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71.
Colm
Cofaigh Justin Taylor Julian A. Dowdeswell Carol J. Pudsey 《Boreas: An International Journal of Quaternary Research》2003,32(1):37-55
The classical model of trough mouth fan (TMF) formation was developed in the Polar North Atlantic to explain large submarine fans situated in front of bathymetric troughs that extend across continental shelves to the shelf break. This model emphasizes the delivery of large volumes of subglacial sediment to the termini of ice streams flowing along troughs, and subsequent re‐deposition of this glacigenic sediment down the continental slope via debris‐flow processes. However, there is considerable variation in terms of the morphology and large‐scale sediment architecture of continental slopes in front of palaeo‐ice streams. This variability reflects differences in slope gradient, the relative contributions of meltwater sedimentation compared with debris‐flow deposition, and sediment supply/geology of the adjacent continental shelf. TMF development is favoured under conditions of a low (<1°) slope gradient; a passive‐margin tectonic setting; abundant, readily erodible sediments on the continental shelf ‐ and thus associated high rates of sediment delivery to the shelf edge; and a wide continental shelf. The absence of large sediment fans on continental slopes in front of cross‐shelf troughs should not, however, be taken to indicate the former absence of palaeo‐ice streams in the geological record. 相似文献
72.
John E. Beckman MartÍ n LÓpez-Corredoira Juan Betancort-Rijo Nieves Castro-RodrÍguez Andrew Cardwell 《Astrophysics and Space Science》2003,284(2):747-751
We present ample evidence for the presence of continuing gaseous infall to the Galactic plane, and then show how interaction
of this gas with the disc gas yields a warp of the observed amplitude and direction. The mechanism works for galaxies in general,
predicting a small proportion of U-shaped warps, as observed.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
73.
KINGA HIPS JÁNOS HAAS MÁRIA VIDÓ ZSUZSANNA BARNA DIVNA JOVANOVIĆ MILAN N. SUDAR ZOLTÁN SIKLÓSY 《Sedimentology》2011,58(4):854-877
A peculiar facies of the Norian–Rhaetian Dachstein‐type platform carbonates, which contains large amounts of blackened bioclasts and dissolutional cavities filled by cements and internal sediments, occurs in the Zlatibor Mountains, Serbia. Microfacies investigations revealed that the blackened bioclasts are predominantly Solenoporaceae, with a finely crystalline, originally aragonite skeleton of fine cellular structure. Blackening of other bioclasts also occurs subordinately. Solenoporacean‐dominated reefs, developed behind the platform margin patch‐reef tract, were the main source of sand‐sized detritus. The blackened and other non‐blackened bioclasts are incorporated in automicrite cement. Radiaxial fibrous calcite cements in the dissolutional cavities are also black, dark grey or white. Reworked black pebbles were reported from many occurrences of peritidal deposits; in those cases, the blackening took place under pedogenic, meteoric diagenetic conditions. In contrast, in the inner platform deposits of the Ilid?a Limestone, the blackening of bioclasts occurred in a marine–meteoric mixing‐zone, as indicated by petrographic features and geochemical data of the skeleton‐replacing calcite crystals. Attributes of mixing‐zone pore waters were controlled by mixing corrosion, different solubility of carbonate minerals and microbial decomposition of organic matter. In the moderate‐energy inner platform environment, large amounts of microbial organic tissue were accumulated and subsequently decomposed, triggering selective blackening in the course of early, shallow burial diagenesis. The δ18O and δ13C values of the mixing‐zone precipitates and replacive calcite do not produce a linear mixing trend. Variation mainly resulted from microbial decomposition of organic matter that occurred under mixing‐zone conditions. The paragenetic sequence implies cyclic diagenetic conditions that were determined by marine, meteoric and mixing‐zone pore fluids. The diagenetic cycles were controlled by sea‐level fluctuations of moderate amplitude under a semi‐arid to semi‐humid climate. 相似文献
74.
ABSTRACT Theoretically, a small drainage basin may be divided into equal areas of downward flow and upward flow of groundwater. In regions where surface water does not obscure the phenomena produced by groundwater, these areas can be differentiated by mapping springs, seepages, groundwater levels, flowing wells, chemical quality of water, natural vegetation, salt precipitates, quality of crops, soap holes, and moist and dry depressions. Mapping and interpretation of field phenomena have been carried out in a section of the Ghostpine Creek valley in a Prairie environment. The relief is gently rolling, the geology is simple, and the climate is cold, humid, and continental. The area of the “north flow-systems” is apportioned as follows: 26 per cent underlain by downward flow; 42 per cent underlain by a mid-line area; and 32 per cent underlain by upward flow. Noting that groundwater flow is nearly parallel to the water table in the vicinity of the mid-line these results comply with the above-mentioned theory of groundwater flow distribution in small drainage basins. Thus, the method is suggested for: 1. A reconnaissance study of the groundwater regime in certain areas, and 2. Specific problems related to groundwater in a Prairie environment, such as: finding suitable locations for dug-out type water supplies, estimating prospects for slough-draining and irrigation, and explanation of the development of certain soil types. For such purposes, the method appears to be competitive with test drilling. 相似文献
75.
LÁSZLÓ IRITZ 《水文科学杂志》2013,58(6):637-651
Abstract The feasibility and success of a forecasting system depend on many factors. Although the models may be of the highest accuracy, they cannot make a forecasting system effective without a well organized database and interpretable output. The interaction between the processes of data management, computation and output presentation should be dynamic. A complete river forecasting system for IBM (or compatible) personal computers aimed at meeting the above demands has been developed at the Department of Hydrology of Uppsala University. The program package sets up the river network, stores a database for it, supplies the appropriate data for a wide choice of forecasting models, and gives interpretable output. The functions are supported by screen graphics. The paper presents this system, the most important points of the algorithms, and an example application. 相似文献
76.
Mark Coughlan Zsuzsanna TÓth Katrien J. J. Van Landeghem Stephen Mccarron Andrew J. Wheeler 《第四纪科学杂志》2020,35(7):907-919
The Wicklow Trough is one of several Irish Sea bathymetric deeps, yet unusually isolated from the main depression, the Western Trough. Its formation has been described as proglacial or subglacial, linked to the Irish Sea Ice Stream (ISIS) during the Last Glacial Maximum. The evolution of the Wicklow Trough and neighbouring deeps, therefore, help us to understand ISIS dynamics, when it was the main ice stream draining the former British–Irish Ice Sheet. The morphology and sub-seabed stratigraphy of the 18 km long and 2 km wide Wicklow Trough is described here from new multibeam echosounder data, 60 km of sparker seismic profiles and five sediment cores. At a maximum water depth of 82 m, the deep consists of four overdeepened sections. The heterogeneous glacial sediments in the Trough overlay bedrock, with indications of flank mass-wasting and subglacial bedforms on its floor. The evidence strongly suggests that the Wicklow Trough is a tunnel valley formed by time-transgressive erosional processes, with pressurised meltwater as the dominant agent during gradual or slow ice sheet retreat. Its location may be fault-controlled, and the northern end of the Wicklow Trough could mark a transition from rapid to slow grounded ice margin retreat, which could be tested with modelling. 相似文献
77.
Forecasting wind gusts in complex terrain 总被引:1,自引:1,他引:0
78.
A first evidence of severe turbulence in the lower stratosphere during easterly tropospheric flow over Greenland is presented. A numerical simulation shows the turbulence to be associated with gravity wave breaking and that simulating with a horizontal resolution of 3 km gives substantially greater and more realistic turbulence than at a 9 km horizontal resolution. It is concluded that real-time simulations at high resolutions would improve aviation forecasts. As the atmospheric flow impinges on South-Greenland a barrier jet, a reverse tip jet and amplified mountain waves with secondary wave breaking are generated at the same time. 相似文献
79.
J. Martinez-FrÍAs A. Delgado M. MillÁN E. Reyes F. Rull D. Travis R. Garcia F. LÓPez-Vera J. A. RodrÍGuez-Losada J. A. Martin-Rubi J. Raya E. Santoyo 《Journal of Atmospheric Chemistry》2005,52(2):185-202
Specific studies about the stable isotope composition (18O/16O and D/H) of atmospheric icy conglomerations are still scarce. The present work offers, for the first time, a very detailed
analysis of oxygen and hydrogen isotopic signatures of unusually large ice conglomerations, or “megacryometeors”, that fell
to the ground in Spain during January 2000. The hydrochemical analysis is based on the bulk isotopic composition and systematic
selective sampling (deuterium isotopic mapping) of eleven selected specimens. δ18O and δD (V-SMOW) of all samples fall into the Meteoric Water Line matching well with typical tropospheric values. The distribution
of the samples on Craig's line suggests either a variation in condensation temperature and/or different residual fractions
of water vapour (Rayleigh processes). Three of the largest megacryometeors exhibited unequivocally distinctive negative values
(δ18O = −17.2%0 and δD = −127 %0 V-SMOW), (δ18O = −15.6%0 and δD = −112%0 V-SMOW) and (δ18O = −14.4%0 and δD = −100%0 V-SMOW), suggesting an atmospheric origin typical of the upper troposphere. Theoretical calculations indicate that the vertical
trajectory of growth was lower than 3.2 km. During the period in which the fall of megacryometeors occurred, anomalous atmospheric
conditions were observed to exist: a substantial lowering of the tropopause with a deep layer of saturated air below, ozone
depression and strong wind shear. Moreover, these large ice conglomerations occurred during non-thunderstorm conditions, suggesting
an alternative process of ice growth was responsible for their formation. 相似文献
80.
Ármann Höskuldsson Níels Óskarsson Rikke Pedersen Karl Grönvold Kristín Vogfjörð Rósa Ólafsdóttir 《Bulletin of Volcanology》2007,70(2):169-182
The 18th historic eruption of Hekla started on 26 February, 2000. It was a short-lived but intense event, emitting basaltic
andesitic (55.5 wt% SiO2) pyroclastic fragments and lava. During the course of the eruption, monitoring was done by both instruments and direct observations,
together providing unique insight into the current activity of Hekla. During the 12-day eruption, a total of 0.189 km3 DRE of magma was emitted. The eruptive fissure split into five segments. The segments at the highest altitude were active
during the first hours, while the segments at lower altitude continued throughout the eruption. The eruption started in a
highly explosive manner giving rise to a Subplinian eruptive column and consequent basaltic pyroclastic flows fed by column
collapses. After the explosive phase reached its maximum, the eruption went through three more phases, namely fire-fountaining,
Strombolian bursts and lava effusion. In this paper, we describe the course of events of the eruption of Hekla and the origin
of its magma, and then show that the discharge rate can be linked to different style of eruptive activity, which are controlled
by fissure geometry. We also show that the eruption phases observed at Hekla can be linked with inferred magma chamber overpressure
prior to the eruption. 相似文献