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101.
102.
Olav Hansen 《Icarus》1977,32(4):458-460
Sets of diameter determinations before and after opposition for the asteriods Ceres, Pallas, Vesta, and Fortuna have been studied statistically for indications of spin direction. All four asteriods are tentatively found to have prograde spin. For Ceres, that conclusion is virtually certain. 相似文献
103.
Olav Hansen 《Icarus》1977,32(2):229-232
A correlation between membership in a dynamically defined asteroid family and membership in a given asteroid spectral class is sought. Examination of 10 families each with five or more classified members indicates a correlation for the 4 families whose existence is best established, and no correlation for the remaining 6 families. This conclusion supports the break-up hypothesis for the origin of some families, while not contradicting that hypothesis for any family. 相似文献
104.
Fish behaviour relevant to fish catchability 总被引:1,自引:0,他引:1
Walsh Stephen J.; Godo Olav Rune; Michalsen Kathrine 《ICES Journal of Marine Science》2004,61(7):1238-1239
105.
106.
The Law of the Sea Convention constrains regional environmental regimes, especially with respect to navigation beyond the territorial sea. Existing soft-law institutions, notably the Arctic Council, have already strengthened environmental governance in the region by (1) improving the knowledge base; (2) preparing practical guidance on risk reduction; (3) highlighting in broader regulatory fora the Arctic dimension of problems like long-range transported hazardous compounds; and (4) supporting the capacity of Arctic states to implement existing commitments. None of those functions would be much enhanced by a legally binding Arctic environmental regime. The political impediments to reaching circumpolar agreement on a single comprehensive legal regime would suggest a flexible approach to norm building that seeks productive interplay with existing institutions. 相似文献
107.
Large asymmetric bedforms known as dunes commonly dominate the bed of sand rivers. Due to the turbulence generation over their stoss and lee sides, dunes are of central importance in predicting hydraulic roughness and water levels. During floods in steep alluvial rivers, dunes are observed to grow rapidly as flow strength increases, undergoing an unstable transition regime, after which they are washed out in what is called upper stage plane bed. This transition of dunes to upper stage plane bed is associated with high transport of bed sediment in suspension and large decrease in bedform roughness. In the present study, we aim to improve the prediction of dune development and dune transition to upper stage plane bed by introducing the transport of suspended sediment in an existing dune evolution model. In addition, flume experiments are carried out to investigate dune development under bed load and suspended load dominated transport regimes, and to get insight in the time scales related to the transition of dunes to upper stage plane bed. Simulations with the extended model including the transport of suspended sediment show significant improvement in the prediction of equilibrium dune parameters (e.g. dune height, dune length, dune steepness, dune migration rate, dune lee side slope) both under bed load dominant and suspended load dominant transport regimes. The chosen modeling approach also allows us to model the transition of dunes to upper stage plane bed which was not possible with the original dune evolution model. The extended model predicts change in the dune shapes as was observed in the flume experiments with decreasing dune heights and dune lee slopes. Furthermore, the time scale of dune transition to upper stage plane bed was quite well predicted by the extended model. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
108.
Olav Møyner 《Computational Geosciences》2017,21(5-6):999-1021
Implicit transport solvers used in reservoir simulation can take longer time steps than explicit solvers, but for long time steps, the commonly used Newton-Raphson’s method will often fail to converge. The convergence issues may manifest themselves as oscillating residuals even though the implicit discretization itself is stable. This behavior occurs because the fractional flow-type flux functions often change between convex and concave during long time steps, resulting in multiple contraction regions for the Newton-Raphson solver. The common strategy to overcome this is to set limits on the saturation changes during the nonlinear iteration, but such a limit has to be determined on a case by case basis, excess iterations may be required, and practical convergence is not guaranteed for a given problem. Previous work on this problem by multiple authors has resulted in solvers based on trust regions, where unconditional convergence can be obtained for incompressible two-phase flow provided a priori analytical knowledge of the flux function exists. The goal of our work is to extend this methodology to a solver where inflection points demarking the different contraction regions do not need to be explicitly known. Instead, these values are estimated during the solution process, giving improved convergence by a local computation for each interface in the simulation model. By systematically reducing updates over regions known to produce convergence issues, it is possible to greatly reduce the computational expense, making the same formulation suitable for an arbitrary number of components. We present a series of numerical results, including arbitrary time-step lengths for two and three-phase gravity segregation, as well as three-dimensional gas and water injection problems with wells and a mixture of both viscous and gravity-dominated flow regimes. The test cases are a systematic validation on a wide variety of both analytical and tabulated relative permeability curves. 相似文献