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Santabrata Das Sandip K. Chakrabarti 《Monthly notices of the Royal Astronomical Society》2008,389(1):371-378
We study the dynamical structure of a cooling dominated rotating accretion flow around a spinning black hole. We show that non-linear phenomena such as shock waves can be studied in terms of only three flow parameters, namely the specific energy , the specific angular momentum (λ) and the accretion rate of the flow. We present all possible accretion solutions. We find that a significant region of the parameter space in the plane allows global accretion shock solutions. The effective area of the parameter space for which the Rankine–Hugoniot shocks are possible is maximum when the flow is dissipation-free. It decreases with the increase of cooling effects and finally disappears when the cooling is high enough. We show that shock forms further away when the black hole is rotating compared to the solution around a Schwarzschild black hole with identical flow parameters at a large distance. However, in a normalized sense, the flow parameters for which the shocks form around the rotating black holes are produced shocks closer to the black hole. The location of the shock is also dictated by the cooling efficiency in that higher the accretion rate , the closer is the shock location. We believe that some of the high-frequency quasi-periodic oscillations may be due to the flows with higher accretion rate around the rotating black holes. 相似文献
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85.
David Moss 《地球物理与天体物理流体动力学》2013,107(2):195-203
The study of laminar flows with simple streamlines in conducting fluids that might support kinematic dynamo action has a long history. Early successful examples include the Gailitis (1970) dynamo, which has two meridional rolls. We show here that a single meridional roll, considered as a limit of a modified Gailitis-like dynamo, can also support kinematic dynamo action in a deep spherical shell. This flow has a claim to be the simplest such flow possible. 相似文献
86.
A. Panaitescu 《Monthly notices of the Royal Astronomical Society》2007,380(1):374-380
In the set of 236 gamma-ray burst (GRB) afterglows observed by Swift between 2005 January and 2007 March, we identify 30 X-ray light-curves that have power-law fall-offs that exhibit a steepening ('break') at 0.1–10 d after they are triggered, to a decay steeper than t −1.5 . For most of these afterglows, the X-ray spectral slope and the decay indices before and after the break can be accommodated by the standard jet model although a different origin of the breaks cannot be ruled out. In addition, there are 27 other afterglows which have X-ray light-curves that may also exhibit a late break to a steep decay, but the evidence is not that compelling. The X-ray emissions of 38 afterglows decay slower than t −1.5 until after 3 d, half of them exhibiting such a slow decay until after 10 d. Therefore, the fraction of well-monitored Swift afterglows with potential jet breaks is around 60 per cent, whether we count only the strongest cases for each type or all of them. This fraction is comparable to the 75 per cent of pre-Swift afterglows which have optical light-curves that displayed similar breaks at ∼1 d. The peak energy of the GRB spectrum of Swift afterglows with light-curve breaks shows the same correlations with the burst isotropic output (Amati relation) and with the burst collimated output (Ghirlanda relation) as previously found for pre- Swift optical afterglows with light-curve breaks. However, we find that the Ghirlanda relation is largely a consequence of Amati's and that the use of the jet-break time leads to a stronger Ghirlanda correlation only when the few objects that do not satisfy the Amati relation are included. 相似文献
87.
We investigate the linear stability of a shocked accretion flow on to a black hole in the adiabatic limit. Our linear analyses and numerical calculations show that, despite the post-shock deceleration, the shock is generally unstable to non-axisymmetric perturbations. The simulation results of Molteni, Tóth & Kuznetsov can be well explained by our linear eigenmodes. The mechanism of this instability is confirmed to be based on the cycle of acoustic waves between the corotation radius and the shock. We obtain an analytical formula to calculate the oscillation period from the physical parameters of the flow. We argue that the quasi-periodic oscillation should be a common phenomenon in accretion flows with angular momentum. 相似文献
88.
The MHD wave instabilities due to non-uniform magnetic field and non-homogeneity of density have been studied. The reference
(coordinate) system considered here is cylindrical type. The General Dispersion Relation (GDR) for the wave propagation in
a gravitating but non-relativistic region has been derived. Similar to common knowledge, the said non-uniformities have been
found to be responsible for the instability of the system. But interestingly many instability factors are produced due to
presence of two types of non-uniformities simultaneously. This theory may add more clues for the event of instabilities, formation
of hot plasma-bed in Galactic Central Region, and mass out-flow from there. Many conditions for instabilities could be obtained
from GDR deduced here. However, a few conditions for critical wavelength of the MHD wave have been obtained in terms of system
parameters (like gradient of magnetic field and rotation).
This theory, in turn, may be helpful for the better understanding of the Explosion Theory of formation of outer structure
of Galaxies like ours. 相似文献
89.
Gui-Ping Wu Guang-Li Huang Yu-Hua Tang Yu Dai Department of Physics Southeast University Nanjing Purple Mountain Observatory Chinese Academy of Sciences Nanjing Department of Astronomy Nanjing University Nanjing 《中国天文和天体物理学报》2007,7(1):141-147
1INTRODUCTIONEnrichment of3He and heavy ions(i.e.,Ne,Mg,Si and Fe),characteristic of impulsive?ares,have beenstudied for more than three decades.It is found that they are generally associated with nonthermal energeticelectron-rich events(Reames et al.1988;Reames1999and references therein;Ho et al.2001;Wang et al.2006)and are related to the peculiar ratio of charge to mass(Mazur et al.1996;Reames1999).Althoughthe abundance of3He ions is not correlated with the abundance of heavy ions,s… 相似文献
90.