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Matthew A. Glaser Noel A. Clark David M. Walba Michael P. Keyes Marc D. Radcliffe Daniel C. Snustad 《Liquid crystals》2013,40(8):1073-1085
Mean field theory and Monte Carlo sampling are applied to the calculation of the spontaneous polarization density of ferroelectric liquid crystals by the ensemble averaging of single molecules confined in mean field potentials reflecting the SmC environment. Molecules are modelled with atomistic detail, using intramolecular interaction potentials derived from ab initio quantum mechanical calculations. This technique is applied to thirteen members of a family of novel fluoro ether-based compounds. Comparison with experiment shows that the observed variation of polarization density with chemical structure is well reproduced in most cases, but that the observed temperature dependence of polarization density is not captured by our model. The features of molecular organization responsible for the discrepancies between theory and experiment are discussed. 相似文献
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Peter D. Clark Shaun T.E. Mesher Alex Primak Hong Yao 《Phosphorus, sulfur, and silicon and the related elements》2013,188(1):413-414
Experiments are described detailing a method for the direct introduction of thiomethyl groups into activated benzenes, thiophene and benzo[b]thiophene using an activated mesoporous clay to promote thiomethyl substitution. Elaboration of 2,3-dithiomethylbenzo[b]thiophene, a product of the clay-catalyzed reaction of benzo[b]thiophene with dimethyl disulfide, to a tetrathiafulvalene derivative is described. 相似文献
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The logarithmic correction for the order of the maximum for two-speed branching Brownian motion changes discontinuously when approaching slopes , which corresponds to standard branching Brownian motion. In this article we study this transition more closely by choosing and . We show that the logarithmic correction for the order of the maximum now smoothly interpolates between the correction in the i.i.d. case , and when . This is due to the localization of extremal particles at the time of speed change, which depends on α and differs from the one in standard branching Brownian motion. We also establish in all cases the asymptotic law of the maximum and characterize the extremal process, which turns out to coincide essentially with that of standard branching Brownian motion. © 2020 the Authors. Communications on Pure and Applied Mathematics published by Wiley Periodicals LLC 相似文献
996.
Trung Le Hao Nguyen Lisa M. Perez Donald J. Darensbourg Marcetta Y. Darensbourg 《Angewandte Chemie (International ed. in English)》2020,59(9):3645-3649
With the goal of generating anionic analogues to MN2S2 ? Mn(CO)3Br we introduced metallodithiolate ligands, MN2S22? prepared from the Cys‐X‐Cys biomimetic, ema4? ligand (ema=N,N′‐ethylenebis(mercaptoacetamide); M=NiII, [VIV≡O]2+ and FeIII) to Mn(CO)5Br. An unexpected, remarkably stable dimanganese product, (H2N2(CH2C=O(μ‐S))2)[Mn(CO)3]2 resulted from loss of M originally residing in the N2S24? pocket, replaced by protonation at the amido nitrogens, generating H2ema2?. Accordingly, the ema ligand has switched its coordination mode from an N2S24? cavity holding a single metal, to a binucleating H2ema2? with bridging sulfurs and carboxamide oxygens within Mn‐μ‐S‐CH2‐C‐O, 5‐membered rings. In situ metal‐templating by zinc ions gives quantitative yields of the Mn2 product. By computational studies we compared the conformations of “linear” ema4? to ema4? frozen in the “tight‐loop” around single metals, and to the “looser” fold possible for H2ema2? that is the optimal arrangement for binucleation. XRD molecular structures show extensive H‐bonding at the amido‐nitrogen protons in the solid state. 相似文献
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A Heteroleptic Ferrous Complex with Mesoionic Bis(1,2,3‐triazol‐5‐ylidene) Ligands: Taming the MLCT Excited State of Iron(II) 下载免费PDF全文
Dr. Yizhu Liu Dr. Kasper S. Kjær Dr. Lisa A. Fredin Dr. Pavel Chábera Tobias Harlang Dr. Sophie E. Canton Prof. Sven Lidin Dr. Jianxin Zhang Prof. Reiner Lomoth Dr. Karl‐Erik Bergquist Prof. Petter Persson Prof. Kenneth Wärnmark Prof. Villy Sundström 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(9):3628-3639
Strongly σ‐donating N‐heterocyclic carbenes (NHCs) have revived research interest in the catalytic chemistry of iron, and are now also starting to bring the photochemistry and photophysics of this abundant element into a new era. In this work, a heteroleptic FeII complex ( 1 ) was synthesized based on sequentially furnishing the FeII center with the benchmark 2,2′‐bipyridine (bpy) ligand and the more strongly σ‐donating mesoionic ligand, 4,4′‐bis(1,2,3‐triazol‐5‐ylidene) (btz). Complex 1 was comprehensively characterized by electrochemistry, static and ultrafast spectroscopy, and quantum chemical calculations and compared to [Fe(bpy)3](PF6)2 and (TBA)2[Fe(bpy)(CN)4]. Heteroleptic complex 1 extends the absorption spectrum towards longer wavelengths compared to a previously synthesized homoleptic FeII NHC complex. The combination of the mesoionic nature of btz and the heteroleptic structure effectively destabilizes the metal‐centered (MC) states relative to the triplet metal‐to‐ligand charge transfer (3MLCT) state in 1 , rendering it a lifetime of 13 ps, the longest to date of a photochemically stable FeII complex. Deactivation of the 3MLCT state is proposed to proceed via the 3MC state that strongly couples with the singlet ground state. 相似文献
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The impact of the combined ascorbic acid and sulfur dioxide antioxidants on white wine oxidation processes was investigated using a range of analytical techniques, including flow injection analysis for free and total sulfur dioxide and two chromatographic methods for ascorbic acid, its oxidative degradation products and phenolic compounds. The combination of different analytical techniques provided a fast and simultaneous means for the monitoring of oxidation processes in a model wine system. In addition, the initial mole ratio of sulfur dioxide to ascorbic acid was varied and the model wine complexity was increased by the inclusion of metal ions (copper(II) and iron(II)). Sulfur dioxide was found not to be a significant binder of ascorbic acid oxidative degradation products and could not prevent the formation of certain phenolic pigment precursors. The results provide a detailed insight into the ascorbic acid/sulfur dioxide antioxidant system in wine conditions. 相似文献