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171.
172.
The main argument for assigning a glacial origin to the basal conglomeratic levels of the west-Congolan geosyncline has been the presence of polyhedral striated pebbles.New observations have enabled us to show that this striation was due to the internal structure of the pebbles which resulted from the breaking up of the underlying quartzitic layers of the Mayombian axis (the Moussouva series).These conglomeratic formations are marine deposits laid down in a geosyncline which had unstable margins, especially on the western side where the Mayombian Belt was being uplifted.This again calls into question the existence of a Precambrian ice-sheet in Central Africa. 相似文献
173.
Bénédicte Fruneau Benoît Deffontaines Jean-Paul Rudant Anne-Marie Le Parmentier 《Comptes Rendus Geoscience》2005,337(13):1173-1183
The Saint-Lazare area in Paris (France) has undergone important water pumping for the construction of the underground Haussmann–Saint-Lazare station for the EOLE subway line. This paper presents the monitoring of the small surface displacements related to this pumping activity, by classical SAR interferometry. Piezometric measurements provided on 87 piezometers by SNCF and IGC as well as precise levelling data acquired on 626 points by SNCF are also examined. Their comparison with interferometric results shows their good agreement and complementarity, as well as the potential ‘operationality’ of SAR interferometric approach in such a study. To cite this article: B. Fruneau et al., C. R. Geoscience 337 (2005). 相似文献
174.
Benoît Laignel Emmanuel Dupuis Alain Durand Jean-Paul Dupont Emmanuel Hauchard Nicolas Massei 《Comptes Rendus Geoscience》2006,338(8):556-564
An accurate quantification of erosion, based on high-frequency monitoring of river discharge and suspended sediment fluxes is proposed for two watersheds in the western Paris Basin, a sensitive area with respect to erosion phenomena. This continuous monitoring makes it possible to include flood events of short duration, but significant erosion potential. The obtained erosion rate (16 and 21 t?km?2?yr?1) is among the weakest of the planet (3.5 to 18?000 t?km?2?yr?1). However, this annual balance does not reflect the behaviour of these rivers which can be torrential in certain cases. To cite this article: B. Laignel et al., C. R. Geoscience 338 (2006). 相似文献
175.
Jean-Clair Duchesne Jean-Paul Liègeois Viorica Iancu Tudor Berza Dmitry I. Matukov Mihai Tatu Sergei A. Sergeev 《International Journal of Earth Sciences》2008,97(4):705-723
The Sichevita and Poniasca plutons belong to an alignment of granites cutting across the metamorphic basement of the Getic
Nappe in the South Carpathians. The present work provides SHRIMP age data for the zircon population from a Poniasca biotite
diorite and geochemical analyses (major and trace elements, Sr–Nd isotopes) of representative rock types from the two intrusions
grading from biotite diorite to biotite K-feldspar porphyritic monzogranite. U–Pb zircon data yielded 311 ± 2 Ma for the intrusion
of the biotite diorite. Granites are mostly high-K leucogranites, and biotite diorites are magnesian, and calcic to calc-alkaline.
Sr, and Nd isotope and trace element data (REE, Th, Ta, Cr, Ba and Rb) permit distinguishing five different groups of rocks
corresponding to several magma batches: the Poniasca biotite diorite (P1) shows a clear crustal character while the Poniasca granite (P2) is more juvenile. Conversely, Sichevita biotite diorite (S1), and a granite (S2*) are more juvenile than the other Sichevita granites (S2). Geochemical modelling of major elements and REE suggests that fractional crystallization can account for variations within
P1 and S1 groups. Dehydration melting of a number of protoliths may be the source of these magma batches. The Variscan basement, a
subduction accretion wedge, could correspond to such a heterogeneous source. The intrusion of the Sichevita–Poniasca plutons
took place in the final stages of the Variscan orogeny, as is the case for a series of European granites around 310 Ma ago,
especially in Bulgaria and in Iberia, no Alleghenian granitoids (late Carboniferous—early Permian times) being known in the
Getic nappe. The geodynamical environment of Sichevita–Poniasca was typically post-collisional of the Variscan orogenic phase. 相似文献
176.
Broad Absorption Lines (BALs) prove the existence of a high velocity outflowing gas with metallicities larger than solar in
the central few parsecs of high redshift quasars. At the same distance from the black hole, accretion disks in quasars and
Active Galactic Nuclei (AGN) are locally gravitationally unstable, and clumps must form with a size of the order of the scale
height of the disk. This is hardly a coincidence, and we have tried to link these two facts. We have assumed that the unstable
clumps give rise to protostars, which become massive stars after a rapid stage of accretion, and explode as supernovae, producing
strong outflows perpendicular to the disk and inducing outward transfer of angular momentum in the plane of the disk. As a
consequence a self-regulated disk made of gas and stars where supernovae sustain the inflow mass rate required by the AGN
is a viable solution in this region of the disk. This model could explain the BALs, and could also account for a pregalactic
enrichment of the intergalactic medium and of the Galaxy, if massive black holes formed early in the Universe.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
177.
Rob Ivison Ian Smail Andrew Blain Jean-Paul Kneib David Frayer 《Astrophysics and Space Science》1999,266(1-2):285-290
We discuss observations of the submm-selected galaxy,SMM J02399-0136, and what has been learnt about it during the yearfollowing its discovery. SMM J02399-0136 was the first distantgalaxy detected in surveys with the Submm Common-User Bolometer Array(SCUBA). Its association with a massive, gas-rich starburst/AGN atz = 2.8 has lead to suggestions that the prevalence of AGN in theearly Universe may be high (Ivison et al. 1998) and that these AGNmay account for a significant fraction of the far-IR background (e.g.Fixsen et al. 1998). 相似文献
178.
Seasonal variations in dissolved organic carbon concentrations and characteristics in a shallow coastal bay 总被引:8,自引:0,他引:8
Dissolved organic matter (DOM) composition and dynamics in temperate shallow coastal bays are not well described although these bays may be important as local sources of organic carbon to ocean waters and are often sites of economically-important fisheries and aquaculture. In this study surface water samples were collected on a monthly to bi-monthly basis over two years from a mid-Atlantic coastal bay (Chincoteague Bay, Virginia and Maryland, USA). Dissolved organic carbon (DOC) concentrations and light absorbance characteristics were measured on sterile-filtered water, and high-molecular weight (> 1 kDa) dissolved OM (DOM) was isolated to determine stable isotope composition and molecular-level characteristics. Our time series encompassed both a drought year (2002) and a year of above-average rainfall (2003). During the dry year, one of our sites developed a very intense bloom of the brown tide organism Aureococcus anophagefferens while during the wet year there were brown tide bloom events at both of our sampling sites. During early spring of the wet year, there were higher concentrations of > 1 kDa DOC; this fraction represented a larger proportion of overall DOC and appeared considerably more allochthonous. Based upon colored dissolved organic matter (CDOM) and high-molecular weight DOM analyses, the development of extensive phytoplankton blooms during our sampling period significantly altered the quality of the DOM. Throughout both years Chincoteague Bay had high DOC concentrations relative to values reported for the coastal ocean. This observation, in conjunction with the observed effects of phytoplankton blooms on DOM composition, indicates that Chincoteague Bay may be a significant local source of “recently-fixed” organic carbon to shelf waters. Estimating inputs of DOC from Chincoteague Bay to the Mid-Atlantic Bight suggests that shallow productive bays should be considered in studies of organic carbon on continental shelves. 相似文献