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21.
22.
Modeling ground deformations of Panarea volcano hydrothermal/geothermal system (Aeolian Islands, Italy) from GPS data 总被引:1,自引:0,他引:1
Alessandra Esposito Marco Anzidei Simone Atzori Roberto Devoti Guido Giordano Grazia Pietrantonio 《Bulletin of Volcanology》2010,72(5):609-621
Panarea volcano (Aeolian Islands, Italy) was considered extinct until November 3, 2002, when a submarine gas eruption began
in the area of the islets of Lisca Bianca, Bottaro, Lisca Nera, Dattilo, and Panarelli, about 2.5 km east of Panarea Island.
The gas eruption decreased to a state of low degassing by July 2003. Before 2002, the activity of Panarea volcano was characterized
by mild degassing of hydrothermal fluid. The compositions of the 2002 gases and their isotopic signatures suggested that the
emissions originated from a hydrothermal/geothermal reservoir fed by magmatic fluids. We investigate crustal deformation of
Panarea volcano using the global positioning system (GPS) velocity field obtained by the combination of continuous and episodic
site observations of the Panarea GPS network in the time span 1995–2007. We present a combined model of Okada sources, which
explains the GPS results acquired in the area from December 2002. The kinematics of Panarea volcano show two distinct active
crustal domains characterized by different styles of horizontal deformation, supported also by volcanological and structural
evidence. Subsidence on order of several millimeters/year is affecting the entire Panarea volcano, and a shortening of 10−6 year−1 has been estimated in the Islets area. Our model reveals that the degassing intensity and distribution are strongly influenced
by geophysical-geochemical changes within the hydrothermal/geothermal system. These variations may be triggered by changes
in the regional stress field as suggested by the geophysical and volcanological events which occurred in 2002 in the Southern
Tyrrhenian area. 相似文献
23.
Combined analyses of pollen, seeds, woods, micro-charcoal and non-pollen palynomorphs from Stagno di Maccarese, an artificially
dried out coastal basin north of the Tiber delta now occupied by the Fiumicino Airport (Rome, Italy), document marked vegetation
and environmental changes during the last 8300 years. Between 8300 and 5400 cal. a BP dense mixed deciduous and evergreen
forests surrounded a eutrophic freshwater basin. An abrupt change around 5400 cal. a BP marks the transition to a marshy environment,
due to a lowering of the water table. An increase of cereals and micro-charcoals matches the presence of a nearby Eneolithic
settlement. Between 5100 and 2900 cal. a BP there is a remarkable expansion of riparian trees, indicating an increase of the
water level. Between 2900 and 2000 cal. a BP, a new development of marshlands points to a progressive lowering of the lake.
After 2000 cal. a BP, during the Roman exploitation of the area, an expansion of arboreal vegetation is recorded, characterized
by evergreen and deciduous oak-dominated forests, while an extensive chenopods marshland matches the presence of saltworks.
On the whole, the Stagno di Maccarese area appears very unstable, due to changes in lake level, introgression of marine water,
eutrophic phases, flood events, desiccations and openings of the forest vegetation. 相似文献
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25.
Alessandra Crosato 《地球表面变化过程与地形》2009,34(15):2078-2086
In meandering rivers, the local channel migration rate increases with increasing bend sharpness until it reaches a maximum at a certain critical value of the bend sharpness. Beyond this critical value, the migration rate decreases if bend sharpness increases. Similarly, reach‐averaged migration rates attain a maximum at a certain river sinuosity. This work investigates the physics of these phenomena by comparing the results of two physics‐based models of different complexity, in which the migration rates are proportional to the near‐bank flow velocity excess. In the computational tests the river was allowed to meander progressively, starting from an almost straight planimetry. Both models reproduced the observed peak in the curve describing the local migration rate as a function of the ratio radius of curvature‐channel width (R/B), with a rising limb at lower R/B values and a falling limb at higher R/B values. The rising limb can be explained by the decrease in relative lag distance between near‐bank flow velocity and forcing curvature as R/B increases. The falling limb results from the decrease in local channel curvature and near‐bank flow velocity excess. Since the models do not include flow separation, the results indicate that this phenomenon is not needed to explain the decrease of channel migration rates in sharp bends. The models reproduced also the peak in the curve describing the reach‐averaged migration rates as a function of river sinuosity The increase and then decrease of reach‐averaged migration rates as sinuosity increases appears to be mainly caused by the variation of the reach‐averaged value of the ratio R/B. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
26.
Alessandra F. S. Ferreira Antônio F. B. A. Prado Othon C. Winter Denilson P. S. Santos 《Astrophysics and Space Science》2018,363(2):24
The objective of the present paper is to derive a set of analytical equations that describe a swing-by maneuver realized in a system of primaries that are in elliptical orbits. The goal is to calculate the variations of energy, velocity and angular momentum as a function of the usual basic parameters that describe the swing-by maneuver, as done before for the case of circular orbits. In elliptical orbits the velocity of the secondary body is no longer constant, as in the circular case, but it varies with the position of the secondary body in its orbit. As a consequence, the variations of energy, velocity and angular momentum become functions of the magnitude and the angle between the velocity vector of the secondary body and the line connecting the primaries. The “patched-conics” approach is used to obtain these equations. The configurations that result in maximum gains and losses of energy for the spacecraft are shown next, and a comparison between the results obtained using the analytical equations and numerical simulations are made to validate the method developed here. 相似文献
27.
Jaroslav Dudík Elena Dzifčáková Nicole Meyer-Vernet Giulio Del Zanna Peter R. Young Alessandra Giunta Barbara Sylwester Janusz Sylwester Mitsuo Oka Helen E. Mason Christian Vocks Lorenzo Matteini Säm Krucker David R. Williams Šimon Mackovjak 《Solar physics》2017,292(8):100
We review the presence and signatures of the non-equilibrium processes, both non-Maxwellian distributions and non-equilibrium ionization, in the solar transition region, corona, solar wind, and flares. Basic properties of the non-Maxwellian distributions are described together with their influence on the heat flux as well as on the rates of individual collisional processes and the resulting optically thin synthetic spectra. Constraints on the presence of high-energy electrons from observations are reviewed, including positive detection of non-Maxwellian distributions in the solar corona, transition region, flares, and wind. Occurrence of non-equilibrium ionization is reviewed as well, especially in connection to hydrodynamic and generalized collisional-radiative modeling. Predicted spectroscopic signatures of non-equilibrium ionization depending on the assumed plasma conditions are summarized. Finally, we discuss the future remote-sensing instrumentation that can be used for the detection of these non-equilibrium phenomena in various spectral ranges. 相似文献
28.
29.
Annual Variation of Benthic Nutrient Fluxes in Shallow Coastal Waters (Gulf of Trieste, Northern Adriatic Sea) 总被引:5,自引:0,他引:5
Abstract. Benthic fluxes of dissolved N. Si and P nutrients, alkalinity, dissolved inorganic C (DIC), and O2 from sediments in the Gulf of Trieste (northern Adriatic, Italy) were measured monthly for 16 months, using laboratory incubated flux chambers at in siru temperatures in the dark. The annual average fluxes were: 02 = -19.3 ± 8.2, DIC = 13.7 ± 9.6, NO3 = -0.04 ± 0.16, NH4 = 0.3 ± 0.4. PO4= 4.001 ± 0.01, Si = 0.9 ± 0.1 mmol m-2 d-1, with strong temporal fluctuations. The highest effluxes of all nutrients and DIC were observed in the summer. Small effluxes of DIC and NH4 and influxes of Si and PO4 were observed in late winter. Only NH4 (ca. 50%) and Si (ca. 70%) fluxes were significantly correlated with temperature. This correlation suggests that the rate of downward input and the quality of sedimented organic matter (autochthonous and allochthonous) were superimposed on the temperature fluctuations. High DIC, NH4 and Si effluxes observed in May 1993 during low temperature were due to the degradation of sedimentary organic matter produced by an early spring bloom of benthic microalgae which occurred about 6 weeks earlies while the autumn phytoplankton bloom was simultaneously reflected in enhanced benthic fluxes due to higher temperature. The role of benthic biological advection in this transport across the sediment-water interface, evaluated by comparison between measured benthic and calculated diffusive fluxes from nutrient pore water concentrations, was of minor importance. This is probably due to low infaunal activity throughout the year it was localized mostly in the narrow surficial layer. The annual average diffusive fluxes of NH4 and PO4 were higher than those measured, probably due to the presence of nitrificationdenitrifi-cation processes and redox-dependent chemical reactions at the oxic sediment-water interface, respectively. Only during bottom-water hypoxia in September 1993 did strong PO4 effluxes prevail. Calculations based on the Redfield stoichiometry of oxic decomposition of organic N to NH4 and NO3, and differences between diffusive and measured NH4 fluxes showed that denitrifkation averaged 0.8 mmol m-2 d-1. Significant correlations between NH4 and PO4 DIC and Si, and NH4 and Si fluxes suggested their parallel regeneration and utilization at the sediment-water interface. The nutrient fluxes observed were not significantly linked to O2 consumption, suggesting also that anaerobic oxidation processes were important at the sediment-water interface in the gulf. The N, P and Si nutriqnts released from sediment pore waters are probably utilized in benthic microalgal and bottorn-hater primary production. This indicates that pelagic and benthic communities in the central part of the Gulf of Trieste function relatively independently of each other. 相似文献