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651.
Receiver functions in northeast China - implications for slab penetration into the lower mantle in northwest Pacific subduction zone 总被引:6,自引:0,他引:6
Seismic studies of the subducting lithosphere and the upper mantle discontinuities in the northwest Pacific subduction zone beneath Japan and northeast China have suggested contrary subduction scenarios. There was little consensus on the issue whether the subducting slab penetrates the upper mantle discontinuities into the lower mantle or it is deflected atop of the 660-km discontinuity over several hundred kilometers. We calculate receiver functions from a recent seismic broadband station network located in northeast China and find topographic variations of the upper mantle discontinuities. A deeper-than-normal 660-km discontinuity is observed over an area of 400 km and it coincides with the stagnant slab imaged by seismic tomography. The 660-km discontinuity is locally depressed by more than 35 km and the transition zone is thickened by more than 20 km in the east of the region where it encounters the slab. These observations provide evidence of the slab accumulating in the mantle transition zone and locally penetrating into the lower mantle. 相似文献
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在矿区水文地质调查中应用手持GPS接收机 总被引:1,自引:0,他引:1
为提高手持GPS接收机在矿区水文地质调查中的点位定位精度,在不同地段选择6个测量已知控制点进行参数测定,在每个点上要求搜索到4颗以上卫星信号,定位时间5min以上。对投影方式及比例参数设定后,再利用矿区不同的测量已知点与手持GPS接收机测量点坐标进行对比。测量成果的可靠性和精确性取决于接收机、处理软件、所测卫星的图形强度和观测环境。经参数校准后,手持式GPS接收机单点定位精度优于±5m,可满足矿区1∶1万及更小比例尺水文地质调查对工程点位的精度要求。 相似文献
657.
A determination of the seismic structure of the crust and uppermost mantle of East Antarctica, in the region of Casey station, Wilkes Land and Dumont DUrville station, Terre Adelie is presented. High-fidelity waveforms from teleseismic earthquakes recorded at stations CASY and DRV (1996-2001) are used to calculate the seismic receiver function, the signal produced as energy passes through layers in the seismic velocity structure under the receiving station. The receiver functions are stacked to improve the signal-to-noise ratio and then modelled using an inverse algorithm to find the structure that best fits the observed waveform at each station. Inferences are made regarding the tectonic structure, in particular, the crustal thickness and character of the seismic Moho.The crustal thickness under Casey Station is found to be 30 km (+/- 2 km) with a fairly sharp Moho, considerably less than Dumont D'Urville Station, where the crustal thickness is 42 km, and there IS a significant low velocity region the deep crust. The structure of the Wilkes Land lithosphere is comparable to that of the Albany-Fraser Orogen, Western Australia, part of its conjugate margin. This places a new constraint on the relative position of East Antarctica and Australia in the reconstruction of Gondwana, and earlier, supercontinents. A recent reinterpretation of Antarctic geology proposes tectonic province boundaries trending perpendicular to the coast with counterparts in southern Australia. Seismic techniques, determining structure beneath regions with no surface exposure, are vital tools in testing such tectonic hypotheses, towards the reconstruction of Gondwana to full lithospheric depth. 相似文献
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S. K. Nath P. Sengupta S. K. Srivastav S. N. Bhattacharya R. S. Dattatrayam R. Prakash H. V. Gupta 《Journal of Earth System Science》2003,112(3):441-462
Site response in and around Delhi is studied using digital seismograms recorded by a thirteen-station VSAT-based 24-bit digital
Delhi telemetry network of the India Meteorological Department. Nine local (M
l ≥ 2.3) and nine regional (M
l ≥ 3.9) earthquakes are selected for the estimation of site amplification factor using the classical standard spectral ratio
for regional events (Ridge Delhi Observatory being the reference station), normalized standard spectral ratio for local events,
horizontal-to-vertical spectral ratio or receiver function and the generalized inversion techniques in the frequency range
of 0.5 to 7.5 Hz. Site response curves at all the thirteen stations exhibit station to station variation of the site amplification
factor reflecting the changes in geologic/geotectonic/soil conditions. A comparison of the site response values obtained by
the generalized inversion with those computed using receiver function technique shows a large scatter even though the pattern
of the curves remain more or less similar. However, the site effects computed by generalized inversion and standard spectral
ratio exhibit a good 1:1 correspondence. The peaks yielded by all the methods have been observed to occur at the same frequencies.
It is evident that the softer fluvial deposits of the newer alluvium of the east Yamuna sector show steeper site amplification
gradient at lower frequencies, while the greater Delhi experiences moderate site amplification. The variation of site response
corroborates the abrupt changes in intensity from one location to another due to local site condition. 相似文献
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Icelandic-type crust 总被引:3,自引:0,他引:3