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51.
UHF and CI calculations, using the direct CI method, and double-zeta plus polarization functions basis sets, have been performed on the more important parts of the energy hypersurface for CH5. The abstraction H + CH4 → H2 + CH3 and the inversion substitution reaction H′ + CH4 → CH3H′ + H have been studied in detail. The predicted barriers for these two reactions are 13.5 and 36.6 kcal/mol, respectively. The abstraction reaction is, in agreement with experiment, found to be almost thermo-neutral with a heat of reaction of 1.5 kcal/mol. 相似文献
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Summary A method is presented, whereby dynamic - polarization, i.e. the correlation effect expressed by simultaneous (-*, -*) excitations, can be approximately included in a multi-reference configuration interaction (MRCI) or multi-configurational self-consistent field (MC-SCF) calculation, without need to explicitly correlate the sigma orbitals. The method, which we call the capacitance matrix method, is based on the use of conventional one-electron integrals, from which a polarization potential (SPP) contribution is computed and added to the one- and two-electron Hamiltonian. In the present form, the method requires one parameter for each type of atom, and one for each type of bond. These parameters were adjusted to reproduce the dynamic - polarization energy, computed by restricted multi-reference CI calculations, of a number of states of different hydrocarbons, and the agreement was within a few percent. Using the same parameters in CAS (Complete Active Space) SCF calculations of various states of benzene gives excitation energies, when SPP is included, which is comparable to those obtained by much more elaborate MRCI calculations. 相似文献
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H. E. Bjørnstad H. N. Lien Yu-Fu Yu B. Salbu 《Journal of Radioanalytical and Nuclear Chemistry》1992,156(1):165-173
Low level90Sr in environmental and biological samples is determined using a combined HDEHP solvent extraction-liquid scintillation procedure. Yttrium-90 is selectively extracted from nitric acid solution into 5% di(2-ethylhexyl) phosphoric acid (HDEHP) in toluene, and90Y in the organic phase is measured directly using an ultra low level liquid scintillation spectrometer.The working program of the Quantulus counter has been optimized. As the counting efficiency using liquid scintillation counting is high and the stripping and precipitation of Yttrium-90 oxalate is omitted, this procedure is simpler and more timesaving than traditional methods. The chemical recoveries of90Y were 85.1% for soil, 75.7% for milk and 65.3% for bone. The detection limit is 8 mBq. 相似文献
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Summary The electronically excited states of formaldehyde are examined by means of multiconfigurational second-order perturbation (CASPT2) theory with extended ANO-type basis sets. The calculations comprised five valence excited states plus all singlet 3s, 3p, and 3d members of the Rydberg series converging on the first ionization. The computed vertical excitation energies were found to be within 0.2 eV of the available experimental energies. Full geometry optimization has been performed for five valence excited states. Assuming a planar geometry, the 0-0 transition for the valence1A1( *) state is calculated to appear near 7.9 eV, close to the (n
y
3p) region. This state is, however, not planar and the true adiabatic energy is 7.4 eV, which is 2.3 eV below the corresponding vertical transition. 相似文献
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Abstract Polymer liquid crystals can occur as polydomain materials where the domain size may be tens of microns. While the material within each domain may be characterized by a common order parameter, the directors of the domains can be more or less randomly distributed. Since the transition from polydomain to monodomain material only involves the removal of grain boundaries and the alignment of directors, the free energy change must necessarily be small. Such a transition can readily be achieved, therefore, by the action of any external field: electrical, magnetic, stress or surface. In this work optical photomicrographs of polymeric liquid crystals with widely varying and in some cases well controlled morphologies are presented. Probable dependence of rheological behaviour on morphology is also discussed. Such dependence is expected to be considerable under certain conditions. Due to experimental and sample limitations, however, direct correlations of rheology and morphology are sparse. Morphological consequences for the rheology of liquid-crystalline materials can be exemplified by the following possibilities. In contrast to the case of isotropic melts, wall effects can be non-negligible. Zero shear rate rheological parameters are not expected to be uniquely defined quantities since the domain sizes are large and the director may not be effectively averaged over typical sample dimensions. Non-zero shear-rate measurements of rheological parameters is effected by the propensity of: (1) individual domain directors to align under the influence of a stress field and (2) flow alignment to dominate surface-induced alignment above some critical shear rate. The effects might be manifested by a non-newtonian regime as well as yield stress behaviour and thixotropy. The kinetics of relaxation from mono- to poly-domain material has implications for the dynamic response and rheological hysterises of the material. 相似文献
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