全文获取类型
收费全文 | 149篇 |
免费 | 12篇 |
专业分类
测绘学 | 4篇 |
大气科学 | 15篇 |
地球物理 | 38篇 |
地质学 | 76篇 |
海洋学 | 9篇 |
天文学 | 15篇 |
综合类 | 1篇 |
自然地理 | 3篇 |
出版年
2022年 | 2篇 |
2021年 | 1篇 |
2020年 | 3篇 |
2019年 | 2篇 |
2018年 | 2篇 |
2017年 | 10篇 |
2016年 | 12篇 |
2015年 | 3篇 |
2014年 | 1篇 |
2013年 | 17篇 |
2012年 | 6篇 |
2011年 | 12篇 |
2010年 | 18篇 |
2009年 | 10篇 |
2008年 | 7篇 |
2007年 | 8篇 |
2006年 | 5篇 |
2005年 | 7篇 |
2004年 | 4篇 |
2003年 | 7篇 |
2002年 | 2篇 |
2001年 | 3篇 |
2000年 | 2篇 |
1999年 | 2篇 |
1998年 | 1篇 |
1996年 | 1篇 |
1995年 | 2篇 |
1988年 | 1篇 |
1986年 | 2篇 |
1984年 | 2篇 |
1979年 | 1篇 |
1978年 | 1篇 |
1969年 | 3篇 |
1948年 | 1篇 |
排序方式: 共有161条查询结果,搜索用时 572 毫秒
101.
102.
Scales as a challenge for vulnerability assessment 总被引:4,自引:4,他引:0
The aim of this paper is to introduce scale as a basic tool for improving the conceptual structure of vulnerability assessments.
The terminology useful for vulnerability assessments and the current use of scale issues in theoretical vulnerability frameworks
will be discussed briefly. Two case studies working on sub-national and on local level will demonstrate problems as well as
benefits resulting from scale implications. Both assessments analyse vulnerability in context to river floods in Germany.
In order to develop a spatial comparison and to integrate topics like environment and society, vulnerability assessments need
to be aware of scale implications. The main point is that a scale debate on a broader spectrum than just in technical spatial
terms is missing in vulnerability and risk conceptualisations so far. Vulnerability assessments and scale are highly intertwined,
not only in technical application but also in conceptualisation, which needs more scientific development. 相似文献
103.
Fabrice G. Renaud Jörn Birkmann Marion Damm Gilberto C. Gallopín 《Natural Hazards》2010,55(3):749-763
External suffusion, as selective erosion of fine particles through the contact with a coarser layer and moving away, is an
important phenomenon in dams which may lead to their failure. To study the initiation of external suffusion, caused by water
level increase upstream the dam, a series of experimental investigations were conducted on laboratory-scale model, in the
hydrodynamic laboratory of école polytechnique de Montreal. On the built model, clay/moraine formed the core, sand was used
as a filter and gravel performed the role of the pervious layer. Several different models (in geometry and constituent materials)
were built and subjected to the water level increase upstream, which resulted in changes in the hydraulic gradient. The results
showed no evidence of considerable suffusion on the clay/moraine and sand interface, while the visual and quantitative data
show the presence of suffusion on the sand and gravel interface. The results of the experiments show that, when focusing on
the critical hydraulic gradient that initiates the movement of the clay/moraine particles, it can be concluded that despite
the differences in test conditions, the critical hydraulic gradient has approximately the same value in all cases. It was
also shown that increasing the length of the filter layer or applying stair-like slopes does not have great impacts on the
initiation of suffusion, whereas the gravel-size distribution has a great impact on the erosion rate. 相似文献
104.
Robert J. Orth Michael R. Williams Scott R. Marion David J. Wilcox Tim J. B. Carruthers Kenneth A. Moore W. Michael Kemp William C. Dennison Nancy Rybicki Peter Bergstrom Richard A. Batiuk 《Estuaries and Coasts》2010,33(5):1144-1163
Chesapeake Bay supports a diverse assemblage of marine and freshwater species of submersed aquatic vegetation (SAV) whose broad distributions are generally constrained by salinity. An annual aerial SAV monitoring program and a bi-monthly to monthly water quality monitoring program have been conducted throughout Chesapeake Bay since 1984. We performed an analysis of SAV abundance and up to 22 environmental variables potentially influencing SAV growth and abundance (1984–2006). Historically, SAV abundance has changed dramatically in Chesapeake Bay, and since 1984, when SAV abundance was at historic low levels, SAV has exhibited complex changes including long-term (decadal) increases and decreases, as well as some large, single-year changes. Chesapeake Bay SAV was grouped into three broad-scale community-types based on salinity regime, each with their own distinct group of species, and detailed analyses were conducted on these three community-types as well as on seven distinct case-study areas spanning the three salinity regimes. Different trends in SAV abundance were evident in the different salinity regimes. SAV abundance has (a) continually increased in the low-salinity region; (b) increased initially in the medium-salinity region, followed by fluctuating abundances; and (c) increased initially in the high-salinity region, followed by a subsequent decline. In all areas, consistent negative correlations between measures of SAV abundance and nitrogen loads or concentrations suggest that meadows are responsive to changes in inputs of nitrogen. For smaller case-study areas, different trends in SAV abundance were also noted including correlations to water clarity in high-salinity case-study areas, but nitrogen was highly correlated in all areas. Current maximum SAV coverage for almost all areas remain below restoration targets, indicating that SAV abundance and associated ecosystem services are currently limited by continued poor water quality, and specifically high nutrient concentrations, within Chesapeake Bay. The nutrient reductions noted in some tributaries, which were highly correlated to increases in SAV abundance, suggest management activities have already contributed to SAV increases in some areas, but the strong negative correlation throughout the Chesapeake Bay between nitrogen and SAV abundance also suggests that further nutrient reductions will be necessary for SAV to attain or exceed restoration targets throughout the bay. 相似文献
105.
Reinhard Jung Marion Schindler Patrick Nami Torsten Tischner 《Comptes Rendus Geoscience》2010,342(7-8):636-643
The article presents a method to derive synthetic flow logs from low rate injection tests in wells, which are otherwise not accessible for logging. The tests were carried out in the 5 km deep geothermal well GPK2 in the Enhanced Geothermal System (EGS) project of Soultz-sous-Forêts (France) and were aimed at characterizing the status of the well before chemical treatments. The method consists of injecting water at constant flow rates into the well initially filled with brine. The wellhead pressure record of this test is transformed into log of the flow velocity versus depth by a technique described in the paper. Applying this method to borehole GPK2, three outlets could be detected and quantified within the cased and uncased section of this borehole. The outlet in the cased section at 3860 m absorbed 15% of the total flow. This depth corresponds to a known casing restriction, which makes the borehole inaccessible for logging operations. The two other outlets are at the casing shoe at 4420 m (15%) and at 4670 m (70%). 相似文献
106.
Government policies for the use of publicly owned environmental resources in Australia are often justified as being for the economic good of the nation. Yet there has been little enquiry about how Australians perceive economic good in the context of the use of environmental resources. The residents of five State government electorates of Perth and one in regional south west Western Australia were surveyed. Their perceptions of economics, the environment and resources in relation to public policy were assessed. The differences in the responses were greater between the different electorates, than between the different socio-economic strata within the same electorate. This paper examines the spatial variability of the results and raises the possibility of developing a socio-locational indicator of attitudes which could provide a tool for policy implementation. 相似文献
107.
Within the scope of the further development of geochemical transport models the consideration of the influence of the heterogeneous structures of the geological layers plays an important role. For the verification and parameter estimation of such models it is necessary to measure the heterogeneous transport and sorption processes inside the samples. Tomographic radiotracer methods (positron emission tomography (PET)) enable nondestructive spatially resolved observations of the transport processes in these layers. A special quantitative evaluation system for geoscientific PET studies was developed. Investigations of the water flow distribution in a drill core of a lignite mining dump and of the migration of Cu ions in a horizontal soil column illustrate the potential of this method. Spatial distribution functions of the flow velocity, the specific mass flow and the longitudinal dispersivity were determined on the basis of PET investigations. 相似文献
108.
Marion GS Dunbar RB Mucciarone DA Kremer JN Lansing JS Arthawiguna A 《Marine pollution bulletin》2005,50(9):931-944
This study introduces a new method of tracing the history of nutrient loading in coastal oceans via delta(15)N analysis of organic nitrogen preserved in the skeleton of the massive Porites coral. Four coral cores were collected in Bali, Indonesia, from reefs exposed to high levels of fertilizers in agricultural run-off, from lagoonal corals impacted by sewage, and from a reef located 30 km offshore. Skeletal delta(15)N in the agriculturally exposed coral declined from 10.7+/-0.4 per thousand in 1970-1971, when synthetic fertilizers (-0.8 per thousand+/-0.2 per thousand) were introduced to Bali, to a depleted "anthropogenic" baseline of 3.5 per thousand+/-0.4% in the mid-1990s. delta(15)N values were negatively correlated with rainfall, suggesting that marine delta(15)N lowers during flood-bourn influxes of waste fertilizers. Reef cores exposed to untreated sewage in terrestrial discharge were enriched (7.8 and 7.3+/-0.4 per thousand), while the offshore core reflected background oceanic signals (6.2+/-0.4 per thousand). delta(15)N, N concentration, and C:N systematics indicate that the N isotopic composition of skeletal organic matter was generally well preserved over 30 years. We suggest that skeletal organic delta(15)N can serve as a recorder of past nitrogen sources. In Bali, this tracer suggests that the intensification of Western style agricultural practices since 1970 are contributing to the degradation of coastal coral reefs. 相似文献
109.
The Mars Global Surveyor, Mars Exploration Rover, and Mars Express missions have stimulated considerable thinking about the surficial geochemical evolution of Mars. Among the major recent mission findings are the presence of jarosite (a ferric sulfate salt), which requires formation from an acid-sulfate brine, and the occurrence of hematite and goethite on Mars. Recent ferric iron models have largely focused on 25 °C, which is a major limitation for models exploring the geochemical history of cold bodies such as Mars. Until recently, our work on low-temperature iron-bearing brines involved ferrous but not ferric iron, also obviously a limitation. The objectives of this work were to (1) add ferric iron chemistry to an existing ferrous iron model (FREZCHEM), (2) extend this ferrous/ferric iron geochemical model to lower temperatures (<0 °C), and (3) use the reformulated model to explore ferrous/ferric iron chemistries on Mars.The FREZCHEM model is an equilibrium chemical thermodynamic model parameterized for concentrated electrolyte solutions using the Pitzer approach for the temperature range from <−70 to 25 °C and the pressure range from 1 to 1000 bars. Ferric chloride and sulfate mineral parameterizations were based, in part, on experimental data. Ferric oxide/hydroxide mineral parameterizations were based exclusively on Gibbs free energy and enthalpy data. New iron parameterizations added 23 new ferrous/ferric minerals to the model for this Na-K-Mg-Ca-Fe(II)-Fe(III)-H-Cl-SO4-NO3-OH-HCO3-CO3-CO2-O2-CH4-H2O system.The model was used to develop paragenetic sequences for Rio Tinto waters on Earth and a hypothetical Martian brine derived from acid weathering of basaltic minerals. In general, model simulations were in agreement with field evidence on Earth and Mars in predicting precipitation of stable iron minerals such as jarosites, goethite, and hematite. In addition, paragenetic simulations for Mars suggest that other iron minerals such as lepidocrocite, schwertmannite, ferricopiapite, copiapite, and bilinite may also be present on the surface of Mars. Evaporation or freezing of the Martian brine led to similar mineral precipitates. However, in freezing, compared to evaporation, the following key differences were found: (1) magnesium sulfates had higher hydration states; (2) there was greater total aqueous sulfate (SO4T = SO4 + HSO4) removal; and (3) there was a significantly higher aqueous Cl/SO4T ratio in the residual Na-Mg-Cl brine. Given the similarities of model results to observations, alternating dry/wet and freeze/thaw cycles and brine migration could have played major roles in vug formation, Cl stratification, and hematite concretion formation on Mars. 相似文献
110.