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91.
S.S.Gao K.H.Liu 《中国海洋大学学报(英文版)》2004,3(2):191-194
1 Introduction Themid oceanridgesystemisthelargestgeologicstructureonEarth .Oneoftheoriginalmodelsonridgeprocessesconsiderstheupwellingoftheunderly ingasthenosphereastheresultoftheactiveascendingofalarge scaleconvectioncellinthemantle (Holmes ,1931;Hess… 相似文献
92.
K.?Bargach P.?Ruano A.?Chabli J.?Galindo-ZaldívarEmail author A.?Chalouan A.?Jabaloy M.?Akil M.?Ahmamou C.?Sanzde Galdeano M.?Benmakhlouf 《Pure and Applied Geophysics》2004,161(3):521-540
—Prerif Ridges are located at the frontal part of the Rif Cordillera, which develops at the Eurasian-African plate boundary. The ridges are formed by recent tectonic structures that also deform foreland basins (Saïss and Gharb basins) and the foreland (Moroccan Meseta). The position of the ridges is the consequence of inversion tectonics undergone in the area. The ENE-WSW trend of the northern edge of the Neogene Saïss basin is determined by the location of Mesozoic basins. Although Prerif ridges probably started to develop since the Early Miocene, the most active deformation phase affecting Pliocene rocks consisted of N-S to NW-SE oriented compression. Striated pebbles show that this compression has prolate stress ellipsoids. The deformation produces southwards vergent folds and NNW-SSE striae on reverse faults at the base of the ridges. The flexure of the Paleozoic basement by the emplacement of the Ridges produced extensional deformation and the development of the Saïss foreland basin. The extension in this basin is oblate and features a well determined NNE-SSW trend near the Ridges, whereas it becomes prolate and pluridirectional near the foreland edge represented by the Rabat region. This part of the Moroccan Meseta, commonly considered to be stable, is deformed by sets of orthogonal joints and faults with short slip that affect up to Quaternary sediments. Southwestward, the Meseta rocks are also deformed by transcurrent faults, which indicate NW-SE and N-S trends of compression. The NW-SE approximation of Eurasia and Africa determines a regional stress field with the same trend of compression. Regional stresses are notably disturbed by the development of the active structures in the Rif, which exhibit alternating trends of compression and extension. The clearest evidence of the relationship between the local deformation and the general plate motion is found at the deformation front of the Cordillera, that is, the Prerif Ridges. 相似文献
93.
The aim of this study was to identify a method for determining the number of tracer particles required to define the mean longshore transport distance of indigenous littoral shingle with a particular level of precision. A method is presented which can be applied to existing tracer data to determine both the precision of the measurements collected and the number of tracers required to achieve a particular level of precision. The method, which utilises well established statistical relationships, is demonstrated by applying it to archive tracer data. The study demonstrates the sensitivity of the number of tracers to the variance of the transport distances of indigenous particles at the site and the precision with which the investigator wishes to define the mean. It is anticipated that application of the method by other practitioners, in the future, will allow a dataset to develop which can be used alongside the method presented here to allow the number of tracers required for a study to be estimated prior to entering the field. Results are presented to initiate the development of this dataset and a “look-up chart” derived using the method is given to aid its application. 相似文献
94.
Propagation of Rossby Waves over Ridges Excited by Interannual Wind Forcing in a Western North Pacific Model 总被引:1,自引:4,他引:1
Numerical experiments with a multi-level general circulation model have been performed to investigate basic processes of westward
propagation of Rossby waves excited by interannual wind stress forcing in an idealized western North Pacific model with ocean
ridges. When the wind forcing with an oscillation period of 3 years is imposed around 180°E and 30°N, far from Japan, barotropic
waves excited by the wind can hardly cross the ridges, such as the Izu-Ogasawara Ridge. On the other hand, a large part of
the first-mode baroclinic waves are transmitted across the ridges, having net mass transport. The propagation speed of the
first-mode baroclinic wave is accelerated (decelerated) when an anticyclonic (cyclonic) circulation is formed at the sea surface,
due to a deeper (shallower) upper layer, and to southward (slightly northward) drift of the circulation. Thus, when the anticyclonic
circulation is formed on the northern side of the cyclonic one, they propagate almost together. The second-mode baroclinic
waves converted from the first-mode ones on the ridges arrive south of Japan, although their effects are small. The resulting
volume transport variation of the western boundary current (the Kuroshio) reaches about 60% of the Sverdrup transport variability
estimated from the wind stress. These characteristics are common for the interannual forcing case with a longer oscillation
period. In the intraseasonal and seasonal forcing cases, on the other hand, the transport variation is much smaller than those
in the interannual forcing cases.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
95.
96.
Nicolas A. Ildefonse B. Boudier F. Lenoir X. Ben Ismail W. 《Marine Geophysical Researches》2000,21(3-4):269-287
Mafic dikes and dunite veins are observed in the mantle section of the Oman – United Arab Emirates (O-UAE) ophiolites, as well as diabase dikes and hydrothermal veins in the crust section. They have been systematically measured during the mapping of this ophiolite and are represented by their trajectories in the folded map 3 in the back of this volume, and by local stereoplots included in this study. Mafic dikes in the mantle section correspond to basaltic melt being injected at decreasing temperatures from above or at peridotite solidus, down to below 450°C. Hydrothermal veins associated with dioritic dikes issued from hydrous melting of host gabbros are observed down to the base of the crust, bearing evidence for sea water penetration into basal gabbros at or above 900°C, that is very close to the ridge axis. Dike orientations record the stress field at the time of their injection. In most places, all types of dikes are dominantly parallel to the general trend of the nearest sheeted dike complex; thus the stress field has not visibly changed from melt injection in the asthenosphere below the ridge of origin to injection in a lithosphere up to a few Myr old, at distances beyond 100 km from the axis. Local preferred orientations, when they are considered in the frame of the paleo-ridge system of O-UAE, result in a coherent model throughout the belt: the sheeted dike complex dips moderately away from the presumed ridge axis and the mantle dikes, toward this axis. These opposite directions are explained by the presumed effect of subsidence toward the axis for the sheeted dikes and by the central feeding from an asthenospheric uprise for the mantle dikes. 相似文献
97.
The Wuqbah peridotite, central Oman Ophiolite: Petrological characteristics of the mantle in a fossil overlapping ridge setting 总被引:2,自引:0,他引:2
Jacques Girardeau Christophe Monnier Laurent Lemée Frédéric Quatrevaux 《Marine Geophysical Researches》2002,23(1):43-56
The Wuqbah peridotites (Wuqbah massif, central Oman Ophiolite) constitute the mantle part of a complete ophiolitic sequence and their field deformation geometry is thought to reflect mantle dynamics in a fossil overlapping ridge settings (Girardeau et al., 2002). These peridotites comprise dominantly residual harzburgites and dunites. Nearly 70% of the harzburgites are clinopyroxene-free, and the rest contains less than 1%. The mineral chemistry of olivine, pyroxenes and spinel, and whole rock major and rare-earth element data, indicate that the Wuqbah peridotites are all strongly refractory and that they record a major percolation event, marked by strong enrichments in incompatible elements. At the massif scale, the Central Zone contains rocks with the most refractory features (20% melt extraction), as expected in an area of mantle upwelling. In the overlapping ridge senario, it corresponds to the overlap zone whose formation is discussed. 相似文献
98.
99.
100.
Patrick G. Quilty 《Australian Journal of Earth Sciences》2013,60(2):171-189
All known Cambrian and Ordovician dendroids and hydroids of Tasmania are reviewed. Protohalecium hallianum Chapman & Thomas is revised at both generic and specific levels. Archaeocryptolaria recta var. flexilis Chapman & Thomas is revised to Protohalecium flexilis. Archaeolafoea serialis (Chapman & Thomas) (Hydroidea) is transferred to Mastigograptus (Dendroidea). The following species are described as new: Acanthograptus antiquus (Cambrian), A. banksi, Desmograptus thomasi (Ordovician). 相似文献