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21.
N. V. Platonova Yu. O. Punin V. D. Franke E. N. Kotelnikova 《Journal of Structural Chemistry》1994,35(5):634-641
In the ammonium chloride crystallization region of the NH4Cl−CuCl2−H2O−CH3ON system, cocrystallization of the impurity with the main substance occurs by epitaxial adsorption of complexes of varying
composition. In NH4Cl crystals, the Cu2+ impurity forms oriented interlayers (ingrowths) simultaneously at the macro-and microlevels. The ratio between the two trapping
forms depends on the growth conditions.
St. Petersburg State University. Translated fromZhurnal Strukturnoi Khimii, Vol. 35, No. 5, pp. 70–78, September–October, 1994.
Translated by L. Smolima 相似文献
22.
23.
D Lathrop D Franke R Maxwell T Tepe R Flesher Z Zhang H Eckert 《Solid state nuclear magnetic resonance》1992,1(2):73-83
The ability of the 90 degrees-t1-180 degrees pulse sequence to produce accurate dipole-dipole coupling information in solids is investigated. To this end, the experimental 31P spin echo decays are measured for eighteen crystalline phosphides and phosphorus chalcogenides and compared with simulations, based on the known internuclear distances in these compounds. The experimental results are generally found accurate in compounds where the dominant contribution to the dipole-dipole coupling arises from nuclei in structurally inequivalent sites with large chemical shift anisotropies. For this situation, the quantum mechanical "flip-flop" term in the dipolar Hamiltonian is suppressed and the dipole-dipole coupling is entirely heteronuclear in character. All of those compounds that do not obey this condition show accelerated spin echo decays due to a fractional contribution of the flip-flop term and possibly incomplete refocusing of chemical shift terms on the time scale of the experiment. The results confirm on an empirical basis that the spin echo NMR technique can provide accurate dipole-dipole coupling information (and thus distance distributions) in disordered solids and glasses. 相似文献
24.
Theoretical equations are given to relate resolution with development distance. Comparative experiments undertaken with quaternary ammonium compounds as test substances and using a selection of basic drugs are presented. As expected, resolution decreases with shorter development distance. However, this effect is less pronounced for compounds with small Rf values and when the spot size at the starting point is kept small. It was also shown that, for correctly assessing resolution in relation to development distance, the amounts of material spotted have to be decreased for shorter development distances. 相似文献
25.
The effect of impurities on the growth of manganese carbonate crystals has been studied. Stereophotogrammetric analysis showed
that all crystal faces have the same Miller indices
and the peanut-shaped forms are twins with twin axis 0001. 相似文献
26.
27.
28.
Dr. Jana Franke Dr. Martin Bock Dr. Richard Dehn Dr. Jörg Fohrer Dr. Santosh B. Mhaske Dr. Antonella Migliorini Dr. Argyrios A. Kanakis Dr. Rolf Jansen Dr. Jennifer Herrmann Prof. Dr. Rolf Müller Prof. Dr. Andreas Kirschning 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(11):4272-4284
The total and semi‐synthesis of 13 new macrolactones derived from thuggacin, which is a secondary metabolite from the myxobacterium Sorangium cellulosum, are reported. The thuggacins have attracted much attention due to their strong antibacterial activity, particularly towards Mycobacterium tuberculosis. This study focuses on 1) thuggacin derivatives that cannot equilibrate by transacylation between the three natural thuggacins A–C, 2) the roles of the thiazole ring, and 3) the hexyl side chain at C2. Semi‐synthetic O‐methylation at C17 suppressed the transacylations without a substantial loss of antibacterial activity. Exchanging the C17–C25 side chain for simplified hydrophobic chains led to complete loss of antibacterial activity. Exchange of the thiazole by an oxazole ring or removal of the hexyl side chain at C2 had no substantial effect on the biological properties. 相似文献
29.
Association and Dissociation of Grignard Reagents RMgCl and Their Turbo Variant RMgCl⋅LiCl
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Christoph Schnegelsberg Sebastian Bachmann Marlene Kolter Thomas Auth Dr. Michael John Prof. Dr. Dietmar Stalke Prof. Dr. Konrad Koszinowski 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(23):7752-7762
Grignard reagents RMgCl and their so‐called turbo variant, the highly reactive RMgCl?LiCl, are of exceptional synthetic utility. Nevertheless, it is still not fully understood which species these compounds form in solution and, in particular, in which way LiCl exerts its reactivity‐enhancing effect. A combination of electrospray‐ionization mass spectrometry, electrical conductivity measurements, NMR spectroscopy (including diffusion‐ordered spectroscopy), and quantum chemical calculations is used to analyze solutions of RMgCl (R=Me, Et, Bu, Hex, Oct, Dec, iPr, tBu, Ph) in tetrahydrofuran and other ethereal solvents in the absence and presence of stoichiometric amounts of LiCl. In tetrahydrofuran, RMgCl forms mononuclear species, which are converted into trinuclear anions as a result of the concentration increase experienced during the electrospray process. These trinuclear anions are theoretically predicted to adopt open cubic geometries, which remarkably resemble structural motifs previously found in the solid state. The molecular constituents of RMgCl and RMgCl?LiCl are interrelated via Schlenk equilibria and fast intermolecular exchange processes. A small portion of the Grignard reagent also forms anionic ate complexes in solution. The abundance of these more electron‐rich and hence supposedly more nucleophilic ate complexes strongly increases upon the addition of LiCl, thus rationalizing its beneficial effect on the reactivity of Grignard reagents. 相似文献
30.
The present contribution deals with a variationally consistent Mortar contact algorithm applied to a phase-field fracture approach for finite deformations, see [4]. A phase-field approach to fracture allows for the numerical simulation of complex fracture patterns for three dimensional problems, extended recently to finite deformations (see [2] for more details). In a nutshell, the phase-field approach relies on a regularization of the sharp (fracture-) interface. In order to improve the accuracy, a fourth-order Cahn-Hilliard phase-field equation is considered, requiring global C1 continuity (see [1]), which will be dealt with using an isogeometrical analysis (IGA) framework. Additionally, a newly developed hierarchical refinement scheme is applied to resolve for local physical phenomena e.g. the contact zone (see [3] for more details). The Mortar method is a modern and very accurate numerical method to implement contact boundaries. This approach can be extended in a straightforward manner to transient phase-field fracture problems. The performance of the proposed methods will be examined in a representative numerical example. (© 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献