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121.
Jin-LinHan RichardWielebinski 《中国天文和天体物理学报》2002,2(4):293-294
Magnetic fields are observed everywhere in the universe. In this review, we concentrate on the observational aspects of the magnetic fields of Galactic and extragalactic objects. Readers can follow the milestones in the observations of cosmic magnetic fields obtained from the most important tracers of magnetic fields, namely, the star-light polarization, the Zeeman effect, the rotation measures (RMs, hereafter) of extragalactic radio sources, the pulsar RMs, radio polarization observations, as well as the newly implemented sub-mm and mm polarization capabilities. The magnetic field of the Galaxy was first discovered in 1949 by optical polarization observations. The local magnetic fields within one or two kpc have been well delineated by starlight polarization data. The polarization observations of diffuse Galactic radio background emission in 1962 confirmed unequivocally the existence of a Galactic magnetic field. The bulk of the present information about the magnetic fields in the Galaxy comes from anal 相似文献
122.
This review begins with a discussion of the techniques needed for observations of scattered light from cometary dust. After
an introduction into the basic concepts of the scattering process, observations of the phase curves of brightness, colour
and polarization are covered. Images of colour and polarization are presented and the observed relation of colour and polarization
in jets and shells is discussed. The interpretation of the measurements is based on the power law size distributions of dust
grains observed from space. The power index must lie between 2 and 4 to provide the mass budget and visibility of the dust
coma in accordance with the basic facts of cometary physics. Application of mechanical (radiation pressure) theory to cometary
images allows us to derive related power law distributions for comets not explored by spacecraft. Grain scattering models
are presented and compared with observations. A prediction is made of the spatial distribution of Stokes parameters U and
V in the presence of aligned particles. Up to now such patterns have not been observed. Future work should include the exploration
of comets at small and possibly very small phase angles and a detailed comparison of polarization and colour images of comets
with thermal images and with models based on mechanical theory.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
123.
Harris W. M. Nordsieck K. H. Scherb F. Mierkiewicz E. J. 《Earth, Moon, and Planets》1997,78(1-3):161-167
We report on the reduction and analysis of UVpolarimetric images of CI (λ1657 Å) and dust continuum (2696 Å emissions from C/1995 O1 (Hale-Bopp) taken using the Wide Field Imaging Survey Polarimeter (WISP) sounding rocket on 8 April, 1997. These observations represent the first imaging polarimetry of comets in the UV, and were performed in consort with ground based measurements of gas and dust polarization and distribution. The continuum results show 9% polarization across the image field with a polarization phase angle close to the 129° prediction. Comparison with ground based data implies minimal color dependence for Hale-Bopp in either the degree of polarization and in the position angle. The carbon polarimetry implies that most production occurs in the dense inner coma, and that it leaves that area in thermodynamic equilibrium. Its radial profile further constrains the carbon outflow speed to be sufficient to travel ≥5 × 106 km without photoionization. 相似文献
124.
M. Shimon Y. Rephaeli B. W. O'Shea M. L. Norman 《Monthly notices of the Royal Astronomical Society》2006,368(2):511-511
Scattering of the cosmic microwave background (CMB) in clusters of galaxies polarizes the radiation. We explore several polarization components which have their origin in the kinematic quadrupole moments induced by the motion of the scattering electrons, either directed or random. Polarization levels and patterns are determined in a cluster simulated by the hydrodynamical enzo code. We find that polarization signals can be as high as ∼1 μK , a level that may be detectable by upcoming CMB experiments. 相似文献
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We explore the detailed polarization behaviour of pulsar 0823 + 26 using the technique of constructing partial ‘mode-separated’
profiles corresponding to the primary and secondary polarization modes. The characteristics of the two polarization modes
in this pulsar are particularly interesting, both because they are anything but orthogonal and because the secondary mode
exhibits a structure seen neither in the primary mode nor in the total profile. The new leading and trailing features in the
secondary mode, which appear to represent a conal component pair, are interpreted geometrically on the basis of their width
and the associated polarization-angle traverse as an outer cone.
If the secondary-mode features are, indeed, an outer cone, then questions about the significance of the pulsar’s postcursor
component become more pressing. It seems that 0823 + 26 has a very nearly equatorial geometry, in that both magnetic poles
and the sightline all fall close to the rotational equator of the star. We thus associate the postcursor component with emission
along those bundles of field lines which are also equatorial and which continue to have a tangent in the direction of our
sight line for a significant portion of the star’s rotation cycle. It seems that in all pulsars with postcursor components,
this emission follows the core component, and all may thus have equatorial emission geometries. No pulsars with precursors
in this sense — including the Crab pulsar — are known.
The distribution of power between the primary and secondary modes is very similar at both 430 and 1400 MHz. Our analysis shows
that in this pulsar considerable depolarization must be occurring on time scales that are short compared to the time resolution
of our observations, which is here some 0.5–1.0 milliseconds. One of the most interesting features of the modeseparated partial
profiles is a phase offset between the primary and secondary modes. The secondary-mode ‘main pulse’ arrives some 1.5 ± 0.1‡
before the primary-mode one at 430 MHz and some 1.3 +0.1 ‡ at 21 cm. Given that the polar cap has an angular diameter of 3.36‡,
we consider whether this is a geometric effect or an effect of differential propagation of the two modes in the inner magnetosphere
of the pulsar. 相似文献