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111.
Individual X-ray photons in the keV energy range produce hundreds of photoelectrons in a single pixel of a CCD array detector.
The number of photoelectrons produced is a linear function of the photon energy, allowing the measurement of spectral information
with an imaging detector system. Most solar X-ray telescopes, such as Yohkoh/SXT and Hinode/XRT, use CCD detectors in an integrating mode and are designed to make temperature estimates from multiband filter photometry.
We show how such instruments can be used in a new way to perform a limited type of this photon spectroscopy. By measuring
the variance in intensity of a series of repeated images through a single filter of an X-ray source, the mean energy per detected
photon can be determined. This energy is related to the underlying coronal spectrum, and hence it can be used to deduce the
mean plasma temperature. We apply this technique to data from the Yohkoh Soft X-Ray Telescope and compare the temperatures obtained with this technique with the temperatures derived using the standard
filter ratio method for a postflare loop system. Given the large dynamic range of the soft X-ray flux observed from the Sun,
we describe the requirements for a future instrument that would be better suited to performing photon spectroscopy.
B.J. Labonte deceased 24 October 2005. 相似文献
112.
TeV Gamma Rays From the Galactic Center Direct and Indirect Links to the Massive Black Hole in Sgr A
The recent detection of TeV gamma-radiation from the direction of the Galactic Center within several arc-minutes around Sgr
A* is the first model-independent evidence of existence of high-energy particle accelerator(s) in the central 10 pc region of
our Galaxy. This is an extraordinary site that harbours many remarkable objects with the compact radio source Sgr A* – a hypothetical super-massive black hole (SMBH) – in the dynamical center of the Galaxy. Here we explore the possible direct and indirect links of the reported TeV emission to the SMBH. We show that at least three γ-ray production scenarios that take place close
to the event horizon of the SMBH can explain the reported TeV fluxes. An alternative (or additional) channel of TeV radiation
is related to the run-away protons accelerated in Sgr A*. Quasi-continuous injection of relativistic protons into the surrounding dense gas environment initiates detectable high-energy
gamma-ray emission. The absolute flux and the energy spectrum of this radiation component strongly depend on the history of
particle injection and the character of diffusion of protons during the last 105 yr. For a reasonable combination of a few model parameters, one can explain the detected gamma-ray flux solely by this diffuse
component. 相似文献
113.
Near infrared coronal line emission at 1.98 ± 0.02Μm due to [Si VI] detected in the spectrum of Nova Herculis 1991 about 17
days after optical maximum is reported. The early appearance of coronal emission is yet another unusual feature of this fast
nova in which early onset of dust formation processes and X-ray detection five days after outburst have already been reported.
The coronal line observations reported here are consistent with X-ray detection and support a hot shocked circumstellar envelope
at the periphery of the dust formation zone in the nova. 相似文献
114.
Some observations indicate the presence of Doppler-shifted emission lines in the X-ray spectra of black hole candidates and
active galactic nuclei. Motivated by which, we studied the observed profile of emission lines from relativistic outflows around
black holes in great detail, but jets are simply treated as pencil beams. It was found that the observed line emission shows
a doubly peaked profile at large viewing angles for extreme Kerr black holes. In this work, we study the observed profile
of an emission line from a more realistic, cone-shaped jet, and we find that an intrinsically narrow line is basically singly
peaked, which is different from our previous results. Therefore, we conclude that the double peaks in our previous results
is due to the simplified assumption on the geometrical structure of jets. This finding emphasizes the difference between the
observed line profile in the jet case and those in the disc case in which there are generally double peaks in the observed
spectra. 相似文献
115.
Ya-Yuan Wen Jing-Xiu Wang Yu-Zong Zhang National Astronomical Observatories Chinese Academy of Sciences Beijing 《中国天文和天体物理学报》2007,7(2):265-280
Using Nancay Radioheliograph (NRH) imaging observations, combined with SOHO/Michelson Doppler Imager (MDI) magnetogram observations and coronal magnetic field extrapolation, we studied the magnetic nature of metric noise storms that are associated with coronal mass ejections (CMEs). Four events are selected: the events of 2000 July 14, 2001 April 26, 2002 August 16 and 2001 March 28. The identified noise storm sources cover or partially cover the active regions (ARs), but the centers of storm sources are offset from the ARs. Using extrapolated magnetic field lines, we find that the noise storm sources trace the boundary between the open and closed field lines. We demonstrate that the disappearance of noise storm source is followed by the appearance of the burst source. The burst sources spread on the solar disk and their distributions correspond to the extent of the CME in LASCO C2 field of view. All the SOHO/Extreme Ultraviolet Imaging Telescope (EIT) dimmings associ- ated with noise storm sources are located at the periphery of noise storms where the magnetic lines of force were previously closed and low-lying. When the closed field becomes partially or fully open, the basic configurations of noise storm sources are changed, then the noise storm sources are no longer observed. These observations provide the information that the variations of noise storms manifest the restructuring or reconfiguring of the coronal magnetic field. 相似文献
116.
The magnetic field in an accretion disk is estimated assuming that all of the angular momentum within prescribed accretion
disk radii is removed by a jet. The magnetic field estimated at the base of the jet is extrapolated to the blazar emission
region using a model for a relativistic axisymmetric jet combined with some simplifying assumptions based on the relativistic
nature of the flow. The extrapolated magnetic field is compared with estimates based upon the synchrotron and inverse Compton
emission from three blazars, MKN 501, MKN 421 and PKS 2155-304. The magnetic fields evaluated from pure synchrotron self-Compton
models are inconsistent with the magnetic fields extrapolated in this way. However, in two cases inverse Compton models in
which a substantial part of the soft photon field is generated locally agree well, mainly because these models imply magnetic
field strengths consistent with an important Poynting Flux component. This comparison is based on estimating the mass accretion
rate from the jet energy flux. Further comparisons along these lines will be facilitated by independent estimates of the mass
accretion rate in blazars and by more detailed models for jet propagation near the black hole. 相似文献
117.
In the present paper we report on the difference in angular sizes between radio-loud and radio-quiet CMEs. For this purpose
we compiled these two samples of events using Wind/WAVES and SOHO/LASCO observations obtained during 1996 – 2005. We show that the radio-loud CMEs are almost twice as wide
as the radio-quiet CMEs (considering expanding parts of CMEs). Furthermore, we show that the radio-quiet CMEs have a narrow
expanding bright part with a large extended diffusive structure. These results were obtained by measuring the CME widths in
three different ways. 相似文献
118.
We consider the cooling of neutron stars with superfluid cores composed of neutrons, protons, and electrons (for singlet proton pairing and triplet neutron pairing). The emphasis is on triplet neutron pairing with the component of the total moment of neutron pairs along the quantization axis |m J | = 2. This case stands out in that it leads to power-law rather than exponential suppression of the main neutrino processes by neutron superfluidity. For the chosen critical neutron temperatures T cn, the cooling with |m J | = 2 proceeds either almost in the same way as the commonly considered cooling with m J =0 or appreciably faster. The cooling with variable (over the core) critical temperatures T cn(ρ) and T cp(ρ) can generally be described by the cooling with some effective constant temperatures T cn and T cp. The hypothesis of strong neutron superfluidity with |m J | = 2 is in conflict with the observational data on the thermal radiation from isolated neutron stars; the hypothesis of weak neutron superfluidity of any type is consistent with the observations. 相似文献
119.
This paper reports on the first measurements of the color index of the coronal suprathermal streams. Observations performed during the total eclipse of 2001 in Angola imply that the color index of streams differs markedly from that for adjacent parts of the surrounding corona taken as reference. The registered drifts to the longwave and shortwave domains of the spectrum are in agreement with theoretical results obtained recently by the authors.Published in Astrofizika, Vol. 48, No. 1, pp. 79–85 (February 2005). 相似文献
120.
Based on an analogy between stellar and solar flares, we investigate the ten-second oscillations detected in the U and B bands on the star EV Lac. The emission pulsations are associated with fast magnetoacoustic oscillations in coronal loops. We have estimated the magnetic field, B ≈ 320 G; the temperature, T ≈ 3.7 × 107 K; and the plasma density, n ≈ 1.6 × 1011 cm?3, in the region of energy release. We provide evidence suggesting that the optical emission source is localized at the loop footpoints. 相似文献