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An experimental study of rip channel flow 总被引:2,自引:0,他引:2
Nils Drnen Harshinie Karunarathna Jrgen Fredse B. Mutlu Sumer Rolf Deigaard 《Coastal Engineering》2002,45(3-4)
A laboratory study of the flow over a bar with a single rip channel has been performed. First, the well-known pattern of a bar circulation cell with a strong offshore-directed current out through the rip channel and a weaker onshore-directed return flow over the bar is documented. Then measurements of the three-dimensional structure of the flow in the area where the rip channel, the bar and the trough meet and well inside the rip channel are presented. These measurements reveal that 3D effects play an important role, and that a depth-integrated viewpoint may not always be sufficient for predicting the flow in the near bed region. Particle-tracking experiments illustrate the near bed flow pattern over the entire area. These demonstrate how the overall trajectory pattern changes as a function of the distance of wave breaking from the bar crest: For some conditions, the rip current is fed from the trough and for other conditions it is fed directly from the bar. Both the 3D measurements and the trajectory tests show the existence of a weaker onshore-directed near-bed drift in the area where the rip current ceases. Finally, in a series of sensitivity tests, measurements of the rip current intensity for different wave climate and water level conditions reveal a strong correlation between the rip current intensity and the wave height (both normalized). 相似文献
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Nils Edelman 《International Journal of Earth Sciences》1967,56(1):362-363
Ohne Zusammenfassung 相似文献
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Eutrophication in a Small Stream in Central Sweden 总被引:1,自引:0,他引:1
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Prof. Dr. Nils Spjeldnaes 《International Journal of Earth Sciences》1964,54(1):24-45
Summary Traces of the Eocambrian glaciation are found in three district in Norwegian territory, 1) in the south-east, at and north of the lake MjØsa, 2) in north-east, in Finnmark, and 3) in Spitzbergen. The two first districts are connected by a number of localities in Sweden, along the margin of the Caledonian Mountain chain. The glacial beds form the base of the Eocambrian, which is taken as the lowest part of the Cambrian. They generally rests with a more or less pronounced disconformity on dolomitic rocks of the Esmarkian (the upper part of the Riphean system). In some cases they rest directly on the crystalline Precambrian basement. This is due either to Esmarkian tectonic movements, to deep glacial erosion or both. The glacial beds are varied lithologically, but the characteristic rock types are tillites, boulder-shales and varved mudtones. All tillites are not regarded as fossil moraines, formed by ice movement. Some of them are supposed to have been formed by dropping of material from floating ice, either glacier ice or sea ice in a marine or brackish environment. The wide and uniform distribution of the tillite seems to preclude an interpretation as mudflows. Comparison with the Quaternary glacial sediments have given interesting results, and add to the evidence for a glacial origin of the tillites. It is also indicated that the direction of transport will depend on whether the material was rafted with glacial ice, or with drifting sea ice. Much more work has to be done both on the sedimentology, stratigraphy and paleomagnetism of the Norwegian Eocambrian glacial deposits and comparable sediments in order to get a clear and coherent picture of the glaciation, but the present evidence seem to indicate that it was part of a world-wide glaciation of even greater extent than the Permo-Carboniferous and Quarternary ones. 相似文献
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River tributaries as sediment sinks: Processes operating where the Tapajós and Xingu rivers meet the Amazon tidal river
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Aaron T. Fricke Charles A. Nittrouer Andrea S. Ogston Daniel J. Nowacki Nils E. Asp Pedro W. M. Souza Filho Marcio S. da Silva Anna M. Jalowska 《Sedimentology》2017,64(6):1731-1753
The Amazon River is the largest fluvial source of fresh water and sediment to the global ocean and has the longest tidally influenced reach in the world. Two major rivers, the Tapajós and Xingu, enter the Amazon along its tidal reach. However, unlike most fluvial confluences, these are not one‐way conduits through which water and sediment flow downstream towards the sea. The drowned‐river valleys (rias) at the confluences of the Tapajós and Xingu with the Amazon River experience water‐level fluctuations associated not only with the seasonal rise and fall of the river network, but also with semidiurnal tides that propagate as far as 800 km up the Amazon River. Superimposed seasonal and tidal forcing, distinct sediment and temperature signatures of Amazon and tributary waters, and antecedent geomorphology combine to create mainstem–tributary confluences that act as sediment traps rather than sources of sediment. Hydrodynamic measurements are combined with data from sediment cores to determine the distribution of tributary‐derived and Amazon‐derived sediment within the ria basins, characterize the sediment‐transport mechanisms within the confluence areas and estimate rates of sediment accumulation within both rias. The Tapajós and Xingu ria basins trap the majority of the sediment carried by the tributaries themselves in addition to ca 20 Mt year?1 of sediment sourced from the Amazon River. These findings have implications for the interpretation of stratigraphy associated with incised‐valley systems, such as those that dominated the transfer of sediment to the oceans during lowstands in sea level. 相似文献