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排序方式: 共有187条查询结果,搜索用时 15 毫秒
41.
Leopoldo Franco Jimmy Geeraerts Riccardo Briganti Marc Willems Giorgio Bellotti Julien De Rouck 《Coastal Engineering》2009
The paper presents the comparison between the results of small-scale model tests and prototype measurements of wave overtopping at a rubble-mound breakwater. The specific structure investigated is the west breakwater of the yacht harbour of Rome at Ostia (Italy) and is characterized by a gentle seaward slope (1/4) and by a long, shallow foreshore. The laboratory tests firstly aimed at carefully reproducing two measured storms in which overtopping occurred and was measured. The tests have been carried out in two independent laboratories, in a wave flume and in a wave basin, hence using a two-dimensional (2-D) and a three-dimensional (3-D) setup. In the 2-D laboratory tests no overtopping occurred during the storm reproductions; in the 3-D case discharges five to ten times smaller than those observed in prototype have been measured. This indicates the existence of model and scale effects. These effects have been discussed on the basis of the results of several parametric tests, which have been carried out in both laboratories, in addition to the storm reproductions, varying wave and water level characteristics. Final comparison of all the performed tests with 86 prototype measurements still suggests the existence of scale and model effects that induce strong underestimation of overtopping discharge at small scale. The scale reproduction of wave breaking on the foreshore, together with the 3-D features of the prototype conditions and the absence of wind stress in the laboratory measurements, have been individuated as the main sources of scale and model effects. The paper also provides a comparison between the data and a largely used formula for wave overtopping discharges in the presence of structures similar to the one at hand. The suitable value of a roughness factor that appears in that formula is investigated and good agreement is found with other recent researches on rubble-mound breakwaters. 相似文献
42.
Previous research exploring the impacts of long distance commuting (LDC) or, more generally, mining on host regions, struggles to explain the variability of these impacts over time and across space. This article argues that spatial effects should be accounted for explicitly in order to improve the predictive power of contemporary research. We study the extent of LDC in a region in a spatial model disaggregating Australia into 325 subregions. We find evidence that space is an important factor in explaining the extent of LDC in a region, which challenges the validity of studying LDC impacts on host regions in isolation. With regards to the determinants of the extent of LDC, we find that residential attractiveness of a region influences the extent of LDC in a region; the size of the pool of unemployed in a region does not. 相似文献
43.
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45.
Andrea Brogi Enrico Capezzuoli Riccardo Aqué Marilì Branca Mario Voltaggio 《International Journal of Earth Sciences》2010,99(6):1383-1398
Middle–Late Pleistocene tectonic activity has been inferred through studies on travertine deposits exposed in a tract of the
hinterland Northern Apennines. A detailed study on the relationships between tectonics and travertine deposition coupled with
230Th/234U age determination of travertines at Cava Oliviera quarry, located close to Serre di Rapolano village (southern Tuscany,
Northern Apennines), allowed us to recognise Pleistocene faults, whose activity has been referred to 157–24 ka, at least.
Travertine deposition was tectonically controlled by WSW-ENE striking, oblique and normal faults, associated to a main fault
(named as the Violante Fault). This structure dissected a regional normal fault (known as the Rapolano Fault) Early–Middle
Pliocene in age, which bounded the eastern side of the Pliocene Siena Basin, and gave rise to space accommodation for clayey
and sandy marine sediments. Hydrothermal circulation (and related travertine deposition) was favoured by the damaging enhancement
due to the fault–fault intersection. Tectonic activity has been also documented by deformation recorded by travertines, which
suggest a main tectonic event between 64 ± 5 and 40 ± 5 ka. The tectonic activity described for the study area agrees with
the Quaternary tectonic evolution documented in the surrounding areas (e.g. Mt. Amiata and Mt. Vulsini), as well as the Tyrrhenian
margin of the Central Apennines, indicating that a widespread tectonic activity affected the inner part of the Apennines until
the latest Quaternary. 相似文献
46.
Transpressional tectonics and nappe stacking along the Southern Variscan Front of Morocco 总被引:1,自引:0,他引:1
Andrea Cerrina Feroni Alessandro Ellero Marco G. Malusà Giovanni Musumeci Giuseppe Ottria Riccardo Polino Leonardo Leoni 《International Journal of Earth Sciences》2010,99(5):1111-1122
The Southern Variscan Front in the Tinerhir area involves Palaeozoic allochthonous units (Ouaklim and Tilouine units) thrust
onto the northern edge of the West African Craton during late Carboniferous time. Illite crystallinity data highlight an anchizonal
grade for the Ouaklim Unit, and a diagenesis-anchizone transition for the Tilouine Unit during deformation phase D1. The tectonic
stack is crosscut by major dextral reverse faults bounding E–W trending domains of dominant shortening deformation (central
domain) and strike-slip deformation (northern and southern domains), later segmented by a network of post-Variscan faults.
This complex deformation pattern is the result of kinematic partitioning of dextral transpression along the Southern Variscan
Front, coeval with the Neovariscan (300–290 Ma) oblique convergence observed at the scale of the whole Moroccan Variscides.
Partitioning of dextral transpression described in the Tinerhir area is consistent with dextral wrench faulting along the
Tizi n’ Test Fault, and with Appalachian-style south-directed thrusting in the Tinerhir and Bechar-Bou Arfa areas. 相似文献
47.
Pietro Mosca Riccardo Polino Sergio Rogledi Massimo Rossi 《International Journal of Earth Sciences》2010,99(4):833-849
Alps and Apennines are juxtaposed within an approximately 100 km-wide area covered by the Upper Eocene to Miocene successions
of the Tertiary Piedmont Basin. The Upper Eocene–Oligocene evolution of this area was characterized to the north and west
by the propagation of the SE-verging Southalpine thrust-fold belt that can be traced from the Po Plain subsurface until the
Torino Hill-Saluzzese area, and to the south by a high-angle, broadly E–W oriented megashear zone that led to the juxtaposition
of different crustal levels and controlled the development of a mosaic of partly independent sub-basins. Since the latest
Oligocene the N-verging Apenninic tectonics prevailed in the collisional system and the Tertiary Piedmont Basin evolved as
a wide thrust-top basin, bounded to the north by the N-verging Monferrato arc and characterized by a tectono-sedimentary evolution
recording changes of subsidence and shift of depocentres in relation to crustal structures. 相似文献
48.
Folco Giacomini Vittorio Boerio Simona Polattini Massimo Tiepolo Riccardo Tribuzio Alberto Zanetti 《Environmental Earth Sciences》2010,61(8):1621-1639
This work is part of the project study for a road tunnel bypassing the town of Genova and was aimed at evaluating the amount of asbestos fibres in the metaophiolites belonging to the Voltri Group and the Sestri–Voltaggio Zone (Liguria, Northern Italy). The 85 studied rock samples (mainly mafic and ultramafic rocks) derive from exposed outcrops and prospecting boreholes. The study of field relations and petrographic/microtextural investigations under the optical microscope allowed for the identification and characterisation of asbestos-bearing settings and lithotypes. Mineralogy and concentration of asbestos fibres in powdered specimens were determined by means of a scanning electron microscope equipped with an energy-dispersive X-ray spectroscopy device. These investigations were combined with petrography on thin-section, X-ray diffraction analysis and phase contrast optical microscopy on rock powders. Mafic and ultramafic rocks commonly contain asbestos in concentrations below 1,000 mg/kg (considered as the contamination threshold under Italian law). However, the fibre concentration rises abruptly within localised zones, where the metaophiolite sequences were involved into late ductile to brittle tectono-metamorphic events. Two groups of asbestos-bearing settings have been so far identified in the area: (a) fracture networks within serpentinites (dominated by fibrous chrysotile), and (b) boudins of chlorite-tremolite schists, likely deriving from dynamic recrystallisation of mafic rocks under greenschist facies conditions (dominated by fibrous amphibole). Even considering the low volumetric incidence of these settings (metres to few tens of metres), their high asbestos content locally controls the total fibre amount in the excavation products, thus requiring special prevention measures during excavation, management and final storage of the contaminated debris. 相似文献
49.
Rivalenti Giorgio Mazzucchelli Maurizio Vannucci Riccardo Hofmann Albrecht W. Ottolini Luisa Bottazzi Piero Obermiller Walter 《Contributions to Mineralogy and Petrology》1995,122(3):275-288
Field, mineralogical and petrological data are presented on a newly found carbonatite occurrence associated with “kamafugite”
lava at Cupaello, central Italy. This carbonatite occurrence is part of the Late Pleistocene Umbria-Latium ultra-alkaline
district (ULUD) which extends southwards within the Apennines to Mount Vulture, delineating an important magmatic province
along the most peripheral belt of the Tyrrhenian extensional tectonic system. This province is distinct, but probably related
genetically with the more abundant and common leucite-bearing assemblages of the Roman Comagmatic Region and represents the
first reported occurrence of carbonatite assemblages in the Mediterranean Basin. The Cupaello suite indicates that primary
or near-primary mantle silicate melts of “kamafugitic” composition are transitional with Ca-carbonatite liquid and provides
direct evidence of immiscibility of carbonatite from “kamafugite” magma. It is inferred that a primary mantle origin of Ca-carbonatites
is conditional upon a potential silicate magma that may be coupled with the carbonatite, but may not have reached the surface.
The data indicate a strong genetic link between ULUD Ca-carbonatites and some African analogues, supporting the view that
their genesis depends on similar source and associated tectonic conditions.
Received: 17 January 1995 / Accepted: 14 June 1995 相似文献
50.
In this paper a new method to compute in a fast and reliable way the collocation solution is presented. In order to speed up the numerical procedures, some restrictions on input data are needed.The basic assumption is that data are gridded and homogeneous; this implies that the autocovariance matrix entering in the collocation formula is of Toeplitz type. In particular, if observations are placed on a two dimensional planar grid, the autocovariance matrix is a symmetric block Toeplitz matrix and each block is itself a symmetric Toeplitz matrix (Toeplitz/Toeplitz structure). The analysis can be extended to a regular geographical grid, considered as a generalization of the planar one, taking into account the distortions on the Toeplitz/Toeplitz structure induced by the convergence of the meridians. The devised method is based on a combined application of the Preconditioned Conjugate Gradient Method and of the Fast Fourier Transform. This allows a proper exploitation of the Toeplitz/Toeplitz structure of the autocovariance matrix in computing the collocation solution.The numerical tests proved that the application of this algorithm leads to a relevant decrease in CPU time if compared with standard methods used to solve a collocation problem (Cholesky, Levinson). 相似文献