全文获取类型
收费全文 | 1031篇 |
免费 | 108篇 |
国内免费 | 71篇 |
专业分类
化学 | 628篇 |
晶体学 | 1篇 |
力学 | 5篇 |
综合类 | 4篇 |
数学 | 49篇 |
物理学 | 523篇 |
出版年
2023年 | 6篇 |
2022年 | 6篇 |
2021年 | 22篇 |
2020年 | 24篇 |
2019年 | 24篇 |
2018年 | 23篇 |
2017年 | 12篇 |
2016年 | 25篇 |
2015年 | 36篇 |
2014年 | 44篇 |
2013年 | 71篇 |
2012年 | 96篇 |
2011年 | 57篇 |
2010年 | 45篇 |
2009年 | 69篇 |
2008年 | 65篇 |
2007年 | 64篇 |
2006年 | 71篇 |
2005年 | 42篇 |
2004年 | 39篇 |
2003年 | 42篇 |
2002年 | 41篇 |
2001年 | 42篇 |
2000年 | 24篇 |
1999年 | 24篇 |
1998年 | 22篇 |
1997年 | 21篇 |
1996年 | 13篇 |
1995年 | 17篇 |
1994年 | 17篇 |
1993年 | 16篇 |
1992年 | 11篇 |
1991年 | 10篇 |
1990年 | 8篇 |
1989年 | 6篇 |
1988年 | 4篇 |
1987年 | 6篇 |
1986年 | 5篇 |
1985年 | 5篇 |
1984年 | 4篇 |
1982年 | 6篇 |
1981年 | 6篇 |
1980年 | 3篇 |
1979年 | 3篇 |
1978年 | 4篇 |
1976年 | 2篇 |
1974年 | 2篇 |
1972年 | 1篇 |
1970年 | 1篇 |
1968年 | 1篇 |
排序方式: 共有1210条查询结果,搜索用时 312 毫秒
61.
62.
The excess molar enthalpies H
m
E
for the binary mixtures of furfural with the aromatic hydrocarbons namely benzene, toluene, ethylbenzene and o-, m-, and p-xylenes were determined at 35°C. The values for all the mixtures studied are positive over the entire range of composition and follow the order: o-xylene>m-xylene>ethylbenzene>p-xylene>benzene>toluene. The results are discussed in terms of the unlike specific interactions present in the binary mixtures. 相似文献
63.
Sushma Agarwal 《Journal of solution chemistry》1978,7(10):795-798
The excess volume of mixing of some electron-donating aromatic hydrocarbons like benzene, toluene,p-xylene, and mesitylene with an electronaccepting liquid 1,2,4-trichlorobenzene have been measured at 30°C. The results indicate that the interaction between the components increases as the electron-donating power of the hydrocarbons increases. The V
m
e
values are related to the ionization potentials of the hydrocarbons. 相似文献
64.
Experimental density and the refractive index of the ternary mixture acetone + n-hexane + water, and their binary systems were experimentally measured and correlated at 298.15 K and atmospheric pressure. A maximum in refractive indices has been observed for the acetone + water system while the excess molar volume and the molar refraction change are all negative. For the mixture acetone + n-hexane, the excess molar volume is always positive and the molar refraction change of mixing showed a S-shaped dependence on acetone composition. The excess molar volumes and molar refraction changes of mixing were correlated using the Redlich-Kister expression and Cibulka equation. The coefficients and standard deviation between the experimental and fitted values were estimated. Good agreement between both results was obtained. 相似文献
65.
A flow-mixing isothermal microcalorimeter was used to measure excess molar enthalpies for four binary systems of {diethyl oxalate + (methanol, + ethanol, + 1-propanol, and + 2-propanol)} at T = (288.2, 298.2, 313.2, and 328.2) K and p = 101.3 kPa. The densities of the diethyl oxalate at different temperature were measured by using a vibrating-tube densimeter. All systems exhibit endothermic behaviour over the whole composition range, which means that the rupture of interactions is energetically the main effect. The excess molar enthalpies increase with temperature and the molecular size of the alcohols. The experimental results were correlated by using the Redlich–Kister equation and two local-composition models (NRTL and UNIQUAC). 相似文献
66.
67.
Yunus Bekdemir Halil Kutuk Sibel Celik John G. Tillett 《Phosphorus, sulfur, and silicon and the related elements》2013,188(4):973-980
The acid catalysed hydrolysis of some cyclic sulfamates, X-3-(p-tolylsulfonyl)-1,2,3-benzoxathiazole 2,2-dioxides ( 1a , X = Me; 1b , X = H; 1c , X = Cl; 1d , X = NO 2 ) have been studied in concentrated aqueous sulfuric and perchloric acid solutions. Analysis of the data by the Excess Acidity Method, activation parameters, substituent, solvent deuterium isotope effect and order of the catalytic effects of the acids are all in agreement with an A-1 mechanism in the studied range. 相似文献
68.
《Physics and Chemistry of Liquids》2012,50(6):661-672
Experimental measurements of dew points for four methane + water mixtures between 2.6 2 10 5 Pa and 100.4 2 10 5 Pa and the temperature range from 225.5 K to 272.7 K were carried out. The experimental results were analysed in terms of both an equation of state model and an excess function-equation of state method, which reproduced the experimental data within AAD from 1.8 to 3.1 K and from 0.9 to 1.8 K, respectively. 相似文献
69.
《Physics and Chemistry of Liquids》2012,50(2):153-165
Densities and viscosities for the system, water (W)?+?sulfolane (SFL), have been determined for the entire range of composition at temperatures ranging from 303.15 to 323.15?K. Density, excess molar volume, viscosity, excess viscosity and thermodynamic activation parameters for viscous flow have been calculated and plotted against the mole fraction of SFL. The measured properties and some of the derived properties have been fitted to appropriate polynomial equations. These have been explained in terms of such factors, as, dipole–dipole interaction, partial accommodation of water molecules into the structural network of SFL and H-bonding between SFL and H2O. 相似文献
70.
Nonstationarity and related measures for time‐dependent hartree–fock and multiconfigurational models
Anatoliy V. Luzanov 《International journal of quantum chemistry》2013,113(23):2489-2505
Based on an earlier article (Eberly and Singh, Phys. Rev. D 1973 , 7, 359) and related works on short‐time evolution, this article proposes a many‐electron formulation for the nonstationarity degree which can be assigned to quantum system at each time point. The key measure introduced, , is a nonstationarity index that can be thought of as an inverse nominal lifetime at each instance of time. The index is directly computed from the time derivative of one‐electron density matrix and is a size‐consistent quantity. In this article, the approach is developed for the time‐dependent Hartree–Fock (TDHF), single‐excitation (TDCIS), and time‐dependent full configuration interaction (TDFCI) models. As a rule, nonstationarity effects are more pronounced in correlated electron systems, and a joint analysis of and the multiconfigurational character of wave functions apparently provide a deeper insight into dynamical molecular processes. The performed calculations on small molecules in laser fields show a preference for the TDCIS model when comparing TDCIS and TDHF with the “exact” TDFCI model. © 2013 Wiley Periodicals, Inc. 相似文献