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61.
Lemaire S Houpis I Wechselberger R Langens J Vermeulen WA Smets N Nettekoven U Wang Y Xiao T Qu H Liu R Jonckers TH Raboisson P Vandyck K Nilsson KM Farina V 《The Journal of organic chemistry》2011,76(1):297-300
Diastereoselective hydrogenation of 2'-deoxy-2'-exo-methyleneuridine was carried out under homogeneous conditions using a low loading of a chiral Rh catalyst. This, coupled with improvements in the synthesis of the substrate, allowed the smooth pilot plant preparation of the title compound on >10 kg scale. 相似文献
62.
Catheline A Vallés C Drummond C Ortolani L Morandi V Marcaccio M Iurlo M Paolucci F Pénicaud A 《Chemical communications (Cambridge, England)》2011,47(19):5470-5472
Thermodynamics drive the spontaneous dissolution of a graphite intercalation compound (GIC) KC(8) in NMP to form stable solutions. Reduction potential of graphene is measured at +22 mV vs. SCE. Single layer graphene flakes (ca. 1 μm(2)) have been unambiguously identified by electron diffraction. 相似文献
63.
This paper advocates the use of the bionomic algorithm, a recently proposed metaheuristic technique, as an effective method to solve capacitated p-median problems (CPMP). Bionomic algorithms already proved to be an effective framework for finding good solutions to combinatorial optimization problems, when good local optimization algorithms are available. The paper also presents an effective local search technique for the CPMP. Computational results show the effectiveness of the proposed approach, when compared to the best performing heuristics so far presented in the literature. 相似文献
64.
Abstract
We prove existence and uniqueness of a viscosity solution of the Dirichlet problem related to the prescribed Levi mean curvature
equation, under suitable assumptions on the boundary data and on the Levi curvature of the domain. We also show that such
a solution is Lipschitz continuous by proving that it is the uniform limit of a sequence of classical solutions of elliptic
problems and by building Lipschitz continuous barriers.
Keywords: Levi mean curvature, Quasilinear degenerate elliptic PDE’s, Viscosity solutions, Comparison principle, Global Lipschitz estimates 相似文献
65.
66.
Simona Lai Emanuela Locci Giuseppe Saba Ivan Husu Giancarlo Masci Vittorio Crescenzi Adolfo Lai 《Journal of polymer science. Part A, Polymer chemistry》2003,41(20):3123-3131
Dry and hydrated poly(vinyl alcohol) (PVA) gels with 55% (a‐PVA) and 61% (s‐PVA) syndiotacticity and related PVA/lactyl chitosan (LC) blends have been investigated with 129Xe and cross‐polarization/magic‐angle‐spinning 13C NMR techniques. Although the dry gels exhibit two broad 129Xe resonances in the slow‐to‐intermediate exchange limit, both hydrated gels show three resonances. The corresponding dry blends exhibit two signals, the chemical shifts and line widths of which change with respect to those of pure PVA, whereas one (a‐PVA/LC) or two (s‐PVA/LC) signals appear in the spectra of the hydrated blends. A comparative analysis of the data demonstrates that LC rearranges the domains of the polymeric matrix in both the dry and hydrated blends according to the syndiotacticity of the PVA chains. Information on the molecular motions of the amorphous and swollen polymeric domains in the kilohertz range has been obtained from an analysis of the spin‐lattice relaxation times. These data indicate that the dynamics and arrangement of the PVA chains in the gels are strongly affected by their tacticity and the addition of the copolymer LC. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 3123–3131, 2003 相似文献
67.
The polymorphism of isotactic poly-α-butene is studied on the basis of a complete conformational analysis of the chain. The results show that chain polymorphism occurs between two different minima of the energy surface separated by a very low energy gap. The complete determination of the structure of form 2 is also an object of the present work. A possible slight distortion from the perfect s(3·65) helical symmetry of the chain in the form 2 is indicated. 相似文献
68.
Giuseppina Castronuovo Vittorio Elia Filomena Velleca 《Journal of solution chemistry》1996,25(1):51-59
Enthalpies of dilution of binary and ternary aqueous solutions containing L-and D-proline, cis-L- and cis-D-4-hydroxy proline, trans-L-4-hydroxy proline, have been determined by flow calorimetry at 25°C. Pairwise self-and cross-interaction coefficients of the virial expansion of the excess enthalpies were evaluated. They are positive for solutions of unsubstituted prolines. On the contrary, upon the introduction of a hydroxy group, they become negative, reaching the largest value for the cis-L-lcis-D-4-hydroxy proline system. The results are interpreted in terms of preferential configurations, stabilized by interactions between the hydrophilic groups. 相似文献
69.
Calculations of the conformational and of the packing energy have been performed for the three main crystalline modifications of isotactic poly-α-butene. Calculations of the conformational energy have been performed first through minimizations of the energy of the isolated chains under the constraint of maintaining the experimental helical symmetry and periodicity for each modification. In this way accurate conformations have been determined for the helices corresponding to the three modifications. These conformations have been used for calculation of the packing energy of the three modifications of poly-α-butene. The considered space groups are those experimentally observed; for each modification also the possibility of statistical up and down positioning of the chains has been examined. The differences between the packing energies are greater than those between the conformational energies for the three different modifications. The relative stabilities of the three modifications of poly-α-butene, as obtained by our calculations, are discussed. 相似文献
70.
Andrea Maldotti Claudio Chiorboli Carlo A. Bignozzi Carlo Bartocci Vittorio Carassiti 《国际化学动力学杂志》1980,12(12):905-913
The photooxidation of the 1,3-butadiene–NO–air system at 298 ± 2 K was investigated in an environmental chamber under simulated atmospheric conditions. The irradiation gave rise to the formation of acrolein in a 55% yield, based on 1,3-butadiene initial concentration for all the experimental runs. The rate of formation of acrolein was the same as that of 1,3-butadiene consumption, indicating that acrolein is the major product of the 1,3-butadiene oxidation in air. The dependence of acrolein concentration on irradiation time showed thata secondary process, identified as an oxidation of acrolein by ?OH radicals, was occurring during the photochemical runs. The rate constant of this secondary process was determined by measuring the relative rates of disappearance of acrolein and n-butane during the irradiation of acrolein-n-butane-NO-air mixtures. The so obtained relative rate constant value was placed on an absolute basis using a reported rate constant for the n-butane + ?OH reaction; a value of (1.6 ± 0.2) × 1010 M?1 sec?1 was obtained. 相似文献