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71.
72.
Tomas Szabo Brendan M. O'Leary Julius Rebek Jr. 《Angewandte Chemie (International ed. in English)》1998,37(24):3410-3413
A modular strategy has been applied to synthesize large, porous, self-assembling capsules. The coupling of tricyclic building blocks incorporating glycoluril hydrogen-bonding units and derivatives of triethylbenzene produces monomers which readily form homo- and heterodimeric assemblies (calculated structure is shown). Large guests can be trapped while small solvent molecules flow freely through the pores of the capsules. 相似文献
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Rachele Stefania Dr. Lorenzo Tei Dr. Alessandro Barge Dr. Simonetta Geninatti Crich Dr. Ibolya Szabo Dr. Claudia Cabella Dr. Giancarlo Cravotto Prof. Silvio Aime Prof. 《Chemistry (Weinheim an der Bergstrasse, Germany)》2009,15(1):76-85
Three new magnetic resonance imaging probes that target glutamine transporters have been synthesized. They consist of a Gd‐DOTA‐monoamide moiety (DOTA=1,4,7,10‐tetraazacyclododecane‐1,4,7,10‐tetraacetic acid) linked through a six carbon atom chain to a vector represented by a glutamine residue bound through α‐carboxylic, γ‐carboxamidic, or α‐amino functionalities. Their uptake by HTC (rat hepatocarcinoma) and healthy rat hepatocytes has shown that the system containing the glutamine vector bound through the α‐carboxylic group displays a markedly higher affinity for tumor cells. The observed behavior is rationalized in terms of the exploitation of an additional glutamine transporter active in hepatic tumor cells. 相似文献
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Dongmei Jiang Dr. Atsushi Urakawa Dr. Maxim Yulikov Dr. Tamas Mallat Dr. Gunnar Jeschke Prof. Dr. Alfons Baiker Prof. Dr. 《Chemistry (Weinheim an der Bergstrasse, Germany)》2009,15(45):12255-12262
{Cu(bpy)(H2O)2(BF4)2(bpy)} (Cu‐MOF; MOF=metal–organic framework; bpy=4,4′‐bipyridine), with a 3D‐interpenetrated structure and saturated Cu coordination sites in the framework, possesses unexpectedly high activity in the ring‐opening reaction of epoxides with MeOH, although the reaction rate drops remarkably with more bulky alcohols. This (apparent) size selection and the single Cu2+ sites in an identical environment of the crystalline matrix resemble zeolites. The real nature of active sites was investigated by attenuated total reflection infrared (ATR‐IR), Raman, EPR, and UV/Vis spectroscopies. Cu‐MOF has highly dynamic structural properties that respond to MeOH; its framework dimensions change from 3D to 2D by restructuring to a symmetric coordination of four bpy units to Cu. This interaction is accompanied by the partial dissolution of Cu‐MOF as multi‐Cu clusters, in which Cu2+ ions are connected with bpy ligands. Although both molecular and surface catalysis contribute to the high rate of alcoholysis, the soluble oligomeric species (Cumbpyn) are far more active. Finally, addition of diethyl ether to the reaction mixture induces the reconstruction of dissolved and solid Cu‐MOF to the original framework structure, thereby allowing excellent recyclability of Cu‐MOF as an apparent heterogeneous catalyst. In contrast, the original Cu‐MOF structure is maintained upon contact with larger alcohols, such as iPrOH and tBuOH, thus leading to poor activity in epoxide ring opening. 相似文献
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Diezi S Ferri D Vargas A Mallat T Baiker A 《Journal of the American Chemical Society》2006,128(12):4048-4057
In the Pt-catalyzed hydrogenation of 1,1,1-trifluoro-2,4-diketones, addition of trace amounts of cinchonidine, O-methyl-cinchonidine, or (R,R)-pantoyl-naphthylethylamine induces up to 93% ee and enhances the chemoselectivity up to 100% in the hydrogenation of the activated carbonyl group to an OH function. A combined catalytic, NMR and FTIR spectroscopic, and theoretical study revealed that the two phenomena are coupled, offering the unique possibility for understanding the substrate-modifier-metal interactions. The high chemo- and enantioselectivities are attributed to the formation of an ion pair involving the protonated amine function of the chiral modifier and the enolate form of the substrate. DFT calculations including the simulation of the interaction of a protonated amine with the enolate adsorbed on a Pt 31 cluster revealed that only the C-O bond next to the CF3 group of the substrate is in direct contact with Pt and can be hydrogenated. The present study illustrates the fundamental role played by the metal surface and indicates that also the enol form can be the reactive species in the hydrogenation of the activated ketone on chirally modified Pt. 相似文献
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Richard J. Szabo 《General Relativity and Gravitation》2010,42(1):1-29
A pedagogical introduction to some of the main ideas and results of field theories on quantized spacetimes is presented, with
emphasis on what such field theories may teach us about the problem of quantizing gravity. We examine to what extent noncommutative
gauge theories may be regarded as gauge theories of gravity. UV/IR mixing is explained in detail and we describe its relations
to renormalization, to gravitational dynamics, and to deformed dispersion relations in models of quantum spacetime of interest
in string theory and in doubly special relativity. We also discuss some potential experimental probes of spacetime noncommutativity. 相似文献