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791.
Dr. Esteban Mejía Dr. Shu‐Ping Luo Dr. Michael Karnahl Aleksej Friedrich Dr. Stefanie Tschierlei Dr. Annette‐Enrica Surkus Dr. Henrik Junge Prof. Dr. Serafino Gladiali Prof. Dr. Stefan Lochbrunner Prof. Dr. Matthias Beller 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(47):15972-15978
A series of heteroleptic copper(I) complexes with bidentate $\widehat{PP}$ and $\widehat{NN}$ chelate ligands was prepared and successfully applied as photosensitizers in the light‐driven production of hydrogen, by using [Fe3(CO)12] as a water‐reduction catalyst (WRC). These systems efficiently reduces protons from water/THF/triethylamine mixtures, in which the amine serves as a sacrificial electron donor (SR). Turnover numbers (for H) up to 1330 were obtained with these fully noble‐metal‐free systems. The new complexes were electrochemically and photophysically characterized. They exhibited a correlation between the lifetimes of the MLCT excited state and their efficiency as photosensitizers in proton‐reduction systems. Within these experiments, considerably long excited‐state lifetimes of up to 54 μs were observed. Quenching studies with the SR, in the presence and absence of the WRC, showed that intramolecular deactivation was more efficient in the former case, thus suggesting the predominance of an oxidative quenching pathway. 相似文献
792.
Dr. Nathalie Lunau Dipl.‐Chem. Katrin Seelhorst Dipl.‐Chem. Stefanie Kahl Dr. Kathrin Tscherch Dr. Christina Stacke Prof. Dr. Sascha Rohn Prof. Dr. Joachim Thiem Prof. Dr. Ulrich Hahn Prof. Dr. Chris Meier 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(51):17379-17390
Fucosylation is often the final process in glycan biosynthesis. The resulting glycans are involved in a variety of biological processes, such as cell adhesion, inflammation, or tumor metastasis. Fucosyltransferases catalyze the transfer of fucose residues from the activated donor molecule GDP‐β‐L ‐fucose to various acceptor molecules. However, detailed information about the reaction processes is still lacking for most fucosyltransferases. In this work we have monitored α1,3‐fucosyltransferase activity. For both donor and acceptor substrates, the introduction of a fluorescent ATTO dye was the last step in the synthesis. The subsequent conversion of these substrates into fluorescently labeled products by α1,3‐fucosyltransferases was examined by high‐performance thin‐layer chromatography coupled with mass spectrometry as well as dual‐color fluorescence cross‐correlation spectroscopy, which revealed that both fluorescently labeled donor GDP‐β‐L ‐fucose‐ATTO 550 and acceptor N‐acetyllactosamine‐ATTO 647N were accepted by recombinant human fucosyltransferase IX and Helicobacter pylori α1,3‐fucosyltransferase, respectively. Analysis by fluorescence cross‐correlation spectroscopy allowed a quick and versatile estimation of the progress of the enzymatic reaction and therefore this method can be used as an alternative method for investigating fucosyltransferase reactions. 相似文献
793.
Stefanie Wernisch Francesca Bisi Addolorata S. Cazzato Michal Kohout Wolfgang Lindner 《Analytical and bioanalytical chemistry》2013,405(25):8011-8026
2-Acetyldimedone and 12 related compounds were employed as UV-active pre-column derivatizing agents for amino acids. Direct enantioseparation of the products was achieved using chiral anion exchanger stationary phases in polar-organic mobile phase mode. Under basic conditions, the reagents´ cyclic β-tricarbonyl motifs can give rise to exo- and endocyclic enols through tautomerization. However, with primary amines (proteinogenic and unusual amino acids, aminosulfonic and aminophosphonic acids), we exclusively observed the formation of exocyclic enamine-type products. Reaction yields depended strongly on the 2-acyl modification of the reagent; in particular, we observed a significant decrease when electronegative or sterically demanding substituents were present in α-position to the exocyclic carbonyl group. In addition to improving UV detectability of the products, the introduction of this protective group facilitated successful enantiomer separations of the amino acid derivatives on Cinchona-based chiral anion exchangers. Particularly high enantiomer selectivity was observed in combination with stationary phases bearing a new variation of selectors with π-acidic (electron-poor) bis(trifluoromethyl)phenyl groups. No racemization of the analytes occurred at any stage of the analytical method including the deprotection, which was achieved with hydrazine. Figure
Enantiomer separation of 2-undecenoyldimedone derivatives of proteinogenic amino acids phenylalanine and tryptophan on a chiral stationary phase with anion-exchange characteristics 相似文献
794.
Carbon fiber reinforced plastics (CFRP) are mostly used in multilayered laminates, which consist of several very thin layers stacked over each other. For such laminated structures, delamination represents one of the most critical states of failure. In order to predict both the onset as well as the propagation of delamination, a cohesive zone-like continuum damage model is proposed in this paper. This damage model is directly incorporated into a solid-shell finite element with finite thickness. Further, the formulation is capable of considering the interaction of different failure modes. (© 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
795.
In this paper, a finite element formulation is defined in the framework of the discontinuous Galerkin method. Discontinuous Galerkin (dG) methods are classically used in fluid mechanics, however recently their application in solid mechanics has become more vivid among scientists. Of special interest is their application in elliptic problems with constraints such as incompressibility which leads to volumetric locking phenomenon and also in some structural models of shells, plates and beams with compatibility constraints, which brings about shear locking [1]. While classical standard Galerkin methods must be continuous, dG methods can be applied for discontinuities across element boundaries, where a jump of a value (displacement) can be observed. In the present work, a dG method is applied to a linear elastic bar, where a weak discontinuity is allowed in the bar. (© 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
796.
Sheet metal forming processes play a key role in a vast number of manufacturing cycles. The pursuit of novel approaches and enhancements of process chains is limited by the tremendous cost of experimental investigations. Hence, virtual process design is a suitable tool to overcome this limitation and to investigate new aspects of the processes via computer aided design. This work focuses on the optimization of a class of triggering pulses utilized in combined quasi-static and electromagnetic high-speed forming that avoid reverse currents. As typical example double exponential pulses are treated. Non-linear, constrained optimization exploiting a LSDYNA simulation of the forming process is used to determine parameters defining a triggering current pulse, yielding an enhanced forming result, in terms of sharper drawing radii. A more detailed discussion of the method is presented in [1]. (© 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
797.
798.
Computational resources can be used more efficiently by introducing reduced-order models, instead of solving large systems of equations of the original model. In this contribution, the Krylov subspace method, a reduced-order modeling method, is studied and compared to the modal decomposition for a rubber wheel model. (© 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
799.
800.
Cu‐Based Catalyst Resulting from a Cu,Zn,Al Hydrotalcite‐Like Compound: A Microstructural,Thermoanalytical, and In Situ XAS Study
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Dr. Stefanie Kühl Dr. Andrey Tarasov Dr. Stefan Zander Dr. Igor Kasatkin Dr. Malte Behrens 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(13):3782-3792
A Cu‐based methanol synthesis catalyst was obtained from a phase pure Cu,Zn,Al hydrotalcite‐like precursor, which was prepared by co‐precipitation. This sample was intrinsically more active than a conventionally prepared Cu/ZnO/Al2O3 catalyst. Upon thermal decomposition in air, the [(Cu0.5Zn0.17Al0.33)(OH)2(CO3)0.17] ? mH2O precursor is transferred into a carbonate‐modified, amorphous mixed oxide. The calcined catalyst can be described as well‐dispersed “CuO” within ZnAl2O4 still containing stabilizing carbonate with a strong interaction of Cu2+ ions with the Zn–Al matrix. The reduction of this material was carefully analyzed by complementary temperature‐programmed reduction (TPR) and near‐edge X‐ray absorption fine structure (NEXAFS) measurements. The results fully describe the reduction mechanism with a kinetic model that can be used to predict the oxidation state of Cu at given reduction conditions. The reaction proceeds in two steps through a kinetically stabilized CuI intermediate. With reduction, a nanostructured catalyst evolves with metallic Cu particles dispersed in a ZnAl2O4 spinel‐like matrix. Due to the strong interaction of Cu and the oxide matrix, the small Cu particles (7 nm) of this catalyst are partially embedded leading to lower absolute activity in comparison with a catalyst comprised of less‐embedded particles. Interestingly, the exposed Cu surface area exhibits a superior intrinsic activity, which is related to a positive effect of the interface contact of Cu and its surroundings. 相似文献