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181.
Silvia Pellegrini Luca Ciotti 《Monthly notices of the Royal Astronomical Society》2006,370(4):1797-1803
NGC 3379 is a well-studied nearby elliptical for which optical investigations have claimed a little dark matter content, or even no dark matter. Recently, its total mass profile M ( r ) has been derived by exploiting Chandra observations of its extended and X-ray emitting interstellar medium, based on the hypothesis of hydrostatic equilibrium for the hot gas. The resulting total mass within the effective radius R e has been claimed to be a few times larger than that found by optical studies. Here, we show that part of the discrepancy can be due to an underestimate of the optically derived mass, and the remaining discrepancy of a factor of ∼2 can be explained by deviations from hydrostatic equilibrium of the hot gas. By using hydrodynamical simulations tailored to reproduce the observed hot gas properties of NGC 3379, and by assuming as input for the simulations the total mass profile derived optically, we show that (i) the hot gas at the present time has X-ray properties consistent with those observed only if it is outflowing over most of the galactic body, and (ii) an overestimate of M of the same size found in the recent X-ray analysis is recovered when assuming hydrostatic equilibrium. We also show that the hot gas is outflowing even for a dark matter fraction within R e as large as derived with the standard X-ray procedure based on the hydrostatic equilibrium assumption, which shows the unapplicability of the method for this galaxy. Finally, we find that the whole range of dark mass amount and distribution allowed for by optical studies is compatible with a hot gas flow with the observed X-ray properties. 相似文献
182.
183.
Carbon mass-balance modelling and carbon isotope exchange processes in dynamic caves 总被引:3,自引:0,他引:3
Silvia Frisia Ian J. Fairchild Renza Miorandi Andrea Borsato 《Geochimica et cosmochimica acta》2011,75(2):380-400
Diverse interpretations have been made of carbon isotope time series in speleothems, reflecting multiple potential controls. Here we study the dynamics of 13C and 12C cycling in a particularly well-constrained site to improve our understanding of processes affecting speleothem δ13C values. The small, tubular Grotta di Ernesto cave (NE Italy) hosts annually-laminated speleothem archives of climatic and environmental changes. Temperature, air pressure, pCO2, dissolved inorganic carbon (DIC) and their C isotopic compositions were monitored for up to five years in soil water and gas, cave dripwater and cave air. Mass-balance models were constructed for CO2 concentrations and tested against the carbon isotope data. Air advection forces winter pCO2 to drop in the cave air to ca. 500 ppm from a summer peak of ca. 1500 ppm, with a rate of air exchange between cave and free atmosphere of approximately 0.4 days. The process of cave ventilation forces degassing of CO2 from the dripwater, prior to any calcite precipitation onto the stalagmites. This phase of degassing causes kinetic isotope fractionation, i.e. 13C-enrichment of dripwater whose δ13CDIC values are already higher (by about 1‰) than those of soil water due to dissolution of the carbonate rock. A subsequent systematic shift to even higher δ13C values, from −11.5‰ in the cave drips to about −8‰ calculated for the solution film on top of stalagmites, is related to degassing on the stalagmite top and equilibration with the cave air. Mass-balance modelling of C fluxes reveals that a very small percentage of isotopically depleted cave air CO2 evolves from the first phase of dripwater degassing, and shifts the winter cave air composition toward slightly more depleted values than those calculated for equilibrium. The systematic 13C-enrichment from the soil to the stalagmites at Grotta di Ernesto is independent of drip rate, and forced by the difference in pCO2 between cave water and cave air. This implies that speleothem δ13C values may not be simply interpreted either in terms of hydrology or soil processes. 相似文献
184.
Waste rock dump investigation at Roşia Montană gold mine (Romania): a geostatistical approach 总被引:1,自引:1,他引:0
Diego Servida Sara Comero Mara Dal Santo Luisa de Capitani Giovanni Grieco Pietro Marescotti Silvia Porro Ferenc Lázár Forray Ágnes Gál Alexandru Szakács 《Environmental Earth Sciences》2013,70(1):13-31
Ro?ia Montan?, the largest European gold mine, could be re-opened. Environmental problems led to severe pollution of the Ro?ia and Abrud Rivers. The two main potentially toxic element (PTE) sources in mine sites are, in general, the abandoned underground workings and the piles of waste rock. Since the composition of waste rocks is often heterogeneous, this study faces the problem of estimating their mineralogical and chemical features starting from a set of sampling point. Twenty-five samples were collected on the main waste dump of the Ro?ia Montan? mine following a virtual squared grid (knots distance about 25 m). Grain size, color, bulk chemistry, mineralogy, acid mine drainage potential and a set of selected PTE (Ag, As, Cu, Ni, Pb and Zn) concentrations were determined on each sample. In a first approximation two main waste rock groups were identified: WR1 bulk composition is dacite-dominated, while WR2 is andesite-dominated. In both of them the concentrations of PTEs are below the regulatory limits for soils, with the exception of As. In terms of acid mine drainage, WR1 has a net acid-producing potential, while WR2 has a net neutralizing potential. The anisotropy of WR properties were analysed by means of semi-variograms and displayed with contour maps. Application of positive matrix factorization for the analysis of all the data relative to waste rocks allowed defining, in a semi-quantitative way, the factors controlling pollution and their spatial distribution. The processing of score matrix G factor associated with the geostatistical elaboration promises to be a powerful tool to discern the composition of mine dumps and support the exploitation and remediation phases. 相似文献
185.
The cultural gap between Europe and Asia (at first political and then religious) saw an increase with the spread of Islam, which, to the European imagination, was synonymous with ‘foreign’. This separation grew after the discovery of America (1492) with the loss of the central commercial position of the Mediterranean reducing the level of contact between the countries of its basin. Traces of these changes can be recognized on historic Western maps in the transformation of their toponyms (place names). Through a comparative cartographic analysis, this paper examines some of the key changes and phases that occurred during the era. 相似文献
186.
Mariano J. Albano Paulo da Cunha Lana Claudia Bremec Rodolfo Elías César C. Martins Natalia Venturini Pablo Muniz Silvia Rivero Eduardo A. Vallarino Sandra Obenat 《Marine pollution bulletin》2013
We evaluated benthic habitat quality along a presumed contamination gradient in the Mar del Plata port (Southwestern Atlantic) by coupling biological and chemical proxies in a multidisciplinary approach. Organic matter and photosynthetic pigment contents were higher in silty-clay bottoms of the inner port sites. Levels of all fecal steroids decreased from the inner sites to the port inlet. High concentrations of coprostanol in the inner sites seemed to derive from a permanent population of sea lions rather than from sewage outfalls due to coprostanol/epicoprostanol ratio (IV) values <2.5. PAHs levels were also higher in the inner sector, related to both biomass combustion and petroleum combustion associated to local marine traffic. High disturbance and low ecological status were reflected in low benthic diversity and high AMBI values in the inner sites. 相似文献
187.
The current analysis of earthquakes is typically based on linear mathematical models that may fail to describe and forecast particular behaviors, because in many cases the data complexity may induce a highly non linear behavior. In this paper the implementation of an alternative method for seismic time series analysis is presented. The RPs (Recurrence Plots) enables recognition and treatment of measured accelerations. An RP obtained from seismic data allows a more efficient interpretation of the ground motions and this explanation contributes to characterize materials and responses. The nonlinear attributes from RPs analysis can be used as filters to reveal patterns or be combined to predict a seismic property. Automated seismic data characterization, based on nonlinear seismic attributes, could rewrite the rules of earthquake phenomena interpretation. The objective of this work is to establish a new methodology for practical application of nonlinear dynamics in seismic pattern/attributes recognition, an evolving and challenging engineering field. 相似文献
188.
Piazza R Giuliani S Bellucci LG Mugnai C Cu NH Nhon DH Vecchiato M Romano S Frignani M 《Marine pollution bulletin》2010,60(12):2303-2310
Samples from nine Central Vietnam coastal lagoons, together with three soils and sediments collected in two freshwater reservoirs of the Thua Thien-Hué province, were analysed for polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs). Total concentrations are low, from 192 to 2912 pg g−1 and depth profiles in Tam Giang-Cau Hai (TG-CH) sediment cores show only minor changes over time in PCDD/F input and composition. Octachloro dibenzo-p-dioxin (OCDD) is the prevailing congener (approximately 90%), indicating combustion as the main PCDD/F source to these coastal systems, whereas natural formation might be partly responsible for the presence at depth. 2,3,7,8-Tetrachloro dibenzo-p-dioxin (TCDD), largely sprayed together with Agent Orange over the study areas during the war (1961–1971), is absent or very low. This result supports the hypothesis of strong degradation soon after spraying. Multivariate statistical analyses account for the presence of local, short-range sources as observed in the northern part of the TG-CH lagoon. 相似文献
189.
Modelling air pollution data by the skew-normal distribution 总被引:3,自引:3,他引:0
Silvia Bartoletti Nicola Loperfido 《Stochastic Environmental Research and Risk Assessment (SERRA)》2010,24(4):513-517
Particulate matter with an aerodynamic equivalent diameter of up 10 μm is commonly referred to as PM10 and its harmful effects on human health are well known. We model annual means of daily concentrations of PM10 in Italy by the skew-normal distribution, giving theoretical as well as empirical motivations for the model’s choice. Its
adequacy is checked through Anderson–Darling statistic. The skew-normal distribution gives a very good fit to the data and
it is particularly useful in estimating probabilities of high PM10 concentrations. 相似文献
190.
Silvia Román João Manuel Valente Nabais Juan Félix González Carmen María González‐García Angel Luis Ortiz 《洁净——土壤、空气、水》2012,40(7):698-705
The adsorption of fluoxetine onto activated carbons (ACs) prepared from almond tree pruning by steam and CO2 activation under different temperature conditions (650–950°C), was studied. In both series increasing the temperature caused an increase in the BET apparent surface area, yielding ACs with SBET up to 870 and 710 m2 g?1 after steam and CO2 activation, respectively. Also, a slight widening of the porosity was found in both cases. In order to modify the functionality of the ACs, two of them were impregnated with triethylenediamine (TEDA) prior to the adsorption process, which caused a decrease in the AC apparent surface mainly due to micropore blockage. The fluoxetine adsorption isotherms at 25°C showed maximum adsorption capacities between 110 and 224 mg g?1. The adsorption isotherms were analyzed using Langmuir and Freundlich models. Although the impregnation reduced the pore volume, it did not cause a decrease in the fluoxetine maximum adsorption capacity, but a modification in the adsorption mechanism was observed. 相似文献