全文获取类型
收费全文 | 542篇 |
免费 | 79篇 |
国内免费 | 154篇 |
专业分类
测绘学 | 28篇 |
大气科学 | 44篇 |
地球物理 | 137篇 |
地质学 | 324篇 |
海洋学 | 90篇 |
天文学 | 12篇 |
综合类 | 13篇 |
自然地理 | 127篇 |
出版年
2024年 | 1篇 |
2023年 | 1篇 |
2022年 | 6篇 |
2021年 | 14篇 |
2020年 | 19篇 |
2019年 | 15篇 |
2018年 | 17篇 |
2017年 | 16篇 |
2016年 | 18篇 |
2015年 | 21篇 |
2014年 | 21篇 |
2013年 | 41篇 |
2012年 | 32篇 |
2011年 | 31篇 |
2010年 | 16篇 |
2009年 | 29篇 |
2008年 | 38篇 |
2007年 | 45篇 |
2006年 | 45篇 |
2005年 | 55篇 |
2004年 | 35篇 |
2003年 | 28篇 |
2002年 | 18篇 |
2001年 | 31篇 |
2000年 | 24篇 |
1999年 | 21篇 |
1998年 | 25篇 |
1997年 | 13篇 |
1996年 | 24篇 |
1995年 | 17篇 |
1994年 | 10篇 |
1993年 | 15篇 |
1992年 | 10篇 |
1991年 | 6篇 |
1990年 | 2篇 |
1989年 | 2篇 |
1988年 | 6篇 |
1987年 | 2篇 |
1986年 | 1篇 |
1982年 | 1篇 |
1954年 | 3篇 |
排序方式: 共有775条查询结果,搜索用时 15 毫秒
771.
In this paper the effects of four different rheologies on the evolution of a large-scale sea ice pack are determined and compared. Two rheologies are of viscous-plastic form, and two are viscous fluid relations. The initial pack domain is rectangular, and the motion is driven by wind stress and resisted by ocean drag. Two adjacent edges are rigid shore boundaries, and the other two are free boundaries at open water which move during the pack motion, so that the pack domain changes in time. Two different forms of boundary conditions at the rigid shore edges are considered, which also influence the evolution. The governing equations are solved numerically using a finite-element method, and, unlike previous numerical treatments, no artificial viscosity is incorporated to stabilise the algorithm near interfaces between converging and diverging flow. Instability arises when any tensile stress is abruptly cut-off when diverging flow is initiated, and an alternative view is offered. © 1998 John Wiley & Sons, Ltd. 相似文献
772.
Pierfrancesco Dellino Fabio Dioguardi Domenico Maria Doronzo Daniela Mele 《Sedimentology》2020,67(4):2013-2039
Dense gas-particle jets similar to collapsing eruption columns were generated by large-scale experiments. The column collapse resulted in a ground-hugging current forming stratified layers with bedding similar to natural pyroclastic density current deposits. At the impact of the collapsing column on the ground, a thick, massive bed was formed due to a high sedimentation rate that dumped turbulence due to high clast concentration. Down-current, flow expansion favoured turbulence and dilute gas-particle current that formed thin rippled layers deposited under traction. Experiments fed with fine ash (median size 0·066 mm) formed deposits without tractional structures, because fine particles, as other sedimentary fine material, is cohesive and exposes a limited surface to the shear stress. Experimental outcomes show that massive beds are formed where the sedimentation rate per unit width Srw exceeds the bedload transportation rate Qb by two orders of magnitude. A lower ratio generates traction at the base of the flow and formation of shear structures that increase in wavelength and height with a decreasing flux. This study presents a diagram that provides a useful addition for facies analysis of pyroclastic density currents, provided that deposits representing sustained sedimentation can be identified in the field. In the diagram a decrease in the Srw/Qb ratio corresponds to an increase in bedform size. Application of the diagram for hazard assessment purposes allows the reconstruction of the mass eruption rate of the Agnano–Monte Spina eruption at Campi Flegrei, which is the main variable defining the intensity of past eruptions, and of the Bingham rheology of the massive underflow of the Mercato pyroclastic density current at Vesuvius. 相似文献
773.
内蒙古大青山地区是典型的早前寒武纪造山带根部岩石出露区,大量下地壳高级变质-深熔岩石中保留了丰富的流变构造样式,是开展部分熔融岩石流变行为研究的天然实验室。本文对内蒙古大青山地区雪海沟和大庙-忽鸡沟构造带内变形岩石开展了宏观、微观构造解析、EBSD组构以及锆石U-Pb年代学研究,并结合前人研究成果,考查了不同构造层次、不同熔融程度岩石的流变特征及其与造山过程的耦合关系。研究结果表明,雪海沟至大庙-忽鸡沟地区体现了造山带地壳结构层次由深至浅的特点。深部构造层次(雪海沟)高级深熔条件下,宏观上以各种形式的浅色脉体参与岩石流变,深熔熔体夹矿物颗粒流形成网状的断续条带状构造。微观上斜长石受扩散蠕变、颗粒边界滑移和颗粒流动影响,一般没有明显的晶内变形组构,CPO(晶格优选方位)发育不明显。在中深部构造层次(大庙-忽鸡沟)深熔作用相对较弱,宏观上形成平行片麻理的较规则条纹/条带构造。微观上斜长石发生位错蠕变,CPO发育明显。此外,角闪石在不同构造层次下均表现出位错蠕变特征,结晶优选方向受深熔作用影响不大。上述变形样式和机制,体现了造山带根部高级变质-深熔岩石在固-液两相介质中,发生水平层状粘-塑性流动变形特点。随后深熔岩石的塑性流动变形伴随加厚地壳的伸展减薄-隆升过程而逐渐硬化并遭受剥露。 相似文献
774.
775.