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41.
A new one-dimensional model for penetration analysis of a rigid projectile into a soil target is presented. The soil medium is represented by a set of discs of constant thickness, responding in the radial direction under plain strain regime. When penetration through a typical disc occurs, the projectile displaces soil material and a radial plastic shock wave propagates in the disc. The interaction pressure between the projectile and soil material is compatible with the motion of the contact boundary, between them. The instantaneous resistive force is obtained by summation of the contributions of all the discs which are in contact with the nose surface of the projectile. Soil is considered as a ‘floating’ ideally locking material, in which the locking volumetric strain is adjusted to the physical stress–strain properties of the soil material. Friction between projectile and soil is assumed to be negligible. Comparison is made with both twodimensional computer program results and experimental data, and very good agreement is observed. Comparison with other analytical methods reveals that the present model most closely resembles existing experimental results and permits further analysis of the problem as predictions of target response and of stress distribution on the projectile nose. The calculations require very small amounts of computer time. Analysis with the present model yields an efficient and comprehensive means to analyse penetration and perform parameter analysis. 相似文献
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Incision of alluvial channels in response to a continuous base level fall: Field characterization, modeling, and validation along the Dead Sea 总被引:5,自引:1,他引:4
The dramatic lake level drop of the Dead Sea during the twentieth century ( 30 m) provides a field-scale experiment in transport-limited incision of gravel-bed channels in response to quasi-continuous base level fall at approximately constant rate. We apply a one-dimensional numerical incision model based on a linear diffusion equation to seven ephemeral channels draining into the Dead Sea. The model inputs include the measured twentieth century lake level curve, annual shoreline location (i.e., annual channel lengthening following the lake level drop), reconstructed longitudinal profiles of each of the channels based on mapped and surveyed terraces, and the current profiles of the active channels. The model parameters included the diffusion coefficient and the upstream-derived sediment flux. Both were first calibrated using a set of longitudinal profiles of known ages and then validated using additional sets of longitudinal profiles.The maximum at-station total incision observed at each of the studied channels was significantly less then the total lake level drop and varied in response to both drainage area and lake bathymetry. The model applied predicted degradation rates and the pattern of degradation with high accuracy. This suggests that sediment flux in the modeled channels is indeed linearly dependent on slope. Further support for this linear dependency is provided by a linear correlation between the diffusion coefficient and the mean annual rain volume over each basin (a proxy for discharge). The model presented could be a valuable tool for planning in rapid base level fall environments where incision may risk infrastructure. 相似文献
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A model of a heterogeneous neighborhood 总被引:1,自引:0,他引:1
Tel Aviv is a highly ethnic city in which ethnicity is deeply embedded in people’s perceptions of their social milieus. Shapira,
as one of the most heterogeneous neighborhoods in Tel Aviv, supplies a unique demonstration of the inadequacy of the Chicago
model, which assumes the emergence of homogeneous neighborhoods. The study shows that ethnicity is exercised as a major force
in determining social life in Shapira. Interactive segregation indices reveal that residents of Shapira tend to prefer intra-ethnic
social networks although two-thirds of them maintain inter-ethnic networks as well. Despite this, residential and activity
spaces are highly heterogeneous. Residential spaces are heterogeneous on all scales from residents’ immediate surroundings
to the block and the neighborhood as a whole. In most buildings one may find neighbors from two or three different ethnic
groups with only non-Jewish residents excluded from publicly owned buildings. Most residents perform large part of their everyday
life outside the neighborhoods in ethnically heterogeneous surroundings, but nonetheless in choosing their more meaningful
partners for social networks they choose them from their ethnic groups. The fact that residents tend to perform a large part
of their activities out of their neighborhood, and to live in heterogeneous surroundings in social categories that are perceived
by them salient to their daily life, does not undermine the relevance of the neighborhood as a socially constituted entity
in the urban field. People organize and act in order to improve life conditions in the neighborhood, they feel sense of attachment
to the neighborhood and they develop some local social networks in the neighborhood. 相似文献
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