排序方式: 共有26条查询结果,搜索用时 15 毫秒
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北京西山水平分层剪切流变构造初探 总被引:7,自引:2,他引:7
对比国内外关于变质岩区构造变形序列的实例,可知第一世代的构造变形几乎都以发育不同尺度的强烈扁平化平卧褶皱和有关的轴面流劈理或片理,以及近水平的韧性剪切带等构造组合为特征。北京西山的情况也不例外。这可能代表变质岩区早期构造变形的一种普遍模式,可能是地壳较深构造层次发生大规模透入性水平剪切流变的反映 相似文献
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高能射线工业CT最新进展 总被引:3,自引:2,他引:3
本文主要介绍了清华大学在高能射线工业CT研究及产业化方面的新进展,介绍了其中的多项成果:小体积、大功率的直线加速器,低噪声、高效率的阵列固体探测器,旋转极坐标反投影快速图像重建算法等.高能工业CT技术的研制成功及产业化,使我国高能工业CT技术达到国际先进水平,结束了我国无自主研制大型工业CT检测系统的历史,解决了我国大型工件无损检测难题,对提高我国高能无损检测技术水平具有重大意义. 相似文献
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近年来人们对"气候变暖"及其机制的争论达到了前所未有的程度,这可能是因为气候变化不再是单纯研究大气变化规律的科学,而变成一门与"减排方案"和"征收碳税"有关的政治与经济问题相联系,与国家经济利益有关的崭新课题."气候变暖"既与利益有关,就会难免偏离公正,偏离纯理论科学.本研究对国内外"气候变暖"最新动态进行回顾分析,得出以下认识和结论.1)过去百年城市发展,极大地影响了器测温度数据,如果没有对"热岛效应"进行矫正,无疑高估了过去百年全球升温的幅度;2)过去百年全球有所变暖是事实,但不同学者增温估算不一致.不仅升温幅度不确定,而且人类和自然因素对升温贡献各占多少也不确定;如果考虑到城市发展对增温估算的影响,过去百年增温应当比0.4℃更低,远没有达到历史上次级波动的变化范围.3)尽管过去百年地球有所变暖,但在万年轨道尺度上,现在地球处于变冷的大趋势过程中.对现在气候变暖更合理解释,是属于变冷大趋势中的次级变暖波动;4)不论过去还是现在,大气CO2浓度变化总是落后于温度变化,即总是温度驱动着CO2变化,而不是CO2浓度驱动地球增温. 相似文献
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葛建华 《沉积与特提斯地质》2009,29(4):96-99
在使用全谱直读等离子体发射光谱仪分析铅时,发现Cu221.810线对Pb220.3线形成干扰。产生这种干扰的原因是由于全谱直读等离子体发射光谱仪采用了固态阵列检测器和中阶梯光栅,从而在两条谱带之间发生了纵向干扰校正。可以采用干扰系数校正法或者选择在灵敏度稍低的VIS段摄谱进行干扰。 相似文献
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珠江河口地区可持续发展评价研究 总被引:4,自引:0,他引:4
未来发展对珠江河口区的资源环境承载能力和生态服务功能提出了前所未有的要求,在此认识基础上,构建了基于资源承载力的可持续发展评价指标体系,并进行了河口区发展水平、可持续性水平、可持续发展能力及其可持续发展状态变化的定量分析,得出:① 珠江河口区总体已进入经济资源驱动阶段;② 在自然子系统、经济子系统、社会子系统中,社会子系统滞后;③ 可持续发展能力处于中等可持续发展水平。 相似文献
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Metamorphic zircon formation by solid-state recrystallization of protolith igneous zircon 总被引:162,自引:0,他引:162
Protolith zircon in high‐grade metagranitoids from Queensland, Australia, partially recrystallized during granulite‐grade metamorphism. We describe the zircon in detail using integrated cathodoluminescence, U–Pb isotope, trace element and electron backscatter diffraction pattern (EBSP) analyses. Primary igneous oscillatory zoning is partially modified or obliterated in areas within single crystals, but is well preserved in other areas. A variety of secondary internal structures are observed, with large areas of transgressive recrystallized zircon usually dominant. Associated with these areas are recrystallization margins, interpreted to be recrystallization fronts, that have conformable boundaries with transgressive recrystallized areas, but contrasting cathodoluminescence and trace element chemistry. Trace element analyses of primary and secondary structures provide compelling evidence for closed‐system solid‐state recrystallization. By this process, trace elements in the protolith zircon are purged during recrystallization and partitioned between the enriched recrystallization front and depleted recrystallized areas. However, recrystallization is not always efficient, often leaving a ‘memory’ of the protolith trace element and isotopic composition. This results in the measurement of ‘mixed’ U–Pb isotope ages. Nonetheless, the age of metamorphism has been determined. A correlation between apparent age and Th/U ratio is indicative of incomplete re‐setting by partial recrystallization. Recrystallization is shown to probably not significantly affect Lu–Hf ages. Recrystallization has been determined by textural and trace element analysis and EBSP data not to have proceeded by sub‐grain rotation or local dissolution/re‐precipitation, but probably by grain‐boundary migration and defect diffusion. The formation of metamorphic zircon by solid‐state recrystallization is probably common to high‐grade terranes worldwide. The recognition of this process of formation is essential for correct interpretation of zircon‐derived U–Pb ages and subsequent tectonic models. 相似文献
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Patrick G. Hatcher 《Organic Geochemistry》1990,16(4-6)
Examination of a series of coalified gymnospermous woods ranging in rank from brown coal to subbituminous coal by solid-state 13C NMR and analytical pyrolysis has provided sufficient information to construct structural models depicting the changes that occur to lignin, the primary precursor of vitrinite, during coalification. Progressive changes in the chemistry of coalified wood suggest the following series of reactions: (1) demethylation to form catechol-like structures that are dominant components of brown coal and lignite A; (2) cleavage of aryl ether linkages to form phenols and reactive carbocations that alkylate the catechol rings; (3) dehydration of the catechol rings; (3) dehydration of the catechol-like structures to form the structures of subbituminous coal dominated by alkylphenols; and (4) reduction of the 3-carbon alkyl side chain derived from lignin to form propyl substituents. The models developed for each stage of coalification are derived from chemical modifications of the structure of lignin. 相似文献