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121.
Although the long-term effects and the fate of petroleum hydrocarbons in marine and freshwater environments are not fully
understood, it is generally recognized that much of the oil released by accidental spills or by various land sources ends
up in the sediment where it may remain for at least several years The present study was undertaken to collect some initial
data on the hydrocarbon concentrations in surficial sediments of lakes St Clair, Erie, and Ontario
The distribution of hydrocarbons in these lakes followed the general patterns found for a number of contaminants, in that
the distribution tended to coincide with the outlines of the sedimentary basins The highest concentrations were found in the
Western Basin of Lake Erie and in the inshore zone around the west end of the lake, suggesting major inputs from the Detroit
River Apart from some spots of high concentration around known dumping grounds, the concentrations gradually diminish toward
the east The distribution pattern in Lake Ontario may be more readily ascribed to water circulation patterns than to any specific
source around the lake The hydrocarbon levels were found to be significantly lower than those in Lake Erie in Lake St Clair
only trace quantities of hydrocarbons were found, suggesting either low inputs or low sedimentation/accumulation rates due
to its shallowness
Although the present survey was limited to the top 3 cm of the sediments, the resulting distribution patterns indicate the
western end of Lake Erie as the area with the heaviest hydrocarbon loadings The results may also facilitate the selection
of specific areas where core sampling coupled with more complete analysis of the extracts could yield significant information
on the long-term accumulation of anthropogenic hydrocarbons, and on their persistence and transformations in Great Lakes sediments 相似文献
122.
Benedek Nagy 《Transactions in GIS》2023,27(7):2042-2098
Digital geometry is a field in the intersection of discrete mathematics and geometry having various applications including geographical information systems (GIS). In digital spaces, in grids, distances can be defined based on steps in paths in somewhat similarly as in graph theory. However, the grids have more definite structures, thus one may obtain more concrete results, for example, close formulae, than on arbitrary graphs. In this article, the weighted (also called chamfer) distances, and based on them, the distance transform are investigated on the regular triangular grid. Three types of neighborhood relations are used on the grid, and therefore, three weights are used to define a distance function. Natural conditions are used on the weights such as they are positive and a larger step (in the usual and also in the Euclidean sense) cannot have a smaller weight than a smaller one. Some properties of the weighted distances are discussed; for example, they are proven to be metrics. We also give algorithms and formulae that compute the weighted distance of any point pair on a triangular grid. Algorithm for weighted distance transform is provided based on wave-front propagation. Therefore, these new distance functions are ready for further applications in GIS, in image processing tasks, in computer vision, in graphics, in networking, and also in other applied fields. 相似文献
123.
Benedek Nagy 《Transactions in GIS》2023,27(2):388-407
There are various tessellations of the plane, including three regular and eight semi-regular tilings. The square grid is self-dual, and the hexagonal and triangular tilings are dual to each other. The semi-regular tessellations are based on more than one type of regular tiles, while their dual tilings are based on a sole but not a regular tile. In various applications, including Geographical Information Systems, it is worth considering non-regular grids instead of the most used square grid. In this article, we are interested in the dual of the semi-regular truncated quadrille tiling, T(8,8,4), which is also known as the Khalimsky grid due to its connectedness structure. In our grid, which is called the tetrakis square or kisquadrille tiling, while it is denoted by D(8,8,4), we consider the right-angled triangle regions of the usual two-dimensional Khalimsky graph as tiles/pixels. We give an easy-to-use coordinate frame addressing the triangles of all the four different orientations. Neighbor relations are described mathematically based on this frame. Based on the shortest path algorithm, a closed formula is proven to compute the digital, that is, path-based distance on this grid. Some properties of the distance function have also been studied. Hierarchical coarsening is a frequently used technique both in Geometric and Geographical Information Systems to rescale some parts of the map. The tetrakis square grid is apt for hierarchical coarsening, and thus, it can easily be used in image compression and multigrid and other related methods. 相似文献