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排序方式: 共有329条查询结果,搜索用时 31 毫秒
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Silicon-29 chemical shifts of methyl, ethyl, chloro and trimethylsilyl derivatives of silicic acids are compared to those of silicic acid anions found in aqueous solutions. Although the chemical shifts of the silicate anions vary with pH and concentration, a good correlation is obtained for the chloro and alkoxi derivatives. The chemical shifts of the trimethylsilyl esters are of limited comparability to the data of the silicates only. 相似文献
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Volcanic gases, black smokers, and the great oxidation event 总被引:3,自引:0,他引:3
Heinrich D. Holland 《Geochimica et cosmochimica acta》2002,66(21):3811-3826
This paper proposes that gradual changes in the composition of volatiles that have been added to the atmosphere-ocean system are responsible for the Great Oxidation Event (G.O.E.) ca. 2.3 Ga. Before ca. 2.3 Ga, the composition of these volatiles was probably such that 20% of the carbon gases could be reduced to organic matter and all of the sulfur gases could be reduced to pyrite. Since 2.3 Ga, the composition of these volatiles has been such that 20% of the carbon gases could be reduced to organic matter, but only a fraction of the sulfur gases could be reduced to pyrite. This change led to the oxygenation of the atmosphere and to a large increase in the SO4−2 concentration of seawater. A considerable body of observational data supports these proposals. 相似文献
127.
Landslides and their hydraulic effects are studied by numerical and experimental means. A two-dimensional model based on Navier–Stokes equations has been developed considering the sediments and water as a mixture. A Bingham law written in effective stress and an erosion–diffusion law at the water–sediment interface have been introduced into the model. Laboratory experiments consisting in the sliding of a block, a coarse gravel and a fine sand have been carried out. The results are compared with the numerical model. These experiments show the importance of sediment rheology and interstitial pressure in slide velocity and water wave generation. Copyright © 1999 John Wiley & Sons, Ltd. 相似文献
128.
A U(1) model of gravitational, Higgs and, gauge fields is analysed. Two phases of the system are considered. In the case with broken symmetry we have the Nielsen-Olesen configuration. In the symmetric phase we find a space-time metric S2 × E12. This appears in full analogy to the Freund-Rubin compactification due to an antisymmeric tensor field. The connection of these structures with cosmic string phenomenology is analysed. 相似文献
129.
Cordrie Louise Gailler Audrey Escartin Javier Feuillet Nathalie Heinrich Philippe 《Natural Hazards》2020,103(2):2103-2129
Natural Hazards - The arc of the Lesser Antilles is associated with a significant tectonic activity due to the subduction of the Atlantic oceanic plate under the Caribbean plate. Earthquakes in... 相似文献
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Friedemann Baur Matias Di Benedetto Thomas Fuchs Carolyn Lampe Simone Sciamanna 《Marine and Petroleum Geology》2009
For the first time, a new approach to petroleum systems analysis is presented which allows full integration of tectonic and palinspastic restoration with three-dimensional (3D), PVT-controlled, multi-component, three-phase petroleum migration analysis through time. A systematic modeling study has been applied to a study area dominated by fold and thrust belts located in the Sub Andean orogeny near Tarija, Bolivia. The project has been performed with a special focus on the simulation technique and on the correct distribution of temperature, source-rock maturity and pressure development through time with reference to its input data. This is the first pilot project presenting a 3D numerical model in a compressional structural regime to which the basin modeling approach has been applied to explain the observed distribution of temperature, pressure, maturity and petroleum accumulations in general. 相似文献