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71.
Daniel Malmberg Francesca De Angeli Melvyn B. Davies Ross P. Church Dougal Mackey Mark I. Wilkinson 《Monthly notices of the Royal Astronomical Society》2007,378(3):1207-1216
The stars that populate the solar neighbourhood were formed in stellar clusters. Through N -body simulations of these clusters, we measure the rate of close encounters between stars. By monitoring the interaction histories of each star, we investigate the singleton fraction in the solar neighbourhood. A singleton is a star which formed as a single star, has never experienced any close encounters with other stars or binaries, or undergone an exchange encounter with a binary. We find that, of the stars which formed as single stars, a significant fraction is not singletons once the clusters have dispersed. If some of these stars had planetary systems, with properties similar to those of the Solar System, the planets' orbits may have been perturbed by the effects of close encounters with other stars or the effects of a companion star within a binary. Such perturbations can lead to strong planet–planet interactions which eject several planets, leaving the remaining planets on eccentric orbits. Some of the single stars exchange into binaries. Most of these binaries are broken up via subsequent interactions within the cluster, but some remain intact beyond the lifetime of the cluster. The properties of these binaries are similar to those of the observed binary systems containing extrasolar planets. Thus, dynamical processes in young stellar clusters will alter significantly any population of Solar System-like planetary systems. In addition, beginning with a population of planetary systems exactly resembling the Solar System around single stars, dynamical encounters in young stellar clusters may produce at least some of the extrasolar planetary systems observed in the solar neighbourhood. 相似文献
72.
Roland Walter 《Astrophysics and Space Science》2007,309(1-4):5-9
INTEGRAL is operational since more than three years and producing high quality data that allows to detect fainter new hard
X-ray sources. The new sources, identified until now, are mostly active galactic nuclei and absorbed or transient high mass
X-ray binaries. TeV emission could be expected from the new high mass X-ray binaries accreting dense clumps of stellar wind.
INTEGRAL sources with TeV counterparts are discussed.
Based on observations with INTEGRAL, an ESA project with instruments and science data centre funded by ESA member states (especially
the PI countries: Denmark, France, Germany, Italy, Switzerland, Spain), Czech Republic and Poland, and with the participation
of Russia and the USA. 相似文献
73.
74.
75.
G. S. Dubey U. S. Pandey J. P. Singh L. K. Singh S. N. Singh 《Journal of Astrophysics and Astronomy》1990,11(1):23-28
The equation governing the equilibrium of a centrally-symmetric, self-gravitating distribution of matter is obtained by assuming
that matter is described by magnetofluid and it is shown that the equation of stellar structure described by an ideal fluid
is recovered when magnetic fieldh is vanishing 相似文献
76.
77.
R.F.G. Wyse 《Astronomische Nachrichten》2010,331(5):526-534
The kinematics and elemental abundances of resolved stars in the nearby Universe can be used to infer conditions at high redshift, trace how galaxies evolve and constrain the nature of dark matter. This approach is complementary to direct study of systems at high redshift, but I will show that analysis of individual stars allows one to break degeneracies, such as between star formation rate and stellar Initial Mass Function, that complicate the analysis of unresolved, distant galaxies (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
78.
J.R. Donnison 《Planetary and Space Science》2010,58(10):1169-1179
The dynamical stability of a bound triple system composed of a small binary or minor planetary system moving on a orbit inclined to a central third body is discussed in terms of Hill stability for the full three-body problem. The situation arises in the determination of stability of triple star systems against disruption and component exchange and the determination of stability of extrasolar planetary systems and minor planetary systems against disruption, component exchange or capture. The Hill stability criterion is applied to triple star systems and extrasolar planetary systems, the Sun-Earth-Moon system and Kuiper Belt binary systems to determine the critical distances for stable orbits. It is found that increasing the inclination of the third body decreases the Hill regions of stability. Increasing the eccentricity of the binary also produces similar effects.These type of changes make exchange or disruption of the component masses more likely. Increasing the eccentricity of the binary orbit relative to the third body substantially decreases stability regions as the eccentricity reaches higher values. The Kuiper Belt binaries were found to be stable if they move on circular orbits. Taking into account the eccentricity, it is less clear that all the systems are stable. 相似文献
79.
Abdel-Fattah Attia H. A. Ismail I. M. Selim A. M. Osman I. A. Isaa M. A. Marie A. A. Shaker 《中国天文和天体物理学报》2005,5(4):347-355
We present a new method for determining the age and relative contribution of different stellar populations in galaxies based on the genetic algorithm. We apply this method to the barred spiral galaxy NGC 3384, using CCD images in U, B, V, R and I bands. This analysis indicates that the galaxy NGC 3384 is mainly inhabited by old stellar population (age >109yr). Some problems were encountered when numerical simulations are used for determining the contribution of different stellar populations in the integrated color of a galaxy. The results show that the proposed genetic algorithm can search efficiently through the very large space of the possible ages. 相似文献
80.
Christopher M. Wright 《Astrophysics and Space Science》2007,311(1-3):47-55
The position angle of mid-infrared polarisation can be directly related to the magnetic field direction projected onto the
plane of the sky. Such observations, from both ground and space-based platforms, have been used to investigate the relation
between the magnetic field and other “symmetry axes” associated with embedded young stars, such as the interstellar magnetic
field, bipolar outflow and disk/toroid axes. Interpretation of the results in terms of hydromagnetic driving mechanisms of
bipolar outflow is discussed. 相似文献