全文获取类型
收费全文 | 962篇 |
免费 | 37篇 |
国内免费 | 48篇 |
专业分类
化学 | 761篇 |
晶体学 | 5篇 |
力学 | 12篇 |
综合类 | 1篇 |
数学 | 67篇 |
物理学 | 201篇 |
出版年
2023年 | 6篇 |
2022年 | 7篇 |
2021年 | 12篇 |
2020年 | 8篇 |
2019年 | 28篇 |
2018年 | 21篇 |
2017年 | 19篇 |
2016年 | 22篇 |
2015年 | 15篇 |
2014年 | 32篇 |
2013年 | 77篇 |
2012年 | 82篇 |
2011年 | 35篇 |
2010年 | 34篇 |
2009年 | 38篇 |
2008年 | 45篇 |
2007年 | 52篇 |
2006年 | 59篇 |
2005年 | 51篇 |
2004年 | 30篇 |
2003年 | 23篇 |
2002年 | 32篇 |
2001年 | 15篇 |
2000年 | 21篇 |
1999年 | 29篇 |
1998年 | 27篇 |
1997年 | 13篇 |
1996年 | 22篇 |
1995年 | 29篇 |
1994年 | 18篇 |
1993年 | 15篇 |
1992年 | 11篇 |
1991年 | 16篇 |
1990年 | 17篇 |
1989年 | 5篇 |
1988年 | 4篇 |
1987年 | 11篇 |
1986年 | 9篇 |
1985年 | 5篇 |
1984年 | 6篇 |
1982年 | 6篇 |
1981年 | 7篇 |
1980年 | 7篇 |
1979年 | 3篇 |
1978年 | 3篇 |
1977年 | 5篇 |
1975年 | 4篇 |
1974年 | 2篇 |
1973年 | 2篇 |
1972年 | 5篇 |
排序方式: 共有1047条查询结果,搜索用时 46 毫秒
41.
Excess and excess partial molar volumes of mixing of the system N,N-dibutyl-2-ethylhexylamide (DBEHA) + dodecanol (DDA) were determined at 25, 35, 45, 55 and 65°C. The excess molar volumes exhibit a maxima at each temperature at approximatelyx
DBEHA = 0.3 and a minima close tox
DBEHA = 0.9. The values of the excess volumes in general increase with the temperature. The partial excess molar volumes are calculated from the smoothed data and the results are discussed in the light of postulated amide-alcohol interactions. 相似文献
42.
Densities,ρ, ultrasonic speeds, u, viscosities,η, and refractive indices, n, of pure benzene, benzyl alcohol (BA), benzonitrile (BN), benzoyl chloride (BC), chlorobenzene (CB) and their thirty six binary mixtures, with benzene as common component, were measured at 303.15 K over the entire mole fraction range. From these experimental data the values of deviations in ultrasonic speed, △u, isentropic compressibility, △ks,excess acoustic impedance, ZE, deviation in viscosity, Dh, and excess Gibbs free energy of activation of viscous flow, G*E, and partial molar isentropic compressibility, Kφ,20 of BA, BN, BC and CB in benzene were computed. The variation of these derived functions with composition of the mixtures suggested the increased cohesion
(molecular order) in the solution and that interaction (A-B)>(A-A) or (B-B).Moreover, theoretical prediction of ultrasonic speed, viscosity and refractive index of all the four binary mixtures was made on the basis of empirical and semi-empirical relations by using the experimental values of the pure components. Comparison of theoretical results with the experimental values was made in order to assess the suitability of these relations in reproducing the
experimental values of u, η and n. Also, molecular radii of pure liquids and the average molecular radii of binary mixtures were evaluated using the corresponding refractive indices of pure liquids and binary mixtures. The average molecular radii of binary mixtures were found to be additive with respect to mole fraction of the pure component. 相似文献
43.
S. M. Bardavid G. C. Pedrosa M. Katz M. A. Postigo P. García 《Journal of solution chemistry》1996,25(11):1125-1135
Exces molar volumes, and excess viscosities of then-hexane+dichloromethane+tetrahydrofuran system have been determined at 25°C by measuring densities and viscosities. Different expressions exist in the literature to predict these excess properties from binary data. The empirical correlation of Cibulka is shown to be the best in this system. 相似文献
44.
Osmotic and activity coefficients in the aqueous quaternary system sodium chloride-potassium chloride-calcium chloride were derived from isopiestic measurements at 25°C. The isopiestic data were treated by the various procedures of Scatchard, Friedman, and Reilly, Wood, and Robinson. The results obtained showed good agreement with those obtained by pseudo-ternary transforms. Interaction parameters obtained indicated the preponderance of pairwise interactions. Excess Gibbs free energies of mixing were calculated. 相似文献
45.
S.?Didaoui-NemouchiEmail author A.?Ait-Kaci M.?Rogalski 《Journal of Thermal Analysis and Calorimetry》2005,79(1):85-88
Enthalpies of mixing H have been measured for liquid binary mixtures of diisopropylether (DIPE)+benzene or cyclohexane and for liquid ternary mixtures diisopropylether+benzene+cyclohexane at 303.15 K and constant pressure using a C80 calorimeter. A Redlich-Kister type equation was used to correlate experimental results. 相似文献
46.
The molar conductance of dilute solutions of HCl in wet (68.5% methanol + 31.5% tetrahydrofurane mixtures at 25°C have been measured. The data were analyzed using the Fuoss-Hsia equation to calculate the infinite dilution molar conductances and association constants. The trend of the limiting conductances in these mixtures as a function of the water content shows, once more, the peculiar minimum due to the anomalous proton conductance mechanism. From these data the limiting molar conductance in the anhydrous binary solvent system was evaluated. The percentage excess proton mobility with respect to potassium ion has also been determined. All these data are compared to those found in a binary isodielectric methanol mixture containing as cosolvent 1,4-dioxane. This comparison shows that proton mobilities are very similar in both solvent mixtures. The dielectric constants, refractive indices, viscosities and densities of the methanol-tetrahydrofuran mixtures in the whole mole fraction range have been measured and are reported. An analysis of the excess molar volumes and viscosities shows a slight deviation of this system from ideality. 相似文献
47.
The adsorption isotherms of the binary mixtures of ethanol/n-Octane, ethanol/n-hexadecane and n-octane/n-hexadecane onto the activated carbon TA 95 were measured at 278 K, 288 K, 298 K and 308 K and described with mathematical functions. About 300 experimental values of the adsorption excess of the ternary mixture ethanol/n-octane/n-hexadecane onto activated carbon TA 95 at 298 K were measured by gas chromatography inside the ternary triangle. The ternary miscibility gap was determined at three temperatures. A good representation of the ternary data and the calculated activity coefficients (using the UNIFAC model) in three-dimensional space was possible with the help of transformation of coordinates. It was possible, too, by utilization of the conception of the quasi two-component representation of the mole fractions with and without miscibility gap. Several influencing factors on ternary adsorption isotherms were discussed for the system ethanol/n-octane/n-hexadecane/TA 95. 相似文献
48.
Excess molar volumes VmE of the binary mixtures of (trifluoroethanol + 1-propanol), (trifluoroethanol + 2-propanol), (acetone + water), (methanol + water), (ethanol + water), (1-propanol + water), (2-propanol + water), and the ternary mixtures of (trifluoroethanol + methanol + water), (trifluoroethanol + ethanol + water), (trifluoroethanol~+ 1-propanol + water), (trifluoroethanol + 2-propanol + water) and (trifluoroethanol + acetone + water) were measured with a vibrating tube densimeter at the temperature of 298.15 K and the pressure 101 kPa. The extrema in VmE of trifluoroethanol mixtures occur at –0.690 cm3-mol–1 for (trifluoroethanol + 1-propanol), at –0.990~cm3-mol–1 for (trifluoroethanol + 2-propanol); at 0.562 and –0.973 cm3-mol–1 for (trifluoroethanol + methanol + water), at 0.629 and –0.973 cm3-mol–1 for (trifluoroethanol + ethanol + water), at 1.082 and –0.659 cm3-mol–1 for (trifluoroethanol~+ 1-propanol + water), at 0.998 and –0.991 cm3-mol–1 for (trifluoroethanol~+ 2-propanol + water), and at 0.515 and –1.472 cm3-mol–1 for (trifluoroethanol + acetone + water). The experimental ternary VmE values were predicted by empirical expressions using binary solution data. 相似文献
49.
A. Lainez M. M. Rodrigo Emmerich Wilhelm J. -P. E. Grolier 《Journal of solution chemistry》1992,21(1):49-65
Excess molar volumes V
E
and excess molar heat capacities C
P
/E
at constant pressure have been obtained, as a function of mole fraction x1, for several binary liquid mixtures belonging either to series I: pyridine+n-alkane (ClH2l+2), with l=7, 10, 14, 16, or series II: piperidine+n-alkane, with l=7, 8, 10, 12, 14. The instruments used were a vibrating-tube densimeter and a Picker flow microcalorimeter, respectively. V
E
of pyridine+n-heptane shows a S-shaped composition dependence with a small negative part in the region rich in pyridine (x1>0.90). All the other systems show positive V
E
only. The excess volumes increase with increasing chain length l of the n-alkane. The excess molar heat capacities of the mixtures belonging to series II are all negative, except for a small positive part for piperidine+n-heptane in the region rich in piperidine (x1>0.87). The C
P
/E
at the respective minima, C
P
/E
(x1,min
), become more negative with increasing l, and the x1,min
values range from about 0.26 (l=7) to 0.39 (l=14). Most interestingly, mixtures of series I exhibit curves of C
P
/E
against x1 with two minima and one maximum, the so-called W-shape curves.Dedicated to Professor A. Néckel on the occasion of his 65th birthday. Communicated in part at the XVIIèmes Journées de Calorimétrie, d'Analyse Thermique et de Thermodynamique Chimique, Ferrara, Italy, 27–30 October, 1986. 相似文献
50.