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131.
Mesozoic and Cenozoic vertical movements in the Atlas system (Algeria, Morocco, Tunisia): An overview 总被引:5,自引:0,他引:5
Dominique Frizon de Lamotte Pascale Leturmy Sami Khomsi Omar Saddiqi André Michard 《Tectonophysics》2009,475(1):9-28
The E-W trending Atlas System of Maghreb consists of weakly shortened, intra-continental fold belts associated with plateau areas (“Mesetas”), extending between the south-westernmost branch of the Mediterranean Alpine Belt (Rif-Tell) and the Sahara Platform. Although the Atlas system has been erected contemporaneously from Morocco to Algeria and Tunisia during the Middle Eocene to Recent, it displays a conspicuous longitudinal asymmetry, with i) Paleozoic outcrops restricted to its western part; ii) highest elevation occurring in the west, both in the Atlas System and its foreland (Anti-Atlas); iii) low elevation corridors (e.g. Hodna) and depressed foreland (Tunisian Chotts and Sahel area) in the east. We analyse the origin of these striking contrasts in relation with i) the Variscan heritage; ii) crustal vertical movements during the Mesozoic; iii) crustal shortening during the Cenozoic and finally, iv) the occurrence of a Miocene-Quaternary hot mantle anomaly in the west. The Maghreb lithosphere was affected by the Variscan orogeny, and thus thickened only in its western part. During the Late Permian-Triassic, a paleo-high formed in the west between the Central Atlantic and Alpine Tethys rift systems, giving birth to the emergent/poorly subsident West Moroccan Arch. During the late Middle Jurassic-Early Cretaceous, Morocco and western Algeria were dominantly emergent whereas rifting lasted on in eastern Algeria and Tunisia. We ascribe the uplift of the western regions to thermal doming, consistent with the Late Jurassic and Barremian gabbroic magmatism observed there. After the widespread transgression of the high stand Cenomanian-Turonian seas, the inversion of the Atlas System began during the Senonian as a consequence of the Africa-Eurasia convergence. Erosion affected three ENE-trending uplifted areas of NW Africa, which we consider as lithospheric anticlines related to the incipient Africa-Europe convergence. In contrast, in eastern Algeria and Tunisia a NW-trending rift system developed contemporaneously (Sirt rifting), normal to the general trend of the Atlas System. The general inversion and orogenesis of the Atlas System occurred during two distinct episodes, Middle-Late Eocene-Oligocene and Late Miocene-Pliocene, respectively, whereas during the intervening period, the Africa-Europe convergence was mainly accommodated in the Rif-Tell system. Inversion tectonics and crustal thickening may account for the moderate uplift of the eastern Atlas System, not for the high elevation of the western mountain ranges (Middle Atlas, High Atlas, Anti-Atlas). In line with previous authors, we ascribe part of the recent uplift of the latter regions to the occurrence of a NE-trending, high-temperature mantle anomaly, here labelled the Moroccan Hot Line (MHL), which is also marked by a strip of late Miocene-Quaternary alkaline magmatism and significant seismicity. 相似文献
132.
Faisal I. Shalabi Husam A. Al-Qablan Omar H. Al-Hattamleh 《Geotechnical and Geological Engineering》2009,27(2):237-248
Lining contact pressure and ground deformation of Raghadan transportation tunnel (Amman, Jordan) were investigated. The tunnel
is 1.1 km in length and 13.5 m in diameter. This study was intended to integrate useful relations among the widely used rock
classification system (RMR: rock mass rating), Hoek–Brown classification, and lining-ground interaction. The materials encountered
along the tunnel alignment were limestone, dolomatic limestone, marly limestone, dolomite, and sillicified limestone. The
ground conditions along the tunnel alignment including bedding planes, joint sets and joint conditions, rock quality, water
flow, and rock strength were evaluated based on the drilled boreholes and rock exposures. Elasto-plastic finite element analyses
were conducted to study the effect of rock mass conditions and tunnel face advance on the behavior of lining-ground interaction.
The results of the analyses showed that lining contact pressure decreases linearly with the increase in RMR value. Also the
results showed that tunnel lining contact pressure and crown inward displacement decreases with the increase in the unsupported
distance (distance between tunnel face and the end of the erected lining). Ground displacement above the tunnel crown was
found to be increases in an increasing rate with the decrease in the depth above the crown. This displacement was also found
to be affected by the RMR value and the unsupported distance. 相似文献
133.
Luigi Sorrentino Omar AlShawa Luis D. Decanini 《Bulletin of Earthquake Engineering》2011,9(5):1617-1642
Existing unreinforced masonry buildings frequently suffer out-of-plane local collapse mechanisms when undergoing earthquake
ground motion. The energy damping that occurs during the motion, due to impacts of a wall against the foundation or against
other walls, is a relevant parameter on the response. An experimental investigation has been carried out to estimate the dissipation
of kinetic energy that takes place during free oscillations. Restraint conditions allow for two-sided rocking (wall resting
on a foundation) and one-sided rocking (wall resting on a foundation adjacent to transverse walls). Five specimens have been
tested, modelling walls acted out-of-plane (fa?ades). When one-sided rocking is under consideration, different depths of the
contact surface between fa?ade and transverse walls are considered. In the case of two-sided rocking, the experimental coefficient
of restitution is slightly lower than the analytic coefficient. In the case of one-sided rocking, an analytic formulation
is proposed and this is compared against experimental data. Although the coefficient of restitution of one-sided rocking is
less than half that of two-sided rocking, it is not equal to zero. Thus, it cannot induce a sudden stop of the motion. Hence,
nonlinear time history analyses performed under this assumption may prove unsafe. Moreover, a comparison has been carried
out between overturning maps, induced by twenty natural accelerograms, computed for the analytic coefficient of restitution
and those computed for the experimental coefficient of restitution. The increased energy dissipation reduces the frequency
of overturning and causes a more regular behaviour. 相似文献
134.
Laura Edith Grecco Eduardo Alberto G��mez Sandra Elizabeth Bott�� ��ngel Omar Marcos Jorge Eduardo Marcovecchio Diana Graciela Cuadrado 《Ocean Dynamics》2011,61(2-3):285-293
The geochemistry, mineralogy, and grain size distribution of several estuarine cohesive sediment samples from potentially human-influenced areas without such an influence were analyzed to determine the natural heavy metal content and evaluate its impact on the Bahía Blanca estuarine environment. The data were compared with different ranges of concentrations for heavy metals in marine sediments established by the NOAA Screening Quick Reference Tables in which values range from background levels to those considered toxic to the marine environment. Our total heavy metal contents were below the established hazardous levels in all the analyzed samples, even though the potentially human-influenced areas (harbors, industry, urban spread) showed the highest total concentration values as well as greater percentages of bioavailable compounds. This would imply a low and not extensive anthropogenic input into the environment. The relatively high proportions in which Cd, Pb, and Cr appear as bioavailable compounds at some sites not influenced by human activity suggest the presence of a natural source for these elements. This could be attributed to the weathering of naturally occurring volcanic minerals, indicating that special care must be taken when monitoring of sediment for anthropogenic activity is carried out within this environment. According to the results obtained, and in order to minimize the environmental impact caused by periodic water injection dredging, relocation of sewage outfalls from vessel mooring areas into open waters is strongly recommended. 相似文献
135.
Elisa Soana Erica Racchetti Alex Laini Marco Bartoli Pierluigi Viaroli 《洁净——土壤、空气、水》2011,39(11):956-965
A nitrogen mass balance, realized for the lower Oglio River basin (Po River Plain, northern Italy), suggested an elevated impact of agricultural activities in this watershed. Livestock manure, synthetic fertilizers, biological fixation, atmospheric deposition, and wastewater sludge contributed 51, 34, 12, 2, and 1% of total N (TN) input, respectively (basin average 450 kg N ha?1 arable land (AL) year?1, overall input 100 115 t N year?1). Crop uptake, ammonia volatilization and denitrification in soils contributed 65, 21, and 14%, respectively, of TN output (basin average 270 kg N ha?1 AL year?1, overall output 60 060 t N year?1). N inputs exceeded outputs by 40 056 t N year?1, resulting in a basin average surplus of about 180 kg N ha?1 AL year?1. About 34% of the N surplus was exported annually from the basin while the remaining amount (about 26 800 t N year?1) underwent other unaccounted for processes within the watershed. The relevance of nitrogen removal via denitrification in aquatic compartments within the watershed was evaluated. Denitrification in the secondary drainage network can represent a relevant nitrogen sink due to great linear extension (over 12 500 km), with estimated nitrogen loss up to 8500 t N year?1. Denitrification in the riverbed and in perifluvial wetlands have the potential to remove only a small fraction of the nitrogen surplus (<3%). Evidence suggests the relevance of groundwater as a site of nitrogen accumulation. 相似文献
136.
Salih Muhammad Awadh Maysoon Omar Ali Rana Abbas Ali 《Arabian Journal of Geosciences》2011,4(7-8):1261-1271
This work was done on the representative section (230 cm) in Dora site which located in Baghdad in the central of the Mesopotamian Plain. Eleven soil samples were examined mineralogically and palynologically. Grain size analyses showed that silt is the higher fraction (61%), clay is the least (9%), whereas sand forms 30%. Translucent and opaque heavy minerals contributed 57% from the sand fraction, whereas the light minerals formed just 43%. The type of heavy minerals and its maturity defined four provenances—they are granitic, basic igneous and metamorphic rocks—that belong to the high lands of south Turkey and north of Iraq. The fourth provenance is the sedimentary rocks which are located north of Mesopotamian Plain around the Tigris River and their tributaries. Dinoflagellate within thin bed of marine origin clearly indicated the transgression of the Arabian Sea northward through Tigris and Euphrates valleys or high marine waves reached to Baghdad before 10,000 years P.B. approximately. This means that the marine sediments were also an additional source of the Mesopotamian Plain. Three specific climatic features are identified via palynological interpretation; a temperate-wet climate extended from 10,000 to 5,000 years P.B. followed by dry period extended from 5,000 to 3,500 years P.B. and the last climatic feature is characterized by oscillation of wet to dry periods which is dominant since 3,500 till now. 相似文献
137.
Mindaugas Zilius Marco Bartoli Mariano Bresciani Marija Katarzyte Tomas Ruginis Jolita Petkuviene Irma Lubiene Claudia Giardino Paul A. Bukaveckas Rutger de Wit Arturas Razinkovas-Baziukas 《Estuaries and Coasts》2014,37(3):680-694
We investigated the dissolved oxygen metabolism of the Curonian Lagoon (Baltic Sea) to assess the relative contributions of pelagic and benthic processes to the development of transient hypoxic conditions in shallow water habitats. Metabolism measurements along with the remote sensing-derived estimates of spatial variability in chlorophyll a were used to evaluate the risk of hypoxia at the whole lagoon level. Our data demonstrate that cyanobacterial blooms strongly inhibit light penetration, resulting in net heterotrophic conditions in which pelagic oxygen demand exceeds benthic oxygen demand by an order of magnitude. The combination of bloom conditions and reduced vertical mixing during calm periods resulted in oxygen depletion of bottom waters and greater sediment nutrient release. The peak of reactive P regeneration (nearly 30 μmol m?2 h?1) coincided with oxygen depletion in the water column, and resulted in a marked drop of the inorganic N:P ratio (from >40 to <5, as molar). Our results suggest a strong link between cyanobacterial blooms, pelagic respiration, hypoxia, and P regeneration, which acts as a feedback in sustaining algal blooms through internal nutrient cycling. Meteorological data and satellite-derived maps of chlorophyll a were used to show that nearly 70 % of the lagoon surface (approximately 1,000 km2) is prone to transient hypoxia development when blooms coincide with low wind speed conditions. 相似文献
138.
Habibeh Valizadeh Alvan Shattri Mansor Husaini Omar Farid H. Azad 《Arabian Journal of Geosciences》2014,7(11):4889-4897
Recently, new theories on underground geophysical and geochemical interactions which had been reported to occur during the preparation stages of earthquakes and the remotely measurable variations have been put to test and some warning factors were suggested as earthquake precursors. Data vendors are providing daily basis information from the earth's surface by combining remote sensing data and in situ observations. In this paper, we analyze atmospheric, oceanic, and surface changes in the ocean, coast, and land lying near the epicenters of two recent major earthquakes. The changes are studied in terms of the regional fault locations which have been reported by the U.S. Geological Survey as the shake triggering geological structures. Our detailed analyses showed anomalous increases of surface latent heat flux (SLHF) for both the earthquakes. Meaningfully limited to the geographical extents of the regional active faults, the SLHF variation patterns suggest pre-seismic activity 2–3 weeks before the main events. The agreement of these variations with abnormalities in other climatic and surface factors like relative humidity and temperature represents an unusual situation during the same period as well. Spatiotemporal variations of chlorophyll-a was also studied as another earthquake indicator. Abnormal rises in these factors are possibly caused by the formation of micro-cracks, heat production, evaporation, ionization, and upwelling of nutrient-rich water produced by pre-seismic activity prior to the main events. 相似文献
139.
shawky Omar Altahrany Ayman I. Elmeligy Mahmoud 《Geotechnical and Geological Engineering》2022,40(9):4487-4516
Geotechnical and Geological Engineering - Negative skin friction on piles represents a severe problem when piles were installed in soft clay due to consolidation process. It reduces the bearing... 相似文献
140.
The present study is an attempt to construct a morpho-structural model for the Korek anticline that is located within the High folded zone of the Zagros Fold and Thrust Belt in the Northern Iraq-Kurdistan region. A detail geological map constructed for this structure, the stratigraphic succession that is exposed in the area was deposited from the middle Jurassic up to upper Cretaceous, and consists of nine formations. The most important morphological landscape and landforms in the studied area are due to endogenic and exogenic processes. Accordingly, the area is divided into four main units, which are units of structural, denudational, fluvial and solution origins. Each unit characterized by its own morphological feature differs from one another. According to structural point of view the field data are analyzed from two point of the viewing, one from map view and secondly from cross sections. The geometrical properties from map view of the Korek Anticline indicated that this fold is an asymmetrical double plunging, open to gentle, non-cylindrically curviplanar fold. The Korek Anticline becomes sharper with the depth, but broader and more open upward, this is one of the most characteristic features of the parallel fold (Class 1B). The presence of numerous reverse faults and strike-slip faults which affect the architecture of the Korek Anticline indicates that this Anticline formed by a Fault-propagation fold mechanism. Detailed balanced and retro-deformable cross sections along this anticline indicate that the shortening percentage can be differentiated in space and times, while the depth to detachment gives values that iscoincident with the Ora Shale Formation of Paleozoic age. A morpho-structural model was constructed for this structure and it consists of two main stages and five substages were responsible for the formation of the Korek structure. The first main stage belongs to structural construction, which consists of three sub-stages, while the main second stage is belonging to morphological destruction, which consist also two sub-stages. The effect of these stages and sub-stages makes the anticline to take the nowadays architects shape. 相似文献