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151.
Calculations for the complex of thymine and adenine are used to show that the supermolecule second-order Moller-Plesset perturbation theory (MP2) approach for evaluating interaction energies fails in certain cases because of the behavior of one of its components: the uncoupled Hartree-Fock dispersion energy. A simple approach for correcting the MP2 supermolecule interaction energies is proposed. It focuses on correcting a relatively small difference between the MP2 and coupled cluster interaction energies, which is a very appealing feature of the new approach considering a benchmark role played by coupled cluster results. 相似文献
152.
Sek S Chen M Brosseau CL Lipkowski J 《Langmuir : the ACS journal of surfaces and colloids》2007,23(25):12529-12534
Electrochemical scanning tunneling microscopy (EC-STM) has been employed to study the structure of a film formed by cationic surfactant N-decyl-N,N,N-trimethylammonium triflate (DeTATf) adsorbed on the Au(111) electrode surface. The film is disordered at potentials corresponding to either large negative charge densities or to positive charge densities. At small negative charge densities, an ordered adlayer of flat-lying DeTATf molecules is formed. High-resolution images of this adlayer reveal that the triflate anion is coadsorbed with the N-decyl-N,N,N-trimethylammonium cation, effectively forming an ion pair at the electrode surface. This is a significant result because it explains why this surfactant behaves like a zwitterionic surfactant at the metal/solution interface. 相似文献
153.
Understanding the reactivity and regioselectivity of [3 + 2] cycloaddition reactions between substituted nitrile oxides and methyl acrylate. A molecular electron density theory study
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Ibrahim Mbouombouo Ndassa Abel Idrice Adjieufack Joseph Mbadcam Ketcha Slawomir Berski Mar Ríos‐Gutiérrez Luis R. Domingo 《International journal of quantum chemistry》2017,117(24)
The [3 + 2] cycloaddition (32CA) reactions of three nitrile oxides (NOs) (R‐CNO; R = Ph, CO2Me, and Br) with methyl acrylate (MA) have been theoretically studied within the molecular electron density theory. Topological analysis of the electron localization function of these NOs permits to establish that they will participate in zw‐type 32CA reactions. Analysis of the conceptual DFT indices indicates that these zw‐type 32CA reactions will have a low polar character as a consequence of the relatively low electrophilic character of MA and the low nucleophilic character of NOs, in agreement with the global electron density transfer computed at the corresponding TSs. The activation enthalpies associated with these 32CA reactions range from 8.2 to 12.7 kcal·mol?1. The presence of the bromide atom provokes the larger acceleration. While the 32CA reaction involving the CO2Me substituted NO is highly ortho regioselective, the other two reactions are poorly ortho regioselective. A bonding evolution theory study of the more favorable ortho regiosiomeric channel associated with the 32CA reaction involving the Br substituted NO indicates that this reaction is associated to a nonconcerted two‐stage one‐step mechanism, in which the activation energy is mainly related to the initial rupture of the C? N triple bond of the NO. 相似文献
154.
Dr. Shuguang Yuan Prof. Krzysztof Palczewski Dr. Qian Peng Dr. Michal Kolinski Prof. Horst Vogel Prof. Slawomir Filipek 《Angewandte Chemie (International ed. in English)》2015,54(26):7560-7563
G‐protein‐coupled receptors (GPCRs) are important targets for treating severe diseases. However why certain molecules act as activators whereas others, with similar structures, block GPCR activation, is poorly understood since the same molecule can activate one receptor subtype while blocking another closely related receptor. To shed light on these central questions, we used all‐atom, long‐time‐scale molecular dynamics simulations on the κ‐opioid and μ‐opioid receptors (κOR and μOR). We found that water molecules penetrating into the receptor interior mediate the activating versus blocking effects of a particular ligand–receptor interaction. Both the size and the flexibility of the bound ligand regulated water influx into the receptor. The solvent‐accessible inner surface area was found to be a parameter that can help predict the function of the bound ligand. 相似文献
155.
Malgorzata Basko Andrzej Duda Slawomir Kazmierski Przemyslaw Kubisa 《Journal of polymer science. Part A, Polymer chemistry》2013,51(22):4873-4884
Cationic copolymerization of racemic‐β‐butyrolactone (β‐BL) with l,l ‐lactide (LA) initiated by alcohol and catalyzed by trifluoromethanesulfonic acid proceeding by activated monomer (AM) mechanism was investigated. Although both comonomers were present from the beginning in the reaction mixture, polymerization proceeded in sequential manner, with poly‐BL formed at the first stage acting as a macroinitiator for the subsequent polymerization of LA. Such course of copolymerization was confirmed by following the consumption of both comonomers throughout the process as well as by observing the changes of growing chain‐end structure using 1H NMR. 13C NMR analysis and thermogravimetry revealed the block structure of resulting copolymers. The proposed mechanism of copolymerization was confirmed by the studies of changes of 1H NMR chemical shift of acidic proton in the course of copolymerization, providing an indication that indeed protonated species and hydroxyl groups are present throughout the process, as required for AM mechanism. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013 , 51, 4873–4884 相似文献
156.
Zhuoqi Tang Nigel C. Neate David Furniss Slawomir Sujecki Trevor M. Benson Angela B. Seddon 《Journal of Non》2011,357(11-13):2453-2462
Rare earth (RE)-doped chalcogenide glasses are an important promising material for active photonic devices, including mid-infrared (mid-IR) fiber lasers and amplifiers. Here we report on dysprosium ion (Dy3+)-doped GeAsGaSe chalcogenide glasses based on 10 atomic (at.) % Ga. A series of Dy3+-doped GeAsGaSe glasses, with increasing levels of Dy3+ dopant from 0 ppm to 2000 ppm added to the Ge16.5As9Ga10Se64.5 (at. %) base glass, is synthesized and characterized using: Fourier transform infrared spectrometry; X-ray diffraction (XRD); imaging and analysis using a high resolution transmission electron microscope, with selected area electron diffraction (HRTEM-SAED), and energy dispersive X-ray spectroscopy (HRTEM-EDX) and an environmental scanning electron microscope with energy dispersive X-ray spectroscopy (ESEM-EDX) and with secondary electron mapping. At the higher levels of Dy3+ doping, the glasses exhibit bulk crystallization; XRD, HRTEM-EDX and ESEM-EDX indicate the crystals are predominantly a modified, face centered cubic α-Ga2Se3, with some substitution of Ge. In addition, features on the bulk glass surface are shown to comprise Dy3+, sometimes accompanied by Si and [O] which, it is suggested, are due to contamination from the silica glass melting ampoule. 相似文献
157.
We establish a supersymmetric version of the Golden-Thompson inequality.Supported in part by the Department of Energy under grant DE-FG02-88ER25065. 相似文献
158.
The photochemistry of phenyl azide 1 and 13C-labeled phenyl azide 13C-1 incarcerated inside a hemicarcerand 4 was investigated. Low-temperature photolysis of hemicarceplex 41 and 413C-1 yields incarcerated 1-azacyclohepta-1,2,4,6-tetraene 42 and 413C-2 (18-50%), respectively, which were characterized by low-temperature FT-IR and 1H NMR and 13C NMR spectroscopy. After correction for the hemicarcerand-induced upfield shift, the 13C chemical shifts of incarcerated 13C-2 compare very well (Deltadelta = 3.5 ppm) with the GIAO chemical shift tensors calculated at the PBE1PBE/6-311G++(2d,2p) level. Incarcerated 2 has a lifetime of 32 min at 194.4 K and decomposes by ring contraction to singlet phenylnitrene 1PN. 1PN intersystem crosses to triplet phenylnitrene, which reacts with the surrounding host. From the time dependence of the characteristic ketenimine IR absorption of 2 at 1886 cm-1, the rate constant, kobs, for decay of 2 was measured between 198.3 and 174.3 K. Under the assumption that the intersystem-crossing rate constant kISC and the ring-expansion rate constant k1 in pentane (Gritsan, N. P.; Zhu, Z.; Hadad, C. M.; Platz, M. S. J. Am. Chem. Soc. 1999, 121, 1202) and in the inner phase are identical, the rate constant k' = 1011.0 +/- 0.7 x exp(-12.3 +/- 0.6 kcal/mol/RT) for the ring contraction of 2 was calculated. The activation energy compares very well with those calculated at the CASPT2N/6-311G(2d,p) (Karney, W. L.; Borden, W. T. J. Am. Chem. Soc. 1997, 119, 1378) and B3LYP/6-311+G(2d,p) (Tsao, M.-L.; Platz, M. S. J. Am. Chem. Soc. 2003, 125, 12014) level of theory. 相似文献
159.
Friedlein R von Kieseritzky F Braun S Linde C Osikowicz W Hellberg J Salaneck WR 《Chemical communications (Cambridge, England)》2005,(15):1974-1976
Thin films of aligned supramolecular architectures built from newly synthesized thiophene-substituted porphyrins have been processed from solution on surfaces. 相似文献
160.
Rumsey F Zielinski S Kassier R Bech S 《The Journal of the Acoustical Society of America》2005,117(6):3832-3840
The preferences of a large number of na?ve listeners were elicited in response to a selection of multichannel audio items that had been degraded in quality by using band-limiting and down-mixing algorithms. Relationships were sought between these preference ratings and the quality judgements of experienced listeners in an attempt to determine whether one could be predicted from the other. Results suggest that a simple regression model can be used to do this with adequate results, but that a better prediction can be successfully based on experienced listener ratings of timbral and spatial fidelity. There is a difference between na?ve and experienced listeners in the weightings of the fidelities and their relationship to overall quality. 相似文献