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71.
Colin C. Ferguson 《Mathematical Geology》1979,11(3):329-336
This paper considers an ellipse, produced by the intersection of a triaxial ellipsoid and a plane (both arbitrarily oriented), and derives explicit expressions for its axis ratio and orientation. The relationship between central and noncentral sections, and the problem of intersection probability, are discussed. The resulting equations have obvious applications in structural geology and optical mineralogy, and in stereological modeling of grain-size and grain-shape distributions. 相似文献
72.
73.
Turbulence and heat fluxes in the marine atmospheric boundary layer (MABL) for the roll vortex regime, observed during the Genesis of Atlantic Lows Experiment (GALE) over the western Gulf Stream, have been studied. The spectral analysis suggests that cloud streets (roll vortices) are vertically organized convection in the MABL having the same roll scale for both the cloud layer and subcloud layer, and that the roll spacing is about three times the MABL depth. The roll circulations contribute significantly to the sensible (temperature) and latent heat (moisture) fluxes with importance increasing upward. Near the MABL top, these fluxes are primarily due to roll vortices which transfer both sensible heat and moisture upward in the lower half of the convective MABL. Near the MABL top, the roll circulations transfer sensible heat downward and moisture upward in the clear thermal-street region, but roll vortices influenced by evaporative cooling can transfer sensible heat upward and moisture downward in the cloud-street region. Near the cloud-top, the upward buoyancy flux due to evaporative cooling is highly related to the roll circulations near the inversion.For the lower half of the MABL, the normalized temperature flux decreases upward more rapidly than the humidity flux, which is mainly because potential temperature () increases slightly upward while humidity (q) decreases slightly upward above the unstable surface layer. The gradient production (associated with the gradient) is a source for the temperature flux in the unstable surface layer but changes to a sink in the mixed layer, while the gradient production (associated with the q gradient) acts as a source for the humidity flux in both the unstable surface and mixed layers. The results suggest that the entrainment at the MABL top might affect the budgets of temperature and humidity fluxes in the lower MABL, but not in the unstable surface layer.Caelum Research Corporation, Silver Spring, MD, 20901, U.S.A. 相似文献
74.
75.
Sarah J. Kelloway Steven Craven Mark Pecha William R. Dickinson Martin Gibbs Timothy Ferguson Michael D. Glascock 《Geoarchaeology》2014,29(1):47-60
We present U‐Pb ages of zircons extracted from olive jars recovered from two sites associated with Alvaro de Mendaña y Neyra's colonising expedition to the Solomon Islands, c. 1595–1596 A.D. The olive jars were previously associated with Panamanian and Peruvian origins based on petrological and geochemical studies. To further define provenance, 143 zircons were extracted from five olive jar sherds, analyzed and dated. The resultant U‐Pb ages range from the Archaean to the Cenozoic (2977.2 ± 29.0–3.2 ± 4.0 Ma), but the dominance of Cretaceous and Palaeogene ages (∼ 90% of the total age population is between ∼ 145 and 23 Ma) supports a Peruvian origin based on comparative geology, with the Coastal Batholith of Peru a prime candidate area of ceramic production. These results are significant for the characterization of 16th Century Peruvian‐made pottery and our understanding of its production and trade. 相似文献
76.
77.
A. P. Huxor N. R. Tanvir M. J. Irwin R. Ibata J. L. Collett A. M. N. Ferguson T. Bridges G. F. Lewis 《Monthly notices of the Royal Astronomical Society》2005,360(3):1007-1012
We present three new clusters discovered in the halo of M31 which, although having globular-like colours and luminosities, have unusually large half-light radii, ∼30 pc. They lie at projected galactocentric distances of ≈15 to ≈35 kpc. These objects begin to fill the gap in parameter space between globular clusters and dwarf spheroidals, and are unlike any clusters found in the Milky Way, or elsewhere to date. Colour–magnitude diagrams, integrated photometric properties and derived King profile fit parameters are given, and we discuss possible origins of these clusters and their relationships to other populations. 相似文献
78.
79.
M.D. Gregg M.J. Drinkwater M.J. Hilker Steven Phillipps J. Bryn Jones Henry C. Ferguson 《Astrophysics and Space Science》2003,285(1):113-117
We have discovered a new type of galaxy in the Fornax Cluster: `ultra-compact' dwarfs (UCDs). The UCDs are unresolved in ground-based
imaging and have spectra typical of old stellar systems. Although the UCDs resemble overgrown globular clusters, based on
VLT UVES echelle spectroscopy, they appear to be dynamically distinct systems with higher internal velocity dispersions and
M/L ratios for a given luminosity than Milky Way or M31 globulars. Our preferred explanation for their origin is that they
are the remnant nuclei of dwarf elliptical galaxies which have been tidally stripped, or `threshed' by repeated encounters
with the central cluster galaxy, NGC1399. If correct, then tidal stripping of nucleated dwarfs to form UCDs may, over a Hubble
time, be an important source of the plentiful globular cluster population in the halo of NGC1399, and, by implication, other
cD galaxies. In this picture, the dwarf elliptical halo contents, up to 99% of the original dwarf luminosity, contribute a
significant fraction of the populations of intergalactic stars, globulars, and gas in galaxy clusters.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
80.
The effects of both small perturbations and large deformations to the array's shape on both conventional and adaptive beamformers are shown for two frequencies: the spatial Nyquist frequency (or design frequency) of the array and a frequency about three times greater. Large shape deformations lead to a decrease in the conventional beamformer's output power for a beam steered in the direction of the signal source, together with an increase in the sidelobe levels (or secondary maxima), while small perturbations in the array shape have little effect. Signal suppression is observed to be far greater for the adaptive beamformer because it is very sensitive to system errors. The imposition of a weight norm constraint on the adaptive beamformer reduces the signal suppression only for small shape perturbations array shape estimation techniques are needed to reduce signal suppression for large shape deformations. The adverse effects of a nonlinear array shape on both conventional and adaptive beamforming are shown to be substantially reduced by applying techniques that estimate the coordinates of the hydrophones prior to beamforming 相似文献