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301.
302.
Neil K. Ganju Melanie Hayn Shih-Nan Chen Robert W. Howarth Patrick J. Dickhudt Alfredo L. Aretxabaleta Roxanne Marino 《Estuaries and Coasts》2012,35(5):1285-1298
Increased nutrient loading to estuaries has led to eutrophication, degraded water quality, and ecological transformations. Quantifying nutrient loads in systems with significant groundwater input can be difficult due to the challenge of measuring groundwater fluxes. We quantified tidal and freshwater fluxes over an 8-week period at the entrance of West Falmouth Harbor, Massachusetts, a eutrophic, groundwater-fed estuary. Fluxes were estimated from velocity and salinity measurements and a total exchange flow (TEF) methodology. Intermittent cross-sectional measurements of velocity and salinity were used to convert point measurements to cross-sectionally averaged values over the entire deployment (index relationships). The estimated mean freshwater flux (0.19?m3/s) for the 8-week period was mainly due to groundwater input (0.21?m3/s) with contributions from precipitation to the estuary surface (0.026?m3/s) and removal by evaporation (0.048?m3/s). Spring?Cneap variations in freshwater export that appeared in shorter-term averages were mostly artifacts of the index relationships. Hydrodynamic modeling with steady groundwater input demonstrated that while the TEF methodology resolves the freshwater flux signal, calibration of the index?Csalinity relationships during spring tide conditions only was responsible for most of the spring?Cneap signal. The mean freshwater flux over the entire period estimated from the combination of the index-velocity, index?Csalinity, and TEF calculations were consistent with the model, suggesting that this methodology is a reliable way of estimating freshwater fluxes in the estuary over timescales greater than the spring?Cneap cycle. Combining this type of field campaign with hydrodynamic modeling provides guidance for estimating both magnitude of groundwater input and estuarine storage of freshwater and sets the stage for robust estimation of the nutrient load in groundwater. 相似文献
303.
Organic carbon,phosphorus and nitrogen in surface sediments of the marine-coastal region north and south of the Paria Peninsula,Venezuela 总被引:2,自引:1,他引:1
The organic carbon, phosphorus and nitrogen content of silt and clay fractions of surface sediments from the marine-coastal
region north and south of the Paria Peninsula (PP) were quantified. Organic carbon concentrations (Corg) were determined by
dry combustion after decarbonation with 10% hydrochloric acid, and total phosphorus (TP) and total nitrogen (TN). This information
was then used to produce maps of the iso-concentrations of the distribution of these elements in the sub-marine continental
shelf north of the PP and in the Gulf of Paria (GP). In the silt fraction, the Corg concentration, TP and TN showed average
values of 1.53, 0.04 and 0.03%, respectively. The highest Corg, PT and NT values were recorded from silts from the PP with
a gradual increase towards the west and the lowest figures were found in the GP. In the clay fraction, Corg, TN and TP had
mean values of 1.64, 0.13 and 0.04%, respectively, and showed a spatial distribution very similar to the silt fraction, indicating
the influence of ocean currents and coastal upwelling patterns. The C/N ratio had an average of 23.67 and showed that the
Corg present in the PP sediments is of marine origin, resulting from primary productivity, especially towards the west. This
zone has been identified as the most productive in this region due to coastal upwelling and the influence of the Orinoco and
Amazon rivers (Gomez 1996; Monente 1997). In contrast, a greater variability in the parameters measured was found in the GP sediments, probably due to the mixing
of marine and continental Corg, confirming the influence of the Orinoco and Amazon waters brought by the Guyana Current. 相似文献
304.
Protection of groundwater intended for human consumption: a proposed methodology for defining safeguard zones 总被引:1,自引:1,他引:0
A. Jiménez-Madrid F. Carrasco-Cantos C. Martínez-Navarrete 《Environmental Earth Sciences》2012,65(8):2391-2406
Carbonate aquifers constitute a water reserve of essential importance for human supply. For this, it is necessary to establish
suitable protection measures in order to achieve the good status of groundwater bodies intended for human supply according
to the requirements of the Water Framework Directive. The objective of this paper is to present a methodology to define safeguard
zones for the protection of carbonate groundwater bodies intended for human consumption. To do this, firstly the risk of groundwater
contamination is evaluated through a combination of characterising pressures and the evaluation of the intrinsic vulnerability
to contamination. Secondly, the existing water abstraction points are identified and their zones of contribution are delineated
in order to establish priorities when defining protective measures in the region. Finally, the existing wellhead protection
areas and those defined according to the proposed methodology must be integrated into the delineated safeguard zones. The
results obtained in a carbonate groundwater body in southern Spain are consistent with the existing quality data and they
show the percentage of land that must be protected to preserve the quality of water intended for human consumption, thus facilitating
their future integration into adequate land use planning tools. 相似文献
305.
María del Carmen Blanco Juan Darío Paoloni Hector Morrás Carmen Fiorentino Mario Eduardo Sequeira Nilda N. Amiotti Oscar Bravo Silvana Diaz Martín Espósito 《Environmental Earth Sciences》2012,66(7):2075-2084
Excessive arsenic concentrations above the Argentinean and WHO guidelines for drinking water (10 μg L−1) affects shallow aquifers of the southern Pampean Plain (Argentina) hosted in the Pampean and the Post Pampean formations
(loess and reworked loess; Plio-Pleistocene–Holocene). Health problems related to high As concentrations in drinking waters
are known as Endemic Regional Chronic Hydroarsenicism. Hydrochemistry of shallow groundwaters and soil geochemistry were investigated
aiming to (1) understand the partition of As in the solid phase and its relationship with unacceptable As concentrations in
waters, (2) identify the provision source of As to groundwaters. Only 5% of the samples had As concentrations <10 μg L−1; in 27% As concentrations ranged from 10 to 50 μg L−1 and in 58% it reached 60–500 μg L−1. The coarse fraction (50–2,000 μm) hosts about 27% of the total As in the solid phase, being positively correlated to Ba
(p < 0.01; r
2 = 0.93). About 70% is included in the <2 μm fraction and had positive correlations of As–Fe (p < 0.05; r
2 = 0.85) and As–Cr (p < 0.05; r
2 = 0.68). Soils and sediment sand fractions of vadose zones are the primary sources of As in shallow groundwater while adsorption–desorption
processes, codisolution–coprecipitation, and evaporation during the dry seasons raise As concentrations in waters exceeding
the guideline value for drinking water. 相似文献
306.
Recent studies on Teide–Pico Viejo (TPV) complex have revealed that explosive activity of phonolitic and basaltic magmas, including plinian and subplinian eruptions, and the generation of a wide range of pyroclastic density currents (PDCs) have also been significant. We perform a statistical analysis of the time series of past eruptions and the spatial extent of their erupted products, including lava flows, fallout and PDCs. We use an extreme value theory statistical method to calculate eruption recurrence. The analysis of past activity and extent of some well-identified deposits is used to calculate the eruption recurrence probabilities of various sizes and for different time periods. With this information, we compute several significant scenarios using the GIS-based VORIS 2 software (Felpeto et al., J Volcanol Geotherm Res 166:106–116, 2007) in order to evaluate the potential extent of the main eruption hazards that could be expected from TPV. The simulated hazard scenarios show that the southern flank of Tenerife is protected by Las Cañadas caldera wall against lava flows and pyroclastic density currents, but not against ash fallout. The Icod Valley, and to a minor extent also the La Orotava valley, is directly exposed to most of TPV hazards, in particular to the gravity driven flows. This study represents a step forward in the evaluation of volcanic hazard at TPV with regard to previous studies, and the results obtained should be useful for intermediate and long-term land-use and emergency planning. 相似文献
307.
Lourdes Vazquez‐Gomez Achille de Battisti Sergio Ferro Monica Cerro Silvia Reyna Carlos A. Martínez‐Huitle Marco A. Quiroz 《洁净——土壤、空气、水》2012,40(4):408-415
The electrochemical oxidation (EO) of diethyl phthalate (DEP) in aqueous solution was studied at Pb/PbO2 and Ti/SnO2 anode materials under galvanostatic‐experimental conditions. Results obtained clearly demonstrated that the anode plays a significant role for the optimization of the oxidation process, deciding the mechanisms and by‐products formed. DEP and by‐products of oxidation were also analyzed during various stages of the electrolysis reaction by HPLC and GC/MS techniques. Before the analysis by GC/MS technique, the samples were treated by solid phase microextraction (SPME) in order to concentrate the compounds from the reaction solution and identify all electrolysis intermediates. Current efficiencies (instantaneous current efficiency; ICE and total current efficiency; TCE) achieved during EO experiments were dependent on anode used and current density (20–40 mA cm?2) at 40°C. The results obtained demonstrated that the environmental electrochemical methods can be a feasible alternative for the wastewater treatment containing hazardous phthalates. 相似文献
308.
Marta Tárraga Servando De La Cruz-Reyna Ana T. Mendoza-Rosas Roberto Carniel Alicia Martínez-Bringas Alicia García Ramon Ortiz 《Acta Geophysica》2012,60(3):664-681
The continuous background seismic activity contains information on the internal state of a volcanic system. Here, we report
the influence of major regional tectonic earthquakes (M > 5 in most cases) on such state, reflected as changes in the spectral and dynamical parameters of the volcano continuous
seismic data. Although changes do not always occur, analysis of five cases of earthquake-induced variations in the signals
recorded at Popocatépetl volcano in central México reveal significant fluctuations following the tectonic earthquakes. External
visible volcanic activity, such as small to moderate explosions and ash emissions, were related to those fluctuations. We
briefly discuss possible causes of the variations. We conclude that recognition of fluctuations in the dynamical parameters
in volcano monitoring seismic signals after tectonic earthquakes, even those located in the far field, hundreds of kilometers
away, may provide an additional criterion for eruption forecasting, and for decision making in the definition of volcanic
alert levels. 相似文献
309.
310.
Automatic Sunspots Detection on Full-Disk Solar Images using Mathematical Morphology 总被引:1,自引:0,他引:1
Sunspots are solar features located in active regions of the Sun, whose number is an indicator of the Sun’s magnetic activity.
Therefore accurate detection and classification of sunspots are fundamental for the elaboration of solar activity indices
such as the Wolf number. However, irregularities in the shape of the sunspots and their variable intensity and contrast with
the surroundings, make their automated detection from digital images difficult. Here, we present a morphological tool that
has allowed us to construct a simple and automatic procedure to treat digital photographs obtained from a solar telescope,
and to extract the main features of sunspots. Comparing the solar indices computed with our algorithm against those obtained
with the previous method exhibit an obvious improvement. A favorable comparison of the Wolf sunspot number time series obtained
with our methodology and from other reference observatories is also presented. Finally, we compare our sunspot and group detection
to that of other observatories. 相似文献