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11.
12.
S. Benetti E. Cappellaro I. J. Danziger M. Turatto F. Patat & M. Della Valle 《Monthly notices of the Royal Astronomical Society》1998,294(3):448-456
Extensive photometric and spectroscopic observations of SN 1994aj until 540 d after maximum light have been obtained. The photometry around maximum suggests that the SN belongs to the Type II Linear class, with a peak absolute magnitude of M V ∼−17.8 (assuming H 0 =75 km s−1 Mpc−1 ). The spectra of SN 1994aj were unusual, with the presence of a narrow line with a P Cygni profile on top of the broad Balmer line emission. This narrow feature is attributed to the presence of a dense superwind surrounding the SN. At 100–120 d after maximum light the SN ejecta start to interact with this circumstellar material. The SN luminosity decline rates slowed down [γ R =0.46 mag (100 d)−1 ], becoming less steep than the average late luminosity decline of normal SN II [∼1 mag (100 d)−1 ]. This dense ( ˙M / u W ∼1015 g cm−1 ) wind was confined to a short distance from the progenitor ( R out =∼5×1016 cm), and results from a very strong mass-loss episode ( ˙M =10−3 M⊙ yr−1 ), which terminated shortly before explosion (∼5–10 yr). 相似文献
13.
Kohji Tomisaka 《Monthly notices of the Royal Astronomical Society》1998,298(3):797-810
The importance of the interstellar magnetic field is studied in relation to the evolution of superbubbles with a three-dimensional (3D) numerical magnetohydrodynamical (MHD) simulation. A superbubble is a large supernova remnant driven by sequential supernova explosions in an OB association. Its evolution is affected by the density stratification in the galactic disc. After the superbubble size reaches 2–3 times the density scaleheight, it expands preferentially in the z -direction, until finally it can punch out a hole in the gas disc (blowout). On the other hand, the magnetic field running parallel to the galactic disc has the effect of preventing it from expanding in the direction perpendicular to the field. The density stratification and the magnetic fields have completely opposite effects on the evolution of the superbubble. We present results of a 3D MHD simulation in which both effects are included. As a result, it is concluded that when the magnetic field has a much larger scaleheight than the density, even for a model in which the bubble would blow out from the disc if the magnetic field were absent, a magnetic field with a strength of 5 μG can confine the bubble in | z |≲300 pc for ≃ 20 Myr (confinement). In a model in which the field strength decreases in the halo as B ∝ ρ1/2 , the superbubble eventually blows out like a model with B = 0 even if the magnetic field in the mid-plane is as strong as B = 5 μG. 相似文献
14.
Recent advances in the understanding of the properties of supernova remnant shocks have been precipitated by theChandra and XMM X-ray Observatories, and the HESS Atmospheric Čerenkov Telescope in the TeV band. A critical problem for this field
is the understanding of the relative degree of dissipative heating/energization of electrons and ions in the shock layer.
This impacts the interpretation of X-ray observations, and moreover influences the efficiency of injection into the acceleration
process, which in turn feeds back into the thermal shock layer energetics and dynamics. This paper outlines the first stages
of our exploration of the role of charge separation potentials in non-relativistic electron-ion shocks where the inertial
gyro-scales are widely disparate, using results from a Monte Carlo simulation. Charge density spatial profiles were obtained
in the linear regime, sampling the inertial scales for both ions and electrons, for different magnetic field obliquities.
These were readily integrated to acquire electric field profiles in the absence of self-consistent, spatial readjustments
between the electrons and the ions. It was found that while diffusion plays little role in modulating the linear field structure
in highly oblique and perpendicular shocks, in quasi-parallel shocks, where charge separations induced by gyrations are small,
and shock-layer electric fields are predominantly generated on diffusive scales. 相似文献
15.
Neutrino energy spectra have been calculated based on the recently measured energy spectra of Galactic very high energy γ-ray
sources. Based on these neutrino spectra the expected event rates in the ANTARES neutrino telescope and KM3NeT, a future neutrino
telescope in the Mediterranean Sea with an instrumented volume of one km3, have been calculated. For the brightest γ-ray sources we find event rates of the order of one neutrino per year. Although
the neutrino event rates are comparable to the background from atmospheric neutrinos the detection of individual sources seems
possible. 相似文献
16.
We investigate a possibility that non-thermal X-ray emission in a supernova remnant(SNR) is produced by jitter radiation,
which is the analogue of synchrotron radiation in small-scale random magnetic fields. We can fit the multi-wavelength data
of SNRs RX J1713.7-3946 (G347.3-0.5) and RX J0852.0-4622 (G266.6-1.2) by constructing pure jitter and inverse Compton (IC)
emission models. We find that the physical fit parameters of random magnetic fields take values of several tens of μG strength
and of the order of ∼107 cm correlation length. These properties of random magnetic fields in collisionless shock of SNRs are discussed.
相似文献
17.
S. Nagataki 《Astrophysics and Space Science》2007,307(1-3):203-206
We have performed 2-dimensional MHD simulations of collapsars with magnetic fields and neutrino cooling/heating processes.
It is found that explosion energy of a hypernova is not obtained from the neutrino heating process. However, strong jet is
found when magnetic fields are included, and total energy of the jet component can be of the order of 1052 erg, which is comparable to the one of a hypernova. 相似文献
18.
19.
M. Stupar M. D. Filipović Q. A. Parker G. L. White T. G. Pannuti P. A. Jones 《Astrophysics and Space Science》2007,307(4):423-435
The Parkes–MIT–NRAO (PMN) radio survey has been used to generate a quasi all-sky study of Galactic Supernova Remnants (SNRs)
at a common frequency of 4.85 GHz (λ=6 cm). We present flux densities estimated for the sample of 110 Southern Galactic SNRs (up to δ=−65°) observed with the Parkes 64-m radio telescope and an additional sample of 54 from the Northern PMN (up to δ=+64°) survey undertaken with the Green Bank 43-m (20 SNRs) and 91-m (34 SNRs) radio telescopes. Out of this total sample
of 164 selected SNRs (representing 71% of the currently 231 known SNRs in the Green catalogue) we consider 138 to provide
reliable estimates of flux density and surface brightness distribution. This sub-sample represents those SNRs which fall within
carefully chosen selection criteria which minimises the effects of the known problems in establishing reliable fluxes from
the PMN survey data. Our selection criteria are based on a judicious restriction of source angular size and telescope beam
together with careful evaluation of fluxes on a case by case basis. Direct comparison of our new fluxes with independent literature
values gives excellent overall agreement. This gives confidence in the newly derived PMN fluxes when the selection criteria
are respected. We find a sharp drop off in the flux densities for Galactic SNRs beyond 4 Jy and then a fairly flat distribution
from 5 to 9 Jy, a slight decline and a further flat distribution from 9 to 20 Jy though the numbers of SNR in each Jy bin
are low. We also re-visit the contentious Σ–D (radio surface brightness–SNRs diameter) relation to determine a new power law index for a sub-sample of shell type SNRs
which yields β=−2.2±0.6. This new evaluation of the Σ–D relation, applied to the restricted sample, provides new distance estimates and their Galactic scale height distribution.
We find a peak in the SNR distribution between 7–11 kpc with most restricted to ±100 pc Galactic scale height. 相似文献
20.
Jian-Jun Zhou Xi-Zheng Zhang Hong-Bo Zhang Jarken Esimbek Ju-Yong Zhang Bing-Gang Ju 《中国天文和天体物理学报》2007,7(5):705-711
We made the first CO(I—0) mapping to SNR G21.8-0.6 and SNR G32.8-0.1, both associated with OH 1720 MHz maser.Based on the morphological correspondence and velocity and position agreement between the radio remnant and the CO clouds,we tentatively identify the clouds that are respectively interacting with the two SNRs. 相似文献