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31.
32.
《Physics and Chemistry of Liquids》2012,50(6):712-734
Excess molar volumes and viscosity deviations in N,N-dimethylacetamide?+?dimethylformamide binary mixtures at 298.15, 308.15 and 318.15?K were calculated from experimental density and viscosity data presented in the previous work. Here these experimental values were used to test the applicability of the correlative reduced Redlich–Kister equation and the recently proposed Herráez equation. Their correlation ability at different temperatures, and the use of different number of parameters, is discussed for the case of limited experimental data. These relative functions are important to reduce the effect of temperature and, consequently, to reveal the effects of different types of interactions. Limiting excess partial molar volumes at infinite dilution were deduced from different methods, parameters of molar Gibbs energy of activation of viscous flow against compositions were investigated. The results of these observations have been interpreted in terms of structural effects of the solvents. 1H-NMR studies of these mixtures are also reported. 相似文献
33.
The ferroelectric ceramics Ba5RTi3V7O30 (R=Ho, Gd, La) have been synthesized by solid-state reaction technique. Preliminary X-ray structural analysis confirmed a single-phase formation of the compound in orthorhombic structure. Surface morphology of the compounds was studied by scanning electron microscopy (SEM). Detailed studies of electrical properties (i.e., dielectric constant, loss tangent, ac conductivity) as a function of temperature (RT-773 K) and at four different frequencies (1 kHz, 10 kHz, 100 kHz and 1 MHz) show ferroelectric–paraelectric phase transition of the compounds of diffuse-type. The activation energy has been evaluated from ac conductivity following Arrhenius equation. The conductivity pattern shows that it is strongly frequency dependent and obeys Jonscher's power relation. 相似文献
34.
An appraisal of the trends discerned in the recent literature concerned with solid-state decompositions suggests that this
research area lacks a general theoretical framework and, hence, order in the subject is difficult to recognize. There have
been surprisingly few reviews of the field. Many of the continuing flow of research publications may be of individual value,
but most do not contribute to the overall development of the topic. For example, in many studies of reversible dissociations
the sensitivity of rate characteristics to prevailing conditions is not discussed so that the fit of data to rate equations
and the magnitudes of calculated Arrhenius parameters may be of empirical value only. Some studies report kinetic results
without mechanistic discussions supported by complementary observations. Progress forward from an apparent state of stagnation
depends upon more critical examination of the existing literature, coupled with better designed experiments to establish the
reproducibility and reliability of kinetic conclusions. Techniques capable of providing insights into the bond redistribution
steps that occur during reactions in crystals are also urgently needed.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
35.
Min WANG You Gang MAO* Yan Ying LU Ren Fei YANG Fei LI Jia Cong SHEN Key Laboratory for Supramolecular Structure Spectroscopy of Ministry of Education Jilin University Changchun 《中国化学快报》2001,(11)
It has been known that the propagation rate coefficient (kp) will change with monomer conversion, Friss, Hamielec et al.1-5 have proposed many formulas about kp to fit this change. In order to obtain the relation between Arrhenius parameters and monomer conversion, a group of kp values at the same monomer conversion must be measured. We adopted a new method through analysis of kp values measured by usual experimental techniques for this purpose. Firstly, we chose a value of monomer convers… 相似文献
36.
This paper first reviews the history of the temperature dependence of reaction rate in reaction kinetics. The various equations which are in use today for expressing this dependence were delineated by van't Hoff almost one hundred years ago. Since an exponential form best describes this dependence for most thermal analysis reactions and, due to the fact that the simple Arrhenius equation (with a temperature-independent preexponential factor) has traditionally been used for this purpose, the mathematically intractable temperature integral often has become a necessary evil in the analysis of thermal analysis kinetics. Methods which avoid the temperature integral in kinetics analysis are discussed. The merits of various evaluations and approximations for the temperature integral are described and assessed in this paper. 相似文献
37.
Werner Kunz 《Computational Statistics》2007,22(4):521-531
This paper presents a method for visualizing competitive market structures based on scanner panel data where asymmetries are
taken into account. For this, I combined consumer choice models based on mixed logit models with three-mode principal component
analysis. This approach can be used to unfold a competitive market structure map. The methodology presented is able to quantify
the clout and receptivity of various brands. The results can then be visualized over time. Using this approach, guidelines
for promotional activities of new brands can be provided, and possible threats from the competition detected. 相似文献
38.
M. S. A. Rani N. S. Mohamed 《International Journal of Polymer Analysis and Characterization》2015,20(6):491-503
In the present work, an attempt has been made to prepare a new natural biopolymer blend electrolyte of carboxymethyl cellulose/chitosan impregnated with NH4NO3 by the solution casting technique. The conductivity for the system was measured by impedance spectroscopy. The incorporation of 40 wt.% NH4NO3 optimized the ambient temperature conductivity of the electrolyte up to 1.03 × 10?5 S cm?1. All electrolytes were found to follow the Arrhenius relationship. Dielectric studies confirmed that the electrolytes obey non-Debye behavior. The temperature dependence of the power law exponent s for the highest conducting film can be represented by the correlated barrier hopping model. 相似文献
39.
The rutile phase Sn0.99-xMnxCr0.01O2 (x = 0.00, 0.01, 0.03, 0.05 and 0.07) nanoparticles were synthesized by facile chemical co-precipitation method using poly ethylene glycol (PEG) as a capping agent. The samples were characterized by EDAX to confirm the expected stoichiometry. The X-ray diffraction (XRD), transmission electron microscopy (TEM) and Fourier transform infrared (FTIR) spectroscopy analyses of these samples showed the formation of impurity free crystals with a single phase rutile type tetragonal crystal structure as that of (P42/mnm) of SnO2. Optical absorption spectra and corresponding Tauc's plots showed a redshift of the absorption edge in SnO2 after being co-doped with Cr and Mn. The samples were examined for its magnetic property using vibrating sample magnetometer which indicated that transition of magnetic signals from ferromagnetic to the paramagnetic nature with inclusion of Mn content in SnO2: Cr host matrix. The observed magnetic behavior is well supported with the bound magnetic polarons (BMPs) model. 相似文献
40.
Adsorption of the anionic surfactant sodium dodecyl sulfate on a C18 column under micellar and high submicellar conditions in reversed‐phase liquid chromatography 下载免费PDF全文
C. Ortiz‐Bolsico M. J. Ruiz‐Angel M. C. García‐Alvarez‐Coque 《Journal of separation science》2015,38(4):550-555
Micellar liquid chromatography makes use of aqueous solutions or aqueous‐organic solutions containing a surfactant, at a concentration above its critical micelle concentration. In the mobile phase, the surfactant monomers aggregate to form micelles, whereas on the surface of the nonpolar alkyl‐bonded stationary phases they are significantly adsorbed. If the mobile phase contains a high concentration of organic solvent, micelles break down, and the amount of surfactant adsorbed on the stationary phase is reduced, giving rise to another chromatographic mode named high submicellar liquid chromatography. The presence of a thinner coating of surfactant enhances the selectivity and peak shape, especially for basic compounds. However, the risk of full desorption of surfactant is the main limitation in the high submicellar mode. This study examines the adsorption of the anionic surfactant sodium dodecyl sulfate under micellar and high submicellar conditions on a C18 column, applying two methods. One of them uses a refractive index detector to obtain direct measurements of the adsorbed amount of sodium dodecyl sulfate, whereas the second method is based on the retention and peak shape for a set of cationic basic compounds that indirectly reveal the presence of adsorbed monomers of surfactant on the stationary phase. 相似文献