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861.
The two-neutron halo nucleus (14)Be has been investigated in a kinematically complete measurement of the fragments ((12)Be and neutrons) produced in dissociation at 35 MeV/nucleon on C and Pb targets. Two-neutron removal cross sections, neutron angular distributions, and invariant mass spectra were measured, and the contributions from electromagnetic dissociation (EMD) were deduced. Comparison with three-body model calculations suggests that the halo wave function contains a large nu(2s(1/2))(2) admixture. The EMD invariant mass spectrum exhibited enhanced strength near threshold consistent with a nonresonant soft-dipole excitation.  相似文献   
862.
This paper describes an equivalent but improved least-squares formulation for the numerical approximation of the solution of partial differential equations. Instead of using variational analysis to impose the conditions for minimizing the residual, the residuals are minimized directly, thus leading to a method we will denote by Direct Minimization (DM). DM circumvents setting up the normal equations which consists of matrix–matrix multiplications. Matrix–matrix multiplications are expensive, may lead to loss of accuracy and destroy the sparsity pattern present in the original system. The condition number of the DM formulation is the square root of the condition number which would be obtained if variational analysis was employed. An element-by-element procedure will be presented which allows for parallelization of DM. A computational comparison between DM and the conventional least-squares formulation based on variational analysis will be presented.  相似文献   
863.
N.G. de Almeida 《Physica A》2008,387(12):2745-2749
A formal correspondence between the q-distribution obtained from the Tsallis entropy and non-Maxwellian distributions obtained from the Boltzmann-Gibbs (BG) entropy is obtained. This formal correspondence is obtained by imposing an infinite number of constraints when one maximizes the BG entropy. Different from the approach of Tsallis, Prato and Plastino [C. Tsallis, D. Prato, A.R. Plastino, Astrophys. Space Sci., 290 (2004) 259-274], we relate the constraints to the central moments, providing a natural meaning to the q-parameter.  相似文献   
864.
A search for a sidereal modulation in the MINOS near detector neutrino data was performed. If present, this signature could be a consequence of Lorentz and CPT violation as predicted by the effective field theory called the standard-model extension. No evidence for a sidereal signal in the data set was found, implying that there is no significant change in neutrino propagation that depends on the direction of the neutrino beam in a sun-centered inertial frame. Upper limits on the magnitudes of the Lorentz and CPT violating terms in the standard-model extension lie between 10(-4) and 10(-2) of the maximum expected, assuming a suppression of these signatures by a factor of 10(-17).  相似文献   
865.
Coarse graining techniques offer a promising alternative to large-scale simulations of complex dynamical systems, as long as the coarse-grained system is truly representative of the initial one. Here, we investigate how the dynamical properties of oscillator networks are affected when some nodes are merged together to form a coarse-grained network. Moreover, we show that there exists a way of grouping nodes preserving as much as possible some crucial aspects of the network dynamics. This coarse graining approach provides a useful method to simplify complex oscillator networks, and more generally, networks whose dynamics involves a Laplacian matrix.  相似文献   
866.
A surface study of electrodeposited cerium oxide based coatings is presented. Different surface analytical techniques were used in order to obtain complementary information to fully characterize such complex systems. X-ray Photoelectron Spectroscopy was used as the main technique to determine the surface composition of the coating. The analysis of the core level peaks of the elements provides additional information about the functional groups present on the surface. A mixture of Ce (III) and Ce (IV) was found in the coating and their proportion was calculated at different depths. The analysis of the O 1s core level peak revealed a triple structure whose origin will be discussed. To support the results obtained, electron stimulated desorption was performed. The study was completed with Auger electron spectroscopy and Raman spectroscopy, both techniques having different surface sensitivities. From all these results, it is derived that incomplete electrochemical reactions occurred during the growth of the coatings. This led to rather complex compositions, in which defective cerium oxides are the major species. In addition, hydroxides, carbonates and nitrates are also present, together with adsorbed water.  相似文献   
867.
A geometric approach is used to study the Abel first-order differential equation of the first kind. The approach is based on the recently developed theory of quasi-Lie systems which allows us to characterise some particular examples of integrable Abel equations. Second order Abel equations will be discussed and the inverse problem of the Lagrangian dynamics is analysed: the existence of two alternative Lagrangian formulations is proved, both Lagrangians being of a non-natural class. The study is carried out by means of the Darboux polynomials and Jacobi multipliers.  相似文献   
868.
A simple, rapid and effective analytical method based on fluorescence spectroscopy for the determination of coumarin in pharmaceutical formulations without pre-treatment or pre-concentration step was development. Coumarin had maximum excitation and emission at 310 nm and 390 nm, respectively. Optimum conditions for the detection of coumarin were investigated. Under optimized conditions, we observed a linear behavior for the sign of coumarin in the concentration range of 2.5 × 10−6 to 1.0 × 10−4 mol L−1, with linearity of 0.998 and sensitivity of 2.9 × 1010 u.a/mol L−1. The proposed method was validated in terms of accuracy, precision and specificity of coumarin using the standard addition and external calibration. It was noted that the results support (P < 0.05), indicating that the matrices were not an interference in the determination of coumarin by fluorescence spectroscopy. The results were favorable compared with those obtained by reference chromatographic methods.  相似文献   
869.
This is a report on the synthesis, characterization and spectroscopic study of 24 lanthanide-crown ether coordination compounds, where Eu(III), Tb(III) and Gd(III) were complexes to 12-crown-4 (12C4), 15-crown-5 (15C5), 1,10-phenanthroline (phen) and 2,2′-dipyridyl (dipy). The compounds were synthesized in an ethanol/acetone solution at room temperature and analyzed using CHN elemental analysis and infrared, absorption and emission spectroscopies. The polarizability that the ligand exerts on the emission process was verified and found remarkable. The Eu-15C5-phen complex showed the highest quantum efficiency (71.6%) because of its low non-radiative rate and highest polarizability with reference to the ligands system.  相似文献   
870.
Giardia duodenalis is a human parasite that colonises the small intestine. In some studies, it may be necessary to estimate the parasite-host adhesion index. When working in vitro, it is very difficult to determine the relative number of parasites adhered to intestinal cells because parasites might be removed from enterocytes during specimen preparation. We have encountered such difficulties with sample analyses when using light and conventional scanning electron microscopy, including the loss of adherent cells during the processing steps. In this study, we showed that environmental scanning electron microscopy (ESEM), which allows the examination of specimens at normal atmospheric pressure or in very low vacuum without any previous treatment, can be used effectively in quantitative studies of the parasite-host relationship.  相似文献   
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