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21.
Filippo Ridolfi Alberto Renzulli Matteo Puerini 《Contributions to Mineralogy and Petrology》2010,160(1):45-66
This work focuses on a rigorous analysis of the physical–chemical, compositional and textural relationships of amphibole stability
and the development of new thermobarometric formulations for amphibole-bearing calc-alkaline products of subduction-related
systems. Literature experimental results (550–1,120°C, <1,200 MPa, −1 ≤ ΔNNO ≤ +5), H2O–CO2 solubility models, a multitude of amphibole-bearing calc-alkaline products (whole-rocks and glasses, representing 38 volcanoes
worldwide), crustal and high-P (1–3 GPa) mantle amphibole compositions have been used. Calcic amphiboles of basalt-rhyolite volcanic products display tschermakitic
pargasite (37%), magnesiohastingsite (32%) and magnesiohornblende (31%) compositions with aluminium number (i.e. Al# = [6]Al/AlT) ≤ 0.21. A few volcanic amphiboles (~1%) show high Al# (>0.21) and are inferred to represent xenocrysts of crustal or mantle
materials. Most experimental results on calc-alkaline suites have been found to be unsuitable for using in thermobarometric
calibrations due to the high Al# (>0.21) of amphiboles and high Al2O3/SiO2 ratios of the coexisting melts. The pre-eruptive crystallization of consistent amphiboles is confined to relatively narrow
physical–chemical ranges, next to their dehydration curves. The widespread occurrence of amphiboles with dehydration (breakdown)
rims made of anhydrous phases and/or glass, related to sub-volcanic processes such as magma mixing and/or slow ascent during
extrusion, confirms that crystal destabilization occurs with relatively low T–P shifts. At the stability curves, the variance of the system decreases so that amphibole composition and physical–chemical
conditions are strictly linked to each other. This allowed us to retrieve some empirical thermobarometric formulations which
work independently with different compositional components (i.e. Si*, AlT, Mg*, [6]Al*) of a single phase (amphibole), and are therefore easily applicable to all types of calc-alkaline volcanic products (including
hybrid andesites). The Si*-sensitive thermometer and the fO2–Mg* equation account for accuracies of ±22°C (σest) and 0.4 log units (maximum error), respectively. The uncertainties of the AlT-sensitive barometer increase with pressure and decrease with temperature. Near the P–T stability curve, the error is <11% whereas for crystal-rich (porphyritic index i.e. PI > 35%) and lower-T magmas, the uncertainty increases up to 24%, consistent with depth uncertainties of 0.4 km, at 90 MPa (~3.4 km), and 7.9 km,
at 800 MPa (~30 km), respectively. For magnesiohornblendes, the [6]Al*-sensitive hygrometer has an accuracy of 0.4 wt% (σest) whereas for magnesiohastingsite and tschermakitic pargasite species, H2Omelt uncertainties can be as high as 15% relative. The thermobarometric results obtained with the application of these equations
to calc-alkaline amphibole-bearing products were finally, and successfully, crosschecked on several subduction-related volcanoes,
through complementary methodologies such as pre-eruptive seismicity (volcano-tectonic earthquake locations and frequency),
seismic tomography, Fe–Ti oxides, amphibole–plagioclase, plagioclase–liquid equilibria thermobarometry and melt inclusion
studies. A user-friendly spreadsheet (i.e. AMP-TB.xls) to calculate the physical–chemical conditions of amphibole crystallization
is also provided. 相似文献
22.
Günther J. Redhammer Fernando Cámara Matteo Alvaro Fabrizio Nestola Gerold Tippelt Sebastian Prinz Jan Simons Georg Roth Georg Amthauer 《Physics and Chemistry of Minerals》2010,37(10):685-704
A synthetic clinopyroxene with composition LiFe3+Ge2O6, monoclinic s.g. P21/c, a = 9.8792(7), b = 8.8095(5), c = 5.3754(3) Å, β = 108.844(6)°, V = 442.75(16) Å3, has been studied by in situ low- and high-temperature single-crystal X-ray diffraction. The variation of lattice parameters and the intensity of the b-type reflections (h + k = 2n + 1, only present in the P-symmetry) with increasing temperature showed a displacive phase transition from space group P21/c to C2/c at a transition temperature T tr = 789 K, first order in character, with a sudden volume increase of 1.6% and a decrease of β by 1° at the transition. This spontaneous dilatation is reversible, shows a limited hysteresis of ±10°C, and corresponds to the vanishing of the b-type reflections, thus indicating a symmetry increase to space group C2/c. Below T tr an expansion is observed for all the cell parameters, while the β angle remained almost constant; at T > T tr the thermal volume expansion is due to dilatation of the structure in the $(\bar{1}\,0\,1) A synthetic clinopyroxene with composition LiFe3+Ge2O6, monoclinic s.g. P21/c, a = 9.8792(7), b = 8.8095(5), c = 5.3754(3) ?, β = 108.844(6)°, V = 442.75(16) ?3, has been studied by in situ low- and high-temperature single-crystal X-ray diffraction. The variation of lattice parameters
and the intensity of the b-type reflections (h + k = 2n + 1, only present in the P-symmetry) with increasing temperature showed a displacive phase transition from space group P21/c to C2/c at a transition temperature T
tr = 789 K, first order in character, with a sudden volume increase of 1.6% and a decrease of β by 1° at the transition. This spontaneous dilatation is reversible, shows a limited hysteresis of ±10°C, and corresponds
to the vanishing of the b-type reflections, thus indicating a symmetry increase to space group C2/c. Below T
tr an expansion is observed for all the cell parameters, while the β angle remained almost constant; at T > T
tr the thermal volume expansion is due to dilatation of the structure in the ([`1] 0 1)(\bar{1}\,0\,1) plane, mostly along [0 1 0], and pure shear in the (0 1 0) plane due to the decrease of β. From comparison with silicate analogues, the germanate clinopyroxenes are more expansible, while the P21/c expands more than the C2/c phase. The evolution of Q
2 (calculated as the normalized intensity of b-type reflections) with T in the framework of the Landau theory has been done using a standard expression for a first order phase transition. We observe
a jump of Q
02 = 0.538(2) at T
tr, with T
c of 481(7) K, b/a = −2,290 K, and c/a = 3,192 K, and thus far from being tri-critical point. A closely related composition (LiFe3+Si2O6) shows an equivalent phase transition at 228 K, which is very close to the tri-critical point and 561 K cooler. This result
indicates that a change in the composition of tetrahedral sites can have dramatic effects on the P21/c ↔ C2/c displacive phase transition in clinopyroxenes. The major changes observed in the evolution of the crystal structure with
T are observed in the M2 polyhedron, with a volume decrease by ca. 13.3%, compared to ca. 1.3% observed in the M1 polyhedron.
The tetrahedra behave as rigid units with neither a significant change of volume at T > T
tr (<1‰), nor a change of tilting of the basal plane. No change in coordination is observed at T > T
tr in the M2 polyhedron, which remains sixfold coordinated although a strong deformation of this polyhedron is observed. This
deformation is related to a strong change by 51.4° at T
tr of the kinking angle (O3–O3–O3 angle) of the B-chain of tetrahedra, which switches from O-rotated to S-rotated [from 143.3(5)°
to 194.7(6)°]. The A-chain is S-rotated at T < T
tr [206.8(5)° at 703 K] and extends by 12° at the transition. 相似文献
23.
Digital elevation models (DEMs) at different resolutions (180, 360, and 720 m) are used to examine the impact of different levels of landscape representation on the hydrological response of a 690‐km2 catchment in southern Quebec. Frequency distributions of local slope, plan curvature, and drainage area are calculated for each grid size resolution. This landscape analysis reveals that DEM grid size significantly affects computed topographic attributes, which in turn explains some of the differences in the hydrological simulations. The simulations that are then carried out, using a coupled, process‐based model of surface and subsurface flow, examine the effects of grid size on both the integrated response of the catchment (discharge at the main outlet and at two internal points) and the distributed response (water table depth, surface saturation, and soil water storage). The results indicate that discharge volumes increase as the DEM is coarsened, and that coarser DEMs are also wetter overall in terms of water table depth and soil water storage. The reasons for these trends include an increase in the total drainage area of the catchment for larger DEM cell sizes, due to aggregation effects at the boundary cells of the catchment, and to a decrease in local slope and plan curvature variations, which in turn limits the capacity of the watershed to transmit water downslope and laterally. The results obtained also show that grid resolution effects are less pronounced during dry periods when soil moisture dynamics are mostly controlled by vertical fluxes of evaporation and percolation. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
24.
Landslides - Rockslide-debris flow may cause catastrophic damages because of its high speed and long run-out distance. The influences of slope gradient and gully channel on the entrainment,... 相似文献
25.
26.
Andrea Merloni Sebastian Heinz Tiziana Di Matteo 《Astrophysics and Space Science》2005,300(1-3):45-53
We examine the disc-jet connection in stellar mass and supermassive black holes by investigating the properties of their compact
emission in the hard X-ray and radio bands. We compile a sample of ∼100 active galactic nuclei with measured mass, 5 GHz core
emission, and 2–10 keV luminosity, together with eight galactic black holes with a total of ∼50 simultaneous observations
in the radio and X-ray bands. Using this sample, we study the correlations between the radio (LR) and the X-ray (LX) luminosity and the black hole mass (M). We find that the radio luminosity is correlated with both M and LX, at a highly significant level. We show how this result can be used to extend the standard unification by orientation scheme
to encompass unification by mass and accretion rate. 相似文献
27.
A Fundamental Plane of black hole activity 总被引:1,自引:0,他引:1
28.
29.
The higher-order scalar concentration fluctuation properties are examined in the context of Monin–Obukhov similarity theory
for a variety of greenhouse gases that have distinct and separate source/sink locations along an otherwise ideal micrometeorological
field site. Air temperature and concentrations of water vapour, carbon dioxide and methane were measured at high frequency
(10 Hz) above a flat and extensive peat-land soil in the San Joaquin–Sacramento Delta (California, USA) area, subjected to
year-round grazing by beef cattle. Because of the heterogeneous distribution of the sources and sinks of CO2 and especially CH4 emitted by cattle, the scaling behaviour of the higher-order statistical properties diverged from predictions based on a
balance between their production and dissipation rate terms, which can obtained for temperature and H2O during stationary conditions. We identify and label these departures as ‘exogenous’ because they depend on heterogeneities
and non-stationarities induced by boundary conditions on the flow. Spectral analysis revealed that the exogenous effects show
their signatures in regions with frequencies lower than those associated with scalar vertical transport by turbulence, though
the two regions may partially overlap in some cases. Cospectra of vertical fluxes appear less influenced by these exogenous
effects because of the modulating role of the vertical velocity at low frequencies. Finally, under certain conditions, the
presence of such exogenous factors in higher-order scalar fluctuation statistics may be ‘fingerprinted’ by a large storage
term in the mean scalar budget. 相似文献
30.
Despite their importance for pollutant dispersion in urban areas, the special features of dispersion at street intersections
are rarely taken into account by operational air quality models. Several previous studies have demonstrated the complex flow
patterns that occur at street intersections, even with simple geometry. This study presents results from wind-tunnel experiments
on a reduced scale model of a complex but realistic urban intersection, located in central London. Tracer concentration measurements
were used to derive three-dimensional maps of the concentration field within the intersection. In combination with a previous
study (Carpentieri et al., Boundary-Layer Meteorol 133:277–296, 2009) where the velocity field was measured in the same model,
a methodology for the calculation of the mean tracer flux balance at the intersection was developed and applied. The calculation
highlighted several limitations of current state-of-the-art canyon dispersion models, arising mainly from the complex geometry
of the intersection. Despite its limitations, the proposed methodology could be further developed in order to derive, assess
and implement street intersection dispersion models for complex urban areas. 相似文献