全文获取类型
收费全文 | 720篇 |
免费 | 32篇 |
国内免费 | 104篇 |
专业分类
化学 | 637篇 |
晶体学 | 7篇 |
力学 | 4篇 |
综合类 | 1篇 |
数学 | 37篇 |
物理学 | 170篇 |
出版年
2024年 | 1篇 |
2023年 | 11篇 |
2022年 | 13篇 |
2021年 | 16篇 |
2020年 | 24篇 |
2019年 | 16篇 |
2018年 | 13篇 |
2017年 | 14篇 |
2016年 | 22篇 |
2015年 | 15篇 |
2014年 | 32篇 |
2013年 | 37篇 |
2012年 | 50篇 |
2011年 | 42篇 |
2010年 | 46篇 |
2009年 | 39篇 |
2008年 | 41篇 |
2007年 | 48篇 |
2006年 | 38篇 |
2005年 | 41篇 |
2004年 | 23篇 |
2003年 | 23篇 |
2002年 | 17篇 |
2001年 | 22篇 |
2000年 | 15篇 |
1999年 | 19篇 |
1998年 | 20篇 |
1997年 | 20篇 |
1996年 | 13篇 |
1995年 | 20篇 |
1994年 | 16篇 |
1993年 | 18篇 |
1992年 | 13篇 |
1991年 | 13篇 |
1990年 | 10篇 |
1989年 | 6篇 |
1988年 | 4篇 |
1987年 | 4篇 |
1986年 | 3篇 |
1985年 | 3篇 |
1984年 | 1篇 |
1983年 | 1篇 |
1982年 | 3篇 |
1981年 | 2篇 |
1980年 | 2篇 |
1979年 | 4篇 |
1974年 | 1篇 |
1971年 | 1篇 |
排序方式: 共有856条查询结果,搜索用时 46 毫秒
761.
Ternary diffusion coefficients of diethanolamine (DEA) and N-methyldiethanolamine (MDEA) in aqueous solutions containing DEA and MDEA using the Taylor dispersion technique have been measured for temperatures (303.2, 313.2, and 323.2 K). The systems studied were aqueous solutions containing total amine concentrations of 2.5 and 4.0 kmol m−3, each having four different amine molar ratios. The density and viscosity of the blended amine solutions were also measured. The mutual diffusion coefficients of aqueous DEA and aqueous MDEA solutions were also reported. The main diffusion coefficients (D11 and D22) and the cross-diffusion coefficients (D12 and D21) were reported as function of temperature and concentration of alkanolamines. The limiting conditions for the main diffusion coefficients and the cross-diffusion coefficients were discussed at first, and a comparison between the ratios of the cross-diffusion coefficients to the main diffusion coefficients for DEA and MDEA was made. The dependence of the main diffusion coefficients on the viscosity of solutions was also investigated. 相似文献
762.
763.
764.
765.
Montavon G Hennig C Janvier P Grambow B 《Journal of colloid and interface science》2006,300(2):482-490
The speciation of Eu complexed with polyacrylic acid (PAA) and alumina-bound PAA (PAA(ads)) was studied at pH 5 in 0.1 M NaClO(4). Structural parameters were obtained from (7)F(0) -->(5)D(0) excitation spectra measured by laser-induced fluorescence spectroscopy as well as from Eu L(III)-edge extended X-ray absorption fine structure (EXAFS) spectra. The coordination mode was also investigated by infrared spectroscopy. To elucidate the nature of the complexed species, Eu-acetate complexes were used as references. The spectroscopic techniques show that two carboxylate groups with 2-3 (EuPAA) and 4-5 (EuPAA(ads)) water molecules are coordinated to Eu in the first coordination sphere. For EuPAA(ads), the coordination between carboxylate groups and Eu appears to be bidendate. A similar coordination is probable for EuPAA but the EXAFS data indicate a slightly distorted coordination. The results show that the degree of freedom of carboxylate groups is not the same for free or adsorbed PAA. For PAA, the degree of freedom is constrained by the flexibility of the methylene chain. When PAA is adsorbed on alumina, the polymer chains cannot any more be treated as independent chains. One may rather assume formation of aggregates that form an organic layer at the mineral surface presenting a complex arrangement of carboxylate groups. 相似文献
766.
For any interpolatory ternary subdivision scheme with two-ring stencils for a regular triangular or quadrilateral mesh, we show that the critical Hölder smoothness exponent of its basis function cannot exceed , where the critical Hölder smoothness exponent of a function is defined to be On the other hand, for both regular triangular and quadrilateral meshes, we present several examples of interpolatory ternary subdivision schemes with two-ring stencils such that the critical Hölder smoothness exponents of their basis functions do achieve the optimal smoothness upper bound . Consequently, we obtain optimal smoothest interpolatory ternary subdivision schemes with two-ring stencils for the regular triangular and quadrilateral meshes. Our computation and analysis of optimal multidimensional subdivision schemes are based on the projection method and the -norm joint spectral radius.
767.
《Analytical letters》2012,45(14):2708-2720
Abstract A simple, sensitive, and direct spectrophotometric method has been developed for the assay of sparfloxacin in bulk and pharmaceutical preparations. The proposed method is based on the formation of ternary complex between an investigated drug, palladium(II) ion and eosin in the presence of methylcellulose as surfactant and acetate buffer of pH 4.2. Spectrophotometrically, under the optimum conditions, the ternary complex showed absorption maximum at 550 nm, with apparent molar absorptivity of 2.69×104 l mol?1 cm?1, Sandell's sensitivity of 0.01458 µg ml?1 and linearity in the concentration range 1.6–16 µg ml?1. The composition of the ternary complex was studied by Job's method of continuous variation and the result indicated that the molar ratio of SPFX: Pd: eosin is 1∶1∶1. The optimum reaction conditions and other analytical parameters are evaluated. The proposed method was successfully applied for the determination of SPFX in its pharmaceutical product with mean percentage recoveries of 99.71%. The observed data has been subjected to statistical analysis, which revealed high accuracy and precision. 相似文献
768.
《Physics and Chemistry of Liquids》2012,50(5):459-465
The phase diagrams for the ternary systems H2O?+?2-butanol?+?K2HPO4/KH2PO4 (pH?=?7) and H2O?+?2-butanol?+?Na2CO3 at 298.15?K were determined. Experimental binodals and tie lines for these systems are presented. The experimental results were correlated using an improved regular solution theory. The agreement between the correlation and experimental data is good. 相似文献
769.
《Physics and Chemistry of Liquids》2012,50(5):567-581
Abstract Densities and viscosities of the ternary mixture (benzene + 1-propanol + ethyl acetate) and the corresponding binary mixtures (benzene + 1-propanol, benzene + ethyl acetate and 1-propanol + ethyl acetate) have been measured at the temperature 298.15 K. From these measurements excess volumes, VE , excess viscosities, ηE, and excess Gibbs energies of activation for viscous flow, G*E , have been determined. The equation of Redlich-Kister has been used for fitting the excess properties of binary mixtures. The excess properties of the ternary system were fitted to Cibulka's equation. 相似文献
770.
Volker Presser Michael Naguib Laurent Chaput Atsushi Togo Gilles Hug Michel W. Barsoum 《Journal of Raman spectroscopy : JRS》2012,43(1):168-172
Here, we report, for the first time, on the Raman spectra of Ti2AlN, Ti2AlC0.5N0.5, (Ti0.5V0.5)2AlC, Ti3AlC2, and Ti3GeC2 and compare the results with those of Ti2AlC and V2AlC reported previously. The first‐order mode peaks of the end members are narrower than those of their respective solid‐solution compounds. The Ti3AlC2 and Ti3GeC2 phases show, in addition to atomic displacements of the ‘M’ and ‘A’ atomic planes, modes that correspond with vibrations of the ‘X’ sublattice relative to itself. We also predict the Raman modes using density functional theory. The agreement between theory and experiment was found to be satisfactory. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献