全文获取类型
收费全文 | 84篇 |
免费 | 5篇 |
国内免费 | 3篇 |
专业分类
测绘学 | 6篇 |
大气科学 | 6篇 |
地球物理 | 12篇 |
地质学 | 27篇 |
海洋学 | 3篇 |
天文学 | 31篇 |
综合类 | 2篇 |
自然地理 | 5篇 |
出版年
2023年 | 2篇 |
2021年 | 1篇 |
2020年 | 2篇 |
2019年 | 6篇 |
2018年 | 1篇 |
2017年 | 5篇 |
2016年 | 4篇 |
2015年 | 7篇 |
2014年 | 3篇 |
2013年 | 8篇 |
2012年 | 3篇 |
2011年 | 8篇 |
2010年 | 6篇 |
2009年 | 4篇 |
2008年 | 1篇 |
2007年 | 1篇 |
2006年 | 2篇 |
2005年 | 2篇 |
2004年 | 2篇 |
2003年 | 2篇 |
2002年 | 3篇 |
2001年 | 7篇 |
2000年 | 1篇 |
1998年 | 4篇 |
1997年 | 1篇 |
1995年 | 1篇 |
1994年 | 1篇 |
1990年 | 1篇 |
1989年 | 1篇 |
1983年 | 1篇 |
1979年 | 1篇 |
排序方式: 共有92条查询结果,搜索用时 62 毫秒
51.
Farhana Jabeen Alvaro A.A. Fernandes 《International journal of geographical information science》2013,27(4):815-844
Existing sensor network query processors (SNQPs) have demonstrated that in-network processing is an effective and efficient means of interacting with wireless sensor networks (WSNs) for data collection tasks. Inspired by these findings, this article investigates the question as to whether spatial analysis over WSNs can be built upon established distributed query processing techniques, but, here, emphasis is on the spatial aspects of sensed data, which are not adequately addressed in the existing SNQPs. By spatial analysis, we mean the ability to detect topological relationships between spatially referenced entities (e.g. whether mist intersects a vineyard or is disjoint from it) and to derive representations grounded on such relationships (e.g. the geometrical extent of that part of a vineyard that is covered by mist). To support the efficient representation, querying and manipulation of spatial data, we use an algebraic approach. We revisit a previously proposed centralized spatial algebra comprising a set of spatial data types and a comprehensive collection of operations. We have redefined and re-conceptualized the algebra for distributed evaluation and shown that it can be efficiently implemented for in-network execution. This article provides rigorous, formal definitions of the spatial data types, points, lines and regions, together with spatial-valued and topological operations over them. The article shows how the algebra can be used to characterize complex and expressive topological relationships between spatial entities and spatial phenomena that, due to their dynamic, evolving nature, cannot be represented a priori. 相似文献
52.
Integrated Water Resource Management (IWRM) becomes increasingly important in arid watersheds, where water resources are
scarce and demands are rising under increased population pressure. In this case study, we present the results from the Elqui Valley
in Chile, where water resources are shared between agriculture, mining operations, hydropower generation and drinking water for
nearby cities. An IWRM model was applied to visualize water resources distribution in the catchment and determine irrigation and
water use efficiencies. After calibration with observed surface and groundwater measurements, the model showed large differences
in efficiencies between different irrigation sectors. Most notably, irrigation sectors with the highest irrigation security, i.e.,
higher water rights per hectare, were characterized with lower water use efficiencies. Frequent water deficits were present in sectors
downstream of the main reservoir, which was related to limited water rights per hectare, lower irrigation efficiencies and
higher water demands due to larger agricultural areas. In subsequent scenario analyses, the model was used to evaluate the impact
of improved irrigation and water use efficiencies in these downstream sectors, to confirm an important reduction in water deficits,
except for drought years when surface water resources are insufficient. In a third scenario, groundwater resources were allowed to
compensate for water deficits, effectively reducing these in most irrigation sectors, especially during droughts. Expansion of the
current agricultural area by 37% was evaluated, as a future scenario, and was found to be unsustainable, as aquifer levels are lowered
to such levels that make annual recharge insufficient. 相似文献
53.
Karnit Bahartan Mohammad Zibdah Alvaro Israel Avigdor Abelson 《Marine pollution bulletin》2010,60(5):759-764
The current state of health of the coral reefs in the northern Gulf of Aqaba (Red Sea), notably the Eilat reefs, is under debate regarding both their exact condition and the causes of degradation. A dearth of earlier data and unequivocal reliable indices are the major problems hinder a clear understanding of the reef state. Our research objective was to examine coral-algal dynamics as a potential cause and an indication of reef degradation. The community structure of stony corals and algae along the northern Gulf of Aqaba reveal non-seasonal turf algae dominancy in the shallow Eilat reefs (up to 72%), while the proximate Aqaba reefs present negligible turf cover (<6%). We believe that turf dominancy can indicate degradation in these reefs, based on the reduction in essential reef components followed by proliferation of perennial turf algae. Our findings provide further evidence for the severe state of the Eilat coral reefs. 相似文献
54.
Aurélie Guilbert Alvaro Alvarez-Candal Maria Antonietta Barucci Catherine de Bergh 《Icarus》2009,201(1):272-283
We present in this work the observations performed with SINFONI in the framework of a new ESO-Large Program (2006-2008) on Trans-Neptunian Objects (TNOs) and Centaurs. We obtained 21 near-infrared (1.49 to 2.4 microns) spectra of high quality, including 4 spectra of objects never observed before. We search for the presence of features due to ices, particularly water ice. Eris is the only object showing deep methane ice absorption bands. The spectra of 4 objects are featureless, and 6 others show clearly the presence of water ice. For 7 objects, the detections are more ambiguous, but absorption bands could be embedded in the noise. The 3 remaining spectra are too noisy to draw any reliable conclusion. The possible amount of water ice on each object's surface has been computed. The analysis shows that some objects present strong compositional heterogeneities over the surface (e.g. Chariklo), while some others are completely homogeneous (e.g. Quaoar). 相似文献
55.
Herbert W. Schnopper Eric Silver Stephen Murray Suzanne Romaine Simon Bandler Christine Jones William Forman Norman Madden Jeffery Beeman Eugene Haller Finn Christensen Niels Westergaard Juan Fabregat Victor Reglero Alvaro Gimenez Noah Brosch Elia Liebowitz Hagai Netzer Marco Barbera Alfonso Collura Salvatore Sciortino 《Astrophysics and Space Science》2001,276(1):49-65
The X-Ray Spectroscopic Explorer (XRASE) has a unique combination of features that will make it possible to address many of NASA's scientific goals. These include how galaxy clusters form, the physics and chemistry of the ISM, the heating of stellar coronae, the amount and content of intergalactic baryonic matter, the mass of black holes and the formation of disks and jets in AGN and galactic binaries. XRASE has a thin foil, multilayered telescope with a large collecting area up to 10 keV, especially in the Fe K region (1100 cm2). Its microcalorimeter array combines high energy resolution (7 eV at 6 keV) and efficiency with a field-of-view of 26 arcmin2 . A deep orbit allows for long, continuous observations. Monitoring instruments in the optical (WOM-X), UV (TAUVEX) and hard X-RAY (GRAM) bands will offer exceptional opportunities to make simultaneous multi-wavelength observations. 相似文献
56.
The upper mixed layer (UML) depth obtained from temperature is very close to that from density:the maximum is about 15m. This indicates that temperature is a good indicator of mixed layer during measurements. When the surface heat flux is balanced by a cross-shore heat flux, the surface mixed layer depth obtained from the WM model (Weatherly and Martin, 1978),hPRT, is roughly the same as observed. The mixed layer depth calculated from the PWP model (Price, Weller and Pinkel, 1986) is close to the depth obtained from thermistor chain temperature data. The results show that both the WM model and PWP model can provide a good estimate of stratification in the study area during the cruise. The value of log( h/u3) is about 9.5 in the study area, which shows that the study area is strongly stratified in summer. Observations on the northern Portugal shelf reveal high variability in stability, giving rise to semi-diurnal, semi-monthly and diurnal oscillations, and long term variations. The fortnightly oscillatio 相似文献
57.
58.
Seung-Hyun Jeong Norman W. Paton Alvaro A. A. Fernandes Tony Griffiths 《Transactions in GIS》2005,9(2):129-156
Many applications capture, or make use of, spatial data that changes over time. This requirement for effective and efficient spatio‐temporal data management has given rise to a range of research activities relating to spatio‐temporal data management. Such work has sought to understand, for example, the requirements of different categories of application, and the modelling facilities that are most effective for these applications. However, at present, there are few systems with fully integrated support for spatio‐temporal data, and thus developers must often construct custom solutions for their applications. Developers of both bespoke solutions and of generic spatio‐temporal platforms will often need to support the fusion of large spatio‐temporal data sets. Supporting such requests in a database setting involves the use of join operations with both spatial and temporal conditions – spatio‐temporal joins. However, there has been little work to date on spatio‐temporal join algorithms or their evaluation. This paper presents an evaluation of several approaches to the implementation of spatio‐temporal joins that build upon widely available indexing techniques. The evaluation explores how several algorithms perform for databases with different spatial and temporal characteristics, with a view to helping developers of generic infrastructures or custom solutions in the selection and development of appropriate spatio‐temporal join strategies. 相似文献
59.
To fulfil the need to generate more realistic solutions, stochastic inverse simulations in hydrogeology are now constrained on both piezometric head and hydraulic conductivity data. These inverse techniques, often based on geostatistics, allow modifications of an initial solution conditioned only on hydraulic conductivity data to arrive at a final solution that also matches observed heads. By repeating the process as many times as necessary with different initial solutions, one generates an ensemble of final solutions thereby addressing the uncertainty of the inverse problem. This requires a method able to handle the whole ensemble and to work on its relevant characteristics. From this standpoint, the analysis by Empirical Orthogonal Functions (EOF) appears promising. The method builds an orthogonal decomposition of the covariance matrix, calculated over the whole set of solutions, and the areas in space where the first functions have a greater influence corresponding to locations of maximum uncertainty in the solutions. These locations depend both on the hydraulic characteristics of the flow problem and on the spatial distribution of available data. The EOF analysis is used on a synthetic problem that mimics a possible behavior of the Culebra aquifer of the Waste Isolation Pilot Plant (WIPP, New Mexico). The method also allows new solutions to be generated at lower computational cost by a random composition of the functions obtained by the EOF analysis. These new solutions keep the main characteristics of the initial ensemble and because they can be conditioned, they return very good results when they are used to solve the direct problem. 相似文献
60.
Analytical solutions for the water flow and solute transport equations in the unsaturated zone are presented. We use the Broadbridge and White nonlinear model to solve the Richards’ equation for vertical flow under a constant infiltration rate. Then we extend the water flow solution and develop an exact parametric solution for the advection-dispersion equation. The method of characteristics is adopted to determine the location of a solute front in the unsaturated zone. The dispersion component is incorporated into the final solution using a singular perturbation method. The formulation of the analytical solutions is simple, and a complete solution is generated without resorting to computationally demanding numerical schemes. Indeed, the simple analytical solutions can be used as tools to verify the accuracy of numerical models of water flow and solute transport. Comparison with a finite-element numerical solution indicates that a good match for the predicted water content is achieved when the mesh grid is one-fourth the capillary length scale of the porous medium. However, when numerically solving the solute transport equation at this level of discretization, numerical dispersion and spatial oscillations were significant. 相似文献