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71.
J. P. McKean I. W. A. Browne N. J. Jackson L. V. E. Koopmans M. A. Norbury T. Treu † T. D. York A. D. Biggs R. D. Blandford A. G. de Bruyn C. D. Fassnacht S. Mao S. T. Myers T. J. Pearson P. M. Phillips A. C. S. Readhead D. Rusin P. N. Wilkinson 《Monthly notices of the Royal Astronomical Society》2005,356(3):1009-1016
We present observations of CLASS B2108+213, the widest separation gravitational lens system discovered by the Cosmic Lens All-Sky Survey. Radio imaging using the VLA at 8.46 GHz and MERLIN at 5 GHz shows two compact components separated by 4.56 arcsec with a faint third component in between which we believe is emission from a lensing galaxy. 5-GHz VLBA observations reveal milliarcsecond-scale structure in the two lensed images that is consistent with gravitational lensing. Optical emission from the two lensed images and two lensing galaxies within the Einstein radius is detected in Hubble Space Telescope imaging. Furthermore, an optical gravitational arc, associated with the strongest lensed component, has been detected. Surrounding the system is a number of faint galaxies which may help explain the wide image separation. A plausible mass distribution model for CLASS B2108+213 is also presented. 相似文献
72.
Mark Clampin Marco Sirianni George F. Hartig Holland C. Ford Garth D. Illingworth Bill Burmester William Koldewynd Andre R. Martel Adam Riess Ronald J. Schrein Pamela C. Sullivan 《Experimental Astronomy》2002,14(2):107-115
The Advanced Camera for Surveys (ACS), installed in the Hubble Space telescope in March 2002, will significantly extend HST's
deep, survey imaging capabilities. ACS has met, or exceeded, all of its key performance specifications. In this paper we briefly
review the in-flight performance of the instrument's CCD detectors and preview early ACS science observations.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
73.
John S. Myers 《Precambrian Research》1978,6(1):43-64
The development of finely layered gneisses by progressive deformation of a variety of granitoid intrusions, leucogabbroa, anorthosites, and basic and intermediate volcanic rocks is described and illustrated.Gneissose layering developed by the tectonic distortion of: magmatic and volcanic layering; particles such as pillow lavas, igneous crystals, and rock fragments in volcanic and plutonic breccias; patchy igneous textures; and vein networks. The products of extreme deformation during amphibolite facies metamorphism are uniformly layered gneisses. 相似文献
74.
Spectropolarimetric observations from 5000 to 8000 Å have been obtained for comets P/Austin (1982g) and P/Churyumov-Gerasimenko (1982f). The observations were spaced over phase angles of 50–125° for comet Austin and 10–40° for comet Churyumov-Gerasimenko. The use of spectropolarimetry allowed an evaluation of continuum polarization without molecular line contamination. Especially for comet Churyumov-Gerasimenko, the curve of polarization versus phase angle resembles curves for asteroids, where the polarization is negative (electric vector maximum parallel to the scattering plane) for phase angles less than 20° and the most negative polarization is from ?1 to ?2%. The negative polarization at backscattering angles may be due to multiple scattering in agglomerated grains, as assumed for asteroids, or to Mie scattering by small dielectric particles. If multiple scattering is important in comet dust, polarization measurements may imply a low albedo, less than 0.08. The polarization of comet Austin remained steady during a large change in the dust production rate. Both comets increased continuum flux by a factor of 2 near perihelion. The continuum of comet Churyumov-Gerasimenko had the shape of the solar spectrum with derivations less than 5%. The equivalent width of spectral features of C2, NH2, and O varied as r?2. 相似文献
75.
P. M. Phillips M. A. Norbury L. V. E. Koopmans I. W. A. Browne N. J. Jackson P. N. Wilkinson A. D. Biggs R. D. Blandford A. G. de Bruyn C. D. Fassnacht P. Helbig S. Mao D. R. Marlow S. T. Myers T. J. Pearson A. C. S. Readhead D. Rusin E. Xanthopoulos 《Monthly notices of the Royal Astronomical Society》2000,319(2):L7-L11
High-resolution MERLIN observations of a newly discovered four-image gravitational lens system, B0128+437, are presented. The system was found after a careful re-analysis of the entire CLASS data set. The MERLIN observations resolve four components in a characteristic quadruple-image configuration; the maximum image separation is 542 mas and the total flux density is 48 mJy at 5 GHz. A best-fitting lens model with a singular isothermal ellipsoid results in large errors in the image positions. A significantly improved fit is obtained after the addition of a shear component, suggesting that the lensing system is more complex and may consist of multiple deflectors. The integrated radio spectrum of the background source indicates that it is a gigahertz peaked spectrum source. It may therefore be possible to resolve structure within the radio images with deep VLBI observations and thus to constrain the lensing mass distribution better. 相似文献
76.
A coupled ocean and sea-ice pan-Arctic model forced by the Intergovernmental Panel on Climate Change A1B climate scenario is used to study the evolution of ice and ocean surface conditions within the Canadian Arctic Archipelago (CAA) during the twenty-first century. A summer ice-free CAA is likely by the end of our simulation. Sea ice undergoes significant changes from the mid-2020s to the mid-2060s in both concentration and thickness. The simulation shows a shrinking of 65% and a thinning of 75% in summer over the 40 years, resulting in a partially open Northwest Passage by the 2050s. However, ice in central Parry Channel might increase due to a decrease in export from April to June, linked to a reduced cross-channel sea surface height (SSH) gradient, before melting thermodynamically. On a larger scale, the central CAA throughflow will experience a significant decrease in both volume and freshwater transport after 2020, which is related to the change in the SSH difference between the two ends of Parry Channel, particularly the lifting of SSH in Baffin Bay. With a lower albedo, a warmer ocean is simulated, particularly in summer. The sea surface salinity within the CAA demonstrates a strong decadal oscillation without a clear trend over the entire simulation. A north–south pattern, separated by Parry Channel, is also found in the changes of ocean temperature and salinity fields due to different ice conditions. 相似文献
77.
78.
79.
Four variogram models for regional groundwater geochemical data are presented. These models were developed from an empirical study of the sample variograms for more than 10 elements in groundwaters from two geologic regions in the Plainview quandrangle, Texas. A procedure is given for the estimation of the variogram in the isotropic and anisotropic case. The variograms were found useful for quantifying the differences in spatial variability for elements within a geologic unit and for elements in different geologic units. Additionally, the variogram analysis enables assessment of the assumption of statistical independence of regional samples which is commonly used in many statistical procedures. The estimated variograms are used in computation of kriged estimates for the Plainview quadrangle data. The results indicate that an inverse distance weighting model was superior for prediction than simple kriging with the particular variograms used. 相似文献
80.