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941.
Transmissions of oblique incident wave from a row of rectangular piles are analyzed theoretically. The incident angle of plane wave is taken as , there then is the transmission coefficient (This is a paradox). In this paper, by means of the approximate relation between the transmitted and incident wave angle found from the shape of a slit, the paradoxical phenomenon is removed. On the basis of the continuality of the pressure and flux and the analysis of flow resistance at the row of rectangular piles, formulas of reflection and transmission coefficients are obtained. The transmission and reflection coefficients predicted by the present model quite agree with those of laboratory experiments in previous references 相似文献
942.
943.
Interval velocity analysis using post‐stack data has always been a desire, mainly for 3D data sets. In this study we present a method that uses the unique characteristics of migrated diffractions to enable interval velocity analysis from three‐dimensional zero‐offset time data. The idea is to perform a standard three‐dimensional prestack depth migration on stack cubes and generate three‐dimensional common image gathers that show great sensitivity to velocity errors. An efficient ‘top‐down’ scheme for updating the velocity is used to build the model. The effectiveness of the method is related to the incorporation of wave equation based post‐stack datuming in the model building process. The proposed method relies on the ability to identify diffractions along redatumed zero‐offset data and to analyse their flatness in the migrated local angle domain. The method can be considered as an additional tool for a complete, prestack depth migration based interval velocity analysis. 相似文献
944.
945.
946.
Seismic tomography has been one of the primary tools to image the interior of the earth and other elastic structures. To date the inversions of compressional ( P ) and shear ( S ) wave speeds have been carried out separately under the assumption that P traveltimes are affected only by the P wave speed of the elastic media and S traveltimes by the S wave speed. Using numerical and analytical solutions, we show that for finite-frequency seismic waves, S wave speed perturbations may have significant effects on P waveforms. This suggests that when waveform-derived traveltime and amplitude anomalies are used in tomographic inversions, the P -wave measurements should be related to not only P wave speed perturbations but also S wave speed perturbations. 相似文献
947.
A. L. McNamara Z. Kuncic K. Wu 《Monthly notices of the Royal Astronomical Society》2008,386(4):2167-2172
Compton scattering within the accretion column of magnetic cataclysmic variables (mCVs) can induce a net polarization in the X-ray emission. We investigate this process using Monte Carlo simulations and find that significant polarization can arise as a result of the stratified flow structure in the shock-ionized column. We find that the degree of linear polarization can reach levels up to ∼8 per cent for systems with high accretion rates and low white dwarf masses, when viewed at large inclination angles with respect to the accretion column axis. These levels are substantially higher than previously predicted estimates using an accretion column model with uniform density and temperature. We also find that for systems with a relatively low-mass white dwarf accreting at a high accretion rate, the polarization properties may be insensitive to the magnetic field, since most of the scattering occurs at the base of the accretion column where the density structure is determined mainly by bremsstrahlung cooling instead of cyclotron cooling. 相似文献
948.
N. G. Barri 《Earth, Moon, and Planets》2008,102(1-4):395-401
This work is devoted to modeling of the transverse scattering of meteoroid fragments in the atmosphere by adopting supersonic
gas dynamics around a system of bodies. Artem’eva and Shuvalov (1996, Shock Waves, 367) and Zhdan et al. (2004, Dokl. Phys.,
315–317) found that the transverse force decreases with the increase of the distance between fragments, that is, fragments
do not separate in a transverse direction under the action of constant repulsion force. This work on the decreasing transverse
force uses the values of the transverse force coefficient by Zhdan et al. (2004, Dokl. Phys., 315–317) obtained from numerical
modeling for spheres in a supersonic flow to derive the analytical solution of the dynamic equation for a fragment. The new
model of layer-by-layer scattering of meteoroid fragments moving as a system of bodies is constructed on the basis of the
analytical solutions derived in this work and the numerical data by Zhdan et al. (2005, Dokl. Phys., 514–518). 相似文献
949.
In order to choose a numerical method for solving the time dependent equations of radiative transport, we obtain an exact
solution for the time dependent radiation field in a one dimensional infinite medium with monochromatic, isotropic scattering
for sources with an arbitrary spatial distribution and an arbitrary time variation of their power. The Lax-Wendroff method
seems to be the most suitable. Because it is assumed that radiation delay is caused by the finite speed of light, the following
difficulty arises when the numerical method is used: the region of variation of the variables (position τ and time t) is triangular (the inequality τ ≤ t). This difficulty is overcome by expanding the unknown functions in series in terms of small values of the time and position.
By comparing the numerical and exact solutions for a point source with a given time dependence for its power and with pure
scattering, the number of steps in the variables required to obtain a desired accuracy is estimated. This numerical method
can be used to calculate the intensity and polarization of the radiation from sources in the early universe during epochs
close to the recombination epoch.
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Translated from Astrofizika, Vol. 51, No. 1, pp. 109–123 (February 2008). 相似文献
950.