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A box model of the inter-hemispheric Atlantic meridional overturning circulation is developed, including a variable pycnocline depth for the tropical and subtropical regions. The circulation is forced by winds over a periodic channel in the south and by freshwater forcing at the surface. The model is aimed at investigating the ocean feedbacks related to perturbations in freshwater forcing from the atmosphere, and to changes in freshwater transport in the ocean. These feedbacks are closely connected with the stability properties of the meridional overturning circulation, in particular in response to freshwater perturbations. A separate box is used for representing the region north of the Antarctic circumpolar current in the Atlantic sector. The density difference between this region and the north of the basin is then used for scaling the downwelling in the north. These choices are essential for reproducing the sensitivity of the meridional overturning circulation observed in general circulation models, and therefore suggest that the southernmost part of the Atlantic Ocean north of the Drake Passage is of fundamental importance for the stability of the meridional overturning circulation. With this configuration, the magnitude of the freshwater transport by the southern subtropical gyre strongly affects the response of the meridional overturning circulation to external forcing. The role of the freshwater transport by the overturning circulation (M ov ) as a stability indicator is discussed. It is investigated under which conditions its sign at the latitude of the southern tip of Africa can provide information on the existence of a second, permanently shut down, state of the overturning circulation in the box model. M ov will be an adequate indicator of the existence of multiple equilibria only if salt-advection feedback dominates over other processes in determining the response of the circulation to freshwater anomalies. M ov is a perfect indicator if feedbacks other than salt-advection are negligible. 相似文献
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Influence of topography on tide propagation and amplification in semi-enclosed basins 总被引:3,自引:2,他引:1
An idealized model for tide propagation and amplification in semi-enclosed rectangular basins is presented, accounting for
depth differences by a combination of longitudinal and lateral topographic steps. The basin geometry is formed by several
adjacent compartments of identical width, each having either a uniform depth or two depths separated by a transverse topographic
step. The problem is forced by an incoming Kelvin wave at the open end, while allowing waves to radiate outward. The solution
in each compartment is written as the superposition of (semi)-analytical wave solutions in an infinite channel, individually
satisfying the depth-averaged linear shallow water equations on the f plane, including bottom friction. A collocation technique is employed to satisfy continuity of elevation and flux across
the longitudinal topographic steps between the compartments. The model results show that the tidal wave in shallow parts displays
slower propagation, enhanced dissipation and amplified amplitudes. This reveals a resonance mechanism, occurring when the
length of the shallow end is roughly an odd multiple of the quarter Kelvin wavelength. Alternatively, for sufficiently wide
basins, also Poincaré waves may become resonant. A transverse step implies different wavelengths of the incoming and reflected
Kelvin wave, leading to increased amplitudes in shallow regions and a shift of amphidromic points in the direction of the
deeper part. Including the shallow parts near the basin’s closed end (thus capturing the Kelvin resonance mechanism) is essential
to reproduce semi-diurnal and diurnal tide observations in the Gulf of California, the Adriatic Sea and the Persian Gulf. 相似文献
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Advancing New Testament interpretation through spatio‐temporal analysis: Demonstrated by case studies 下载免费PDF全文
This article explores, via three case studies, how spatio‐temporal analysis can advance New Testament text interpretation. Acts 2, verse 9 to 11 is the text of study. Case study 1 applies network analysis to data representing the Roman road network constrained by parameters valid for ancient times. This analysis provided new information on the background of people attending a festival in Jerusalem. Case study 2 located geographical entities from the text in a cartographic visualization and provided supportive information to compare contemporary textual resources. For the disciplines of textual and conjectural criticism (case study 3), spatio‐temporal analysis opens a new window to study what would be the most probable variant of the original text. The case study puts emendations that have been proposed over centuries in a 3D spatial context and provides in this way a sophisticated tool to relate different alternative variants of a specific text. From the case studies, it can be concluded that spatializing, visualizing, and spatially analyzing geographical concepts from the texts in Acts 2 contributes to the field of New Testament interpretation. Further work will elaborate on the findings. 相似文献
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Massimiliano Tardio Francesca Sangiorgi Henk Brinkhuis Maria Letizia Filippi Marco Cantonati André F. Lotter 《Journal of Paleolimnology》2006,36(3):315-318
This paper documents the discovery of peridinioid organic walled dinoflagellate cysts in Holocene sediments of the freshwater, low-alkalinity, high mountain Lake Nero di Cornisello (Adamello mountain range, Trentino, Italy). Among the three main cyst morphotypes found in the samples, the dominant one is acavate, with a smooth and light brown colored wall, with a clear conical shape, elongated with a pointy to rounded end in the antapical-ventral part, with the epicyst broader than the hypocyst and displays a typical peridinioid archeopyle. Comparison with data available in literature, besides pointing out the general scarcity of observations on dinocysts in lakes sediments, suggested a strong morphological similarity with the marine genus Brigantedinium. This finding pinpoints the need for more detailed studies on cysts in freshwater environments offering a new tool for paleoenvironmental interpretations. 相似文献
69.
Massimo Craglia Ian Masser Henk Scholten 《International journal of geographical information science》2013,27(5):463-470
Abstract In January 1993 the European Science Foundation launched a four-year scientific programme on geographical information systems. The programme aims at overcoming the existing fragmentation of GIS research in Europe and addresses three key areas: European-wide data base design, data integration, and social and environmental applications. In each of these areas a number of priorities have been identified which provide the focus of the initiatives and collaborative ventures envisaged by the programme. This article describes the programme's research agenda and sets it in the context of the activities of the European Science Foundation. 相似文献
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