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441.
A. S. Baranov 《Astrophysics》2006,49(4):543-554
The stability of the charged particle velocity distributions resulting from intermixing of neighboring flows of interstellar
medium are examined, in particular, within the confines of spiral galaxies. It is shown for a specific example that the customary
electrostatic instability shows up when the difference in the systematic velocities of both flows is sufficiently large compared
to the thermal speed. On the other hand, the electromagnetic instability occurs, in principle, for an arbitrarily small difference
in the flow velocities. The characteristic time for this instability to develop is much longer than for the electrostatic
instability, but is still short compared to the ordinary evolution time for the interstellar medium.
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Translated from Astrofizika, Vol. 49, No. 4, pp.637–649 (November 2006). 相似文献
442.
Tao Hu Zheng-Yi Shao Qiu-He Peng Department of Astronomy Nanjing University Nanjing Shanghai Astronomical Observatory Chinese Academy of Sciences Shanghai Joint Institute for Galaxies Cosmology Chinese Academy of Sciences Shanghai Joint Astrophysics Center of Chinese Academy of Sciences-Peking University Beijing The Open Laboratory of Cosmic Ray High Energy Astrophysics Chinese Academy of Sciences Beijing 《中国天文和天体物理学报》2006,6(2):175-180
We have studied some properties including surface brightness in the u, g, r, i, and z bands of the nearly face-on galaxy PGC 35105. By subtracting a model surface brightness distribution from the observed image we obtain the residual image that shows only the spiral arms freed from the contamination by the bulge. From this we measured the the inclination, pitch angle, and forbidden radius (identified with the innermost point of the arm) for each of the two arms; and that for each of the five observing bands. We found these three parameters are largely independent of the observing band. 相似文献
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447.
Porphyroblast inclusion trails have the potential to provide critical information about tectonometamorphic events. Recently, however, traditional interpretations of inclusion trails have been called into question by the suggestions that porphyroblasts do not rotate during non-coaxial deformation and that apparent spiral inclusion trails can be generated in coaxial deformation. We present a new computer model that simulates inclusion trail development. Model results suggest: (1) that the extent of porphyroblast rotation is controlled by conditions at the porphyroblast-matrix boundary; (2) that curved inclusion trails may develop in unrotated porphyroblasts; (3) that classic "snowball" inclusion trails are most simply explained by rotational growth histories; and (4) that some of the observations used to support the view that porphyroblasts do not rotate (e.g. weakly sigmoidal inclusion trails, apparent truncations of inclusion trails) can be accounted for by variations in the growth rate of rotating porphyroblasts. 相似文献
448.
Stephen F. Helsdon Trevor J. Ponman Ewan O'Sullivan Duncan A. Forbes 《Monthly notices of the Royal Astronomical Society》2001,325(2):693-706
We have derived the X-ray luminosities of a sample of galaxies in groups, making careful allowance for contaminating intragroup emission. The L X : L B and L X : L FIR relations of spiral galaxies in groups appear to be indistinguishable from those in other environments, however the elliptical galaxies fall into two distinct classes. The first class is central-dominant group galaxies, which are very X-ray luminous and may be the focus of group cooling flows. All other early-type galaxies in groups belong to the second class, which populates an almost constant band of L X / L B over the range 9.8< log L B <11.3 . The X-ray emission from these galaxies can be explained by a superposition of discrete galactic X-ray sources together with a contribution from hot gas lost by stars, which varies a great deal from galaxy to galaxy. In the region where the optical luminosity of the non-central group galaxies overlaps with the dominant galaxies, the dominant galaxies are over an order of magnitude more luminous in X-rays.
We also compared these group galaxies with a sample of isolated early-type galaxies, and used previously published work to derive LX : L B relations as a function of environment. The non-dominant group galaxies have mean L X / L B ratios very similar to those of isolated galaxies, and we see no significant correlation between L X / L B and environment. We suggest that previous findings of a steep L X : L B relation for early-type galaxies result largely from the inclusion of group-dominant galaxies in samples. 相似文献
We also compared these group galaxies with a sample of isolated early-type galaxies, and used previously published work to derive L
449.
Peter I. Brooker 《Mathematical Geology》1985,17(1):81-90
Journel (1974) developed the turning-bands method which allows a three-dimensional data set with specified covariance to be obtained by the simulation of several one-dimensional realizations which have an intermediate covariance. The relationship between the threedimensional and one-dimensional covariance is straightforward and allows the one-dimensional covariance to be obtained immediately. In theory a dense uniform distribution of lines in three-dimensional space is required along which the one-dimensional realizations are generated; in practice most workers have been content to use the fifteen axes of the regular icosahedron. Many mining problems may be treated in two dimensions, and in this paper a turning-bands approach is developed to generate two-dimensional data sets with a specified covariance. By working in two dimensions, the area on which the data is simulated may be divided as finely as desired by the lines on which the one-dimensional realizations are first generated. The relationship between the two-dimensional and one-dimensional covariance is derived as a nontrivial integral equation. This is solved analytically for the onedimensional covariance. The method is applied to the generation of a two-dimensional data set with spherical covariance. 相似文献
450.
The tsunami similar to the one that has occurred in December 26, 2004 (Boxing Day Tsunami) in the Indian Ocean is simulated using the expression derived from Modified Weibull Distribution (for maximum wave height simulation) for extreme wave height predictions. The tuning coefficient plays a significant role in estimating the tsunami heights at various stages. It follows well defined mathematical laws at different stages. It is time dependent in the first three stages and depth dependent in the last two stages. The beach run-up heights estimated by the expression derived from the work-energy relation are comparable with observed values with reasonable accuracy. 相似文献