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71.
Benthic exchange of nutrients in Galveston Bay, Texas 总被引:4,自引:0,他引:4
Kent W. Warnken Gary A. Gill Peter H. Santschi Lawrence L. Griffin 《Estuaries and Coasts》2000,23(5):647-661
Nutrient regeneration rates were determined at three sites increasing in distance from the Trinity River, the main freshwater
input source, to Galveston Bay, Texas, from 1994 through 1996. Diffusive fluxes generally agreed in direction with directly
measured benthic fluxes but underestimated the exchange of nutrients across the sediment-water interface. While the fluxes
of ammonium and phosphate were directed from the sediment into the overlying waters, the fluxes of silicate and chloride changed
in both magnitude and direction in response to changing Trinity River flow conditions. Oxygen fluxes showed benthic production
during both summer 1995 and winter 1996, while light-dark deployments showed production-consumption, respectively. Benthic
inputs of nutrients were higher at either the middle or outer Trinity Bay regions, most likely due to a higher quality and
quantity of the autochthonous organic matter deposited. This feature is consistent with and gives evidence for previously
observed non-conservative mixing behaviors reported for nutrients in this region of Galveston Bay. Calculated turnover times,
between 7 to 135 d for phosphate, 4 to 56 d for silicate, and 0.3 to 10 d for ammonium were significantly shorter than the
average Trinity Bay water residence time of 1.5 yr for the period September 1995 through October 1996. During periods of decreased
Trinity River flow and increased residence times, benthic inputs of ammonium and phosphate were 1 to 2 orders of magnitude
greater than Trinity River inputs and were the dominant input source of these nutrients to Trinity Bay. The sediments, a sink
for silicate when overlying water column concentrations of silicate were elevated, became a source of silicate to the overlying
waters of Trinity Bay under reduced flow, high salinity conditions. 相似文献
72.
The continental margin of northern Sinai and Israel, up to Haifa Bay, is the northeastern limb of the submarine Nile Delta Cone. It is made up predominantly of clastics from the Nile and its predecessors. The continental shelf and coastal plain of Israel are built of a series of shore-parallel ridges composed of carbonate-cemented quartz sandstone (locally named kurkar), a lithification product of windblown sands that were piled up into dunes during the Pleistocene. The drop in global sea level and regression during the last glacial period exposed the continental shelf to subaerial erosion and created a widespread regional erosional unconformity which is expressed as a prominent seismic reflector at the top of the kurkar layers. The subsequent Holocene transgression abraded much of the westernmost kurkar ridges, drowned their cores, and covered the previous lowstand deposits with marine sands, which were in turn covered by a sequence of sub-Recent clayey silts. The Mediterranean coasts of Sinai and Israel are part of the Nile littoral cell. Since the building of the Aswan dams the sand supplied to Israel's coastal system is derived mainly from erosion of the Nile Delta and from sands offshore Egypt that are stirred up by storm waves. The sands are transported by longshore and offshore currents along the coasts of northern Sinai and Israel. Their volume gradually declines northward with distance from their Nile source. The longshore transport terminates in Haifa Bay where some sand is trapped, and the test escapes to deeper water by bottom currents and through submarine canyons, thus denying Nile-derived sand supply to the 40-km-long 'Akko-Rosh Haniqra shelf. The sand balance along Israel's coastal zone is a product of natural processes and human intervention. Losses due to the outgoing longshore transport, seaward escape, and landward wind transport exceed the natural gains from the incoming longshore transport and the abrasion of the coastal cliffs. The deficit is aggravated by the construction of (1) seaward-projecting structures that trap sands on the upstream side and (2) offshore detached breakwaters that trap sands between themselves and the coast. The negative sand balance is manifested by the removal of sand from the seabed and the consequent exposure of archaeological remains that were hitherto protected by it. The sediments that escape seaward from the longshore transport system form a 2.5- to 4-km-wide sandy apron adjacent to the shore that extends to where the water is 30 - 40 m deep. The apron's slope (0.5 - 0.8) is steeper than the theoretical equilibrium slope for the median grain-size diameter in this zone (0.1 - 0.3 mm). The beach sands and the apron's surficial sands are well sorted. Their grain size decreases with distance from shore, from 0.2 - 0.3 mm nearshore to 0.11 - 0.16 mm by the drowned ridge. The coarse-grained fraction consists of skeletal debris (commonly 5 - 12% carbonate matter) and wave-milled kurkar grains (locally named zifzif). In deeper water, the basal sands underlying the fine-grained sediment cover consist of 1- to 30-cm layers whose composition ranges from silty sands to various types of sands (fine, medium, coarse, and gravelly) to zifzif. For the most part, they contain large amounts of skeletal debris (20 - 60%) and small fragments of kurkar. Two types of kurkar rock were encountered offshore: a well-sorted, fine- to medium-grained (0.074 - 0.300 mm) lithified dune sand with variable amounts of carbonate cement, ranging from hard rock of low permeability to loose sand; and a porous sandstone made up predominantly of algal grains and skeletal debris (calcarenite). 相似文献
73.
74.
Public engagement with carbon and climate change: To what extent is the public ‘carbon capable’? 总被引:1,自引:0,他引:1
The relevance of climate change for society seems indisputable: scientific evidence points to a significant human contribution in causing climate change, and impacts which will increasingly affect human welfare. In order to meet national and international greenhouse gas (GHG) emissions reduction targets, there is an urgent need to understand and enable societal engagement in mitigation. Yet recent research indicates that this involvement is currently limited: although awareness of climate change is widespread, understanding and behavioral engagement are far lower. Proposals for mitigative ‘personal carbon budgets’ imply a need for public understanding of the causes and consequences of carbon emissions, as well as the ability to reduce emissions. However, little has been done to consider the situated meanings of carbon and energy in everyday life and decisions. This paper builds on the concept of ‘carbon capability’, a term which captures the contextual meanings associated with carbon and individuals’ abilities and motivations to reduce emissions. We present empirical findings from a UK survey of public engagement with climate change and carbon capability, focusing on both individual and institutional dimensions. These findings highlight the diverse public understandings about ‘carbon’, encompassing technical, social, and moral discourses; and provide further evidence for the environmental value-action gap in relation to adoption of low-carbon lifestyles. Implications of these findings for promoting public engagement with climate change and carbon capability are discussed. 相似文献
75.
Weimin Huang Gill E. Wu S. Biyang Wen Zijie Yang Jiechang Hou 《Oceanic Engineering, IEEE Journal of》2004,29(4):1032-1037
The extraction of full wind vectors from data obtained by single-site (monostatic) high-frequency ground-wave radar (HFGWR) is an ongoing challenge because of the inherent directional ambiguities. Here, a new algorithm for resolving the ambiguity of wind direction from monostatic data is presented. The true wind direction is determined by minimizing the sum of the difference among three wind directions derived from three different radar look angles. The wind directions estimated by applying the algorithm to data obtained from the OSMAR2000 HFGWR situated at the Eastern China Sea are compared with values obtained from ship-borne instrumentation. The mean difference between the ground-truthed values and those obtained from the radar data is approximately 20/spl deg/. The distance limit for wind direction sensing using the OSMAR2000 is about 200 km, which is the range for which signal-to-noise ratios typically exceed about 23 dB in the relevant first-order portions of the backscatter spectra. 相似文献
76.
Karstified carbonate aquifers may receive significant recharge contributions from losing streams, hence, the knowledge about surface water-groundwater (SW-GW) interactions is crucial with regard to water management (e.g., source protection zone delineation). The dynamics of SW-GW interactions may depend on factors such as the relative water levels between streams and aquifers, resulting in a temporal variation of exchange, which imposes complexity to the understanding of such dynamics. This study highlights the use of high-resolution time series and multiresolution analysis to help to gain insights into such complex dynamics. Wavelet coherence is applied on hourly time series of rainfall, stream, and spring discharges of a low-lying karstified spring catchment to yield a correlation in the time-frequency domain. This analysis provides comprehensive information on the overall impact of the river on the spring, which is supported by the cross-correlation function, as well as by more detailed information, including time-variant influences such as a threshold level of influence. Field observations of turbidity sampling at the spring appear to support this interpretation. This innovative approach relies on basic hydrological parameters, water level, or discharge, and is therefore applicable to many other systems with such existing time series. 相似文献
77.
Philip E.BETT Gill M.MARTIN Nick DUNSTONE Adam A.SCAIFE Hazel E.THORNTON Chaofan LI 《大气科学进展》2021,38(12):2212-2220
Seasonal forecasts for Yangtze River basin rainfall in June, May–June–July (MJJ), and June–July–August (JJA) 2020 are presented, based on the Met Office GloSea5 system. The three-month forecasts are based on dynamical predictions of an East Asian Summer Monsoon (EASM) index, which is transformed into regional-mean rainfall through linear regression. The June rainfall forecasts for the middle/lower Yangtze River basin are based on linear regression of precipitation. The forecasts verify well in terms of giving strong, consistent predictions of above-average rainfall at lead times of at least three months. However, the Yangtze region was subject to exceptionally heavy rainfall throughout the summer period, leading to observed values that lie outside the 95% prediction intervals of the three-month forecasts. The forecasts presented here are consistent with other studies of the 2020 EASM rainfall, whereby the enhanced mei-yu front in early summer is skillfully forecast, but the impact of midlatitude drivers enhancing the rainfall in later summer is not captured. This case study demonstrates both the utility of probabilistic seasonal forecasts for the Yangtze region and the potential limitations in anticipating complex extreme events driven by a combination of coincident factors. 相似文献
78.
Rohan Wickramasuriya Laurie A. Chisholm Marji Puotinen Nicholas Gill Peter Klepeis 《International journal of geographical information science》2013,27(8):1497-1513
Spatial simulation models have become a popular tool in studying land use/land cover (LULC) change. An important, yet largely overlooked process in such models is the land subdivision, which is known to govern LULC change and landscape restructuring to a large extent. To fill this gap, we propose an efficient and straightforward method to simulate dynamic land subdivision in LULC change models. Key features in the proposed method are implementing a hierarchical landscape where adjacent cells of the same LULC type form patches, patches form properties, and properties form the landscape and incorporating real subdivision layouts. Furthermore, we use a queue-based modified flood-fill algorithm to dynamically reset LULC patches following a subdivision. The proposed subdivision method is demonstrated in action using a prototype agent-based LULC model developed for an amenity landscape in Australia. Results show that it is computationally feasible to run the subdivision method even as spatial resolution is increased, thus providing a proven means for spatial simulation models to dynamically split parcel land. 相似文献
79.
Geographers have been slow to address issues about abstinence, drinking and drunkenness, but the importance of alcohol on the social and political agenda has underpinned recent growth in this field. Explorations of the gendered geographies of drinking are one important strand in this emerging field, but there is currently a paucity of research on women and gender (as opposed to men), and a dearth of research which looks beyond a rather narrowly specified range of public drinking environments. This paper addressed these short-comings through a quantitative and qualitative examination of different men’s and women’s alcohol consumption in private as well as diverse public drinking environments in 21st Century Britain. The paper emphasises the importance of gendered moralities in shaping gender and intra-gender differences in drinking levels, locations and motivations, and explores the connections between apparently separate public and private drinking environments. 相似文献
80.