全文获取类型
收费全文 | 128篇 |
免费 | 6篇 |
国内免费 | 1篇 |
专业分类
测绘学 | 1篇 |
大气科学 | 18篇 |
地球物理 | 34篇 |
地质学 | 49篇 |
海洋学 | 10篇 |
天文学 | 7篇 |
综合类 | 1篇 |
自然地理 | 15篇 |
出版年
2022年 | 1篇 |
2021年 | 4篇 |
2020年 | 4篇 |
2019年 | 3篇 |
2018年 | 9篇 |
2017年 | 4篇 |
2016年 | 8篇 |
2015年 | 1篇 |
2014年 | 2篇 |
2013年 | 11篇 |
2012年 | 8篇 |
2011年 | 7篇 |
2010年 | 6篇 |
2009年 | 8篇 |
2008年 | 8篇 |
2007年 | 7篇 |
2006年 | 3篇 |
2005年 | 6篇 |
2004年 | 7篇 |
2003年 | 2篇 |
2002年 | 2篇 |
2000年 | 1篇 |
1999年 | 4篇 |
1998年 | 2篇 |
1997年 | 1篇 |
1996年 | 1篇 |
1994年 | 1篇 |
1993年 | 1篇 |
1992年 | 1篇 |
1991年 | 1篇 |
1983年 | 1篇 |
1981年 | 2篇 |
1980年 | 1篇 |
1979年 | 2篇 |
1974年 | 3篇 |
1973年 | 2篇 |
排序方式: 共有135条查询结果,搜索用时 15 毫秒
71.
Lulseged Ayalew Dietmar Moeller Gerhard Reik 《Geotechnical and Geological Engineering》2009,27(6):713-728
Road construction in the Blue Nile basin is largely determined by geotechnical factors. The area is characterized by steep
slopes and has a history of landsliding. The geological formations range from Mesozoic sedimentary to Tertiary volcanic rocks
making the stratigraphic makeup sensitive to deformation and failure. The heterogeneity of these rocks also means it is difficult
to depend on results of stability analyses alone for road design and construction. As an alternative, ratios of cut-slope
lengths to cut-slope heights have been developed in this study based on the performances of unsupported natural and artificial
cuts and some stability analyses. Hence, road cuts on cliffs of hard rocks need a horizontal to vertical ratio of 0.25:1.
Slopes made up of weak rocks can remain stable at a threshold angle of 45°. For heterogeneous slopes, it is advisable to use
different road cuts depending on material makeup, and the degree of weathering and consolidation. 相似文献
72.
John R. Moeller G. Wayne Minshall Kenneth W. Cummins Robert C. Petersen C.E. Cushing James R. Sedell R.A. Larson Robin L. Vannote 《Organic Geochemistry》1979,1(3):139-150
Transport of dissolved organic carbon (DOC) in four river systems in different physiographic regions of the United States was related to link magnitude by a power function, log Y = ?0.84 + 1.24 log X. Multiple linear regression indicated that discharge, watershed area, and link magnitude explained almost all variation in DOC transport. For purposes of ecosystem comparison, link magnitude appeared superior to other classification systems, such as stream order.In two of the river systems, the largest fraction of DOC was transported in the spring. A third has a winter transport maximum; the last had bimodal spring and fall maxima.Streams transporting similar total amounts of DOC may vary widely in DOC concentration (mg. 1?1). Particulate organic matter concentration was not simply related to that of DOC.Ranges and means of DOC concentration, mean DOC: POC ratios, annual load of transported DOC as well as annual watershed DOC output were tabulated for 45 streams and rivers, representing a broad range of stream systems and physiographic regions. Mean DOC concentration for these 45 waterways ranged from 0.7 to 28 mg. 1?1. The very low DOC values are found in undisturbed streams; many of the higher values are associated with larger streams influenced by human activities. Most DOC outputs fell within the range 0.21–5.42 metric tons. km?2.yr?1; mean DOC:POC ranged between 0.09 and 70.A comparison was made among several biomes of the ratio of experted DOC to watershed gross and net primary production. DOC, while playing a major role in aquatic ecosystem organic budgets, appears to be of little significance in the nutrient balance of watersheds. 相似文献
73.
Eolian and subaqueous landforms composed of gypsum sand provide geomorphic evidence for a wet episode at the termination of glacial climate in southwestern North America. Drying of pluvial Lake Estancia, central New Mexico, occurred after ca. 12,000 14C yr B.P. Thereafter, eolian landforms on the old lake floor, constructed of gypsum sand, were overridden by rising lake water, modified by subaqueous processes, and organized into beach ridges along the lake's eastern shore. Preservation of preexisting eolian landforms in the shallow lake suggests abupt changes in lake level and climate. Available radiocarbon ages suggest that the final highstand recorded by beach ridges may have developed during the Younger Dryas (YD) stade. The beach ridges provide information about lake surface area, which was 45% of the lake area reached during the maximum highstands of the late Pleistocene. A similar proportional response has been reported for YD climate changes outside the North Atlantic region. 相似文献
74.
75.
Future extreme events in European climate: an exploration of regional climate model projections 总被引:7,自引:0,他引:7
Martin Beniston David B. Stephenson Ole B. Christensen Christopher A. T. Ferro Christoph Frei Stéphane Goyette Kirsten Halsnaes Tom Holt Kirsti Jylhä Brigitte Koffi Jean Palutikof Regina Schöll Tido Semmler Katja Woth 《Climatic change》2007,81(1):71-83
This paper compares how well satellite versus weather station measurements of climate predict agricultural performance in
Brazil, India, and the United States. Although weather stations give accurate measures of ground conditions, they entail sporadic
observations that require interpolation where observations are missing. In contrast, satellites have trouble measuring some
ground phenomenon such as precipitation but they provide complete spatial coverage of various parameters over a landscape.
The satellite temperature measurements slightly outperform the interpolated ground station data but the precipitation ground
measurements generally outperform the satellite surface wetness index. In India, the surface wetness index outperforms station
precipitation but this may be reflecting irrigation, not climate. The results suggest that satellites provide promising measures
of temperature but that ground station data may still be preferred for measuring precipitation in rural settings. 相似文献
76.
77.
Field observations by divers indicated that a high rate of predation of whelks (Buccinum undatum) by starfish (Asterias rubens) occurred in an area disturbed by scallop dredging, although these whelks mostly appeared to be alive and externally undamaged. The ability of whelks to escape from starfish was tested in the laboratory after they were dropped or rolled to simulate direct physical contact with bottom fishing gear. Dropping whelks did not significantly affect their escape behaviour, but whelks which had been rolled took significantly longer to right themselves and were significantly less likely to perform an escape response than whelks that had not experienced this treatment. This study suggests that demersal fishing may indirectly increase whelk mortality by increasing their risk of predation. 相似文献
78.
In physical geography, systems are seen as a unity of parts and relationships, whereas human geographers using a second-order sociological systems approach define systems in terms of the difference between system and environment. Starting from this, dialogue between physical and human geographers using terms derived from systems theory is mostly in vain. This article explores some of the consequences that follow for dialogue in geography: the differences in defining systems, in the understanding of processes, the problem of system borders, the inconsistent understanding of the 'environment' itself as well as the different epistemology that comes with it (or leads to it). The article tries to bring systems theory back into geography with the decisive aim of enhancing the potentials for interaction between human and physical geographers and, therefore, to explore the possibility of connecting the social with the physical world – deviating from systems theory. 相似文献
79.
Thomas Heberer Dirk Feldmann Kirsten Reddersen Hans‐Juergen Altmann Thomas Zimmermann 《洁净——土壤、空气、水》2002,30(1):24-33
In military out of area missions of the Bundeswehr, it can be necessary to produce drinking water even from highly polluted surface waters containing a variety of organic, inorganic, and microbiological contaminants. Thus, mobile drinking water purification systems must be able to remove such contaminants as far as possible to meet the requirements of the German and European drinking water regulation/directive. Presently, two novel drinking water purification units applying membrane filtration undergo intensive long‐term trials carried out by the Bundeswehr. If these trials positively proof the functionality of these units and their ability to remove all possible contaminants they shall substitute so far available devices which use large amounts of chemicals and charcoal filtration for water purification.In the course of a research project, the functionality of the new devices and their efficacy to remove high amounts of algae, microbes, and organic and inorganic pollutants are additionally tested in “worst‐case” field studies. In September 2000, the first mobile drinking water purification unit was tested at the Teltowkanal in Berlin, Germany.This canal was chosen because it carries high burdens of municipal sewage effluents. The results from the fatigue test confirmed the ability of the water purification unit to reduce the concentrations of all contaminants meeting the maximum tolerance levels set by the German/European drinking water regulation.The pre‐filtration device was very effective in removing algae and solid particles to protect the membranes from clogging and to enable an almost maintenance‐free operation. Residues of pharmaceuticals and some other organic contaminants have almost totally been removed from the surface water where they were detected at individual concentrations up to the μg/L‐level. 相似文献
80.
Stephan A. Klapp Gerhard Bohrmann Werner F. Kuhs M. Mangir Murshed Thomas Pape Helmut Klein Kirsten S. Techmer Katja U. Heeschen Friedrich Abegg 《Marine and Petroleum Geology》2010
Gas hydrate samples from various locations in the Gulf of Mexico (GOM) differ considerably in their microstructure. Distinct microstructure characteristics coincide with discrete crystallographic structures, gas compositions and calculated thermodynamic stabilities. 相似文献