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101.
Mark A. Fonstad James T. Dietrich Brittany C. Courville Jennifer L. Jensen Patrice E. Carbonneau 《地球表面变化过程与地形》2013,38(4):421-430
The production of topographic datasets is of increasing interest and application throughout the geomorphic sciences, and river science is no exception. Consequently, a wide range of topographic measurement methods have evolved. Despite the range of available methods, the production of high resolution, high quality digital elevation models (DEMs) requires a significant investment in personnel time, hardware and/or software. However, image‐based methods such as digital photogrammetry have been decreasing in costs. Developed for the purpose of rapid, inexpensive and easy three‐dimensional surveys of buildings or small objects, the ‘structure from motion’ photogrammetric approach (SfM) is an image‐based method which could deliver a methodological leap if transferred to geomorphic applications, requires little training and is extremely inexpensive. Using an online SfM program, we created high‐resolution digital elevation models of a river environment from ordinary photographs produced from a workflow that takes advantage of free and open source software. This process reconstructs real world scenes from SfM algorithms based on the derived positions of the photographs in three‐dimensional space. The basic product of the SfM process is a point cloud of identifiable features present in the input photographs. This point cloud can be georeferenced from a small number of ground control points collected in the field or from measurements of camera positions at the time of image acquisition. The georeferenced point cloud can then be used to create a variety of digital elevation products. We examine the applicability of SfM in the Pedernales River in Texas (USA), where several hundred images taken from a hand‐held helikite are used to produce DEMs of the fluvial topographic environment. This test shows that SfM and low‐altitude platforms can produce point clouds with point densities comparable with airborne LiDAR, with horizontal and vertical precision in the centimeter range, and with very low capital and labor costs and low expertise levels. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
102.
Agnès Bouchez Noémie Pascault Cècile Chardon Marc Bouvy Philippe Cecchi Luc Lambs Mélanie Herteman François Fromard Patrice Got Christophe Leboulanger 《Marine pollution bulletin》2013,66(1-2):39-46
Mangroves are threatened ecosystems that provide numerous ecosystem services, especially through their wide biodiversity, and their bioremediation capacity is a challenging question in tropical areas. In a mangrove in Mayotte, we studied the potential role of microbial biofilm communities in removing nutrient loads from pre-treated wastewater. Microbial community samples were collected from tree roots, sediments, water, and from a colonization device, and their structure and dynamics were compared in two areas: one exposed to sewage and the other not. The samples from the colonization devices accurately reflected the natural communities in terms of diversity. Communities in the zone exposed to sewage were characterized by more green algae and diatoms, higher bacteria densities, as well as different compositions. In the area exposed to sewage, the higher cell densities associated with specific diversity patterns highlighted adapted communities that may play a significant role in the fate of nutrients. 相似文献
103.
The present study investigates the reconstruction of the 3D dynamics of a turbulent mesoscale eddy field driven at a depth by a baroclinic instability of the Phillips type. It uses a high-resolution primitive equation simulation as a testbed. The method of reconstruction is based on potential vorticity principles and extends an earlier approach (Lapeyre and Klein, J Phys Oceanogr 36:165–176, 2006) to a regime where the signature of surface density anomalies on the dynamics is weak. The crux and the originality of the reconstruction lie in the estimation from sea surface height and surface density anomalies of the interior quasigeostrophic potential vorticity (PV) anomalies and its subsequent inversion. The estimation of PV anomalies relies on the vertical correlation between PV anomalies and on the knowledge on stratification and horizontal gradients of background PV. PV anomalies are accurately estimated over the first 500 m of the water column and over a wide range of wavenumbers. Density anomalies play a minor role in the PV estimation, though their omission leads to an overestimation of PV by a factor of less than 2 at scales of order 20 km and less. Inversion of the estimated PV leads to a geostrophic streamfunction which in turn provides reliable reconstructions of the relative vorticity and vertical velocity (via the omega equation). 相似文献
104.
Pierre Bastien François Ménard Patrice Corporon Nadine Manset Frédérick Poidevin Gaspard Duchêne Jean-Louis Monin 《Astrophysics and Space Science》2004,292(1-4):427-433
We obtained linear polarization observations of 82 A/B-type stars in the young cluster NGC 6611, in order to probe the circumstellar material and to search for any evidence of intracluster or interstellar material that could also contribute to the polarization. We found linear polarization values that reach up to 14%. We consider the distribution of the polarization, its position angle, correlations with extinction and membership probability, polarization variability and wavelength distribution to identify the origin of the polarization toward NGC 6611. The polarization is found to be dominated by interstellar polarization, although some stars also have some circumstellar polarization. There is no evidence for intracluster dust. Rather, the dust must be located in a low density cloud toward the general line of sight to NGC 6611 and in front of it. The depth of that cloud along the line of sight increases slowly from the south–east to the north–west. The cloud is threaded by a very uniform magnetic field. 相似文献
105.
Mohamad Fakih Mlanie Davranche Aline Dia Bernd Nowack Patrice Petitjean Xavier Chtellier Grard Gruau 《Applied Geochemistry》2008,23(12):3372-3383
The aim of this study was to design and test a new tool for (i) the quantitative in situ monitoring of Fe(III) reduction in soils and (ii) the tracking of the potential mineralogical changes of Fe-oxides. The tool consists of small (2 × 2 × 0.2 cm) striated polymer plates coated with synthetic pure ferrihydrite or As-doped ferrihydrite (Fh–As). These slides were then inserted within two different horizons (organo-mineral and albic) located in a wetland soil with alternating redox conditions. Dissolution was quantified by X-ray fluorescence (XRF) analyses of total metal contents before and after insertion into the soil. The crystallographic evolution of Fe-oxides was characterized by scanning electron microscope equipped with an energy-dispersive spectrometer (SEM–EDS). Over the months, the ferrihydrite progressively disappeared, at rates comparable to those previously measured in laboratory studies, i.e. in the 1–10 × 10−12 mol Fe m−2 s−1 range. SEM observations indicate that the supports were highly colonized by bacteria and biofilms in the organo-mineral horizon, suggesting a biological-mediated process, while the albic horizon appeared to be characterized by a mostly chemical-mediated process. In the albic horizon, Fe-sulphide and other micro-precipitates were formed after 7 months of incubation in balance with a quasi dissolution of initial Fe-oxides. 相似文献
106.
Narcís Coll Marité Guerrieri 《International journal of geographical information science》2017,31(7):1467-1484
In this paper, we propose a new graphics processing unit (GPU) method able to compute the 2D constrained Delaunay triangulation (CDT) of a planar straight-line graph consisting of points and segments. All existing methods compute the Delaunay triangulation of the given point set, insert all the segments, and then finally transform the resulting triangulation into the CDT. To the contrary, our novel approach simultaneously inserts points and segments into the triangulation, taking special care to avoid conflicts during retriangulations due to concurrent insertion of points or concurrent edge flips. Our implementation using the Compute Unified Device Architecture programming model on NVIDIA GPUs improves, in terms of running time, the best known GPU-based approach to the CDT problem. 相似文献
107.
108.
Vargas Marcelle Martins Beskow Samuel de Mello Carlos Rogério de Moura Maíra Martim Nunes Maria Cândida Moitinho Faria Lessandro Coll Aquino Leandro Sanzi 《Natural Hazards》2021,109(1):593-614
Natural Hazards - Process-based hydrological models are of great importance to understand hydrological processes and support decision making. The LImburg Soil Erosion Model (LISEM) requires... 相似文献
109.
Yuan Yong Guan Patrice Coll Didier Chaput Hervé Cottin 《Planetary and Space Science》2010,58(10):1327-1996
Solar UV radiation is a major source of energy for chemical evolution of organic materials in the Solar System. Therefore studies on the photostability of organic compounds in extraterrestrial environments are of prime importance for the understanding of the extraterrestrial origin of organic materials on Earth. A series of organic samples have been photolysed in Earth orbit during the ESA BIOPAN 6 mission (14-26/09/2007). Their photochemical lifetime has been measured and compared to results recorded in the laboratory using a lamp that simulates the solar radiation in the VUV domain. The half-lives at a distance of 1 AU from the Sun have been measured for glycine, xanthine, hypoxanthine, adenine, guanine, urea, carbon suboxide polymer ((C3O2)n) and HCN polymer. They range from a few days to a lower limit of a few tens of days for the most photoresistant (e.g. adenine, guanine, hypoxanthine). Lifetimes measured in terrestrial orbit are very different from those derived with laboratory experiments. These measurements confirm that it is difficult to simulate the solar spectrum below 200 nm in the laboratory. Results are discussed and highlight the necessity to conduct experiments in orbit, and for longer duration. It also appears that the laboratory measurements made in VUV must be extrapolated very cautiously to the different environments they are supposed to simulate. 相似文献
110.
Frédéric Christophoul Patrice Baby Jean-Claude Soula Michel Rosero José Burgos 《Comptes Rendus Geoscience》2002,334(14):1029-1037
A sedimentological study of the Neogene continental infill of the Subandean foreland basin of Ecuador led us to define an evolution of the fluvial system from an alluvial plain to an alluvial fan with an increasing slope in the same time as the drainage changed from mostly longitudinal to transverse. Combined with the data presently available on palaeotopography, exhumation, tectonic evolution and geomorphology, these results enable us to infer that, in contrast with the other Subandean foreland basins of Bolivia and Peru, the progradation of the Neogene alluvial fans proceeded by an overall expansion, associated with a relatively small tectonic shortening and not as a result of the development of successive thrust-related depocentres. This also indicates that the surrection of the Cordillera progressed in Ecuador throughout the Neogene. To cite this article: F. Christophoul et al., C. R. Geoscience 334 (2002) 1029–1037. 相似文献