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171.
Forde GK Kedzierski P Sokalski WA Forde AE Hill GA Leszczynski J 《The journal of physical chemistry. A》2006,110(6):2308-2313
The physical nature of interactions within the active site of cytosine-5-methyltransferase (CMT) was studied using a variation-perturbation energy decomposition scheme defining a sequence of approximate intermolecular interaction energy models. These models have been used to analyze the catalytic activity of residues constituting cytosine-5-methyltransferase active site as well their role in the binding group of de novo designed inhibitors. Our results indicate that Glu119, Arg163, and Arg165 appear to play the dominant role in stabilizing the protonated transition state structure and their influence can be qualitatively approximated by electrostatic interactions alone. The stabilization of neutral structures of the alternative reaction pathway is small, which might suggest the protonated pathway as preferred by the enzyme. Exchange and delocalization terms are negligible in most cases, or they cancel each other to some extent. Interactions of inhibitors with the CMT active site are dominated by electrostatic multipole contributions in analogy with previously studied transition state analogue inhibitors of leucyl aminopeptidase. 相似文献
172.
Caban K Lewera A Zukowska GZ Kulesza PJ Stojek Z Jeffrey KR 《Analytica chimica acta》2006,575(1):144-150
Two methods have been used for examination of transport of charge in gels soaked with DMF and containing dissolved polyoxometallates. The first method is based on the analysis of both Cottrellian and steady-state currents and therefore is capable of giving the concentration of the electroactive redox centres and their transport (diffusion-type) coefficient. The second method provides the real diffusion coefficients, i.e. transport coefficients free of migrational influence, for both the substrate and the product of the electrode reaction. Several gels based on poly(methyl methacrylate), with charged (addition of 1-acrylamido-2-methyl-2-propanesulphonic acid to the polymerization mixture) and uncharged chains, have been used in the investigation. The ratio obtained for the diffusion coefficient (second method) and transport coefficient (first method) was smaller for the gels containing charged polymer chains than for the gels with uncharged chains. In part these changes could be explained by the contribution of migration to the transport of polyoxomatallates in the gels. However, the impact of the changes in the polymer-channel capacity at the electrode surface while the electrode process proceeds was also considered. These structural changes should affect differently the methods based on different time domains. 相似文献
173.
Molecular-dynamics simulations are conducted to elucidate the critical factors affecting the transport properties of isolated polymer chains in strictly two dimensions. The relevance of surface inhomogeneity is critically examined. We unequivocally find that surface inhomogeneity is critical in obtaining transport behavior consistent with the recent measurements of surface diffusion for polymers adsorbed at the solid-liquid interface. For a systematic investigation of this point, heterogeneity was introduced by decorating the surface with impenetrable elements and we find that chain diffusivity crossed over from Rouse-type behavior to reptationlike with increasing surface coverage of obstacles. This transition in behavior occurred when the mean distance between obstacles is approximately equal to the end-to-end distance, Re, of the two-dimensional chain. Our results underscore the importance of surface disorder (not only literal obstacles but by reasonable extension also to other types of disorder) in determining the transport behavior of chains adsorbed to solids. 相似文献
174.
On the influence of microsolvation by argon atoms on the electron affinity properties of water dimer
Wielgus P Gora RW Szefczyk B Roszak S Leszczynski J 《The Journal of chemical physics》2006,124(9):94304
This work provides a comparison of neutral (H2O)2Ar(n) and negatively charged (H2O)(2-)Ar(n) complexes. The excess electron stabilizes the complexes and leads to the trans to cis rearrangement within the water dimer core. In the case of small complexes (n < or = 4) the microsolvation of the dimer by argon atoms arises on the trans side with respect to the donor water molecule. The stabilization of an excess electron is enhanced by the delocalization of the electronic charge density due to microsolvation. The process of cis to trans rotation is induced by the electric field of the approaching negative charge. The interaction energy decomposition suggests a more ionic character of binding in the negatively charged complexes. The attachment of an electron is controlled by the correlation energy. 相似文献
175.
Weihua Zhang Pawel Mekarski Jonathan Lam Kurt Ungar 《Journal of Radioanalytical and Nuclear Chemistry》2010,286(1):235-240
This paper describes a Monte Carlo (MC) simulation method for calculating radioxenon beta-gamma coincidence spectral information.
These spectral components include detector response simulations by Geant4 modeling, detector energy and resolution calibrations
using the histograms of detector response, beta-gamma coincidence efficiency values and spectral interference ratios. The
work presented in this paper demonstrates the feasibility of using the spectral information to create beta-gamma coincidence
spectra at various radioxenon activity concentrations. The analysis of these synthetic spectra by XECON software shows an
excellent correlation between the analysed radioxenon activity concentration and number of MC samplings. 相似文献
176.
Viktor Bezugly Pawel Wielgus Miroslav Kohout Frank R. Wagner 《Journal of computational chemistry》2010,31(12):2273-2285
Electron localizability indicators based on the electron pair density ELI–D and ELIA Electron localizability indicators ELI‐D and ELIA based on the electron pair density are studied for the correlated ground‐state wavefunctions of N2, O2, F2, and Ne2 diatomics. Different basis sets and reference spaces are used for the multireference configuration interaction method following the complete active space calculations to investigate the local effect of electron correlation on the extent of electron localizability in position space determined by the two indicators. The results are complemented by calculations of effective bond order, vibrational frequency, and Laplacian of the electron density at the bond midpoint. It turns out that for O2 and F2, the reliable topology of ELI–D is obtained only at the correlated level of theory. © 2010 Wiley Periodicals, Inc. J Comput Chem 2010 相似文献
177.
Weihua Zhang Pawel Mekarski Jonathan Lam Kurt Ungar Eric Pellerin 《Journal of Radioanalytical and Nuclear Chemistry》2010,285(3):475-482
In this work, a Monte Carlo (MC) simulation model is established to accurately characterize a phoswich beta-gamma coincidence detector system. This model can be easily used to predict the beta-gamma coincidence efficiencies of xenon radioisotopes at various stable xenon concentrations in the counting cell. The results demonstrate that there is a significant inverse correlation between beta-gamma coincidence efficiency and stable xenon concentration. The influence of stable xenon concentration on beta-gamma coincidence counting efficiency has been investigated for each individual xenon radioisotope. The results indicate that the effect of stable xenon concentration on beta-gamma coincidence efficiency depends on the xenon radioisotope and its decay modes. The coincidence efficiency of 133Xe with 31.0-keV X-ray decay mode is the most affected one; and then followed by 131mXe, 133Xe with 81.0-keV gamma-ray decay mode, 133mXe and finally 135Xe. The study also indicates that the gamma absorption by xenon gas plays more of a role in the decrease of beta-gamma coincidence efficiency for 133Xe and 135Xe, and that the conversion electron spectrum shifting and broadening plays more of a role in the reduction of beta-gamma coincidence efficiency for the metastable radioxenon of 131mXe and 133mXe. 相似文献
178.
Here, we present a miniaturized version of the flowing atmospheric-pressure afterglow (miniFAPA) ion source and use it for sheathless coupling of CE with MS. The simple design of the CE-miniFAPA-MS interface makes it easy to separate the electric potentials used for CE and for ionization. A pneumatically assisted nebulization of the CE effluent transfers the analytes from the liquid phase into the gas phase before they are ionized by interacting with reactive species produced by the FAPA. An important advantage of this interface is its high stability during operation: optimization of five different parameters indicated that the interface is not sensitive to minor deviations from the optimum values. Other advantages include ease of construction and maintenance, as well as relatively low cost. Samples with complex matrices, such as yeast extract, soil extract and urine, spiked with the test compounds, were successfully analyzed using the CE-miniFAPA-MS setup. 相似文献
179.
Boguslaw Buszewski Pawel Olszowy Tomasz Ligor Malgorzata Szultka Jacek Nowaczyk Maciej Jaworski Marek Jackowski 《Analytical and bioanalytical chemistry》2010,397(1):173-179
Five adrenolytic drugs have been analyzed by liquid chromatography–mass spectrometry (LC–MS). Samples were prepared by solid-phase
microextraction (SPME) using polypyrrole fibers coated on stainless steel support as an adsorbent for the drugs. Adsorption
efficiencies were 95% and were close for all the drugs investigated. Relative standard deviations (RSD), calculated for samples
prepared in standard solutions, were in the range 2.5–13%, however RSD values for the drugs in human plasma were 2.5–4.5%.
Using LC–MS the limit of detection (LOD) and the limit of quantification (LOQ) were in the ranges 0.11–0.18 and 0.39–0.54 ng mL−1, respectively, for the five drugs. 相似文献
180.
The stable benzylazido-boronate ester 1 is presented as an example of a dual-functional linker that allows the synthetically valuable boronate motif to be clicked onto other molecules under mild conditions. The utility of the azido-boronate motif as a modular building block is demonstrated in the rapid synthesis of drug-like structures employing sequential catalytic azide-alkyne cycloaddition and Suzuki coupling reactions. 相似文献