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101.
Jean-Claude Hippolyte Didier Bourls Rgis Braucher Julien Carcaillet Laëtitia Lanni Maurice Arnold Georges Aumaitre 《Geomorphology》2009,108(3-4):312-320
Sackungs are the largest gravitational deformation observed in mountains. They are characterized by the long-term slowness of the movements, but their mechanism is still not well understood. Nowadays cosmic ray exposure (CRE) dating methods allow dating the morphologic structures involved in sackung and can contribute at the understanding of their origin. In the Alps, the 5.3 km long Arcs sackung initiated during the activity of rock glaciers. Three samples from these faulted rock glaciers provide their first CRE ages and show that at 2000 m elevation these block accumulations moved during the Younger Dryas and stopped in early Holocene. Six 10Be ages of fault scarps show that the Arcs sackung lasted only a few thousand years and stopped at about 8462 ± 432 10Be yr. They also reveal that deformation migrated upslope in agreement with a mechanism of flexural toppling of vertical layers. This unique and long gravitational event, characterized by migration of the deformation, does not support earthquake shaking as triggering mechanism for individual faults. It shows that, in the upper Isère valley, slope deformation was delayed of several thousand years after glacial debuttressing, and is not anymore active despite its fresh morphology. 相似文献
102.
Sarah Lambart Didier Laporte Pierre Schiano 《Contributions to Mineralogy and Petrology》2009,157(4):429-451
We performed experiments in a piston-cylinder apparatus to determine the effects of focused magma transport into highly permeable
channels beneath mid-ocean ridges on: (1) the chemical composition of the ascending basalt; and (2) the proportions and compositions
of solid phases in the surrounding mantle. In our experiments, magma focusing was supposed to occur instantaneously at a pressure
of 1.25 GPa. We first determined the equilibrium melt composition of a fertile mantle (FM) at 1.25 GPa-1,310°C; this composition
was then synthesised as a gel and added in various proportions to peridotite FM to simulate focusing factors Ω equal to 3
and 6 (Ω = 3 means that the total mass of liquid in the system increased by a factor of 3 due to focusing). Peridotite FM
and the two basalt-enriched compositions were equilibrated at 1 GPa-1,290°C; 0.75 GPa-1,270°C; 0.5 GPa-1,250°C, to monitor
the evolution of phase proportions and compositions during adiabatic decompression melting. Our main results may be summarised
as follows: (1) magma focusing induces major changes of the coefficients of the decompression melting reaction, in particular,
a major increase of the rate of opx consumption, which lead to complete exhaustion of orthopyroxene (and clinopyroxene) and
the formation of a dunitic residue. A focusing factor of ≈4—that is, a magma/rock ratios equal to ≈0.26—is sufficient to produce
a dunite at 0.5 GPa. (2) Liquids in equilibrium with olivine (±spinel) at low pressure (0.5 GPa) have lower SiO2 concentrations, and higher concentrations in MgO, FeO, and incompatible elements (Na2O, K2O, TiO2) than liquids produced by decompression melting of the fertile mantle, and plot in the primitive MORB field in the olivine–silica–diopside–plagioclase
tetrahedron. Our study confirms that there is a genetic relationship between focused magma transport, dunite bodies in the
upper mantle, and the generation of primitive MORBs. 相似文献
103.
The concentrations of dissolved and particulate polycyclic aromatic hydrocarbons (PAHs) were monitored in waters of the Rhône River (France) every fortnight for a full calendar year, from June 1994 to May 1995. All flood events occurring over the course of the experiment were sampled at higher frequency to better quantify the impact of these extreme hydrological episodes on the annual export of PAHs to the Mediterranean Sea. This time-series indicates that more than 90% of the annual load of particulate PAHs is transported during flood episodes, with 77% discharged during the course of only one extreme flood event occurring in November 1994. During these intense events, riverine particles are depleted in PAHs while at low river discharge particles are PAH-enriched. Dissolved PAHs were less variable and less abundant than adsorbed PAHs, consistently with the low solubility of these compounds. 相似文献
104.
A new ichthyofauna from southeastern Morocco, comprising five forms, is briefly discussed. The faunal composition differs from the Early Cenomanian Kem Kem and Early Turonian Goulmima assemblages, but is close to that from Jebel Tselfat. We propose a Late Cenomanian age for the new fauna and that from Jebel Tselfat. The evolution of these fish assemblages shows the Moroccan fish faunas to have been related to those from South America until at least the Early Turonian. Central Tethyan influence on faunas seems to have been restricted to a short period of time during the beginning of the Late Cenomanian transgressive phase. 相似文献
105.
Rey Vincent Dufresne Christiane Fuda Jean-Luc Mallarino Didier Missamou Tathy Paugam Caroline Rougier Gilles Taupier-Letage Isabelle 《Ocean Dynamics》2020,70(7):913-933
Ocean Dynamics - A dense network of instruments has been deployed within harbors along the Mediterranean coast, in the Toulon Metropole area, between the Hyères islands and the Sanary Bay in... 相似文献
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109.
Estelle Leroux Marina Rabineau Daniel Aslanian Didier Granjeon Laurence Droz Christian Gorini 《地学学报》2014,26(3):230-238
Determining the relative importance of factors interacting to control stratigraphic organization is a key issue in sedimentology. The Pliocene‐Quaternary chronostratigraphy on the Gulf of Lions platform is still poorly constrained, giving rise to different interpretations of the evolution of its subsidence through time. This paper examines the Pliocene‐Quaternary sedimentary filling of the Gulf of Lion's shelf with Dionisos, a numerical stratigraphic model. Our results show that a constant subsidence rate accurately reproduces the observed geometries, whereas a varying subsidence rate reproduces them only if the acceleration of subsidence is limited. At this time‐scale, a third‐order eustatic curve is also reappraised: a higher resolution curve (built using δ18O measurements) gives a more realistic restitution of our stratigraphic markers. Finally, the constant subsidence rate and sediment fluxes implied in these modellings are discussed relative to climate and local factors of sedimentation. 相似文献
110.
Markus Fuchs Sebastian Kreutzer Denis‐Didier Rousseau Pierre Antoine Christine Hatté France Lagroix Olivier Moine Caroline Gauthier Jiri Svoboda Lenka Lisá 《Boreas: An International Journal of Quaternary Research》2013,42(3):664-677
The Dolní Věstonice loess section in the Czech Republic is well known for its high‐resolution loess–palaeosol sequence of the last interglacial–glacial climatic cycle (Upper Pleistocene). The loess section is situated in a climatic transition zone between oceanic and continental climates and is therefore of great value in reconstructing past regional climate conditions and their interaction with climate systems, in particular that of the North Atlantic. Based on a combination of optically stimulated luminescence (OSL) ages, stratigraphic field observations and magnetic susceptibility measurements, a chrono‐climatic interpretation of the Dolní Věstonice loess section is presented. To establish a reliable Upper Pleistocene chronology, a quartz OSL approach was applied for equivalent dose (De) determination. Monomineralic quartz extracts of three distinct grain sizes, fine (4–11 μm), middle (38–63 μm) and coarse (90–200 μm), were used and compared. Within error limits, the calculated OSL ages are the same for the different grain sizes, and the OSL ages are in stratigraphic order. The established OSL chronology is in agreement with a Weichselian litho‐ and pedostratigraphy. The Dolní Věstonice loess section is characterized by four pedosedimentary subsequences. At the base of the profile, subsequence I is characterized by a distinct Early Glacial soil complex, OSL‐dated to c. 110 to 70 ka, representing one of the most complete records of environmental change in the European loess belt. Subsequence II is allocated to the Lower Pleniglacial and is characterized by laminated sandy loess. Middle Pleniglacial subsequence III is represented by a brown soil complex, and is followed by the uppermost subsequence IV, characterized by a thick body of laminated sandy loess, indicating strong wind activity and a high sedimentation rate of more than ~1 mm a?1 during the Upper Pleniglacial. According to the OSL chronology, as well as to the sedimentological and palaeopedological investigations, it is likely that the sequence at Dolní Věstonice has recorded most of the climatic events expressed in the NGRIP δ18O reference record between 110 and 70 ka. 相似文献