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51.
Shallow-water gravity-flow deposits, Chapel Island Formation, southeast Newfoundland, Canada 总被引:3,自引:0,他引:3
A remarkable suite of shallow-water, gravity-flow deposits are found within very thinly-bedded siltstones and storm-generated sandstones of member 2 of the Chapel Island Formation in southeast Newfoundland. Medium to thick siltstone beds, termed unifites, range from non-graded and structureless (Type 1) to slightly graded with poorly developed lamination (Type 2) to well graded with lamination similar to that described for fine-grained turbidites (Type 3). Unifite beds record deposition from a continuum of flow types from liquefied flows (Type 1) to turbidity currents (Type 3). Calculations of time for pore-fluid pressure dissipation support the feasibility of such transitions. Raft-bearing beds consist of siltstone with large blocks or‘rafts’ of thinly bedded strata derived from the underlying and adjacent substrate. Characteristics suggest deposition from debris flows of variable strength. Estimates of debris strength and depositional slope are calculated for a pebbly mudstone bed using measurable and assumed parameters. An assumed density of 2.0 g cm-1 and a compaction estimate of 50% gives a strength estimate of 79.7 dyn cm-2 and a depositional slope estimate of 0.77°. The lithologies and sedimentary structures in member 2 indicate an overall grain-size distribution susceptible to liquefaction. Inferred high sediment accumulation rates created underconsolidated sediments (metastable packing). Types of sediment failure included in situ liquefaction (‘disturbed bedding’), sliding and slumping. Raft-bearing debrites resulted from sliding and incorporation of water. Locally, hummocky cross-stratified sandstone directly overlies slide deposits and raft-bearing beds, linking sediment failure to the cyclical wave loading associated with large storms. The gravity flows of the Chapel Island Formation closely resemble those described from the surfaces of modern, mud-rich, marine deltas. Details of deltaic gravity-flow deposition from this and other outcrop studies further our understanding of modern deposits by adding a third dimension to studies primarily carried out with side-scan sonar. 相似文献
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HENRY PAUL 《地质学报》1938,(Z1)
Mit 1 Abbildung Nach Abfassung des Manuskriptes meiner Arbeit über"Unterkar-bonische Kalkalgen und Calcisphaeren Deutschlands",die sich u.a.mit 相似文献
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Qualitative and quantitative observations show a general positive correlation between grain size and thickness of cross-bedded units. Greater sand-wave height correlates with greater turbulence which permits more and coarser grains to be transported. A theory is developed which qualitatively explains these relationships. 相似文献
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Abstract Based on some special characteristics between the depths and the cross-sectional areas of a channel, and the use of the stage-discharge relationship, a promising simple method of establishing the runoff for a recurrence interval of about 10 years on the upper frequency curve for an ungaged small stream is presented. This method was tested quite successfully on a number of sample streams in the eastern part of the United States with drainage areas less than 400 square miles. This method applies only to stable natural streams without anyman-made deterrent to the natural development of the stream channel or flood plain. 相似文献
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MARK D. BATEMAN PAUL C. BUCKLAND MARTIN A. WHYTE ROBERT A. ASHURST CLAIRE BOULTER EVA PANAGIOTAKOPULU 《Boreas: An International Journal of Quaternary Research》2011,40(4):573-584
Bateman, M. D., Buckland, P. C., Whyte, M. A., Ashurst, R. A., Boulter, C. & Panagiotakopulu, E. 2011: Re‐evaluation of the Last Glacial Maximum typesite at Dimlington, UK. Boreas, 10.1111/j.1502‐3885.2011.00204.x. ISSN 0300‐9483. Recent erosion has allowed re‐examination of the stratigraphy and sampling for both optically stimulated luminescence dating and palaeoecological analysis of the key sections in the Last Glacial Maximum deposits at Dimlington in East Yorkshire, England. Both stratigraphy and fossil insect evidence support a subaerial origin for laminated and cross‐bedded sediments between two diamictons previously interpreted as synchronous. The fossil biota indicates conditions similar to those of a pond on sandur in the high Arctic, with little or no vegetation cover. The existence of distinct oscillations of the ice front is indicated. The first, within the period 21.7–16.2 ka, appears coincident with climate warming, as deduced from Greenland ice‐core evidence, and is interpreted as an ice stream associated with changing flow patterns within the British–Irish Ice Sheet (BIIS). The second, dating between 16.2 and 15.5 ka, appears to coincide with a climatic cooling, although current models show that the BIIS had by this period already retreated back to ice centres. This new evidence supports the view that the eastern sector of the BIIS did not reach its maximal extent synchronously with other parts of the BIIS. 相似文献
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This article seeks to contribute to the literature on female labour in the pipfruit industry in New Zealand and Chile. As added workers seeking to supplement household incomes by casualised, seasonal employment, these female workers are significant contributors to what are often declining household incomes, given changes in production and the labour market of the 1990s. But this enhanced role continues to exist alongside normative expectations about domestic roles and responsibilities. This research reports on a survey that was completed by female workers in both Chile and New Zealand. While there are differences in the respective labour markets of the two countries concerned, the role of women in balancing employment and domestic responsibilities is characteristic of both situations. It is the intersection between normative expectations and participation in casual/seasonal labour in the two research sites that is the focus of this article. 相似文献