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51.
52.
Laboratory measurements of the autocorrelation and space-time correlations for probe separations alined with the mean flow
are used to test a hypothesis of Pielke and Panofsky (1970) which relates these measures by means of an empirical decay parameter
taken from coherence data. The direct laboratory measurements of the space-time correlations are in good agreement with the
functions estimated using the method of Pielke and Panofsky (1970). However, the decay parameters implied for the laboratory
measurements are much smaller than those reported for atmospheric turbulence. 相似文献
53.
Investigation of an extreme storm surge event revealed the presence of an oscillation in sea level with a period of 2-6 h. The English Channel is well known for its quarter- and sixth-diurnal tides, and it was expected that these oscillations were simply the result of tide-surge interactions. However, results of model experiments permitted the reproduction of oscillations from wind forcing alone. The forcing used was from an extreme wind event in December 1989. In this article we describe these oscillations, and in particular their spatial characteristics. It is shown that the dominant response is a transverse mode of the English Channel, with minimum amplitude in the central Channel and maximum amplitude in the Baie de Seine and the Golfe de St Malo. 相似文献
54.
THE USE OF A GAMMA LOGGER TO DELINEATE GLACIAL AND BEDROCK STRATIGRAPHY IN SOUTHWESTERN OHIO 总被引:1,自引:0,他引:1
Abstract. An evaluation was made of the usefulness of the gamma-ray logger in delineating glacial-drift and bedrock stratigraphy in southwestern Ohio. The logger was useful in delineating gross stratigraphic units in a glacial outwash aquifer. The gamma log also provided a clearer indication of the clay content of sand and gravel units than did the driller's log.
On the uplands, away from the valleys filled with glacial outwash, the logger could not be used to locate the thin, poorly-sorted, interstadial sand and gravel deposits between thicker till sheets. It could, however, be used to distinguish formational contacts in the upper Cincinnatian Series. 相似文献
On the uplands, away from the valleys filled with glacial outwash, the logger could not be used to locate the thin, poorly-sorted, interstadial sand and gravel deposits between thicker till sheets. It could, however, be used to distinguish formational contacts in the upper Cincinnatian Series. 相似文献
55.
David Twichell Elizabeth Pendleton Wayne Baldwin James Flocks 《Geo-Marine Letters》2009,29(6):349-358
The Chandeleur Islands lie on the eastern side of the modern Mississippi River delta plain, near the edge of the St. Bernard
Delta complex. Since abandonment approximately 2,000 years b.p., this delta complex has undergone subsidence and ravinement as the shoreline has transgressed across it. High-resolution
seismic-reflection, sidescan-sonar, and bathymetry data show that seafloor erosion is influenced by locally variable shallow
stratigraphy. The data reveal two general populations of shallow erosional depressions, either linear or subcircular in shape.
Linear depressions occur primarily where sandy distributary-channel deposits are exposed on the seafloor. The subcircular
pits are concentrated in areas where delta-front deposits crop out, and occasional seismic blanking indicates that gas is
present. The difference in erosional patterns suggests that delta-front and distributary-channel deposits respond uniquely
to wave and current energy expended on the inner shelf, particularly during stormy periods. Linear depressions may be the
result of the sandy distributary-channel deposits eroding more readily by waves and coastal currents than the surrounding
delta-front deposits. Pits may develop as gas discharge or liquefaction occurs within fine-grained delta-front deposits, causing
seafloor collapse. These detailed observations suggest that ravinement of this inner shelf surface may be ongoing, is controlled
by the underlying stratigraphy, and has varied morphologic expression. 相似文献
56.
57.
White micas are major rock forming minerals in igneous and metamorphic rocks, and their chemical and isotopic variations can be used to determine pressure, temperature and time (P‐T‐t) histories. We apply 40Ar/39Ar multi‐diffusion domain modelling to white micas from blueschists blocks in serpentinite matrix mélange from the exhumed Baja California subduction complex. Thermal history models yielded T‐t paths suggesting that 40Ar* resides within multiple diffusion domains with varying 40Ar* retentivity. Modelled white mica thermal histories and thermobarometric data were used to forward model continuous P‐T‐t paths. P‐T‐t paths are consistent with previous studies and are interpreted to constrain blueschist block exhumation paths within the Baja accretionary wedge. Our P‐T‐t models use temperature controlled 40Ar/39Ar step heat data in which argon loss by volume diffusion can be demonstrated, and for which the white mica petrogenesis is known. 相似文献
58.
Hazel A. Oxenford Ramon Roach Angelique Brathwaite Leonard Nurse Renata Goodridge Fabian Hinds Kim Baldwin Christine Finney 《Climatic change》2008,87(3-4):435-449
In late summer 2005 a mass coral bleaching event occurred in the Caribbean. Here we quantify coral bleaching in Barbados at
six sites on the island’s sheltered west and exposed southwest coasts, including nearshore fringing and patch reefs and offshore
bank reef habitats. Onset of coral bleaching occurred in late August 2005 and persisted for many months after temperatures
cooled. All reef habitats and virtually all coral taxa were affected, with an average of 70.6% of all colonies bleaching.
Nearshore reefs (<10 m depth) were affected more severely than offshore deeper reefs (>15 m) with an average of 80.6% of all
coral colonies bleaching compared with 60.5% on the latter. Inter-species variation in susceptibility to bleaching was marked
with >90% of colonies bleaching in some species whilst <10% bleached in others. Follow-up surveys revealed low coral mortality,
with an overall mean of 3.8% partial colony death across all species and reefs by February 2006. However, bleached condition
has persisted with a mean of 37.7% of all coral colonies still bleached after 5 1/2 months, indicating that loss of live coral
is likely to continue for some time. This event represents the most severe bleaching episode ever witnessed on Barbados’ reefs
and emphasises the vulnerability of small island states, with a high reliance on healthy coral reef ecosystem services, to
elevated sea water temperatures associated with climate variability and global climate change. 相似文献
59.
Elisabet Beamud Josep Anton Muñoz Paul G. Fitzgerald Suzanne L. Baldwin Miguel Garcés Lluis Cabrera James R. Metcalf 《Basin Research》2011,23(3):309-331
The syntectonic continental conglomerates of the South‐Central Pyrenees record the late stages of thin‐skinned transport of the South‐Pyrenean Central Units and the onset of exhumation of the Pyrenean Axial Zone (AZ) in the core of the orogen. New magnetostratigraphic data of these syntectonic continental conglomerates have established their age as Late Lutetian to Late Oligocene. The data reveal that these materials were deposited during intense periods of tectonic activity of the Pyrenean chain and not during the cessation of the deformation as considered previously. The magnetostratigraphic ages have been combined with new detrital apatite fission track (AFT) thermochronology from AZ‐derived granite cobbles within the syntectonic conglomerates. Distribution of the granitic cobbles with different AFT ages and track lengths combined with their depositional ages reveal information on the timing and rate of episodes of exhumation in the orogen. Some AFT ages are considerably older than the AFT ages of the outcropping AZ granitic massifs, indicating erosion from higher crustal levels within the massifs than presently exposed or from completely eroded plutons. Inverse thermal modelling reveals two well‐defined periods of rapid cooling in the hinterland at ca. 50–40 and ca. 30–25 Ma, with another poorly defined cooling episode at ca. 70–60 Ma. The lowest stratigraphic samples experienced postburial annealing caused by the deposition of younger syntectonic sediments during progressive burial of the south Pyrenean thrust and fold belt. Moreover, samples from the deeper stratigraphic levels also reveal postorogenic cooling during the Late Miocene as a response to the excavation of the Ebro River towards the Mediterranean Sea. Our data strongly support previous ideas about the burial of the South Pyrenean fold and thrust belt by Late Palaeogene syntectonic conglomerates and their subsequent re‐excavation and are consistent with other thermochronological data and thermal modelling from the interior part of the orogen. 相似文献
60.