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61.
Y. A. Moustafa J. Pätzold Y. Loya G. Wefer 《International Journal of Earth Sciences》2000,88(4):742-751
We present a study based on X-ray chronologies and the stable isotopic composition of fossil Porites spp. corals from the northern Gulf of Aqaba (Red Sea) covering the mid-Holocene period from 5750 to 4450 14C years BP (before present). The stable oxygen and carbon isotopic compositions of five specimens reveal regular annual periodicities.
Compared with modern Porites spp. from the same environment, the average seasonal δ
18O amplitude of the fossil corals is higher (by ca. 0.35–0.60‰), whereas annual growth rates are lower (by ca. 3.5 to 2 mm/year).
This suggests stronger seasonality of sea surface temperatures and increased variability of the oxygen isotopic composition
of the sea water due to changes in the precipitation and evaporation regime during the mid-Holocene. Most likely, summer monsoon
rains reached the northern end of the Red Sea at that time. Average annual coral growth rates are diminished probably due
to an increased input and resuspension of terrestrial debris to the shallow marine environment during more humid conditions.
Our results corroborate published reports of paleodata and model simulations suggesting a northward migration of the African
monsoon giving rise to increased seasonalities during the mid-Holocene over northeastern Africa and Arabia.
Received: 4 January 1999 / Accepted: 13 September 1999 相似文献
62.
The reconstruction of the climatic history during the past several hundred years requires a sufficient geographical coverage
of combined climate proxy series. Especially in order to identify causal connections between the atmosphere and the ocean,
inclusion of marine records into composite climate time series is of fundamental importance. We present two skeletal δ
18O chronologies of coral skeletons of Diploria labyrinthiformis from Bermuda fore-reef sites covering periods in the nineteenth and twentieth centuries and compare them with instrumental
temperature data. Both time series are demonstrated to display sea-surface temperature (SST) variability on inter-annual to
decadal time scales. On the basis of a specific modern δ
18O vs instrumental SST calibration we reconstruct a time series of SST anomalies between AD 1350 and 1630 covering periods
during the Little Ice Age. The application of the coral δ
18O vs temperature relationship leads to estimates of past SST variability which are comparable to the magnitude of modern variations.
Parallel to δ
18O chronologies we present time series of skeletal bulk density. Coral δ
18O and skeletal density reveal a strong similarity during Little Ice Age, confirming the reliability of both proxy climate
indicators. The past coral records, presented in this study, share features with a previously published climate proxy record
from Bermuda and a composite time series of reconstructed Northern Hemisphere summer temperatures. The coral proxy data presented
here represent a valuable contribution to elucidate northern Atlantic subtropical climate variation during the past several
centuries.
Received: 9 November 1998 / Accepted: 13 September 1999 相似文献
63.
Mauricio Parra Andrés Mora Carlos Jaramillo Vladimir Torres Gerold Zeilinger Manfred R. Strecker 《Basin Research》2010,22(6):874-903
In order to evaluate the relationship between thrust loading and sedimentary facies evolution, we analyse the progradation of fluvial coarse‐grained deposits in the retroarc foreland basin system of the northern Andes of Colombia. We compare the observed sedimentary facies distribution with the calculated one‐dimensional (1D) Eocene to Quaternary sediment‐accumulation rates in the Medina wedge‐top basin and with a three‐dimensional (3D) sedimentary budget based on the interpretation of ~1800 km of industry‐style seismic reflection profiles and borehole data. Age constraints are derived from a new chronostratigraphic framework based on extensive fossil palynological assemblages. The sedimentological data from the Medina Basin reveal rapid accumulation of fluvial and lacustrine sediments at rates of up to ~500 m my?1 during the Miocene. Provenance data based on gravel petrography and paleocurrents reveal that these Miocene fluvial systems were sourced from Upper Cretaceous and Paleocene sedimentary units exposed to the west in the Eastern Cordillera. Peak sediment‐accumulation rates in the upper Carbonera Formation and the Guayabo Group occur during episodes of coarse‐grained facies progradation in the early and late Miocene proximal foredeep. We interpret this positive correlation between sediment accumulation and gravel deposition as the direct consequence of thrust activity along the Servitá–Lengupá faults. This contrasts with one class of models relating gravel progradation in more distal portions of foreland basin systems to episodes of tectonic quiescence. 相似文献
64.
65.
John P. Hagen Paul N. Swanson Robert W. Haas Fred L. Wefer Raymond W. Vogt 《Solar physics》1971,21(2):286-296
The 7 March, 1970 total solar eclipse was observed at wavelengths of 3.2 and 8.3 mm; the object being to use the knife edge of the Moon as it passed across the Sun to improve angular resolution on the Sun. This in turn would provide a radial brightness distribution of the Sun with an angular resolution of a few seconds of arc.Excellent eclipse curves were obtained at 3 mm; however, some external interference marred the 8 mm record near totality.The 8 mm brightness distribution is subject to some uncertainty, but tends to show limb brightening. The 3 mm brightness distribution shows a well defined complex limb brightening within about 1 arc min of the optical limb. The maximum brightening is approximately 30% above the average disc temperature. 相似文献
66.