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561.
562.
Sandrine Baron Ccile Le-Carlier Jean Carignan Alain Ploquin 《Applied Geochemistry》2009,24(11):2093-2101
The identification of metal provenance is often based on chemical and Pb isotope analyses of materials from the operating chain, mainly ores and metallic artefacts. Such analyses, however, have their limits. Some studies are unable to trace metallic artefacts or ingots to their ore sources, even in well-constrained archaeological contexts. Possible reasons for this difficulty are to be found among a variety of limiting factors: (i) problems of ore signatures, (ii) mixing of different ores (alloys), (iii) the use of additives during the metallurgical process, (iv) metal recycling and (v) possible Pb isotopic fractionation during metal production. This paper focuses on the issue of Pb isotope fractionation during smelting to address the issue of metal provenance. Through an experimental reconstruction of argentiferous Pb production in the medieval period, an attempt was made to better understand and interpret the Pb isotopic composition of ore smelting products. It is shown that the measured differences (outside the total external uncertainties of 0.005 (2*sd) for 206Pb/204Pb ratios) in Pb signatures measured between ores, slag and smoke are not due to Pb mass fractionation processes, but to (1) ore heterogeneity (Δ206Pb/204Pbslag-ores = 0.066) and (2) the use of additives during the metallurgical process (Δ206Pb/204Pbslag-ores = 0.083). Even if these differences are due to causes (1) and/or (2), smoke from the ore reduction appears to reflect the ore mining area without a significant disturbance of its Pb signature for all the isotopic ratios (Δ206Pb/204Pbsmokes-ores = 0.026). Thus, because the isotopic heterogeneity of the mining district and additives is averaged in slags, slag appears as the most relevant product to identify ancient metal provenance. Whereas aiming at identifying a given mine seems beyond the possibilities provided by the method, searching for the mining district through analysis of the smelting workshop materials should provide a more appropriate approach in cases where no archaeological evidence of ancient mining is available. Furthermore, smoke Pb isotopic composition does not seem to be significantly affected by the metallurgical process. Paleopollution recorded in peat deposits could help to detect ancient mining production and workshops. Integrated collaboration between mining archaeologists and geochemists appears crucial to achieve this goal. 相似文献
563.
The study of the creation and evolution of the excavation disturbed zone (EDZ) in argillaceous rocks is a major issue for
the safety of nuclear wastes underground repositories. In this context, the argillaceous Tournemire site has provided a unique
opportunity to study the evolution of the EDZ with time thanks to the existence of three openings of different ages. A thorough
characterization of the EDZ has been conducted by different means such as visual observation, analysis of samples extracted
from drilled boreholes, EDZ permeability measurements, etc. On the basis of these measurements, a conceptual model of the
EDZ initiation and propagation at the Tournemire site has been proposed. In order to validate this model, numerical simulations
of increasing complexity have been carried out. In a first attempt, the response of the rock mass to the excavation phase,
followed by seasonal cyclic variations of temperature and relative humidity inside the opening, has been simulated by means
of a purely mechanical analysis, using a simple elastic material model. The EDZ has been estimated by post-processing the
calculated stress states, using a Mohr–Coulomb failure criterion. The results obtained show that no EDZ could be predicted
unless adopting a low cohesion value for the rock mass. Moreover, the deferred nature of the EDZ formation in Tournemire could
not be reproduced. These limitations have then been suppressed by using a coupled viscoplastic-damaging mechanical model,
the parameters of which have been identified from different laboratory experiments. With this model, a time evolution of the
EDZ could be predicted, but the EDZ pattern could not match the one observed in situ. Finally, in view of the importance of
the hydraulic couplings, unsaturated hydro-mechanical calculations have been carried out to investigate the effect of the
numerous seasonal variations cycles and the resulting shrinkage. 相似文献
564.
Groundwater flow modelling in the central zone of Hanoi, Vietnam 总被引:3,自引:2,他引:1
On the basis of a review of the Quaternary sedimentary architecture in the area of Hanoi city (Vietnam), a numerical, deterministic and three-dimensional groundwater flow model has been built for a simulation between 1995 and 2004. The sedimentary architecture has been constructed on the basis of the data from 32 drillings covering the entire Quaternary sequence (but with little sedimentological detail), as well as hydrographical and hydrogeological data. Both steady- and transient-state conditions were tested. Results calculated by the model seem to indicate that the conceptual hypotheses adopted are reasonable for the modelled domain and period. The simulation allows for calculation of the regional groundwater flow trends. It is also used for assessing the relative importance of the various recharge sources of the shallow aquifer system in Hanoi, and for estimating the interactions between groundwater and the Red River. 相似文献
565.
Application of multiple-point geostatistics on modelling groundwater flow and transport in a cross-bedded aquifer (Belgium) 总被引:3,自引:1,他引:2
Sedimentological processes often result in complex three-dimensional subsurface heterogeneity of hydrogeological parameter values. Variogram-based stochastic approaches are often not able to describe heterogeneity in such complex geological environments. This work shows how multiple-point geostatistics can be applied in a realistic hydrogeological application to determine the impact of complex geological heterogeneity on groundwater flow and transport. The approach is applied to a real aquifer in Belgium that exhibits a complex sedimentary heterogeneity and anisotropy. A training image is constructed based on geological and hydrogeological field data. Multiple-point statistics are borrowed from this training image to simulate hydrofacies occurrence, while intrafacies permeability variability is simulated using conventional variogram-based geostatistical methods. The simulated hydraulic conductivity realizations are used as input to a groundwater flow and transport model to investigate the effect of small-scale sedimentary heterogeneity on contaminant plume migration. Results show that small-scale sedimentary heterogeneity has a significant effect on contaminant transport in the studied aquifer. The uncertainty on the spatial facies distribution and intrafacies hydraulic conductivity distribution results in a significant uncertainty on the calculated concentration distribution. Comparison with standard variogram-based techniques shows that multiple-point geostatistics allow better reproduction of irregularly shaped low-permeability clay drapes that influence solute transport. 相似文献
566.
Pierre Kestener Alain Arneodo 《Stochastic Environmental Research and Risk Assessment (SERRA)》2008,22(3):421-435
Extreme atmospheric events are intimately related to the statistics of atmospheric turbulent velocities. These, in turn, exhibit
multifractal scaling, which is determining the nature of the asymptotic behavior of velocities, and whose parameter evaluation
is therefore of great interest currently. We combine singular value decomposition techniques and wavelet transform analysis
to generalize the multifractal formalism to vector-valued random fields. The so-called Tensorial Wavelet Transform Modulus
Maxima (TWTMM) method is calibrated on synthetic self-similar 2D vector-valued multifractal measures and monofractal 3D vector-valued
fractional Brownian fields. We report the results of some application of the TWTMM method to turbulent velocity and vorticity
fields generated by direct numerical simulations of the incompressible Navier–Stokes equations. This study reveals the existence
of an intimate relationship between the singularity spectra of these two vector fields which are found significantly more intermittent than previously
estimated from longitudinal and transverse velocity increment statistics.
相似文献
Alain ArneodoEmail: |
567.
Alain Bensoussan Pierre Rapha?l Bertrand Alexandre Brouste 《Stochastic Environmental Research and Risk Assessment (SERRA)》2012,26(8):1109-1122
The objective of this article is to study as extensively as possible the uncertainties affecting the annual energy produced by a windmill. In the literature, the general approach is to estimate the mean annual energy from a transformation of a Weibull distribution law. Then the issue is reduced to estimating the coefficients of this distribution. This is obtained by classical statistical methods. Therefore, the uncertainties are mostly limited to those resulting from the statistical procedures. But in fact, the real uncertainty of the random variable which represents the annual energy cannot been reduced to the uncertainty on its mean and to the uncertainties induced from the estimation procedure. We propose here a model, which takes advantage of the fact that the annual energy production is the sum of many random variables representing the 10?min energy production during the year. Under some assumptions, we make use of the central limit theorem and show that an intrinsic uncertainties of wind power, usually not considered, carries an important risk. We also explain an observation coming from practice that the forecasted annual production is always overestimated, which creates a risk of reducing the profitability of the operation. 相似文献
568.
Nutrient fluxes between water column and sediments: Potential influence of the pearl oyster culture 总被引:1,自引:0,他引:1
Gaertner-Mazouni N Lacoste E Bodoy A Peacock L Rodier M Langlade MJ Orempuller J Charpy L 《Marine pollution bulletin》2012,65(10-12):500-505
This study quantifies benthic nutrient fluxes and sedimentation rates in the Ahe Atoll lagoon (French Polynesia), in two stations located under pearl oyster frames, and two control stations away from the pearl culture facility. Dissolved inorganic nitrogen fluxes ranged between 2 and 35μmolNm(-2)h(-1) and Soluble Reactive Phosphorus varied between -3 and 8.2μmolPm(-2)h(-1). Particulate sedimentation rates beneath the oysters were approximately five times higher than in the control zone and the percentage of small particles (?63μm) were about the twice. In contrast, sediment composition was similar under and outside the direct influence of oyster frames. In this ecosystem, where primary production is dependent on the available nitrogen, our study revealed that, while highly variable, benthic fluxes could sometimes contribute up to 28% of the nitrogen demand for primary production. 相似文献
569.
A sodar was deployed at Roissy–Charles de Gaulle airport near Paris, France, in 2008 with the aim of improving the forecast of low visibility conditions there. During the winter of 2008–2009, an experiment was conducted that showed that the sodar can effectively detect and locate the top of fog layers which is signaled by a strong peak of acoustic reflectivity. The peak is generated by turbulence activity in the inversion layer that contrasts sharply with the low reflectivity recorded in the fog layer below. A specific version of the 1D-forecast model deployed at Roissy for low visibility conditions (COBEL-ISBA) was developed in which fogs’ thicknesses are initialized by the sodar measurements rather than the information derived from the down-welling IR fluxes observed on the site. It was tested on data archived during the winters of 2008–2009 and 2009–2010 and compared to the version of the model presently operational. The results show a significant improvement—dissipation times of fogs are better predicted. 相似文献
570.
Oldrich Navratil Olivier Evrard Michel Esteves Cédric Legout Sophie Ayrault Julien Némery Ainhoa Mate‐Marin Mehdi Ahmadi Irène Lefèvre Alain Poirel Philippe Bonté 《地球表面变化过程与地形》2012,37(8):828-846
Influence of the rainfall regime on erosion and transfer of suspended sediment in a 905‐km² mountainous catchment of the southern French Alps was investigated by combining sediment monitoring, rainfall data, and sediment fingerprinting (based on geochemistry and radionuclide concentrations). Suspended sediment yields were monitored between October 2007 and December 2009 in four subcatchments (22–713 km²). Automatic sediment sampling was triggered during floods to trace the sediment origin in the catchment. Sediment exports at the river catchment outlet (330 ± 100 t km‐2 yr‐1) were mainly driven (80%) by widespread rainfall events (long duration, low intensities). In contrast, heavy, local and short duration storms, generated high peak discharges and suspended sediment concentrations in small upstream torrents. However, these upstream floods had generally not the capacity to transfer the sediment down to the catchment outlet and the bulk of this fine sediment deposited along downstream sections of the river. This study also confirmed the important contribution of black marls (up to 70%) to sediment transported in rivers, although this substrate only occupies c. 10% of the total catchment surface. Sediment exports generated by local convective storms varied significantly at both intra‐ and inter‐flood scales, because of spatial heterogeneity of rainfall. However, black marls/marly limestones contribution remained systematically high. In contrast, widespread flood events that generate the bulk of annual sediment supply at the outlet were characterized by a more stable lithologic composition and by a larger contribution of limestones/marls, Quaternary deposits and conglomerates, which corroborates the results of a previous sediment fingerprinting study conducted on riverbed sediment. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献