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Renate?Hartog Wim?Spakman Clifford H.?ThurberEmail author Chad?Trabant 《Pure and Applied Geophysics》2003,160(12):2239-2255
We relocate 81 large nuclear explosions that were detonated at the Balapan and Degelen Mountain subregions of the Semipalatinsk test site in Kazakhstan during the years 1978 to 1989. The absolute locations of these explosions are available, as well as very accurate estimates of their origin times. This ground truth information allows us to perform a detailed analysis of location capability. We use a sparse network of stations with highly accurate first arrival picks measured using a waveform cross-correlation method. These high quality data facilitate very accurate location estimates with only a few phases per event. We contrast two different approaches: 1) a calibration-based approach, where we achieve improved locations by using path corrections, and 2) a model-based approach, where we achieve improved locations by relocating in a recently published global 3-D P-velocity model. Both methods result in large improvements in accuracy of the obtained absolute locations, compared to locations obtained in a 1-D reference earth model (ak135). The calibration-based approach gives superior results for this test site, in particular when arrival times from regional stations are included. Estimated locations remain well within a 1000 km2 region surrounding the ground truth locations when the path corrections for the Balapan and Degelen Mountain subregions are interchanged, but even for the short separation between these two regions, we find variations in the path corrections that cause systematic mislocations. The model-based approach also results in substantially reduced mislocation distances and has the distinct advantage that it is, in principle, transportable to other source regions around the world. 相似文献
75.
Crustal structure under the central High Atlas Mountains (Morocco) from geological and gravity data 总被引:1,自引:0,他引:1
P. Ayarza F. Alvarez-Lobato A. Teixell M.L. Arboleya E. Tesn M. Julivert M. Charroud 《Tectonophysics》2005,400(1-4):67-84
Seismic wide angle and receiver function results together with geological data have been used as constraints to build a gravity-based crustal model of the central High Atlas of Morocco. Integration of a newly acquired set of gravity values with public data allowed us to undertake 2–2.5D gravity modelling along two profiles that cross the entire mountain chain. Modelling suggests moderate crustal thickening, and a general state of Airy isostatic undercompensation. Localized thickening appears restricted to the vicinity of a north-dipping crustal-scale thrust fault, that offsets the Moho discontinuity and defines a small crustal root which accounts for the minimum Bouguer gravity anomaly values. Gravity modelling indicates that this root has a northeasterly strike, slightly oblique to the ENE general orientation of the High Atlas belt. A consequence of the obliquity between the High Atlas borders and its internal and deep structure is the lack of correlation between Bouguer gravity anomaly values and topography. Active buckling affecting the crust, a highly elevated asthenosphere, or a combination of both are addressed as side mechanisms that help to maintain the high elevations of the Atlas mountains. 相似文献
76.
Z. Martinec 《Journal of Geodesy》1998,72(7-8):460-472
Green's function for the boundary-value problem of Stokes's type with ellipsoidal corrections in the boundary condition for
anomalous gravity is constructed in a closed form. The `spherical-ellipsoidal' Stokes function describing the effect of two
ellipsoidal correcting terms occurring in the boundary condition for anomalous gravity is expressed in O(e
2
0)-approximation as a finite sum of elementary functions analytically representing the behaviour of the integration kernel
at the singular point ψ=0. We show that the `spherical-ellipsoidal' Stokes function has only a logarithmic singularity in
the vicinity of its singular point. The constructed Green function enables us to avoid applying an iterative approach to solve
Stokes's boundary-value problem with ellipsoidal correction terms involved in the boundary condition for anomalous gravity.
A new Green-function approach is more convenient from the numerical point of view since the solution of the boundary-value
problem is determined in one step by computing a Stokes-type integral. The question of the convergence of an iterative scheme
recommended so far to solve this boundary-value problem is thus irrelevant.
Received: 5 June 1997 / Accepted: 20 February 1998 相似文献
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V. N. Bajpai 《Journal of Earth System Science》2004,113(3):427-451
The Luni river basin has been evolved as a result of typical hydrogeomorphic processes of arid zone, operating under the influence
of active tectonic lineaments. A detailed analysis of stream morphology in relation to geology and lineaments carried out
on selected windows indicated the morphological control of the streams while flowing over the lineaments from the eastern
to the western part of the basin. Typical valley fills indicated by dark green tone on digitally processed images and the
pediments showing greenish white tone appear in sharp contrast and indicate respectively the graben and horst structures.
A detailed identification of lineaments for the georesources and geological evaluation has been carried out. Earlier analysis
carried out on Bouguer anomalies correlate with graben and horst structures in the subsurface. Quaternary sequences have been
dated from 80 ka to 3 ka indicating a range of fluvial to aeolian deposits reflecting prevailing climatic conditions. However,
the changes in sediment type from coarse and mixed of all size grades to fine in a vertical litho-column warrant further studies
on fine resolution stratigraphy and high resolution stratigraphy for understanding climatic variations in the region 相似文献
80.
Somdev Bhattacharji Rajesh Sharma Nilanjan Chatterjee 《Journal of Earth System Science》2004,113(4):771-784
The western continental margin and the intraplate Narmada-Tapti rifts are primarily covered by Deccan flood basalts. Three-dimensional
gravity modeling of +70mgal Bouguer gravity highs extending in the north-south direction along the western continental margin
rift indicates the presence of a subsurface high density, mafic-ultramafic type, elongated, roughly ellipsoidal body. It is
approximately 12.0 ±1.2 km thick with its upper surface at an approximate depth of 6.0 ±0.6 km, and its average density is
{dy2935} kg/m3. Calculated dimension of the high density body in the upper crust is 300 ±30 km in length and 25 ±2.5 to 40 ±4 km in width.
Three-dimensional gravity modeling of +10mgal to -30mgal Bouguer gravity highs along the intraplate Narmada-Tapti rift indicates
the presence of eight small isolated high density mafic bodies with an average density of {dy2961} kg/m3. These mafic bodies are convex upward and their top surface is estimated at an average depth of 6.5 ±0.6 (between 6 and 8km).
These isolated mafic bodies have an average length of 23.8 ±2.4km and width of 15.9 ±1.5km. Estimated average thickness of
these mafic bodies is 12.4±1.2km. The difference in shape, length and width of these high density mafic bodies along the western
continental margin and the intraplate Narmada-Tapti rifts suggests that the migration and concentration of high density magma
in the upper lithosphere was much more dominant along the western continental margin rift. Based on the three-dimensional
gravity modeling, it is conjectured that the emplacement of large, ellipsoidal high density mafic bodies along the western
continental margin and small, isolated mafic bodies along the Narmada-Tapti rift are related to lineament-reactivation and
subsequent rifting due to interaction of hot mantle plume with the lithospheric weaknesses (lineaments) along the path of
Indian plate motion over the Réunion hotspot. Mafic bodies formed in the upper lithosphere as magma chambers along the western
continental margin and the intraplate Narmada-Tapti rifts at estimated depths between 6 and 8 km from the surface (consistent
with geological, petrological and geochemical models) appear to be the major reservoirs for Deccan flood basalt volcanism
at approximately 65 Ma. 相似文献