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221.
The aim of this paper is to study the feasibility of deriving vertical wind profiles from current satellite observations.
With this aim, we carried out complex empirical orthogonal function (CEOF) analysis of a large number of radiosonde observations
of wind profiles over the Indian Ocean during the monsoon months. It has been found that the first two CEOFs explain 67% of
the total variance in wind fields. While the first principal component is well correlated with the winds at 850 mb (r = 0:80), the second one is highly correlated with winds at 200 mb (r = 0:89). This analysis formed the basis of a retrieval
algorithm which ensures the retrieval of vertical profiles of winds using satellite tracked cloud motion vector winds. Under
the assumption that accurate measurements of wind are available at the above mentioned levels, the r.m.s. error of retrieval
of each component of wind is estimated to range between 2 ms-1 and 6 ms-1 at different levels, which is much less than the natural variance of winds at these levels. For a better visualization of
retrieval, we have provided retrieved and true wind profiles side by side for four typical synoptic conditions during the
monsoon season. 相似文献
222.
We have simulated the return echo of a satellite altimeter from a rough ocean surface using an analytical formula and have
studied its sensitivity with respect to various oceanic and altimeter parameters. Our numerical experiment shows that for
normally observed significant wave heights (SWH) the effect of off-nadir angle (ONA) up to 0.5° on the leading edge is not
severe. Also, small surface roughness skewness seems to have little effect on the overall shape of the echo.
Newton’s iterative scheme has been used to retrieve SWH from the mean return waveform without noise and with additive Gaussian
noise typical of Seasat and Geosat altimeters. It has been observed that SWH can be retrieved in the presence of noise with
an accuracy of ±0.6 m for ONA less than 0.5°. For higher ONA, accurate retrieval requires the use of precomputed look-up table
along with our scheme. 相似文献
223.
The variational technique of data assimilation using adjoint equations has been illustrated using a nonlinear oceanographic
shallow water model. The technique consists of minimizing a cost function representing the misfit between the model and the
data subject to the model equations acting as constraints. The problem has been transformed into an unconstrained one by the
use of Lagrange multipliers. Particular emphasis has been laid on finite difference formulation of the algorithm. Several
numerical experiments have been conducted using simulated data obtained from a control run of the model. Implications of this
technique for assimilating asynoptic satellite altimeter data into ocean models have been discussed. 相似文献
224.
225.
Rotational components of earthquake ground motion have not been considered for seismic analysis, design and performance assessment because recordings of these components are unavailable. A number of procedures have been proposed to extract rotational components of ground motion from translational time series recorded at multiple, closely spaced recording stations. In this paper, a new procedure that is capable of capturing higher frequency content in rotational time‐series is presented. The frequencies at which numerical errors are introduced in the solution, which are a function of apparent wave velocity and array dimension, are identified. Results are presented for the proposed procedure, the widely accepted geodetic method, and a single‐station procedure developed by the authors, all using data recorded at the Lotung array in Taiwan. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
226.
Abhijit Basu D. J. Des Marais J. M. Hayes W. G. Meinschein 《Earth, Moon, and Planets》1975,14(1):129-138
Sample 72161,11 (dark mantle at LRV-3) has a graphic mean grain size (M z) of 3.88 ø, inclusive graphic standard deviation (σ I) of 1.29, and a total carbon content of 204µg C g?1 sample, and is, therefore, quite mature. However, the agglutinate content is only 30% in the 90–177µm particles, indicating an apparent departure from steady state. Analyses of C, CH4, and H2 concentrations in size fractions larger than 149µm show that the volume correlated component of these species increases with increasing grain size. In a homogeneous agglutinate population the volume correlated component is expected to be independent of grain size. The observed increase can be interpreted in terms of the mixing of a dominant local population of coarser agglutinates, with high carbon and hydrogen, with an imported population of finer agglutinates relatively poor in carbon and hydrogen. When analyses of size-fractions from the bulk sample are considered, these effects are apparently obliterated by the admixture of coarse-grained material low in agglutinates. It seems likely that this low agglutinate content is a consequence of the breakdown of the fragile, large agglutinates in the imported material during their movement to the sample site. 相似文献
227.
H.M. Antia S. Basu F. Hill R. Howe R.W. Komm J. Schou 《Monthly notices of the Royal Astronomical Society》2001,327(3):1029-1040
We study the variation of the frequency splitting coefficients describing the solar asphericity in both GONG and MDI data, and use these data to investigate temporal sound-speed variations as a function of both depth and latitude during the period 1995–2000 and a little beyond. The temporal variations in even splitting coefficients are found to be correlated to the corresponding component of magnetic flux at the solar surface. We confirm that the sound-speed variations associated with the surface magnetic field are superficial. Temporally averaged results show a significant excess in sound speed around and latitude of 60°. 相似文献
228.
The Raniganj Formation (late Permian) forms the uppermost economic coal-bearing unit of the Gondwana succession. The dominant facies interpreted from analysis of cores from the Raniganj formation are classified as Sandstone dominated facies, Sandstone - shale heterolith facies, Shale facies and Coal facies. The natural Gamma response of Raniganj Formation shows predominance of repetitive fining upwards cycles. Integration of core analysis and geophysical log data of the Raniganj formation indicates meandering fluvial environment. The lower part of Raniganj Formation is channel dominated which corresponds to thick amalgamated sand bodies while the upper part represent overbank shows predominance of channel avulsion indicating a gradual change in accommodation space. Five major fining upward depositional sequences, bounded by sub-aerial unconformities (sequence boundaries) have been dentified in Raniganj formation, based on changes in depositional style that are correlated regionally. Each sequence comprises of Low accommodation system tract (LAST) at base and high accommodation system tract (HAST) at top. LAST is characterized by vertically stacked, multistory amalgamated channel sandstone dominated facies, while floodplain dominated facies characterize HAST. The coal seams deposited in LAST are thicker and relatively more continuous than the frequent thin seams of HAST. Such facies distribution study would be helpful for the development strategy for CBM blocks based on production priority. 相似文献
229.
Shape classification of the 40-Hz waveforms obtained by the recently launched AltiKa satellite has been attempted in the paper. Since retracking algorithms suitable for altimeter return echoes based on Brown model are not applicable for the echoes from coastal ocean, specific algorithms are to be devised for such echoes. In the coastal ocean, waveforms display a wide variety of shapes due to varying coastline geometry, and topography. Hence, a proper classification strategy is required for classifying the waveforms into various categories so that suitable retracker could be applied to each category for retrieving the oceanic parameters. The algorithm consists of three steps: feature selection, linear discriminant analysis, and Bayesian classifier. The classification algorithm has been applied to the waveforms in the close proximity of Gujarat coast. Independent validation has been done near the eastern coast of India. Confusion matrices obtained for both the coasts are quite encouraging. Individual examples of classification have been provided for the purpose of illustration. 相似文献
230.
A. Basu Sarbadhikari E. V. S. S. K. Babu T. Vijaya Kumar H. Chennaoui Aoudjehane 《Meteoritics & planetary science》2016,51(9):1588-1610
Tissint, a new unaltered piece of Martian volcanic materials, is the most silica‐poor and Mg‐Fe‐rich igneous rock among the “depleted” olivine‐phyric shergottites. Fe‐Mg zoning of olivine suggests equilibrium growth (<0.1 °C h?1) in the range of Fo80–56 and olivine overgrowth (Fo55–18) through a process of rapid disequilibrium (~1.0–5.0 °C h?1). The spatially extended (up to 600 μm) flat‐top Fe‐Mg profiles of olivine indicates that the early‐stage cooling rate of Tissint was slower than the other shergottites. The chemically metastable outer rim of olivine (55) consists of oscillatory phosphorus zoning at the impact‐induced melt domains and grew rapidly compared to the early to intermediate‐stage crystallization of the Tissint bulk. High‐Ca pyroxene to low‐Ca pyroxene and high‐Ca pyroxene to plagioclase ratios of Tissint are more comparable to the enriched basaltic and enriched olivine‐phyric shergottites. Dominance of augite over plagioclase induced augite to control the Ca‐buffer in the residual melt suppressing the plagioclase crystallization, which also caused a profound effect on the Al‐content in the late‐crystallized pyroxenes. Mineral chemical stability, phase‐assemblage saturation, and pressure–temperature path of evolution indicates that the parent magma entered the solidus and left the liquidus field at a depth of 40–80 km in the upper mantle. Petrogenesis of Tissint appears to be similar to LAR 06319, an enriched olivine‐phyric shergottite, during the early to intermediate stage of crystallization. A severe shock‐induced deformation resulted in remelting (10–15 vol%), recrystallization (most Fe‐rich phases), and exhumation of Tissint in a time scale of 1–8 yr. Tissint possesses some distinct characteristics, e.g., impact‐induced melting and deformation, forming phosphorus‐rich recrystallization rims of olivine, and shock‐induced melt domains without relative enrichment of LREEs compared to the bulk; and shared characteristics, e.g., modal composition and magmatic evolution with the enriched basaltic shergottites, evidently reflecting unique mantle source in comparison to the clan of the depleted members. 相似文献