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排序方式: 共有238条查询结果,搜索用时 15 毫秒
101.
地震活动性统计学研究方法的若干进展与讨论 总被引:7,自引:1,他引:6
对统计学方法在地震活动性研究中的部分重要成果、最新研究进展进行了简要地回顾。重点介绍了余震衰减关系和震级、频度关系的相关研究成果及地震活动过程随机模拟等的发展趋势。 相似文献
102.
The study of Mars linked to its climatic history, the presence of water and possible forms of life on the planet, are becoming more and more important in recent years. In this paper we present laboratory reflection measurements on olivine samples which are believed to be the product of alteration induced by their coexistence with water. The reflection spectra have been obtained in the wavelength range from 0.2 to and for different grain sizes; they exhibit, among various bands, some of which due to H2O and OH-, a characteristic absorption feature at about , whose emission wings at 0.56 and near have relative strengths which are size dependent and well correlated. The identification of such feature in the observed spectra of Mars would provide useful information about the grain size of the Martian regolith and, in association with other bands, also about the possible presence of olivine altered by water in the past. 相似文献
103.
104.
P. M. S. Namboodiri K. S. Sastry K. S. V. V. S. Narasimhan 《Astrophysics and Space Science》2006,301(1-4):3-9
Numerical simulations are performed to study the tidal effects of non-merging rapid head-on collision between a disk galaxy
and a spherical galaxy. The disk consists of three components – a disk, a bulge and a halo – and the spherical galaxy is a
Plummer model. The galaxies have the same dimensions with different mass ratios viz., 2, 1 and 0.5. They move in a rectilinear
orbit with a relative velocity of 1000 km s−1.
None of the simulations leads to the merger of the galaxies by tidal capture. The results of our simulations indicate that
although tidal effects are sensitive to both the mass ratio and the inclination of the disk to the orbital plane, it is the
mass ratio which is more important in producing tidal damage to the less massive galaxy. The spherical galaxy undergoes considerable
tidal effects if the mass of the disk is same or larger. On the other hand the collisions in which the mass of the spherical
galaxy is more, result in the formation of a ring structure after the closest approach and the structure disappears by the
end of the simulations. 相似文献
105.
Eclipsing binary stars are gratifying objects because of their unique geometrical properties upon which all important physical parameters such as masses, radii, temperatures, luminosities and distance may be obtained in absolute scale. This poses strict demand on the model to be free of systematic effects that would influence the results later used for calibrations, catalogs and evolution theory. We present an objective scheme of obtaining individual temperatures of both binary system components by means of color-index constraining, with the only requirement that the observational data-set is acquired in a standard photometric system. We show that for a modest case of two similar main-sequence components the erroneous approach of assuming the temperature of the primary star from the color index yields temperatures which are systematically wrong by ∼ 100K. 相似文献
106.
Identification of astronomical dust composition rests on comparison of Infrared (IR) spectra with standard laboratory spectra; frequently, however, a single mineralogical composition is assumed for spectral matching. Advances in laboratory instrumentation have enabled very precise IR spectra to be measured on single grains and zones within grains; with a more complete set of spectral data for planetary dust, better compositional matches will be achieved for astronomical dust. We have compared several FT-IR spectroscopy techniques (open path transmission spectroscopy and diffuse reflectance spectroscopy of powders; microspectroscopy of single grains and powders and ATR spectroscopy of thin sections) to determine their utility for the direct measurement of the mid-IR spectra of small amounts of extraterrestrial grains. We have focussed our investigation on the spectra of the olivine series of silicates, (Mg,Fe)2SiO4, a species frequently identified as one of the major constituents of interstellar dust. The positions of three characteristic SiO4 stretching bands at ∼10.4, 11.3 and 12 μm were measured for comparison of the techniques. All methods gave satisfactory results, although care must be taken to guard against artefacts from sample thickness and orientation effects. Single grains hand-picked from meteorites can be analysed, but results are inaccurate if the grain size is too large (>1-10 μm). Spectra for single grains also show variations that arise from sample orientation effects. Once the analytical artefacts are taken into account, we found that measurement of powder with a diamond compression cell is best suited for the analysis of small amounts of materials. 相似文献
107.
108.
Akira Mizuta Jave O. Kane Marc W. Pound Bruce A. Remington Dmitri D. Ryutov Hideaki Takabe 《Astrophysics and Space Science》2007,307(1-3):183-186
Hydrodynamic instability of an accelerating ionization front (IF) is investigated with 2D hydrodynamic simulations, including
absorption of incident photoionizing photons, recombination in the HII region, and radiative molecular cooling. When the amplitude
of the perturbation is large enough, nonlinear dynamics of the IF triggered by the separation of the IF from the cloud surface
is observed. This causes the second harmonic of the imposed perturbation to appear on the cloud surfaces, whereas the perturbation
in density of ablated gas in the HII region remains largely single mode. This mismatch of modes between the IF and the density
perturbation in the HII region prevents the strong stabilization effect seen in the linear regime. Large growth of the perturbation
caused by Rayleigh-Taylor-like instability is observed late in time. 相似文献
109.
S. Karpov G. Beskin A. Biryukov V. Debur V. Plokhotnichenko M. Redfern A. Shearer 《Astrophysics and Space Science》2007,308(1-4):595-599
The fine structure and the variations of the optical pulse shape and phase of the Crab pulsar are studied on various time
scales. The observations have been carried out on 4-m William Hershel and 6-m BTA telescopes with APD photon counter, photomultiplier
based 4-channel photometer and PSD based panoramic spectrophotopolarimeter with 1 μs time resolution in 1994, 1999, 2003 and
2005–2006 years. The upper limit on the pulsar precession on Dec 2, 1999 is placed in the 10 s–2 hr time range. The evidence
of a varying from set to set fine structure of the main pulse is found in the 1999 and 2003 years data. No such fine structure
is detected in the integral pulse shape of 1994, 1999 and 2003 years.
The drastic change of the pulse shape in the 2005–2006 years set is detected along with the pulse shape variability and quasi-periodic
phase shifts.
This work has been supported by the Russian Foundation for Basic Research (grant No 04-02-17555), Russian Academy of Sciences
(program “Evolution of Stars and Galaxies”), by the Russian Science Support Foundation, and by INTAS (grant No 04-78-7366). 相似文献
110.
A. Frank 《Astrophysics and Space Science》2007,307(1-3):35-39
The expected lifetimes for molecular clouds has become a topic of considerable debate as numerical simulations have shown
that MHD turbulence, the nominal means of support for clouds against self-gravity, will decay on short timescales. Thus it
appears that either molecular clouds are transient features or they are resupplied with turbulent energy through some means.
Jets and molecular outflows are recognized as a ubiquitous phenomena associated with star formation. Stars however form not
isolation but in clusters of different density and composion. The ubiquity and high density of outflows from young stars in
clusters make them an intriguing candidate for the source of turbulence energy in molecular clouds. In this contribution we
present new studies, both observational and theoretical, which address the issue of jet/outflow interactions and their abilityto
drive turbulent flows in molecular clouds. Our studies focus on scales associated with young star forming clusters. In particular
we first show that direct collisions between active outflows are not effective at stirring the ambient medium. We then show
that fossil cavities from “extinct” outflows may provide the missing link in terms of transferring momentum and energy to
the cloud. 相似文献