全文获取类型
收费全文 | 195篇 |
免费 | 6篇 |
国内免费 | 6篇 |
专业分类
测绘学 | 6篇 |
大气科学 | 6篇 |
地球物理 | 68篇 |
地质学 | 83篇 |
海洋学 | 4篇 |
综合类 | 9篇 |
自然地理 | 31篇 |
出版年
2022年 | 2篇 |
2021年 | 1篇 |
2020年 | 1篇 |
2019年 | 4篇 |
2018年 | 3篇 |
2017年 | 2篇 |
2016年 | 5篇 |
2015年 | 2篇 |
2014年 | 8篇 |
2013年 | 3篇 |
2012年 | 5篇 |
2011年 | 10篇 |
2010年 | 5篇 |
2009年 | 11篇 |
2008年 | 13篇 |
2007年 | 16篇 |
2006年 | 17篇 |
2005年 | 8篇 |
2004年 | 8篇 |
2003年 | 7篇 |
2002年 | 3篇 |
2001年 | 7篇 |
2000年 | 4篇 |
1999年 | 3篇 |
1998年 | 4篇 |
1997年 | 3篇 |
1996年 | 3篇 |
1995年 | 3篇 |
1994年 | 3篇 |
1993年 | 4篇 |
1992年 | 8篇 |
1991年 | 3篇 |
1990年 | 3篇 |
1989年 | 1篇 |
1988年 | 4篇 |
1987年 | 1篇 |
1986年 | 2篇 |
1984年 | 1篇 |
1983年 | 2篇 |
1982年 | 1篇 |
1981年 | 3篇 |
1980年 | 2篇 |
1978年 | 6篇 |
1977年 | 1篇 |
1976年 | 1篇 |
排序方式: 共有207条查询结果,搜索用时 15 毫秒
11.
12.
13.
We present a model for pore spaces that consists of two parts related by duality: (1) a decomposition of an open polyhedral pore space into open contractible pore bodies separated by relatively open interfaces and (2) a pore network that is homotopy equivalent to the pore space. The dual model is unique and free of parameters, but it relies on regularity conditions for the pore space. We show how to approximate any pore space by the interior of a polyhedral complex such that the regularity conditions are fulfilled. Thus, we are able to calculate the dual model from synthetic porous media and images of real porous media. The pore bodies are unions of relatively open Delaunay cells with respect to the corners of the pore boundary, and the pore network consists of certain at most two-dimensional (2D) Voronoi cells with respect to the corners of the pore boundary. The pore network describes the neighborhood relations between the pore bodies. In particular, any relatively open 2D Delaunay face f separating two pore bodies has a unique (relatively open) dual network edge. In our model, f is a pore throat only if it is hit by its dual network edge. Thus, as opposed to widespread intuition, any pore throat is convex, and adjacent pore bodies are not necessarily separated by pore throats. Due to the duality between the pore network and the decomposition of the pore space into pore bodies it is straightforward to store the geometrical properties of the pore bodies [pore throats] as attributes of the dual network vertices [edges]. Such an attributed network is used to perform 2D drainage simulations. The results agree very well with those from a pore-morphology based modeling approach performed directly on the digital image of a porous medium. Contractibility of the pore bodies and homotopy equivalence of the pore space and the pore network is proven using discrete Morse theory and the nerve theorem from combinatorial topology. 相似文献
14.
根据成矿作用、成矿环境及矿床特征,金沙江流域(云南段)砂金矿床,可划分为:残坡积、洪积、冲洪积、冲积和冰碛等五种类型。成矿主要受碰撞带、深大断裂、大断裂及其派生断裂、基底岩石、地貌、水质和水化学环境等综合控制。以巨甸-大具及中江街-金江街两片区最具有找矿前景。 相似文献
15.
Jonathan F. Nott 《地球表面变化过程与地形》1992,17(4):361-374
The long-term evolution of streams in the Shoalhaven catchment of southeast New South Wales has been a contentious issue for decades. Several authors have suggested that the Shoalhaven River was captured at the sharp eastward bend near Tallong: this has been used as evidence for the westward migration of the east Australian divide in this area. Other workers, however, have argued that capture did not occur and that the location of the divide has been stable throughout the Tertiary. A vast sheet of sediments which spread across and infill a palaeovalley network cut into a broad undulating plain in the middle Shoalhaven catchment provides a record of stream behaviour since at least the start of the Tertiary. This record shows that the Shoalhaven River and many of its tributaries have maintained almost the same courses since at least the very Early Tertiary. This provides strong evidence against the capture hypothesis. The record further suggests that during the Paleogene these streams were graded to a level within the southeast Australian highlands; their depths of incision thus cannot be used as evidence for the extent of uplift of the southeast Australian highlands during this time. 相似文献
16.
In a basin developed on a stream table, effluent subsurface flow supported a channel network that evolved by a combination of headward growth, lateral widening and divide decay. The area occupied by the developing network increased with time. Circularity was used to characterize network evolution which occurred in three phases (initiation, extension and abstraction). Basin sediment discharge declined exponentially with time. Pronounced quasi-cyclic variability was superimposed upon this general trend. Some of the variability was directly linked to changes in the amount of sediment supplied to the channel. The variation of mean network sediment yield (mean sediment discharge scaled by network area) with time adequately described the general decline in sediment discharge as the network evolved. 相似文献
17.
镇江市是江苏省滑坡地质灾害较为严重的城市,其地质灾害防治工作开展较早,积累了一定的防治管理经验。而焦山索道上站滑坡治理工程是多种滑坡治理技术方法和措施的综合应用,通过混凝土抗滑桩、锚索、锚杆、排水以及挂网喷播复绿等技术方式和措施的应用,成功地完成了焦山索道上站的滑坡治理工程,为镇江市其他滑坡地质灾害的治理提供了一定的参考借鉴作用。 相似文献
18.
19.
The analysis of drainage network composition 总被引:1,自引:0,他引:1
J. S. Smart 《地球表面变化过程与地形》1978,3(2):129-170
The Horton method of analyzing drainage network composition is reviewed, with the conclusion that it has not been very effective either in improving understanding or in developing useful methods of characterizing drainage basins. New methods which are based on the link rather than the Horton (or Strahler) stream are described. A number of detailed examples of the application of these new methods to the topologic and geometric properties of networks are provided. The results are compared with the predictions of the random model. Data used in the analysis were obtained from 1:24,000 U.S.G.S. topographic maps of eastern Kentucky. Thirty drainage basins were selected and their channel networks were outlined first by the contour-crenulation (CC) method and then by another, more objective, method (SC) in which stream sources were identified by a quantitative slope criterion. The CC and SC samples comprise about 8,700 and 1,700 links, respectively. The three most important results of the analysis are: (1) the channel networks are slightly but significantly more elongated than predicted by the random model, (2) there are fewer second magnitude links than predicted, and (3) the length distribution for interior links depends upon the kind of link (interior or exterior) joined downstream. These features are found in both CC and SC networks. 相似文献
20.
D. G. Day 《地球表面变化过程与地形》1978,3(3):319-326
Observations of stream behaviour during rainfall indicate that previous notions of a simple expanding and contracting network need review and refinement. In a small rural catchment near Armidale, N.S.W. changes in flowing stream length during rainfall have been depicted on flow length graphs which indicate a varied network response to similar rainfall amounts. Channel flow phenomena include discontinuous flow, the generation of flow points within the channel and movement of water downslope from saturated depression sources. Localized physical controls have a significant effect on stream growth which is a sensitive indicator of the catchment response to rainfall. During rapid changes in stream length total flowing length and discharge are highly correlated. A model of the pattern of network expansion and contraction involves several phases of flow contraction. 相似文献