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51.
52.
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??????С????????????????????????????????????????????????????????????????????????????·?????????????????????????????????С?????????????????????GPS???????????????????????????????÷??????????? 相似文献
53.
G. Tsiropoula K. Tziotziou T. Wiegelmann Th. Zachariadis C. Gontikakis H. Dara 《Solar physics》2007,240(1):37-48
The temporal variation of a loop system that appears to be changing rapidly is examined. The analyzed data were obtained on 15 May 1999, with the Transition Region and Coronal Explorer (TRACE) during an observing campaign and consist of observations in the Fe ix/Fe x 171?Å and Fe xii 195?Å passbands taken at a cadence of ~10 min. The special interest in this loop system is that it looks like one expanding loop; however, careful examination reveals that the loop consists of several strands and that new loop strands become visible successively at higher altitudes and lower loop strands fade out during the one hour of our observations. These strands have different widths, densities, and temperatures and are most probably consisting of, at least, a few unresolved thinner threads. Several geometric and physical parameters are derived for two of the strands and an effort is made to determine their 3D structure based on the extrapolation of the magnetic field lines. Electron density estimates allow us to derive radiative and conductive cooling times and to conclude that these loop strands are cooling by radiation. 相似文献
54.
Yu. G. Kopylova A. V. Melnikov A. V. Stepanov Yu. T. Tsap T. B. Goldvarg 《Astronomy Letters》2007,33(10):706-713
The dispersion properties of the sausage eigenmodes of oscillations in a thin magnetic flux tube are numerically analyzed in terms of ideal magnetohydrodynamics (MHD). The period of the modes accompanied by the emission of MHD waves into the surrounding medium, which leads to acoustic damping of oscillations, is determined by the radius of the tube, not by its length. The dissipation of the sausage oscillations in comparatively high (?0.7R ⊙) and tenuous (?6 × 108 cm?3) coronal loops is considered. Their Q factor has bound found to be determined by the acoustic damping mechanism. The ratio of the plasma densities outside and inside the loop and the characteristic height of the emission source have been estimated by assuming the quasi-periodic pulsations of meter-wavelength radio emission to be related to the sausage oscillations. 相似文献
55.
O. V. Terekhov A. V. Shevchenko A. G. Kuz’min S. Yu. Sazonov R. A. Sunyaev N. Lund 《Astronomy Letters》2002,28(6):397-400
A quasi-periodic component was found at the maximum of the X-ray light curve for the June 10, 1990 solar flare detected by the Granat observatory. The pulsation period was 143.2±0.8 s. The intensity of the pulsing component is not constant; the maximum amplitude of the pulsations is ~5% of the total flare intensity. An analysis of the data showed the characteristic size of the magnetic loop responsible for these pulsations to be ~(1–3)×1010 cm. 相似文献
56.
日冕加热是太阳物理中一个基本问题。随着一批高性能仪器(如TRACE、SOHO、Yohkoh)投入观测,作为太阳日冕中一种基本结构的冕环,其观测资料日益丰富。冕环加热是日冕加热的一个重要组成部分,越来越得到人们的重视。在简要介绍冕环最新观测和研究进展后,以其一维模型为基础,着重讨论了现有冕环加热结构和加热机制的研究进展。 相似文献
57.
Dejan Urošević 《Astrophysics and Space Science》2003,283(1):75-86
This paper represents the updated empirical Galactic andextragalactic Σ-D relations (relations between the surface brightness Σ and the diameter D) for supernova remnants(SNRs), with checking the connection of the main Galactic radio loops (Loop I, II, III and IV) with
these relations. We present results which suggest, once again, that the radio loops may have an SNR origin. The updated relations
for old SNRs have been measured to have slopes, β ≈ 2 in log-log space. The best Σ-D relations for M31 and M33 galaxies were derived and these relations are shown to be flatter (β ≲2) than those for Galactic
SNRs alone. A Σ-D relation with168 reliable calibrators (both Galactic and extragalactic) is derived.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
58.
主要介绍恒星光干涉仪实验系统的定天镜伺服驱动原理.采用电细分和逐级升、降速的方法来减小定天镜在转动时的振动,提高定位、跟踪精度.由于应用了400的电细分和1000倍的传速比,步进电机的步距角达到0.00648°. 相似文献
59.
We discuss the possible contribution of the thermal cyclotron radiation from hot coronal magnetic loops to the observed characteristics of the microwave emission from solar active regions. Based on the simplest three-dimensional model of a loop in the shape of a hot torus, we have calculated the expected peculiarities of the frequency and polarization structures of microwave emission sources associated with sunspots and containing coronal loops. Our model calculations of the two-dimensional brightness temperature distributions at various wavelengths for the ordinary and extraordinary modes and the wavelength dependences of the brightness temperatures are presented in the first part of the work. The loop size, the electron density, and the source position on the disk have been found to affect these characteristics. Our numerical calculations of the brightness temperature distributions and spectra have confirmed the well-known assumption that under certain conditions the spectrum of a hot filament can contain cyclotron lines and the sense of the polarization can change over the range. The results obtained here refer to the brightness temperature along the line of sight that crosses the photosphere at a point with given coordinates, i.e., these are the emission characteristics at a fixed point of the source. Integrated characteristics (the flux from the entire source and its polarization) and a discussion of the hot loop model will be given in the second part of the work. 相似文献
60.
We use an innovative research technique to analyze combined images from the Coronal Diagnostic Spectrometer (CDS) on the Solar and Heliospheric Observatory (SOHO) and the Transition Region and Coronal Explorer (TRACE). We produce a high spatial and temporal resolution simulated CDS raster or “composite” map from TRACE data and use
this composite map to jointly analyze data from both instruments. We show some of the advantages of using the “composite”
map method for coronal loop studies. We investigate two postflare loop structures. We find cool material (250 000 K) concentrated
at the tips or apex of the loops. This material is found to be above its scale height and therefore not in hydrostatic equilibrium.
The exposure times of the composite map and TRACE images are used to give an estimate of another loop’s cooling time. The
contribution to the emission in the TRACE images for the spectral lines present in its narrow passband is estimated by using
the CDS spectral data and CHIANTI to derive synthetic spectra. We obtain cospatial and cotemporal data collected by both instruments
in SOHO Joint Observations Program (JOP) 146 and show how the combination of these data can be utilized to obtain more accurate
measurements of coronal plasmas than if analyzed individually.
Electronic Supplementary Material The online version of this article () contains supplementary material, which is available to authorized users. 相似文献