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71.
72.
Alaa I. Ibrahim William C. Parke Jean H. Swank Hisham Anwer Roberto Turolla Silvia Zane M. T. Hussein T. El-Sherbini 《Astrophysics and Space Science》2007,308(1-4):43-50
The defining property of Soft Gamma Repeaters is the emission of short, bright bursts of X-rays and soft γ-rays. Here we present the continuum and line spectral properties of a large sample of bursts from SGR 1806-20, observed with
the Proportional Counter Array (PCA) onboard the Rossi X-ray Timing Explorer (RXTE). Using 10 trail spectral models (5 single
and 5 two component models), we find that the burst continua are best fitted by the single component models: cutoff power-law,
optically thin bremsstrahlung, and simple power-law. Time resolved spectroscopy show that there are two absorption lines at
∼5 keV and 20 keV in some bursts. The lines are relatively narrow with 90% upper limit on the line widths of 0.5–1.5 keV for
the 5 keV feature and 1–3 keV for the 20 keV feature. Both lines have considerable equivalent width of 330–850 eV for the
5 keV feature and 780–2590 eV for the 20 keV feature. We examined whether theses spectral lines are dependent upon the choice
of a particular continuum model and find no such dependence. Besides, we find that the 5 keV feature is pronounced with high
confidence in the cumulative joint spectrum of the entire burst sample, both in the individual detectors of the PCA and in
the co-added detectors spectrum. We confront the features against possible instrumental effects and find that none can account
for the observed line properties. The two features do not seem to be connected to the same physical mechanism because (1)
they do not always occur simultaneously, (2) while the 5 keV feature occurs at about the same energy, the 20 keV line centroid
varies significantly from burst to burst over the range 18–22 keV, and (3) the centroid of the lines shows anti-correlated
red/blue shifts. The transient appearance of the features in the individual bursts and in portions of the same burst, together
with the spectral evolution seen in some bursts point to a complex emission mechanism that requires further investigation.
相似文献
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This paper presents a three‐dimensional finite element analysis of the response of battered piles to the combined lateral and vertical pullout loads. Analyses are carried out using an elastoplastic constitutive law based on the non‐associated Mohr–Coulomb criterion. The influence of the contact condition at the pile–soil interface is also investigated. Analyses show that the load's inclination with regard to the pile's axis affects both the lateral and axial response of the battered piles. Analyses also show that the pullout capacity of battered piles is affected by the pile's inclination regarding the vertical axis as well as the load's inclination regarding the pile's axis. The investigation of the influence of the contact condition at the soil–pile interface shows that the possibility of sliding at the soil–pile interface affects the response of battered piles subjected to loads with low inclination regarding the pile's axis. Copyright © 2008 John Wiley & Sons, Ltd. 相似文献
75.
Hend Ahmed Ibrahim Hussein Adam Ricka Tomas Kuchovsky Maged Mostafa El Osta 《Arabian Journal of Geosciences》2017,10(7):170
The demand for water is rapidly increasing in Egypt, because of high population and agriculture production growth rate, which makes research of water resources necessary. The regional multi-aquifer system of the Miocene–Pleistocene age is discharged in Wadi El Natrun area. Intensive aquifer overexploitation and agricultural development in the area are related to groundwater quality deterioration. Hydrochemical and hydrogeological data was evaluated to determine the groundwater origin and quality in the south-eastern part of wadi, which appears to be more significant for water supply owing to lower groundwater salinity. The dominance of the high mineralised Cl groundwater type was found; however, also less mineralised SO4 and HCO3 types were identified there. Based on the ion relations, halite and gypsum dissolution and ion exchange are the most important hydrochemical processes forming the groundwater chemical composition. The Cl dominated groundwater matches the discharge part of the regional hydrogeological system. Contrary, the presence of HCO3 and SO4 hydrochemical types corresponds to the infiltration and transferring parts of the hydrogeological system indicating the presence of zones conducting low mineralised groundwater. The discharge area of the over-pumped aquifer in Wadi El-Natrun lies 23 m beneath the sea level with the shoreline being at the distance of 100 km, thus there is a real risk of seawater intrusion. Using the hydrochemical facies evolution diagram, four samples in the centre of the discharge area indicate advanced seawater intrusion. The zones of the highest demand for groundwater quality protection were indicated based on a spatial pattern of hydrogeochemical composition. 相似文献
76.
Spatially distributed and varying natural phenomena encountered in geoscience and engineering problem solving are typically
incompatible with Gaussian models, exhibiting nonlinear spatial patterns and complex, multiple-point connectivity of extreme
values. Stochastic simulation of such phenomena is historically founded on second-order spatial statistical approaches, which
are limited in their capacity to model complex spatial uncertainty. The newer multiple-point (MP) simulation framework addresses
past limits by establishing the concept of a training image, and, arguably, has its own drawbacks. An alternative to current
MP approaches is founded upon new high-order measures of spatial complexity, termed “high-order spatial cumulants.” These
are combinations of moments of statistical parameters that characterize non-Gaussian random fields and can describe complex
spatial information. Stochastic simulation of complex spatial processes is developed based on high-order spatial cumulants
in the high-dimensional space of Legendre polynomials. Starting with discrete Legendre polynomials, a set of discrete orthogonal
cumulants is introduced as a tool to characterize spatial shapes. Weighted orthonormal Legendre polynomials define the so-called
Legendre cumulants that are high-order conditional spatial cumulants inferred from training images and are combined with available
sparse data sets. Advantages of the high-order sequential simulation approach developed herein include the absence of any
distribution-related assumptions and pre- or post-processing steps. The method is shown to generate realizations of complex
spatial patterns, reproduce bimodal data distributions, data variograms, and high-order spatial cumulants of the data. In
addition, it is shown that the available hard data dominate the simulation process and have a definitive effect on the simulated
realizations, whereas the training images are only used to fill in high-order relations that cannot be inferred from data.
Compared to the MP framework, the proposed approach is data-driven and consistently reconstructs the lower-order spatial complexity
in the data used, in addition to high order. 相似文献
77.
78.
Impact of spatial variations of land surface parameters on regional evaporation: a case study with remote sensing data 总被引:1,自引:0,他引:1
Most precipitation in watersheds is consumed by evaporation, thus techniques to appraise regional evaporation are important to assess the availability of water resources. Many algorithms to estimate evaporation from remotely sensed spectral data have been developed in the recent past. In addition to differences in the physical parameterization of surface fluxes, these algorithms have different solutions for describing spatial variations of the parameters in the soil–vegetation–atmosphere–transfer (SVAT) continuum. In this study, the necessity to spatially distinguish SVAT parameters for computing surface heat fluxes is analysed for the Naivasha watershed in the Kenyan Rift Valley. Landsat Thematic Mapper (TM) spectral data have been used to first delineate the watershed into 15 hydrological units using surface temperature, normalized difference vegetation index and surface albedo as attributes. Thereafter, semi‐empirical relationships between these TM‐based parameters and other SVAT parameters have been applied to compute the spatial variation of SVAT parameters and the associated evaporation from the different hydrological units. The impact of using watershed‐constant or watershed‐distributed SVAT parameters on the fluxes is analysed. The determination of watershed averaged evaporation with area‐aggregated SVAT parameters is feasible without significant loss of accuracy. Distributed evaporation in heterogeneous watersheds, however, can be investigated only with remote sensing flux algorithms that can account for spatially variable air temperature, surface roughness, surface albedo and the stability correction of the temperature profile due to buoyancy. Erroneous results can be expected if area‐aggregated SVAT parameters are used to calculate local evaporation. As most of the recently developed remote sensing flux algorithms are based on areal constant SVAT parameters, direct applications in watersheds are still limited. Copyright © 2001 John Wiley & Sons, Ltd. 相似文献
79.
Hussein Abd-Elmotaal 《Journal of Geodesy》1992,66(4):325-335
Some selected test areas in the Austrian territory are presented. Free-air and Bouguer anomalies as well as isostatic anomalies (based on Vening Meinesz' isostatic model) are computed. Statistics of these anomalies are given. Also, an extensive comparison between their empirical covariance functions is made and will be discussed. The results show that the isostatic anomalies for our test areas still contain, in general, a trend part. 相似文献
80.