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61.
Boundary-Layer Meteorology - When wind blows over the ocean, short wind-waves (of wavelength smaller than 10 m) are generated, rapidly reaching an equilibrium with the overlying turbulence (at... 相似文献
62.
Landslide deposits as stratigraphical markers for a sequence‐based glacial stratigraphy: a case study of a Younger Dryas system in the Eastern Alps 下载免费PDF全文
Mathias G. Bichler Martin Reindl Jürgen M. Reitner Ruth Drescher‐Schneider Christian Wirsig Marcus Christl Irka Hajdas Susan Ivy‐Ochs 《Boreas: An International Journal of Quaternary Research》2016,45(3):537-551
Detailed 10Be and 14C dating and supporting pollen analysis of Alpine Lateglacial glacial and landslide deposits in the Hohen Tauern Mountains (Austria) constrain a sequence‐based stratigraphy comprising a major landslide (13.0±1.1 ka) overlain by till and termino‐lateral moraines of an advancing (12.6±1.0 ka) and retreating (11.3±0.8 ka) glacier in turn overlain by a minor landslide (10.8±1.1 ka). These results define glacier activity during the Younger Dryas age Egesen stadial bracketed by landslide activities during the Bølling‐Allerød interstadial and the Preboreal. In contrast to recent studies on Holocene glaciation in the Alps, no traces of any Holocene glacier advance bigger than during the Little Ice Age are documented. Furthermore, this study demonstrates the advantages of using an allostratigraphical approach based on unconformity‐bounded sedimentary units as a tool for glacial stratigraphy in formerly glaciated mountain regions, rather than a stratigraphy based on either isolated morphological features or lithostratigraphical characteristics. 相似文献
63.
Mathias K. Kirf Christian Dinkel Carsten J. Schubert Bernhard Wehrli 《Aquatic Geochemistry》2014,20(1):39-57
Elements involved in biogeochemical cycles undergo rapid turnover at the oxic–anoxic interface of stratified lakes. Here, the presence or absence of oxygen governs abiotic and biotic processes and rates. However, achieving a detailed sampling resolution to precisely locate the oxic–anoxic interface is difficult due to a lack of fast, drift-free sensors in the working range of 10 to a few 1,000 nmol O2 L?1. Here, we demonstrate that conventional amperometric and optical microsensors can be used to resolve submicromolar oxygen concentrations in a continuous profiling mode. The amperometric drift was drastically reduced by anoxic preconditioning. In situ offset correction in the anoxic layer and a high amplification scheme allowed for an excellent detection limit of < 10 nmol L?1. The optical microsensors also showed a similar performance with a detection limit of < 20 nmol L?1. Their drift stability allowed for a laboratory calibration in combination with a minor in situ anoxic offset correction. The two different sensor systems showed virtually identical profiles during parallel use in stratified lakes. Both sensors were able to resolve the fine-scale structure at the oxic–anoxic interface and revealed hitherto unnoticed extended zones of submicromolar oxygen concentrations even below a steep oxycline. The zones extended up to several meters and showed substantial vertical variability. These results underline the need of a precise localization of the oxic–anoxic interface on a submicromolar scale in order to constrain the relevant aerobic and anaerobic redox processes. 相似文献
64.
65.
C. Aerts P. De Cat G. Handler U. Heiter L. A. Balona J. Krzesinski P. Mathias H. Lehmann I. Ilyin J. De Ridder S. Dreizler A. Bruch I. Traulsen A. Hoffmann D. James E. Romero-Colmenero T. Maas M. A. T. Groenewegen J. H. Telting K. Uytterhoeven C. Koen P. L. Cottrell J. Bentley D. J. Wright J. Cuypers 《Monthly notices of the Royal Astronomical Society》2004,347(2):463-470
66.
Segura Hans Espinoza Jhan Carlo Junquas Clementine Lebel Thierry Vuille Mathias Garreaud Rene 《Climate Dynamics》2020,54(5):2613-2631
Climate Dynamics - Analyzing December–February (DJF) precipitation in the southern tropical Andes—STA ($$12^{\circ }\,\hbox {S}$$–$$20^{\circ }\,\hbox {S}$$; > 3000... 相似文献
67.
Annelies Van Hoesel Wim Z. Hoek Gillian M. Pennock Knut Kaiser Oliver Plümper Michal Jankowski Maartje F. Hamers Norbert Schlaak Mathias Küster Alexander V. Andronikov Martyn R. Drury 《Meteoritics & planetary science》2015,50(3):483-498
The Younger Dryas impact hypothesis suggests that multiple airbursts or extraterrestrial impacts occurring at the end of the Allerød interstadial resulted in the Younger Dryas cold period. So far, no reproducible, diagnostic evidence has, however, been reported. Quartz grains containing planar deformation features (known as shocked quartz grains), are considered a reliable indicator for the occurrence of an extraterrestrial impact when found in a geological setting. Although alleged shocked quartz grains have been reported at a possible Allerød‐Younger Dryas boundary layer in Venezuela, the identification of shocked quartz in this layer is ambiguous. To test whether shocked quartz is indeed present in the proposed impact layer, we investigated the quartz fraction of multiple Allerød‐Younger Dryas boundary layers from Europe and North America, where proposed impact markers have been reported. Grains were analyzed using a combination of light and electron microscopy techniques. All samples contained a variable amount of quartz grains with (sub)planar microstructures, often tectonic deformation lamellae. A total of one quartz grain containing planar deformation features was found in our samples. This shocked quartz grain comes from the Usselo palaeosol at Geldrop Aalsterhut, the Netherlands. Scanning electron microscopy cathodoluminescence imaging and transmission electron microscopy imaging, however, show that the planar deformation features in this grain are healed and thus likely to be older than the Allerød‐Younger Dryas boundary. We suggest that this grain was possibly eroded from an older crater or distal ejecta layer and later redeposited in the European sandbelt. The single shocked quartz grain at this moment thus cannot be used to support the Younger Dryas impact hypothesis. 相似文献
68.
Development of a 3D groundwater model based on scarce data: the Wadi Kafrein catchment/Jordan 总被引:2,自引:2,他引:0
Yajie Wu Wenqing Wang Mathias Toll William Alkhoury Martin Sauter Olaf Kolditz 《Environmental Earth Sciences》2011,64(3):771-785
In this work, a 3D groundwater flow model integrating all important geological features of the hydrogeological system is developed
to investigate hydrological processes in the Wadi Kafrein area of Jordan. A large amount of available geological and hydrological
data is integrated to construct a 3D groundwater flow model for the Wadi Kafrein area. Using the newly developed mapping approach,
the translation of the highly detailed geological formations to an unstructured finite element grids, can be accomplished
with high precision. The existing data set for model calibration is scarce, which is a typical situation for many hydrogeological
case studies. At first, the steady state calibration of the groundwater model is carried out based on the observation wells.
Then, the time and space-dependent recharge from precipitation are applied at the top surface of the finite element model.
The transient simulation is conducted during the period of 1996–2008 considering the abstraction rates of the production wells
and discharge of the springs. The calculated water levels are close to the observed values. The difference is partly caused
by return flows from irrigation and the groundwater inflow from the adjacent aquifers which are not taken into consideration
so far. Since the Wadi Kafrein area is an important agricultural area in the semiarid region of the Lower Jordan Valley, the
model developed in this study can be regarded as a useful tool for analyzing the hydrological processes and improving groundwater
management practices elsewhere affected by similar geological and hydrogeological conditions. 相似文献
69.
Saleh A.S. Yahya Martin Gullström Marcus C. ÖhmanNarriman S. Jiddawi Mathias H. AnderssonYunus D. Mgaya Ulf Lindahl 《Estuarine, Coastal and Shelf Science》2011,94(1):16-23
Degradation and mortality of corals is increasing worldwide and is expected to have significant effects on coral reef fish; hence studies on these effects are essential. In the present study, a field experiment was set up within Mafia Island Marine Park in Tanzania (East Africa) to examine the effects of bleaching and habitat structure on colonisation of coral reef fish assemblages. Live and bleached staghorn coral Acropora formosa was transplanted onto plots in a site dominated by sand and rubble, and the experimental design comprised of three treatments: live coral, bleached coral and eroded coral rubble. There was an immediate increase (within 24 h) in fish abundance and diversity in the two treatments with standing corals. Overall, live and bleached coral plots showed similar effects, but differed from the eroded coral plots which had a much lower abundance and diversity of fish. In general, fish species diversity changed with time over the study period while fish abundance did not. Multivariate analyses showed that while there were differences in fish assemblage structure between standing corals and the eroded coral treatment, there was neither a difference between live and bleached coral treatments nor any temporal effects on fish assemblage structure. Our findings suggest that physical structure and complexity of habitat have stronger effects on colonisation of reef fish assemblages than changes in coral health (such as bleaching) which do not affect coral structure. This may have important implications for appropriate coral reef management. 相似文献
70.
Annual floods in New England (USA) and Atlantic Canada: synoptic climatology and generating mechanisms 总被引:1,自引:1,他引:0
Mathias J. Collins Johnathan P. Kirk Joshua Pettit Arthur T. DeGaetano M. Sam McCown Thomas C. Peterson 《自然地理学》2014,35(3):195-219
New England and Atlantic Canada are characterized by mixed flood regimes that reflect different storm types, antecedent land surface conditions, and flood seasonality. Mixed flood regimes are known to complicate flood risk analyses, yet the synoptic climatology and precipitation mechanisms that generate annual floods in this region have not been described in detail. We analyzed a set of long-term annual flood records at climate-sensitive stream gauges across the region and classified the synoptic climatology of each annual flood, quantitatively describing the precipitation mechanisms, and characterize flood seasonality. We find that annual floods here are dominantly generated by Great Lakes-sourced storms and Coastal lows, known locally as ‘nor’easters.’ Great Lakes storms tend to be associated with lower magnitude annual floods (<75th percentile) and Coastal lows are more clearly associated with higher magnitude events (>75th percentile). Tropical cyclones account for few of all annual floods, including extreme events, despite causing some of the region’s largest and most destructive floods. Late winter/early spring is when the greatest number of annual floods occur region wide, and rainfall is the dominant flood-producing mechanism. Rainfall in combination with snowmelt is also important. Both mechanisms are expected to be impacted by projected regional climate change. We find little evidence for associations between flood-producing synoptic storm types or precipitation mechanisms and large-scale atmospheric circulation indices or time periods, despite upward trends in New England annual flood magnitudes. To more completely investigate such associations, partial duration flood series that include more floods than just the largest of each year, and their associated synoptic climatologies and precipitation mechanisms, should be analyzed. 相似文献