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51.
52.
Hao Tong Qiu-He Peng 《天体物理学报》2007,7(6):809-813
According to recent observational and theoretical progresses, the DUrca process (direct Urca process) may be excluded from the category of neutron star cooling mechanisms. This result, combined with the latest nuclear symmetry energy experiments, will provide us an independent way of testing the EOS (equation of state) for supernuclear density. For example, soft EOSs, such as FPS, will probably be excluded. 相似文献
53.
Axel D. Schwope Valeri Hambaryan Frank Haberl Christian Motch 《Astrophysics and Space Science》2007,308(1-4):619-623
We present a first analysis of a deep X-ray spectrum of the isolated neutron star RBS1223 obtained with XMM-Newton. Spectral
data from four new monitoring observations in 2005/2006 were combined with archival observations obtained in 2003 and 2004
to form a spin-phase averaged spectrum containing 290 000 EPIC-pn photons. This spectrum shows higher complexity than its
predecessors, and can be parameterised with two Gaussian absorption lines superimposed on a blackbody. The line centers, E
2≃2E
1, could be regarded as supporting the cyclotron interpretation of the absorption features in a field B∼4×1013 G. The flux ratio of those lines does not support this interpretation. Hence, either feature might be of truly atomic origin.
相似文献
54.
R. Cornelisse R. Wijnands J. Homan 《Monthly notices of the Royal Astronomical Society》2007,380(4):1637-1641
We observed the neutron star X-ray transient 2S 1803−245 in quiescence with the X-ray satellite XMM–Newton , but did not detect it. An analysis of the X-ray bursts observed during the 1998 outburst of 2S 1803−245 gives an upper limit to the distance of ≤7.3 kpc, leading to an upper limit on the quiescent 0.5–10 keV X-ray luminosity of ≤2.8 × 1032 erg s−1 (3σ). Since the expected orbital period of 2S 1803−245 is several hours, this limit is not much higher than those observed for the quiescent black hole transients with similar orbital periods. 相似文献
55.
The Ginzburg-Landau equations are derived for the magnetic and gluomagnetic gauge fields in the color superconducting core
of a neutron star containing a CFL-condensate of diquarks. The interaction of the diquark CFL-condensate with the magnetic
and gluomagnetic gauge fields is taken into account. The behavior of the magnetic field in a neutron star is studied by solving
the Ginzburg-Landau equations taking correct account of the boundary conditions, including the gluon confinement conditions.
The magnetic field distribution in the quark and hadronic phases of a neutron star is found. It is shown that a magnetic field
generated in the hadronic phase by the entrainment effect penetrates into the quark core in the form of quark vortex filaments
because of the presence of screening Meissner currents.
__________
Translated from Astrofizika, Vol. 50, No. 1, pp. 87–98 (February 2007). 相似文献
56.
Wynn C. G. Ho 《Monthly notices of the Royal Astronomical Society》2007,380(1):71-77
RX J1856.5−3754 is one of the brightest, nearby isolated neutron stars (NSs), and considerable observational resources have been devoted to its study. In previous work, we found that our latest models of a magnetic, hydrogen atmosphere match well the entire spectrum, from X-rays to optical (with best-fitting NS radius R ≈ 14 km, gravitational redshift z g ∼ 0.2 , and magnetic field B ≈ 4 × 1012 G). A remaining puzzle is the non-detection of rotational modulation of the X-ray emission, despite extensive searches. The situation changed recently with XMM–Newton observations that uncovered 7-s pulsations at the level. By comparing the predictions of our model (which includes simple dipolar-like surface distributions of magnetic field and temperature) with the observed brightness variations, we are able to constrain the geometry of RX J1856.5−3754, with one angle <6° and the other angle , though the solutions are not definitive, given the observational and model uncertainties. These angles indicate a close alignment between the rotation and the magnetic axes or between the rotation axis and the observer. We discuss our results in the context of RX J1856.5−3754 being a normal radio pulsar and a candidate for observation by future X-ray polarization missions such as Constellation-X or XEUS . 相似文献
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In many magnetized, dilute astrophysical plasmas, thermal conduction occurs almost exclusively parallel to magnetic field
lines. In this case, the usual stability criterion for convective stability, the Schwarzschild criterion, which depends on
entropy gradients, is modified. In the magnetized long mean free path regime, instability occurs for small wavenumbers when
(∂ P/∂z) (∂ ln T/∂ z) > 0, which we refer to as the Balbus criterion. We refer to the convective-type instability that results
as the magnetothermal instability (MTI). We use the equations of MHD with anisotropic electron heat conduction to numerically
simulate the linear growth and nonlinear saturation of the MTI in plane-parallel atmospheres that are unstable according to
the Balbus criterion. The linear growth rates measured from the simulations are in excellent agreement with the weak field
dispersion relation. The addition of isotropic conduction, e.g. radiation, or strong magnetic fields can damp the growth of
the MTI and affect the nonlinear regime. The instability saturates when the atmosphere becomes isothermal as the source of
free energy is exhausted. By maintaining a fixed temperature difference between the top and bottom boundaries of the simulation
domain, sustained convective turbulence can be driven. MTI-stable layers introduced by isotropic conduction are used to prevent
the formation of unresolved, thermal boundary layers. We find that the largest component of the time-averaged heat flux is
due to advective motions as opposed to the actual thermal conduction itself. Finally, we explore the implications of this
instability for a variety of astrophysical systems, such as neutron stars, the hot intracluster medium of galaxy clusters,
and the structure of radiatively inefficient accretion flows.
J. M. Stone: Program in Applied and Computational Mathematics, Princeton University, Princeton, NJ 08544 相似文献