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91.
A multisite molecular mechanism for Baeyer-Villiger oxidations on solid catalysts using environmentally friendly H2O2 as oxidant 总被引:1,自引:0,他引:1
Boronat M Corma A Renz M Sastre G Viruela PM 《Chemistry (Weinheim an der Bergstrasse, Germany)》2005,11(23):6905-6915
The molecular mechanism of the Baeyer-Villiger oxidation of cyclohexanone with hydrogen peroxide catalyzed by the Sn-beta zeolite has been investigated by combining molecular mechanics, quantum-chemical calculations, spectroscopic, and kinetic techniques. A theoretical study of the location of Sn in zeolite beta was performed by using atomistic force-field techniques to simulate the local environment of the active site. An interatomic potential for Sn/Si zeolites, which allows the simulation of zeolites containing Sn in a tetrahedral environment, has been developed by fitting it to the experimental properties of quartz and SnO2(rutile). The tin active site has been modeled by means of a Sn(OSiH3)3OH cluster, which includes a defect in the framework that provides the flexibility necessary for the interaction between the adsorbates and the Lewis acid center. Two possible reaction pathways have been considered in the computational study, one of them involving the activation of the cyclohexanone carbonyl group by Sn (1) and the other one involving hydrogen peroxide being activated through the formation of a tin-hydroperoxo intermediate (2). Both the quantum-chemical results and the kinetic study indicate that the reaction follows mechanism 1, and that the catalyst active site consists of two centers: the Lewis acid Sn atom to which cyclohexanone has to coordinate, and the oxygen atom of the Sn-OH group that interacts with H2O2 forming a hydrogen bond. 相似文献
92.
Remedios González-Luque Manuela Merchán Piotr Borowski Björn O. Roos 《Theoretical chemistry accounts》1993,86(6):467-476
Summary Multiconfigurational electron correlation methods have been analyzed in order to theoretically compute the electron affinity (EA) of ozone. The near-degeneracy correlation effects, which are so important in O3 and O
3
–
, have been described using complete active space (CAS) SCF wave functions. Remaining dynamic correlation effects are computed using second-order perturbation theory (the CASPT2 method). The best calculated adiabatic value (including zero-point energy corrections), 2.19 eV, is about 0.09 eV larger than the experimental value. Comparative studies using size-consistent coupled pair functional approaches (CPF and ACPF) have also been performed. The harmonic frequencies in O
3
–
have been determined to be: 1=992, 2=572, and 3=879 cm–1, which gives a zero-point energy of 0.151 eV. 相似文献
93.
Romero R Bagur MG Sánchez-Viñas M Gázquez D 《Analytical and bioanalytical chemistry》2003,376(2):162-167
Biogenic amines, as dabsyl derivatives, were determined in beer samples, intermediate products, and raw materials (malt and maize) by HPLC. A procedure for the extraction of the amines from malt and maize with diluted hydrochloric acid was optimised by combining a Response Surface Methodology with a Simultaneous Decision Making Approach. The results of the analysis indicate that, in brewing, technology and hygiene are the decisive factors that determine the amine concentrations in the final product. 相似文献
94.
R. González-Ramírez H. Jiménez-Domínguez O. Solorza-Feria E. Ordóñez-Regil A. Cabral-Prieto S. Bulbulian 《Journal of Radioanalytical and Nuclear Chemistry》1993,174(2):291-298
Conditions for the electrodeposition of59Co and57Co on stainless steel foils have been studied. A set of electrolytic parameters has been determined to get a reasonably good electrodeposited sample. The57Co electrodeposited foil was then introduced in a quartz tube to be annealed in an argon flow. The final product was a 11 Ci Mössbauer source for college experiments which was succesfully tested by obtaining spectra of stainless steel and sodium nitroprusside. 相似文献
95.
A.?González-Pérez J.?M.?RusoEmail author G.?Prieto F.?Sarmiento 《Colloid and polymer science》2004,282(4):351-356
The interactions of sodium dodecyl sulphate with ovalbumin in aqueous solution at room temperature are described for a wide concentration range of both substances. A phase diagram covering a wide range of concentrations shows a total of five different morphologies. Dynamic light scattering of the samples from each morphology offered better understanding of the different structures (between three and four) present in the solution. The amount of ovalbumin present in the solution was confirmed with differential scanning spectroscopy, while the interactions between sodium dodecyl sulphate and ovalbumin were interpreted by zeta potential and electrical conductivity measurements. 相似文献
96.
We report molecular dynamics computer simulations of the surface tension and interfacial thickness of ionic liquid-vapor interfaces modeled with a soft core primitive model potential. We find that the surface tension shows an anomalous oscillatory behavior with interfacial area. This observation is discussed in terms of finite size effects introduced by the periodic boundary conditions employed in computer simulations. Otherwise we show that the thickness of the liquid-vapor interface increases with surface area as predicted by the capillary wave theory. Data on the surface tension of size-asymmetric ionic liquids are reported and compared with experimental data of molten salts. Our data suggest that the surface tensions of size-asymmetric ionic liquids do not follow a corresponding states law. 相似文献
97.
Mercedes de Frutos Alejandro Cifuentes Jose Carlos Diez-Masa 《Journal of separation science》1997,20(1):29-33
The behavior of bovine whey proteins in Reversed-Phase High Performance Liquid Chromatography (RP-HPLC) systems has been investigated. The Linear Solvent Strength (LSS) model has been applied to the separation of these proteins studying how their retention time and band broadening change when different gradient parameters are modified. From our results it is deduced that the LSS model describes the behaviour of the whey proteins in RP-HPLC. Also, it seems that ts (the retention time for non-retained solutes) depends on the size of these proteins. The good fit observed between experimental data and the equations deduced from the LSS model allows the prediction of a gradient shape that permits a rapid analysis of the above mentioned proteins. 相似文献
98.
Reactions of 3-[2-(morpholin-4-yl)vinyl]-1H-indole ( 1 ), the 1,2-dihydro-9H-carbazole 2 , as well as the 3-(tetrahydropyridin-4-yl)-1H-indoles 3a and 3b with some carbo- and heterodienophiles are described. The scope and limitations of the synthetic utility of these amino- (or homoamino)-functionalized 3-vinyl-1H-indoles are reported and some MO calculations for the qualitative prediction of their reactivities are presented. The reactions gave rise to substitution products, redox products, Diels-Alder adducts, ene adducts, and Michael-type adducts (Schemes 2 and 3). 相似文献
99.
González-Bravo L Marrero-Delange D González-Guevara JL 《Journal of chromatography. A》2000,888(1-2):159-173
The method's accuracy of a compound quantitation by chromatography depends on the calibration procedure with a pure standard of the target analyte, if the latter is unavailable uncertainty is unavoidable. The group method is a different approach in GC quantitative analysis that shows a practicable way for avoiding this uncertainty and accurately quantify a mixture containing one or more unavailable components. This paper is concerned with the definition of the group method quantitative parameters, the application procedures for their calculation, the determination of the quantitative proportion of a group of unavailable components of a mixture and the partial or total quantitation of the latter. The paper also describes the steps for carrying out the so-called group-correlation method in the determination of the response factors of unavailable compounds, which belong to a homologous series. The GC experimental corroboration of the group method approach employing model mixtures of compounds is also presented. 相似文献
100.
González-Pérez A. Galán J. J. Rodríguez J. R. 《Journal of Thermal Analysis and Calorimetry》2003,72(2):741-749
The specific conductivities of dodecyldimethylbenzylammonium bromide (C12BBr) have been determined in aqueous butanol and
aqueous benzyl alcohol solutions in the temperature range of 5-40°C. From these data the temperature dependent critical micelle
concentration (cmc) was determined. The molar fraction of alcohol in the micelle was estimated using the theory suggested by Motomura et al. for surfactant binary mixtures. The thermal properties such as standard Gibbs free energy, enthalpy and entropy of solubilization
of alcohols in the micelles were estimated for the phase separation model. The change in heat capacity upon solubilization
of alcohol in the micelle has been estimated form the above properties.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献