN(3)) in solventless conditions. The corresponding 5-substituted 1H-tetrazoles 2 were obtained under mild conditions and in 80-97% yields. 相似文献
62.
The effect of nitrite in the sulfoxidation of organic sulfides catalyzed by myoglobin (Mb) in the presence of hydrogen peroxide has been investigated. A general improvement in enantioselectivity was found for the reaction catalyzed by horse heart metMb and a series of sperm whale metMb derivatives including the wild type protein, the active site mutants T67K Mb, T67R Mb, T67R/S92D Mb, and the T67K Mb derivative reconstituted with the modified prosthetic group protohemin-l- histidine methyl ester. 相似文献
63.
64.
Antonio Selva Pietro Traldi Luigi F. Zerilli Gian Gualberto Gallo 《Journal of mass spectrometry : JMS》1976,11(2):217-218
The retro 1,3-dipolar cycloaddition induced by electron impact on 3,5-diphenyl-1,2,4-oxadiazole is interpreted as a two-step process on the basis of the energetics and kinetics of the fragments [C7H5NO]+., [C6H5CN]+. and [C6H5CO]+. 相似文献
65.
Rolf Holderegger Luigi M. Venanzi Fiorella Bachechi Pasquale Mura Luigi Zambonelli 《Helvetica chimica acta》1979,62(7):2159-2167
The preparation of the nucleophile trans-[RuCl(NO)( 1 )], where 1 is the bidentate ligand Ph2PCH2C18CH2PPh2, and of the five-coordinate species [RuCl(CO)(NO)( 1 )], [RuCl(CO)(NO)(Ph2PCH2Ph)2] and [RuCl(NO)( 2 )( 1 )] are reported. The crystal structure of [RuCl(CO)(NO)( 1 )] shows that the coordination around the metal atom is distorted trigonal bipyramidal with the phosphorus atoms in axial positions. The Ru? N? O bond angle is 142.8°. 1H- and 31P-NMR. and \documentclass{article}\pagestyle{empty}\begin{document}$ \tilde \nu $\end{document}NO IR.-data for the above complexes are reported and related to the coordination geometry. 相似文献
66.
Fabrizio Casarini Luigi Marcheselli Andrea Marchetti Lorenzo Tassi Giuseppe Tosi 《Journal of solution chemistry》1993,22(10):895-905
The relative permittivities for the ternary 1,2-ethanediol (component 1) + 2-methoxyethanol (2) + water (3) solvent system have been measured for 66 mixtures covering the whole mole fraction composition 0X1/X2/X3 1 range at –10, –5 and 0 °C. The experimental data were used to test some empirical relations stating the dependence of = (X1, X2, X3). A comparison between the calculated and experimental data show that these equations can be usefully employed to predict values in correspondence of the experimental data gaps. 相似文献
67.
68.
Andrea Carati Giancarlo Benettin Luigi Galgani 《Communications in Mathematical Physics》1992,150(2):321-336
For classical Hamiltonian systems containing an harmonic oscillator of high frequency, one has the problem of controlling the energy exchange between the oscillator and the remaining slow degrees of freedom; under very general conditions, such an exchange turns out to be exponentially small with the frequency of the oscillator. In the Jeans-Landau-Teller method, one aims to prove the exponential dependence, and to estimate the coefficient of the exponential, by exploiting the analyticity properties of the solution of the differential equations describing the motion of the system. However, in practice, since the exact solution is not known, such properties are inferred from those of an approximate solution, with no control of the difference; this fact might a priori even invalidate the exponential dependence itself. In the present paper a rigorous treatment is given, for a particular model of interest in the domain of atomic collisions, by keeping control of the difference between the exact and the approximate solution. 相似文献
69.
The preparations of the binuclear hydrido-bridged cations [(terdentate ligand)Pd(μ-H)Pd(terdentate ligand)]+ from [(terdentate ligand)Pd(acetone)]+ and NaO2CH and [(terdentate ligand)Pd(μ-H)Pt(terdentate ligand)]+ from [(terdentate ligand)Pd(acetone)]+ and [(terdentate ligand)PtH] (terdentate ligand = 2,6-(Ph2PCH2)2C6H3) are reported. The preparation of the cation [(terdentate ligand)Pt(μ-H)Pt(terdentate ligand)]+ is also reported. 相似文献
70.
Giuseppe Mascolo Mauro Giustini Pier Luigi Luisi Jacques Lang 《Journal of colloid and interface science》1990,140(2)
The coupling reaction between cetylbromide (CB) and trimethylamine (TMA) to yield the surfactant cetyltrimethylammonium bromide (CTAB) is studied in the system chloroform/isooctane (2/1,v/v)/water in which CTAB forms reverse micelles. This system affords an endogenous micelle population growth, i.e., an increase of the concentration of the micelles due to appearance of the surfactant in situ. The reaction is studied in the presence of preexisting CTAB reverse micelles. The rate of CTAB formation is measured by NMR spectroscopy, and the endogenous micelle population growth is directly monitored by time-resolved fluorescence quenching analysis. Under our experimental conditions, a 100% yield of the chemical reaction brings about a fourfold increase in the population of the reverse micelles. Since the water concentration is constant during chemical reaction, the newly formed water pools are formed at the expense of the initial ones, which brings about a decrease of the average water pool radius during micellar growth. The implication of the endogenous micelle population growth as a model for biological systems is briefly discussed. 相似文献