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221.
In this paper, a feasibility of anelastic approach for numerical weather prediction (NWP) is examined. The study concerns
the anelastic nonhydrostatic model EULAG as a prospective candidate for the new dynamical core of a high-resolution NWP model.
Such an application requires a series of benchmark tests to be performed. The study presents the results of dry idealized
two-dimensional linear and non-linear tests. They include evolution of cold and warm density currents in neutrally stratified
atmosphere, inertia-gravity waves in short and long channels, as well as mountain gravity waves for a set of different flow
regimes. Detailed comparison of the results with the reference solutions, based mainly on the results of compressible models,
indicates a high level of conformity for all of the experiments. It verifies the anelastic approach as strongly consistent
with the compressible one for a broad class of atmospheric problems. It also corroborates the robustness of EULAG numerics,
an essential requirement of dynamical core of NWP model. 相似文献
222.
During the operations of purging and disposal of sediments of a reservoir it is necessary to know the values of turbidity in the river downstream in natural condition,in the absence of dams or river training works.The paper shows that under these conditions the ratio of the average values of sediment discharge to the annual maximum value of water discharge is a function of the average annual turbidity.Turbidity can be considered as representative synthetic index of the climatic conditions,the lithological features and the land cover of the basin,and the geometric characteristics of the river network.The proposed relationship of sediment discharge as a function of water discharge were validated on the basis of data collected from different Italian regions that have very different morphological,geo-lithological and rainfall features and that are characterised by a basin area changing between a few dozen and thousands of square kilometres.The results can be considered satisfying. 相似文献
223.
B. Pereira de Oliveira J. M. de la Rosa A. Z. Miller C. Saiz-Jimenez A. Gómez-Bolea M. A. Sequeira Braga A. Dionísio 《Environmental Earth Sciences》2011,63(7-8):1677-1690
In the present study, samples arising from the scaling of a Portuguese granite building were examined in an attempt to understand the mechanisms of surface blackening and detachment. The building, the Third Order of St. Francis Church, is located in the city centre of Porto which is an area characterised by moderate motor traffic. The Mediterranean climate and the façade orientation favoured the proliferation of microorganisms on the Third Order of St. Francis Church, in Porto. The scientific approach carried out in the South façade revealed that these coloured layers are essentially of biological origin. Subsequent chemical analysis confirmed microscope observations and pointed out to the presence of organic matter synthesised by cyanobacteria, algae and lichens. Numerous biological marker compounds indicated a significant presence of biogenically derived material, suggesting that biological activity was playing a major role in the development of coloured layers and in the detachment processes in this historic building. 相似文献
224.
Mid to late Holocene constraints for continental shelf mud deposition in association with river input: the Guadiana Mud Patch (SW Iberia) 总被引:1,自引:1,他引:0
This study correlates Holocene sedimentation with regional environmental changes for the Guadiana middle shelf, SW Iberia,
based on a detailed sedimentological analysis combined with radiocarbon and amino acid racemization dating. The sedimentary
record of vibrocore CRIDA16 (307 cm) from the mud patch off the Guadiana River is characterized by a transgressive signature.
Terrigenous sand–gravel dominates the core base up to ca. 5,000 cal. years b.p., enriched in schist/greywackes and non-reworked quartz. The shelf area was under the direct influence of Guadiana bed load
discharges, as sea level was lower than today but rising, favouring the entrapment of fines during the Guadiana estuary infilling
in the early Holocene. Core upwards, fines dominate the record. Sea-level stabilization at ca. 5,700–3,700 cal. years b.p. led to estuary infilling by coarser sediments and export of suspended sediment to the middle shelf. After ca. 900–700 cal.
years b.p., the formation of the Guadiana Mud Patch signifies deposition in a marine environment dominated by suspended material from
the Guadiana River. Comparison with earlier publications showed that a similar evolutionary mechanism of middle shelf mud
deposition occurred in other parts of the Iberian Margin, pointing to a generalized establishment of this type of sedimentary
body in Iberia since the mid to late Holocene. This suggests that the formation of mud belts on the north and south Iberian
Margin was to a large extent synchronous. It is likely that the evolution of the Guadiana Mud Patch on the shelf was controlled
foremost by the overall climate trends identified for several parts of Iberia during the Holocene (i.e. increased aridity
punctuated by significant humidity stages), and less by human occupation of the region. Enhanced humidity stages led to higher
rainfall and intensified floods, with a consequent increase of discharges to the shelf which ultimately were responsible for
the Guadiana Mud Patch formation. It is expected that this pattern of sedimentary dynamics has been strongly disturbed since
2002, when the closing of the Alqueva Dam (the biggest on the Iberian Peninsula) was completed in the Guadiana River basin. 相似文献
225.
Giovanni Mongelli Michele Paternoster Giovanna Rizzo Rosa Sinisi 《International Journal of Earth Sciences》2014,103(4):1125-1140
There is an increasing interest in the distribution of rare earth elements (REEs) within soils, primarily as these elements can be used to identify pedogenetic processes and because soils may be future sources for REE extraction, despite much attention should be paid to the protection and preservation of present soils. Here, we evaluate the processes that control the distribution of REEs in subsoil horizons developed over differing lithologies in an area of low anthropogenic contamination, allowing estimates of the importance of source rocks and weathering. Specifically, this study presents new data on the distribution of REEs and other trace elements, including transition and high-field-strength elements, in subsoils developed on both Quaternary silica-undersaturated volcanic rocks and Pliocene siliciclastic sedimentary rocks within the Mt. Vulture area of the southern Apennines in Italy. The subsoils in the Mt. Vulture area formed during moderate weathering (as classified using the chemical index of alteration) and contain an assemblage of secondary minerals that is dominated by trioctahedral illite with minor vermiculite. The REEs, high-field-strength elements, and transition metals have higher abundances in subsoils that developed from volcanic rocks, and pedogenesis caused the Mt. Vulture subsoils to have REE concentrations that are an order of magnitude higher than typical values for the upper continental crust. This result indicates that the distribution of REEs in soils is a valuable tool for mineral exploration. A statistical analysis of inter-elemental relationships indicates that REEs are concentrated in clay-rich fractions that also contain significant amounts of low-solubility elements such as Zr and Th, regardless of the parent rock. This suggests that low-solubility refractory minerals, such as zircon, play a significant role in controlling the distribution of REEs in soils. The values of (La/Yb)N and (Gd/Yb)N fractionation indices are dependent on the intensity of pedogenesis; soils in the study area have values that are higher than typical upper continental crust ratios, suggesting that soils, especially those that formed during interaction with near neutral to acidic organic-rich surface waters, may represent an important source of both light REEs and medium REEs (MREEs). In comparison, MREE/heavy REE fractionation in soils that form during moderate weathering may be affected by variations in parent rock lithologies, primarily as MREE-hosting minerals, such as pyroxenes, may control (La/Sm)N index values. Eu anomalies are thought to be the most effective provenance index for sediments, although the anomalies within the soils studied here are not related to the alteration of primary minerals, including feldspars, to clay phases. In some cases, Eu/Eu* values may have a weak correlation with elements hosted by heavy minerals, such as Zr; this indicates that the influence of mechanical sorting of clastic particles during sedimentary transport on the Eu/Eu* values of siliciclastic sediments needs to be considered carefully. 相似文献
226.
Oscar Veses Rosa Mosteo Maria P. Ormad Jose L. Ovelleiro 《Environmental Earth Sciences》2014,72(8):2917-2929
This study was carried out to evaluate sediment pollution related to trace elements such as Cd, Cu, Ni, Pb, Zn, Hg, As and Cr and eight polycyclic aromatic hydrocarbons (PAHs) in 127 sites located in 85 rivers in Spain. Sediment samples were classified according to similar chemical characteristics by means of statistical multivariate techniques (principal component analysis, PCA) and artificial neural networks such as self-organizing maps (SOM). Sediment sample classification provided by PCA was not as useful as the one provided by the SOM, revealing itself as a powerful tool to be incorporated in the first steps of sediment quality assessments. The use of sediment quality guidelines such as the mean-probable effects concentration quotient (m-PECQ) predicted sediment quality and gave an overall view of sediment pollution throughout Spain. Most of the samples (118 out of 127) showed m-PECQ values below 0.5 highlighting their relative low potential risk to cause adverse effects on the benthic fauna. However, some samples presented m-PECQ values higher than 0.5 suggesting a clear potential risk to these fauna. Besides, unusual high concentrations of trace elements and PAHs were related to the human activities carried out near each sampling point. 相似文献
227.
228.
We study the dynamical evolution of the Hilda group of asteroids trough numerical methods, performing also a collisional pseudo-evolution of the present population, in order to calculate the rate of evaporation and its contribution to the cratering history of the Galilean satellites. If the present population of small asteroids in the Hilda's region follows the same size distribution observed at larger radii, we find that this family is the main contributor to the production of small craters (i.e., crater with diameters d∼4 km) on the Galilean system, overcoming the production by Jupiter Family Comets and by Trojan asteroids. The results of this investigation encourage further observational campaigns, in order to determine the size distribution function of small Hilda asteroids. 相似文献
229.
Variations in martian surface heat flow, similar to those observed in terrestrial continental tectonothermally stable areas, could result in elevation differences of kilometric scale through differential thermal isostasy. This effect is enhanced with the increase of heat sources located within the crust. Local differences in the thermal history of the Mars’ lithosphere could have appreciably distorted the original long-wavelength topography of putative martian paleoshorelines. So, this work shows that a paleoequipotential surface does not necessarily have to fit well a present-day equipotential surface when evaluating paleoshorelines through assessment of high-resolution topography. 相似文献
230.
Ana I. Gómez de Castro Willem Wamsteker Martin Barstow Noah Brosch Norbert Kappelmann Wollfram Kollatchny Domitilla de Martino Isabella Pagano Alain Lecavelier des Étangs David Ehenreich Dieter Reimers Rosa González Delgado Francisco Najarro Jeff Linsky 《Astrophysics and Space Science》2006,303(1-4):133-145
Progress of modern astrophysics requires the access to the electromagnetic spectrum in the broadest energy range. The Ultraviolet is a fundamental energy domain since it is one of the most powerful tool to study plasmas at temperatures in the 3,000–300,000 K range as well as electronic transitions of the most abundant molecules in the Universe. Moreover, the UV radiation field is a powerful astrochemical and photoionizing agent.The objective of this review is to describe the crucial issues that require access to the UV range. A summary has been added to the end with a more classic view of UV needs by astronomical object type; this approach is followed at length in the rest of the contributions of this issue. 相似文献