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Alessandro Marconi Roberto Maiolino Romain G. Petrov 《Astrophysics and Space Science》2003,286(1-2):245-254
Interferometry in the optical and near infrared has so far played a marginal role in Extragalactic Astronomy. Active Galactic
Nuclei are the brightest and most compact extragalactic sources, nonetheless only a very limited number could be studied with
speckle interferometry and none with long baseline interferometry. The VLTI will allow the study of moderately faint extragalactic
objects with very high spatial resolution thus opening a new window on the universe. With this paper we focus on three scientific
cases to show how AMBER and MIDI can be used to tackle open issues in extragalactic astronomy.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
53.
Described here is a preliminary and tentative application of a method for fine-classification of stars, selected for studies
of galactic structure. The present investigation is based on about 100 stars within the approximate spectral type range B6-A5,
for which both spectra andUBV photometry have been obtained.
The motivation of the project is the following: For the study of galactic fine-structure it is essential to use as many members
as possible of stellar agglomerations of various type for a statistical treatment of the material. A-type stars are fairly
numerous and reasonably bright, but if all chemically peculiar stars, fast rotators or multiple systems have to be omitted
there is generally too little left for a relevant investigation. Here we perform some experiments in order to find a method
for fine-classification of A stars, both normal and chemically peculiar, within the framework of the M K system.
In this connection it is desirable to reduce the present multitude of CP classifications to a manageable number. It is shown
here that, independenttly of the definition of the degree of peculiarity, there is no sharp borderline separating the CP stars
from the ‘normal’ ones.
Also it is found that spectral classification can on an average be performed with almost the same accuracy for CP stars as
for the ‘normal’ ones provided cases of extreme peculiarity are avoided.
Based on observations collected at European Southern Observatory, La Silla, Chile. 相似文献
54.
M. Dotti M. Ruszkowski L. Paredi M. Colpi M. Volonteri F. Haardt 《Monthly notices of the Royal Astronomical Society》2009,396(3):1640-1646
We study the orbital evolution and accretion history of massive black hole (MBH) pairs in rotationally supported circumnuclear discs up to the point where MBHs form binary systems. Our simulations have high resolution in mass and space which, for the first time, makes it feasible to follow the orbital decay of a MBH either counter- or corotating with respect to the circumnuclear disc. We show that a moving MBH on an initially counter-rotating orbit experiences an 'orbital angular momentum flip' due to the gas-dynamical friction, i.e. it starts to corotate with the disc before a MBH binary forms. We stress that this effect can only be captured in very high resolution simulations. Given the extremely large number of gas particles used, the dynamical range is sufficiently large to resolve the Bondi–Hoyle–Lyttleton radii of individual MBHs. As a consequence, we are able to link the accretion processes to the orbital evolution of the MBH pairs. We predict that the accretion rate is significantly suppressed and extremely variable when the MBH is moving on a retrograde orbit. It is only after the orbital angular momentum flip has taken place that the secondary rapidly 'lights up' at which point both MBHs can accrete near the Eddington rate for a few Myr. The separation of the double nucleus is expected to be around ≲10 pc at this stage. We show that the accretion rate can be highly variable also when the MBH is corotating with the disc (albeit to a lesser extent) provided that its orbit is eccentric. Our results have significant consequences for the expected number of observable double active galactic nuclei at separations of ≲100 pc. 相似文献
55.
Yuping Tang Q.-S. Gu J.-S. Huang Y.-P. Wang 《Monthly notices of the Royal Astronomical Society》2009,397(4):1966-1975
We present the Spitzer Space Telescope Infrared Array Camera observations for a sample of local elliptical galaxies to study later stages of active galactic nucleus (AGN) activity. A sample of 36 elliptical galaxies is selected from the Palomar spectroscopic survey. We detect nuclear non-stellar infrared emission in nine of them. There is unambiguous evidence of circumnuclear dust in these nine galaxies in their optical images. We also find a remarkable correlation between the infrared excess emission and the nuclear radio/X-ray emission, suggesting that infrared excess emission is tightly related to nuclear activity. The possible origin of infrared excess emission from hot dust heated by the central AGN is supported by the spectral indices of the infrared excess emission. 相似文献
56.
We present a method to infer small-scale flatfields for imaging solar instruments using only regular-observation intensity
images with a fixed field of view. The method is related to the flatfielding method developed by Kuhn, Lin, and Loranz (Publ. Astron. Soc. Pac. 103, 1097 – 1108, 1991), but does not require image offsets. Instead, it takes advantage of the fact that the solar image is changing in the CCD
reference frame due to solar rotation. We apply the method to data sets of MDI filtergrams and compare the results to flat
fields derived with other methods. Finally, we discuss the planned implementation of this method in the data processing for
Helioseismic and Magnetic Imager on the Solar Dynamics Observatory. 相似文献
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