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991.
D.P. Ruffle T.W. Hartquist P. Caselli J.M.C. Rawlings D.A. Williams 《Astrophysics and Space Science》1998,262(2):177-185
We have investigated the dependences of the fractional abundances of a number of species on the selective depletions of elemental carbon, nitrogen, oxygen and sulphur, as well as metals. Of the most commonly observed species, HCO+ is the one having the fractional abundance that is least sensitive to the selective elemental depletions and for this reason is a particularly appropriate species to study in efforts to diagnose collapse dynamics in star formation from the analysis of infall signatures in spectral line profiles. We suggest that a combination of molecules could be the focus of observations aimed at the investigation of collapse dynamics. Comparisons of the profiles of spectral features of these species would also give insight into the behaviours of the selective depletions of the different elements in the infalling gas. 相似文献
992.
Marc Elmouttie Bärbel Koribalski Scott Gordon Keith Taylor Sally Houghton Tracy Lavezzi Raymond Haynes & Keith Jones 《Monthly notices of the Royal Astronomical Society》1998,297(1):49-68
The TAURUS-2 Fabry–Perot interferometer, mounted on the 3.9-m Anglo-Australian Telescope, has been used to observe the Circinus galaxy. We have mapped the intensity and velocity distribution of the ionized hydrogen in the galaxy using the Balmer series Hα spectral line.
The semiresolved core (observed with a seeing disc of 30 pc) appears amorphous in shape, which is commonly observed in Seyfert 2 galaxies. Its peak coincides with the core position measured in the radio continuum, suggesting that ionized gas surrounds a non-thermal source.
A circumnuclear ring or spiral of radius 220 pc and a rotational velocity of 350 km s−1 (assuming circular motions) surrounds the core. The inclination angle of this feature, i =40°±10°, is less than that of the previously observed radio continuum disc. The velocity channel maps obtained for the Hα ring show that the kinematics resemble those of a rotating ring and the intensity displays a complex structure indicative of several, unresolved, H II regions. We believe the ring to represent a circumnuclear starburst.
Our Hα data also show the presence of the previously detected [O III ] ionization cone to the north-west of the core, measuring more than 400 pc in length. We suggest that the ionization cone lies in a different plane from that of the starburst ring and is directed away from us. Several kinematic components of the core are derived and we calculate an outflow velocity in excess of 150–200 km s−1 for gas above the core of Circinus. We also present evidence for inflowing ionized gas at the centre of Circinus.
The correlation of the Hα and radio continuum features is discussed, as well as the possible presence of a starburst-driven superwind in the Circinus galaxy. 相似文献
The semiresolved core (observed with a seeing disc of 30 pc) appears amorphous in shape, which is commonly observed in Seyfert 2 galaxies. Its peak coincides with the core position measured in the radio continuum, suggesting that ionized gas surrounds a non-thermal source.
A circumnuclear ring or spiral of radius 220 pc and a rotational velocity of 350 km s
Our Hα data also show the presence of the previously detected [O III ] ionization cone to the north-west of the core, measuring more than 400 pc in length. We suggest that the ionization cone lies in a different plane from that of the starburst ring and is directed away from us. Several kinematic components of the core are derived and we calculate an outflow velocity in excess of 150–200 km s
The correlation of the Hα and radio continuum features is discussed, as well as the possible presence of a starburst-driven superwind in the Circinus galaxy. 相似文献
993.
D. J. Saikia G. F. Holmes A. R. Kulkarni C. J. Salter & S. T. Garrington 《Monthly notices of the Royal Astronomical Society》1998,298(3):877-887
We present total-intensity and linear-polarization observations at a single epoch for a sample of 11 quasars and one BL Lac object. The data were taken with the VLA A array at λλ 20, 18, 6 and 2 cm. We examine the variation of the degree of polarization, p , and polarization position angle, PA, with wavelength, and attempt to determine the rotation measure, RM, of the cores in these sources. The degree of polarization does not exhibit any systematic variation with wavelength, the median values ranging from 2.3 to 3.5 per cent at the different wavelengths. The variation of PA with λ2 is not linear over the entire wavelength range. However, for most sources the λλ 20-, 18- and 6-cm PAs do follow such a linear relationship, yielding a median |RM| of about 15 rad m−2 . In contrast, the λλ 6- and 2-cm observations give a median |RM| of about 129 rad m−2 . The long-wavelength emission is likely to originate from a spatially different part of the milliarcsec-scale jet from the λ 2-cm emission, which could turn over at a higher frequency and is likely to be more compact and located closer to the quasar nucleus. We have attempted to obtain linear fits over the entire wavelength range allowing for n π ambiguities in the PAs, but the fits are not statistically significant. The low values of RM for these core-dominated sources suggest that either the radio emission from the jet intercepts few of the emission-line clouds and their confining medium, or the clouds have a small filling factor and are possibly magnetically confined. 相似文献
994.
C. M. Sykes I. W. A. Browne N. J. Jackson D. R. Marlow S. Nair P. N. Wilkinson R. D. Blandford J. Cohen C. D. Fassnacht D. Hogg T. J. Pearson A. C. S. Readhead D. S. Womble S. T. Myers A. G. de Bruyn M. Bremer G. K. Miley & R. T. Schilizzi 《Monthly notices of the Royal Astronomical Society》1998,301(2):310-314
We report the discovery of the most complex arcsec-scale radio gravitational lens system yet known. B1933+503 was found during the course of the CLASS survey and MERLIN and VLA radio maps reveal up to 10 components. Four of these are compact and have flat spectra; the rest are more extended and have steep spectra. The background lensed object appears to consist of a flat-spectrum core (quadruply imaged) and two compact 'lobes' symmetrically disposed relative to the core. One of the lobes is quadruply imaged while the other is doubly imaged. An HST observation of the system with the WFPC2 shows a galaxy with an axial ratio of 0.5, but none of the images of the background object is detected. A redshift of 0.755 has been measured for the lens galaxy. 相似文献
995.
996.
S. Ferraz-Mello D. Nesvorný T.A. Michtchenko 《Celestial Mechanics and Dynamical Astronomy》1997,69(1-2):171-185
The lack of asteroids in the 2/1-resonance is explained by the global stochasticity of the solutions in the Sun-Jupiter-Saturn-asteroid
model. The explanation is based on data obtained with Laskar's frequency map analysis and on simulations showing the decisive
influence of Jupiter's orbit perturbations related to the "Great Inequality".
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
997.
998.
999.
1000.
1200 strongly flattened galaxies with axis ratio b/a ≤ 0.15 were selected from the UGC catalogue, contained in the Abadumani
Merged Catalogue of Galaxies, and their properties were studied. The possibility of using strongly flattened galaxies and
several other samples of galaxies according to their morphological type as a distance indicator has been examined by the Tully-Fisher
relation. The investigation has shown that angular diameters of strongly flattened as well as flat, seen edge-on galaxies
designated as F and L in the MCG catalogue can be used for the estimation of distance moduli with accuracy O.m7. The distribution of absolute magnitudes of strongly flattened galaxies was approximated by analytic Schechter expression
with main parameters M* = -21.m2 and α = -1.0. The statistical method of the nearest companion applied to the apparent distribution of strongly flattened
galaxies has shown that these galaxies are considerably more frequently found in mixed pairs and multiple systems than spirals.
Published in Astrofizika, Vol. 41, No. 1, pp. 23–34, January-March, 1998. 相似文献