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851.
D. J. Bacon A. N. Taylor M. L. Brown M. E. Gray C. Wolf K. Meisenheimer S. Dye L. Wisotzki A. Borch M. Kleinheinrich 《Monthly notices of the Royal Astronomical Society》2005,363(3):723-733
We present a direct detection of the growth of large-scale structure, using weak gravitational lensing and photometric redshift data from the COMBO-17 survey. We use deep R -band imaging of two 0.5 × 0.5 deg2 fields, affording shear estimates for over 52 000 galaxies; we combine these with photometric redshift estimates from our 17-band survey, in order to obtain a 3D shear field. We find theoretical models for evolving matter power spectra and correlation functions, and fit the corresponding shear correlation functions to the data as a function of redshift. We detect the evolution of the power at the 4.7σ level given reasonable priors, and measure the rate of evolution for 0 < z < 1 . We also fit correlation functions to our 3D data as a function of cosmological parameters σ8 and ΩΛ . We find joint constraints on ΩΛ and σ8 , demonstrating an improvement in accuracy by ≃40 per cent over that available from 2D weak lensing for the same area. 相似文献
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853.
We use a semi-analytic model of halo formation to study the dynamical history of giant field galaxies like the Milky Way.
We find that in a concordance LCDM cosmology, most isolated disk galaxies have remained undisturbed for 8–10 Gyr, such that
the age of the Milky Way's thin disk is unremarkable. Many systems also have older disk components which have been thickened
by minor mergers, consistent with recent observations of nearby field galaxies. We do have a considerable problem, however,
reproducing the morphological mix of nearby galaxies. In our fiducial model, most systems have disk-to-bulge mass ratios of
order 1, and look like S0s rather than spirals. This result depends mainly on merger statistics, and is unchanged for most
reasonable choices of our model parameters. We discuss two possible solutions to this morphology problem in LCDM.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
854.
Roberto De Propris Warrick J. Couch Matthew Colless Gavin B. Dalton Chris Collins Carlton M. Baugh Joss Bland-Hawthorn Terry Bridges Russell Cannon Shaun Cole Nicholas Cross Kathryn Deeley Simon P. Driver George Efstathiou Richard S. Ellis Carlos S. Frenk Karl Glazebrook Carole Jackson Ofer Lahav Ian Lewis Stuart Lumsden Steve Maddox Darren Madgwick Stephen Moody Peder Norberg John A. Peacock Will Percival Bruce A. Peterson Will Sutherland Keith Taylor 《Monthly notices of the Royal Astronomical Society》2002,329(1):87-101
We have carried out a study of known clusters within the 2dF Galaxy Redshift Survey (2dFGRS) observed areas and have identified 431 Abell, 173 APM and 343 EDCC clusters. Precise redshifts, velocity dispersions and new centroids have been measured for the majority of these objects, and this information is used to study the completeness of these catalogues, the level of contamination from foreground and background structures along the cluster's line of sight, the space density of the clusters as a function of redshift, and their velocity dispersion distributions. We find that the Abell and EDCC catalogues are contaminated at the level of about 10 per cent, whereas the APM catalogue suffers only 5 per cent contamination. If we use the original catalogue centroids, the level of contamination rises to approximately 15 per cent for the Abell and EDCC catalogues, showing that the presence of foreground and background groups may alter the richness of clusters in these catalogues. There is a deficiency of clusters at that may correspond to a large underdensity in the Southern hemisphere. From the cumulative distribution of velocity dispersions for these clusters, we derive a space density of clusters of This result is used to constrain models for structure formation; our data favour low-density cosmologies, subject to the usual assumptions concerning the shape and normalization of the power spectrum. 相似文献
855.
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858.
P. A. Rosen B. H. Wilde R. J. R. Williams J. M. Foster P. A. Keiter R. F. Coker T. S. Perry M. J. Taylor A. M. Khokhlov R. P. Drake G. R. Bennett D. B. Sinars R. B. Campbell 《Astrophysics and Space Science》2005,298(1-2):121-128
In recent years, we have carried out experiments at the University of Rochester’s Omega laser in which supersonic, dense-plasma
jets are formed by the interaction of strong shocks in a complex target assembly (Foster et al., Phys. Plasmas 9 (2002) 2251). We describe recent, significant extensions to this work, in which we consider scaling of the experiment, the
transition to turbulence, and astrophysical analogues. In new work at the Omega laser, we are developing an experiment in
which a jet is formed by laser ablation of a titanium foil mounted over a titanium washer with a central, cylindrical hole.
Some of the resulting shocked titanium expands, cools, and accelerates through the vacuum region (the hole in the washer)
and then enters a cylinder of low-density foam as a jet. We discuss the design of this new experiment and present preliminary
experimental data and results of simulations using AWE hydrocodes. In each case, the high Reynolds number of the jet suggests
that turbulence should develop, although this behaviour cannot be reliably modelled by present, resolution-limited simulations
(because of their low-numerical Reynolds number). 相似文献
859.
Darren J. Croton Glennys R. Farrar Peder Norberg Matthew Colless John A. Peacock I. K. Baldry C. M. Baugh J. Bland-Hawthorn T. Bridges R. Cannon S. Cole C. Collins W. Couch G. Dalton R. De Propris S. P. Driver G. Efstathiou R. S. Ellis C. S. Frenk K. Glazebrook C. Jackson O. Lahav I. Lewis S. Lumsden S. Maddox D. Madgwick B. A. Peterson W. Sutherland K. Taylor 《Monthly notices of the Royal Astronomical Society》2005,356(3):1155-1167
We use the 2dF Galaxy Redshift Survey to measure the dependence of the b J -band galaxy luminosity function on large-scale environment, defined by density contrast in spheres of radius 8 h −1 Mpc , and on spectral type, determined from principal component analysis. We find that the galaxy populations at both extremes of density differ significantly from that at the mean density. The population in voids is dominated by late types and shows, relative to the mean, a deficit of galaxies that becomes increasingly pronounced at magnitudes brighter than M b J −5log10 h ≲−18.5 . In contrast, cluster regions have a relative excess of very bright early-type galaxies with M b J −5log10 h ≲−21 . Differences in the mid- to faint-end population between environments are significant: at M b J −5log10 h =−18 early- and late-type cluster galaxies show comparable abundances, whereas in voids the late types dominate by almost an order of magnitude. We find that the luminosity functions measured in all density environments, from voids to clusters, can be approximated by Schechter functions with parameters that vary smoothly with local density, but in a fashion that differs strikingly for early- and late-type galaxies. These observed variations, combined with our finding that the faint-end slope of the overall luminosity function depends at most weakly on density environment, may prove to be a significant challenge for models of galaxy formation. 相似文献
860.