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91.
Marques AN Monna F da Silva Filho EV Fernex FE Fernando Lamego Simões Filho F 《Marine pollution bulletin》2006,52(5):532-539
Zn and Cd concentrations, stable lead isotopes and 210Pb-derived chronology were determined in a sediment core sampled at Sepetiba Bay (South-eastern Brazil). During the last decades, the bay’s watershed has been modified by the increase of industrial activities and human interventions. In particular, Zn and Cd ore treatment plants were built near the coast in 1960 and 1970, respectively, and water has been diverted from the adjacent Paraíba do Sul River watershed since 1950. The core collected at shallow depth near the industrial area exhibits four successive events: (i) at 50 cm depth, a change in the 206Pb/207Pb ratio from about 1.162 to more than 1.18 might be the result of the São Francisco Channel opening and water diversion from Paraíba do Sul river; (ii) at 40 cm depth, Zn concentration starts to increase (up to 0.8 mg g−1) (iii) above 30 cm depth, relatively high Cd concentrations (up to 1.6 μg g−1) are observed and (iv) at 16 cm depth, change in unsupported 210Pb slope is probably related to a waste dam built to prevent strong metal contamination in the bay. Sediment accumulation rates evaluated by Zn and Cd profiles used as time-markers are higher than those calculated from 210Pb-based chronology models. Using the constant initial concentration (CIC) model both events are supposed to date back to about 1884 and 1902, respectively, while using the constant rate of supply (CRS) model it shifts to about 1925 and 1935. Such discrepancies are probably assigned to the fact that these models do not take into account site-specific local sedimentation dynamics. In the study area, particles deposition seems to be controlled by enrichment with unsupported 210Pb transported by runoff from a mangrove flat bank. Chronology derived from a model that assumes an exponential increase of the initial 210Pb activity fits well with the estimated rates obtained from historical events. 相似文献
92.
Fabrice Fraysse Oleg S. Pokrovsky Jacques Schott 《Geochimica et cosmochimica acta》2006,70(8):1939-1951
Although phytoliths, constituted mainly by micrometric opal, exhibit an important control on silicon cycle in superficial continental environments, their thermodynamic properties and reactivity in aqueous solution are still poorly known. In this work, we determined the solubility and dissolution rates of bamboo phytoliths collected in the Réunion Island and characterized their surface properties via electrophoretic measurements and potentiometric titrations in a wide range of pH. The solubility product of “soil” phytoliths ( at 25 °C) is equal to that of vitreous silica and is 17 times higher than that of quartz. Similarly, the enthalpy of phytoliths dissolution reaction is close to that of amorphous silica but is significantly lower than the enthalpy of quartz dissolution. Electrophoretic measurements yield isoelectric point pHIEP = 1.2 ± 0.1 and 2.5 ± 0.2 for “soil” (native) and “heated” (450 °C heating to remove organic matter) phytoliths, respectively. Surface acid-base titrations allowed generation of a 2-pK surface complexation model. Phytoliths dissolution rates, measured in mixed-flow reactors at far from equilibrium conditions at 2 ? pH ? 12, were found to be intermediate between those of quartz and vitreous silica. The dissolution rate dependence on pH was modeled within the concept of surface coordination theory using the equation:
93.
Nonlinear Formulation of the Bulk Surface Stress over Breaking Waves: Feedback Mechanisms from Air-flow Separation 总被引:1,自引:0,他引:1
Historically, our understanding of the air-sea surface stress has been derived from engineering studies of turbulent flows
over flat solid surfaces, and more recently, over rigid complex geometries. Over the ocean however, the presence of a free,
deformable, moving surface gives rise to a more complicated drag formulation. In fact, within the constant-stress turbulent
atmospheric boundary layer over the ocean, the total air-sea stress not only includes the traditional turbulent and viscous
components but also incorporates surface-wave effects such as wave growth or decay, air-flow separation, and surface separation
in the form of sea-spray droplets. Because each individual stress component depends on and alters the sea state, a simple
linear addition of all stress components is too simplistic. In this paper we present a model of the air-sea surface stress
that incorporates air-flow separation and its effects on the other stress components, such as a reduction of the surface viscous
stress in the separated region as suggested by recent measurements. Naturally, the inclusion of these effects leads to a non-linear
stress formulation. This model, which uses a variable normalized dissipation rate of breaking waves and normalized length
of the separation bubble, reproduces the observed features of the drag coefficient from low to high wind speeds despite extrapolating
empirical wave spectra and breaking wave statistics beyond known limits. The model shows the saturation of the drag coefficient
at high wind speeds for both field and laboratory fetches, suggesting that air-flow separation over ocean waves and its accompanying
effects may play a significant role in the physics of the air-sea stress, at least at high wind speeds. 相似文献
94.
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
95.
Fabrice Demeter Elise Patole‐Edoumba Philippe Duringer Anne‐Marie Bacon Pheng Sytha Maxim Bano Vin Laychour Mao Cheangleng Vn Sari 《Geoarchaeology》2010,25(1):75-95
In 1963, E. Saurin and J.‐P. Carbonnel discovered the Sre Sbov site on an alluvial terrace of the Mekong River in central Cambodia. Saurin described a lithic typology dating to the Lower/Middle Pleistocene from this site. Although the original lithic assemblage has been lost, this typology has been used continuously as a reference by Southeast Asian prehistorians. In 2007, a Khmer–French team conducted excavations at Sre Sbov that yielded numerous pebbles and cobbles showing apparently convincing handmade removals, as Saurin had previously described. However, an in‐depth study of this assemblage, combined with a geological survey of the area, led to the conclusion that the stones were, in fact, of natural origin, and that for this reason their typology should be disregarded. Using satellite imagery and geological surveys, we explain how such a misinterpretation may have occurred and define a “buffer zone,” corresponding to the maximal extent of the proto‐Mekong River, where fluvially reworked pebbles and cobbles resembling artifacts may be recovered. © 2009 Wiley Periodicals, Inc. 相似文献
96.
Eric Lantz Jean-Luc Blanchet Luca Furfaro Fabrice Devaux 《Monthly notices of the Royal Astronomical Society》2008,386(4):2262-2270
A multi-imaging strategy is proposed and experimentally tested to improve the accuracy of photon counting with an electron multiplying CCD (EMCCD), by taking into account the random nature of its on-chip gain and the possibility of multiple photodetection events on one pixel. This strategy is based on Bayesian estimation on each image, with a priori information given by the sum of the images. The method works even for images with large dynamic range, with more improvement in the low light level areas. In these areas, two thirds of the variance added by the EMCCD in a conventional imaging mode are removed, making the physical photon noise predominant in the detected image. 相似文献
97.
Guimarães Pedro Veras Ardhuin Fabrice Perignon Yves Benetazzo Alvise Bouin Marie-Noëlle Garnier Valerie Redelsperger Jean-Luc Accensi Mickael Thomson Jim 《Ocean Dynamics》2022,72(8):621-639
Ocean Dynamics - Short waves growth is characterized by nonlinear and dynamic processes that couple ocean and atmosphere. Ocean surface currents can have a strong impact on short wave steepness and... 相似文献
98.
Geophysical studies point to a complex tectonic and geodynamic evolution of the Alboran Basin and Gulf of Cadiz. Tomographic images show strong seismic waves velocity contrasts in the upper mantle. The... 相似文献
99.
Ground penetrating radar application in a shallow marine Oxfordian limestone sequence located on the eastern flank of the Paris Basin, NE France 总被引:5,自引:0,他引:5
Guy Dagallier Ari I. Laitinen Fabrice Malartre Ignace P. A. M. Van Campenhout Paul C. H. Veeken 《Sedimentary Geology》2000,130(3-4):149-165
A Ground Penetrating Radar (GPR) survey has been carried out in Upper Jurassic limestones located on the eastern flank of the Paris Basin (NE France). The potential of the investigation method is assessed for delineating geologically meaningful stratifications in the shallow subsurface. The fundamentals of the GPR technique are described. Penetration depth and vertical resolution depends on the soil conditions, the characteristics of input signal and the configuration of the transmitter–receiver assembly. In the studied carbonates the penetration level is rather good and the electromagnetic signal reaches up to 1000 nanoseconds maximum (i.e. approximately 55 m). Several depositional units are outlined on the GPR profiles. Six different lithological units are recognised with distinct GPR reflection characteristics. The profiles illustrate the internal 3D organisation of the carbonate platform and its geometry. They provide detailed insight into the nature of an Oxfordian reefal build-up. The high-resolution subsurface model is directly calibrated with geological field observations and it results in a predictive 3D depositional working model. The GPR method is a non-destructive remote sensing technique that is cost effective. The method is considered complementary to other conventional high-resolution reservoir characterisation studies. It represents a powerful investigation tool in earth science studies concerning the imaging of the structure of the shallow subsurface. 相似文献
100.
Alexie Heimburger Mickael Tharaud Fabrice Monna Rémi Losno Karine Desboeufs Elisabeth B. Nguyen 《Geostandards and Geoanalytical Research》2013,37(1):77-85
The fifth version of natural river water certified reference material, SLRS‐5 (National Research Council – Conseil National de Recherches Canada), is commonly used to control the quality of major and trace element measurements. Concentrations of silicon and thirty‐one uncertified trace elements have been reported for the certified reference material SLRS‐4, but they are not yet available for SLRS‐5. Here, SLRS‐5/SLRS‐4 ratios were deduced from SLRS‐5 and SLRS‐4 measurements by inductively coupled plasma‐atomic emission spectrometry and high‐resolution inductively coupled plasma‐mass spectrometry for certified elements and thirty‐five uncertified elements (rare earth elements, B, Bi, Br, Cs, Ga, Ge, Hf, Li, Nb, P, Pd, Rb, Rh, S, Sc, Si, Sn, Th, Ti, Tl, Y). Both reference materials were measured directly one after the other, so that calculated elemental ratios would not be notably influenced either by calibration uncertainties or by eventual long‐term instrumental drift. The computed ratios are in good agreement with those deduced from the certified values. We also report concentrations for thirty‐three uncertified elements in SLRS‐5 by combining the measured SLRS‐5/SLRS‐4 ratios and the published SLRS‐4 values. The resulting new data set provides target SLRS‐5 values, which will be useful in quality control procedures. 相似文献