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761.
Diebold AR Straganz GD Solomon EI 《Journal of the American Chemical Society》2011,133(40):15979-15991
The O(2) activating mononuclear nonheme iron enzymes generally have a common facial triad (two histidine and one carboxylate (Asp or Glu) residue) ligating Fe(II) at the active site. Exceptions to this motif have recently been identified in nonheme enzymes, including a 3His triad in the diketone cleaving dioxygenase Dke1. This enzyme is used to explore the role of the facial triad in directing reactivity. A combination of spectroscopic studies (UV-vis absorption, MCD, and resonance Raman) and DFT calculations is used to define the nature of the binding of the α-keto acid, 4-hydroxyphenlpyruvate (HPP), to the active site in Dke1 and the origin of the atypical cleavage (C2-C3 instead of C1-C2) pattern exhibited by this enzyme in the reaction of α-keto acids with dioxygen. The reduced charge of the 3His triad induces α-keto acid binding as the enolate dianion, rather than the keto monoanion, found for α-keto acid binding to the 2His/1 carboxylate facial triad enzymes. The mechanistic insight from the reactivity of Dke1 with the α-keto acid substrate is then extended to understand the reaction mechanism of this enzyme with its native substrate, acac. This study defines a key role for the 2His/1 carboxylate facial triad in α-keto acid-dependent mononuclear nonheme iron enzymes in stabilizing the bound α-keto acid as a monoanion for its decarboxylation to provide the two additional electrons required for O(2) activation. 相似文献
762.
We investigate quantum control of the dissipation of entanglement under environmental decoherence. We show by means of a simple
two-qubit model that standard control methods – coherent or openloop control – will not in general prevent entanglement loss
induced by a Markovian environment. However, we propose a control method utilizing a Wiseman–Milburn feedback/measurement
control scheme which will effectively negate environmental entanglement dissipation. 相似文献
763.
Solomon Jekel 《Journal of Pure and Applied Algebra》2011,215(11):2628-2638
Let Gτ be the topological group of orientation preserving homeomorphisms of the circle, and Gδ the same group with the discrete topology. Motivated by the classical problem of reducing a circle bundle with structure group Gτ to a totally disconnected subgroup K⊂Gδ, and more currently, applications to mapping class groups, we analyze, in a homological algebra setting, the role played by the Topological and Discrete Euler Classes. In particular we describe the Discrete Euler Class of G, and any of its subgroups K, explicitly as a group extension. We apply our constructions to show that the values of the Discrete Euler Class are bounded on any space, and we state triviality and non-triviality conditions for its powers in the based mapping class groups. 相似文献
764.
Del Grosso A Helm MD Solomon SA Caras-Quintero D Ingleson MJ 《Chemical communications (Cambridge, England)》2011,47(46):12459-12461
Electrophilic direct borylation is facilitated, and arene substrate scope enhanced, by using electrophiles derived from inexpensive reagents; specifically an amine, BCl(3) and AlCl(3). 相似文献
765.
Polyakov SV Muller A Flagg EB Ling A Borjemscaia N Van Keuren E Migdall A Solomon GS 《Physical review letters》2011,107(15):157402
Single photons produced by fundamentally dissimilar physical processes will in general not be indistinguishable. We show how photons produced from a quantum dot and by parametric down-conversion in a nonlinear crystal can be manipulated to be indistinguishable. The measured two-photon coalescence probability is 16%, and is limited by quantum-dot decoherence. Temporal filtering to the quantum-dot coherence time and accounting for detector time response increases this to 61% while retaining 25% of the events. This technique can connect different elements in a scalable quantum network. 相似文献
766.
We demonstrate four-wave mixing in silicon-on-insulator coupled-resonator optical waveguides consisting of 35 and 65 microring resonators, using a cw pump with coupled power below 20 mW and observed parametric conversion across more than 10 THz. The conversion efficiency is enhanced by +16 dB relative to a silicon straight waveguide of equivalent length, due to the slowing factor of the coupled-resonator structure. 相似文献
767.
P. Cacioli D. G. Hawthorne R. L. Laslett E. Rizzardo D. H. Solomon 《高分子科学杂志,A辑:纯化学与应用化学》2013,50(7):839-852
Abstract The free-radical copolymerization of ω-unsaturated oligo(methyl methacrylate) (1) with each of ethyl acrylate, styrene, methyl methacrylate, acrylonitrile, and vinyl acetate have been investigated. Incorporation of (1) into the polymer was observed in all cases although the molecular weights of the copolymers were substantially lower than those of the homopolymers obtained in the absence of (1) but under otherwise identical conditions. These experiments, together with a product study of the reactions of (1) with cyanoisopropyl radicals, have shown that the addition of free radicals to the double bond of (1) occurs readily. The sterically hindered radical so formed, however, undergoes facile β-scission, resulting in the termination of chains (chain transfer) in competition with chain propagation. The implications of these findings to the usefulness of (1) in the synthesis of graft copolymers and their relevance to the chemistry of free-radical polymerizations when methyl methacrylate is employed as a monomer or comonomer are discussed. 相似文献
768.
Hydroxy radical-initiated poly(methyl methacrylate) and polystyrene have been reacted with o-sulfobenzoic anhydride to produce dye-active sulfonate groups and these were measured by a dye-partition technique with methylene blue. The important advantages over chlorosulfonic acid, previously employed in the dye-partition analysis for the conversion of hydroxy into sulfate groups, are that o-sulfobenzoic anhydride does not react at sites other than the hydroxy functionality and that it introduces the dye-active moiety (sulfonate) into the polymer via a hydrolytically more stable linkage. 相似文献
769.
We study separated nets Y that arise from primitive substitution tilings of Rd. We show that the question whether Y is a bounded displacement of Zd or not can be reduced, in many cases, to a simple question on the eigenvalues and eigenspaces of the substitution matrix. 相似文献
770.
Chiral Anion Phase Transfer of Aryldiazonium Cations: An Enantioselective Synthesis of C3‐Diazenated Pyrroloindolines 下载免费PDF全文
Dr. Hosea M. Nelson Solomon H. Reisberg Hunter P. Shunatona Jigar S. Patel Prof. Dr. F. Dean Toste 《Angewandte Chemie (International ed. in English)》2014,53(22):5600-5603
Herein is reported the first asymmetric utilization of aryldiazonium cations as a source of electrophilic nitrogen. This is achieved through a chiral anion phase‐transfer pyrroloindolinization reaction that forms C3‐diazenated pyrroloindolines from simple tryptamines and aryldiazonium tetrafluoroborates. The title compounds are obtained in up to 99 % yield and 96 % ee. The air‐ and water‐tolerant reaction allows electronic and steric diversity of the aryldiazonium electrophile and the tryptamine core. 相似文献