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31.
Grégoire M. Maillet Enzo Rizzo André Revil Claude Vella 《Marine Geophysical Researches》2005,26(2-4):317-328
Electrical Resistivity Tomography (ERT) was applied in a sand-infilled paleo-channel located in the Rhône Delta, in Southern France. The detailed pattern and sedimentological evolution of the channel fill deposits – know from both historical and geological sources – made it the ideal site to test the ERT method. A geoelectrical survey was performed, using the ABEM SAS-4000 multi-electrode array system in March 2003. Very low electrical resistivity values were obtained, ranging from 0.3 to 10 Ohm m, consistent with the high salinity measured in situ (the pore water conductivity was found to range from 0.9 to 1.2 S/m at 25 °C). The electrical resistivity profiles reflect mainly salinity variations. Indeed, in this case, salinity is so high that surface conductivity associated with clay minerals can be safely neglected. ERT provided valuable high-resolution information that complemented other exiting data such as historical information, bathymetric, geological, and lithostratigraphic data, which allowed the architecture of the channel to be defined. The ERT was used to determine the infilling dynamics of the Pégoulier Channel, which opens new perspectives in terms of paleoenvironmental reconstruction and paleodynamic studies. 相似文献
32.
33.
M. Viel E. Branchini R. Cen J. P. Ostriker S. Matarrese P. Mazzotta B. Tully 《Monthly notices of the Royal Astronomical Society》2005,360(3):1110-1122
We present a simple method for tracing the spatial distribution and predicting the physical properties of the Warm–Hot Intergalactic Medium (WHIM), from the map of galaxy light in the Local Universe. Under the assumption that biasing is local and monotonic we map the ∼2 h −1 Mpc smoothed density field of galaxy light into the mass-density field, from which we infer the spatial distribution of the WHIM in the Local Supercluster. Taking into account the scatter in the WHIM density–temperature and density–metallicity relation, extracted from the z = 0 outputs of high-resolution and large-box-size hydrodynamical cosmological simulations, we are able to quantify the probability of detecting WHIM signatures in the form of absorption features in the X-ray spectra, along arbitrary directions in the sky. To illustrate the usefulness of this semi-analytical method we focus on the WHIM properties in the Virgo cluster region. 相似文献
34.
35.
J. Sharpe M. Rowan-Robinson A. Canavezes W. Saunders E. Branchini G. Efstathiou C. Frenk O. Keeble R. G. McMahon S. Maddox S. J. Oliver W. Sutherland H. Tadros † S. D. M. White 《Monthly notices of the Royal Astronomical Society》2001,322(1):121-130
We use the Least Action Principle to predict the peculiar velocities of PSC z galaxies inside cz =2000 km s−1 . Linear theory is used to account for tidal effects to cz =15 000 km s−1 , and we iterate galaxy positions to account for redshift distortions. As the Least Action Principle is valid beyond linear theory, we can predict reliable peculiar velocities even for very nearby galaxies (i.e., cz ≤500 km s−1 ). These predicted peculiar velocities are then compared with the observed velocities of 12 galaxies with Cepheid distances. The combination of the PSC z galaxy survey (with its large sky coverage and uniform selection) with the accurate Cepheid distances makes this comparison relatively free from systematic effects. We find that galaxies are good tracers of the mass, even at small (≤10 h −1 Mpc) scales; under the assumption of no biasing, 0.25≤ β ≤0.75 (at 90 per cent confidence). We use the reliable predicted peculiar velocities to estimate the Hubble constant H 0 from the local volume without 'stepping up' the distance ladder, finding a confidence range of 65–75 km s−1 Mpc−1 (at 90 per cent confidence). 相似文献
36.
37.
Fabio Maselli Marta ChiesiAlessandro Montaghi Enzo Pranzini 《ISPRS Journal of Photogrammetry and Remote Sensing》2011,66(5):662-671
Airborne LiDAR techniques can provide accurate measurements of tree height, from which estimates of stem volume and forest woody biomass can be obtained. These techniques, however, are still expensive to apply repeatedly over large areas. The current paper presents a methodology which first transforms mean stand heights obtained from LiDAR over small strips into relevant stem volume estimates. These are then extended over an entire forest by applying two estimation methods (k-NN and locally calibrated regression) to Landsat ETM+ images. The methodology is tested over a coastal area covered by pine forest in the Regional Park of San Rossore (Central Italy). The results are evaluated by comparison with the ground stem volumes of a recent forest inventory, taking into consideration the effect of stand size. In general, the accuracies of two estimation methods are dependent on the size of the forest stands and are satisfactory only when considering stands larger than 5-10 ha. The outputs of the parametric regression procedure are slightly more stable than those of k-NN and more faithfully reproduce the spatial patterns of the ground data. 相似文献
38.
Marco Mucciarelli Marcello Bianca Rocco Ditommaso Marco Vona Maria Rosaria Gallipoli Alessandro Giocoli Sabatino Piscitelli Enzo Rizzo Matteo Picozzi 《Bulletin of Earthquake Engineering》2011,9(3):825-840
In San Gregorio (L’Aquila, Italy) a three-story, reinforced concrete (RC) building had the first floor collapsed following
the earthquake of April 6, 2009. The remaining two stories fell with a displacement in the horizontal projection of about
70 cm. This unusual behaviour is made more puzzling by the fact that buildings located at a short distance and with similar
features had little or no damage reported. To understand the causes of the collapse we performed strong motion recordings,
microtremor measurements, a detailed geological survey, a high-resolution geo-electrical tomography, a borehole with a down-hole
test. On the building we performed a geometrical survey and laboratory tests on concrete cores. The acceleration and noise
recordings have shown a high amplification with uphill-downhill direction. The geological survey has revealed the presence
of co-seismic fractures on stiff soils. Geo-electrical tomography has shown an unexpected, strong discontinuity just below
the building. Taking advantage of excavations in adjacent lots, we have highlighted rare cataclastic decimetric bands with
a very low resistance material incorporated in well-stratified calcarenites. The same soft material has been founded in the
borehole down to 17 m from ground level, showing a shear wave velocity that starts at 250 m/s, increases with depth and has
an abrupt transition in calcarenites at 1,150 m/s. The surface geophysical measurements in the vicinity of the site have not
shown similar situations, with flat HVSR curves as expected for a rock outcrop, except for a lateral extension of the soft
zone. The analysis on the quality of the building materials has yielded values higher than average for the age and type of
construction, and no special design or construction deficiencies have been observed. A strong, peculiar site effect thus appears
to be the most likely cause of the damage observed. 相似文献
39.
Michael A. Dopita Marcella Marconi Gisella Clementini Enzo Brocato 《Astrophysics and Space Science》2012,338(1):1-2
In recent papers we had developed a unified picture of black hole entropy and curvature which was shown to lead to Hawking
radiation. It was shown that for any black hole mass, holography implies a phase space of just one quantum associated with
the interior of the black hole. Here we study extremal rotating and charged black holes and obtain unique values for ratios
of angular momentum to entropy, charge to entropy, etc. It turns out that these ratios can be expressed in terms of fundamental
constants in nature, having analogies with other physical systems, like in condensed matter physics. 相似文献
40.
Massimiliano Favalli Simone Tarquini Paolo Papale Alessandro Fornaciai Enzo Boschi 《Bulletin of Volcanology》2012,74(2):423-439
Mt. Cameroon is one of the most active effusive volcanoes in Africa. About 500,000 people living or working around its fertile
flanks are subject to significant threat from lava flow inundation. Lava flow hazard and risk were assessed by simulating
probable lava flow paths using the DOWNFLOW code. The vent opening probability density function and lava flow length distribution
were determined on the basis of available data from past eruptions at Mt. Cameroon volcano. Code calibration was performed
through comparison with real lava flow paths. The topographic basis for simulations was the 90-m resolution SRTM DEM. Simulated
lava flows from about 80,000 possible vents were used to produce a detailed lava flow hazard map. The lava flow risk in the
area was mapped by combining the hazard map with digitized infrastructures (i.e., human settlements and roads). Results show
that the risk of lava flow inundation is greatest in the most inhabited coastal areas comprising the town of Limbe, which
constitutes the center of Cameroon’s oil industry and an important commercial port. Buea, the second most important town in
the area, has a much lower risk although it is significantly closer to the summit of the volcano. Non-negligible risk characterizes
many villages and most roads in the area surrounding the volcano. In addition to the conventional risk mapping described above,
we also present (1) two reversed risk maps (one for buildings and one for roads), where each point on the volcano is classified
according to the total damage expected as a consequence of vent opening at that point; (2) maps of the lava catchments for
the two main towns of Limbe and Buea, illustrating the expected damage upon venting at any point in the catchment basin. The
hazard and risk maps provided here represent valuable tools for both medium/long-term land-use planning and real-time volcanic
risk management and decision making. 相似文献