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951.
Philippe Volant Catherine Berge-Thierry Pierre Dervin Marc Cushing Georgianna Mohammadioun Franck Mathieu 《Journal of Seismology》2000,4(2):175-189
The Durance fault area is located in South EasternFrance. This fault system is characterized byhistorical earthquakes (one every century, since 1509,with a magnitude between 5.0 and 5.3). This is theonly fault in France with such a periodic historicalseismic activity. In order to study an active fault ina moderate seismic context, the IPSN (Institute forNuclear Safety and Protection) decided to install apermanent network in 1992, surrounding the fault area.Such a permanent seismic network has been installed inthe french Pyrenees in the Arette area (Gagnepain etal., 1980). While the Arette network covers a regionaffected by several major faults, our network isdevoted to the study of the specific Durance fault.Major historical earthquakes are clearly associatedwith this structure. From an instrumental point ofview, few earthquakes have been recorded since 1962with the national network. Our network shows a smallseismic activity, with the epicenters well alignedalong the fault direction. Moreover, focal mechanismscomputed for two events agree with the regionalmicrostructural studies (Cushing et al., 1997).Finally, a study of the shear wave splittingunderlines preferential S wave polarization for twostations. The H/V ratio on noise microtremors has beencomputed for each station in order to check theirpositions in term of site effects. It does not exhibitany amplification effect (except for two stations).The comparisons with H/V ratio on earthquake datasetshow the important biases we can obtain with realearthquakes. 相似文献
952.
Abstract— Electron microprobe and laser ablation, inductively‐coupled plasma mass spectrometer analyses of 24 georgiaites show that these tektites are all Si‐rich (79–83 wt% SiO2) glasses with variable major and trace element abundances (e.g., FeO varies from 2.1 to 3.7 wt%). Glass compositions are similar to but not identical with average upper continental crust. For example, georgiaites are light rare earth element enriched with small negative Eu anomalies (Eu/Eu*=0.73‐0.86) and La‐Th‐Sc systematics are intermediate between that of Archean and post‐Archean continental crust. When the georgiaite data are placed in the context of data for all North American tektites, triangular arrays appear on some oxide‐oxide plots (e.g., FeO‐MgO). Large variations in refractory element abundances and ratios compared to the variation in SiO2 favors mixing over volatilization as a cause of the compositional variation. If all the tektites formed as a result of a single impact, then triangular arrays in oxide‐oxide variation diagrams require at least three source components. These components include a Si‐rich material, probably a quartz‐rich sand that was predominant in the formation of georgiaites. Two relatively silica‐poor and Fe‐rich components have compositional characteristics similar to shales and greywackes. The La‐Th‐Sc systematics of the georgiaites and most other North American tektites are distinctive and could potentially be used to link the tektites to Eocene sediments at the Chesapeake Bay impact structure. 相似文献
953.
Source, type, and quantity of various components of groundwater, as well as their spatial and temporal variations were determined
by different hydrochemical methods in the alluvial aquifer of the upper Rhone River valley, Bois de Finges, Wallis Canton,
Switzerland. The methods used are hydrochemical modeling, stable-isotope analysis, and chemical analysis of surface water
and groundwater. Sampling during high- and low-water periods determined the spatial distribution of the water chemistry, whereas
monthly sampling over three years provided a basis for understanding seasonal variability. The physico-chemical parameters
of the groundwater have spatial and seasonal variations. The groundwater chemical composition of the Rhone alluvial aquifer
indicates a mixing of weakly mineralized Rhone River water and SO4-rich water entering from the south side of the valley. Temporal changes in groundwater chemistry and in groundwater levels
reflect the seasonal variations of the different contributors to groundwater recharge. The Rhone River recharges the alluvial
aquifer only during the summer high-water period.
Electronic Publication 相似文献
954.
Vidal Javier Marcé Rafael Serra Teresa Colomer Jordi Rueda Francisco Casamitjana Xavier 《Aquatic Sciences - Research Across Boundaries》2012,74(2):315-327
The local response of the phytoplankton community to river inflow processes was investigated with modeling and field analyses
in a long and narrow, stratified reservoir in mid-summer. The river water had high concentrations of phosphorus and nitrogen
(ammonium and nitrate) and temperature had large variations at diurnal scales. As a consequence of the large variation in
river temperature, the level of neutral buoyancy (the depth where the river water spreads laterally in the reservoir) oscillated
between the surface (overflows) during the day, and the depth of the metalimnion (interflows) during the night. The reservoir
remained strongly stratified, which favoured the presence of cyanobacteria. It is shown that under these conditions, nutrient-rich
river water injected during overflows into the surface layers promoted the occurrence of localized algal blooms in the zones
where the overflow mixed with the quiescent water of the reservoir. A series of hydrodynamic simulations of the reservoir
were conducted both with synthetic and realistic forcing to assess the importance of river temperatures and wind-driven hydrodynamics
for algal blooms. The simulations confirmed that the river inflow was the main forcing mechanism generating the localized
bloom. 相似文献
955.
Natural groundwater recharge is inherently difficult to quantify and predict, largely because it comprises a series of processes that are spatially distributed and temporally variable. Infiltration ponds used for managed aquifer recharge (MAR) provide an opportunity to quantify recharge processes across multiple scales under semi-controlled conditions. We instrumented a 3-ha MAR infiltration pond to measure and compare infiltration patterns determined using whole-pond and point-specific methods. Whole-pond infiltration was determined by closing a transient water budget (accounting for inputs, outputs, and changes in storage), whereas point-specific infiltration rates were determined using heat as a tracer and time series analysis at eight locations in the base of the pond. Whole-pond infiltration, normalized for wetted area, rose rapidly to more than 1.0 m/d at the start of MAR operations (increasing as pond stage rose), was sustained at high rates for the next 40 d, and then decreased to less than 0.1 m/d by the end of the recharge season. Point-specific infiltration rates indicated high spatial and temporal variability, with the mean of measured values generally being lower than rates indicated by whole-pond calculations. Colocated measurements of head gradients within saturated soils below the pond were combined with infiltration rates to calculate soil hydraulic conductivity. Observations indicate a brief period of increasing saturated hydraulic conductivity, followed by a decrease of one to two orders of magnitude during the next 50 to 75 d. Locations indicating the most rapid infiltration shifted laterally during MAR operation, and we suggest that infiltration may function as a "variable source area" processes, conceptually similar to catchment runoff. 相似文献
956.
The influence of trace metal pollution on the community structure of soft bottom molluscs was investigated in intertidal areas of the Dar es Salaam coast. Significant enrichment of As, Mn, Mo, Sb, and Zn in sediments was recorded. Redundancy analysis indicated that trace metal pollution contributed 68% of the variation in community structure. Monte Carlo permutation test showed that As and Sb contributed significantly to variation in species composition. T-value biplots and van Dobben circles showed that the gastropods Acteon fortis, Assiminea ovata, and Littoraria aberrans, were negatively affected by As and Sb, while the bivalve Semele radiata and the gastropod Conus litteratus were only negatively affected by As. Bioaccumulation of As, Cd, Cu, Mo and Zn occurred in the bivalve Mactra ovalina and the gastropod Polinices mammilla. This calls for regular monitoring and management measures. 相似文献
957.
Metazooplankton communities in the Ahe atoll lagoon (Tuamotu Archipelago, French Polynesia): Spatiotemporal variations and trophic relationships 总被引:1,自引:0,他引:1
Pagano M Sagarra PB Champalbert G Bouvy M Dupuy C Thomas Y Charpy L 《Marine pollution bulletin》2012,65(10-12):538-548
Metazooplankton abundance, biomass (<80μm, 200-500μm and >500μm) and community structure in the Ahe atoll were studied together with their relationships with environmental factors (temperature, salinity, wind) and trophic factors (phytoplankton, bacteria, heterotrophic nanoflagellates (HNF) and ciliates) during three periods in 2008-2009. Meroplankton, mainly bivalve and gastropod larvae, was dominant. Holoplankton was dominated by copepods, the main species being Oithona spp., Paracalanus parvus, Clausocalanus spp., Corycaeus spp., Acartia fossae and Undinula vulgaris. The results suggest a clear wind influence on the structure and horizontal distribution of the zooplankton communities. The metazooplankton appeared to be controlled mainly by food resources, suggesting a bottom-up control. The low nanophytoplankton biomass in contrast to the high abundance of picophytoplankton, HNF and nano-particle grazers (mainly Oithona spp., Paracalanus and bivalve larvae) highlighted the importance of the microbial loop in the food web. 相似文献
958.
Lieven Naudts Oleg Khlystov Nick Granin Alexander Chensky Jeffrey Poort Marc De Batist 《Geo-Marine Letters》2012,32(5-6):395-406
The distribution and origin of shallow gas seeps in the vicinity of the Posolsky Bank in Lake Baikal were studied based on the integration of detailed seismic, multibeam, and hydro-acoustic water-column investigations. In all, 65 acoustic flares have been detected on the Posolsky Fault scarp near the crest of the bank and in a similar, nearby setting at water depths of ?43 to ?332?m. The seismic data reveal BSRs (bottom-simulating reflectors) occurring up to water depths of ?300?m. Calculations involving hydrate stability, heat flow, and topographic modulation based on BSR occurrence and multibeam bathymetry enabled prediction of a methane–ethane gas mixture and heat-flow values that would account for gas hydrate stability in the lake sediments under prevailing ambient conditions. These predictions are supported by ground truth data. The findings suggest that seeps concentrated along the crest of the Posolsky Bank are fed mainly by gas coming from below the base of the gas hydrate stability zone, which would migrate updip via permeable stratigraphic pathways beneath the bank. Gas would ultimately be released into the water column where these pathways are cut off by faults. Figure
Conceptual seep model for the Posolsky Bank, Lake Baikal 相似文献
959.
960.
Florent Renaud Michel Warnau François Oberhänsli Jean-Louis Teyssié Ali Temara Claude Rouleau Marc Metian 《Marine pollution bulletin》2014
Uptake and depuration kinetics of dissolved [14C]C12-6-linear alkylbenzene sulfonate (LAS) were determined in the shrimp Palaemonetes varians using environmentally relevant exposure concentration. The shrimp concentrated LAS from seawater with a mean BCF value of 120 L kg−1 after a 7-day exposure. Uptake biokinetics were best described by a saturation model, with an estimated BCFss, of 159 ± 34 L kg−1, reached after 11.5 days. Shrimp weight influenced significantly BCF value with smaller individuals presenting higher affinity to LAS. To the light of a whole body autoradiography, major accumulation of LAS occurred in the cephalothorax circulatory system (gills, heart, hepatopancreas) and ocular peduncle, but not in the flesh, limiting potential transfer to human consumers. LAS depuration rate constant value of the shrimp was 1.18 ± 0.08 d−1 leading to less than 1% of remaining LAS in its tissues after 8 days of depuration. 相似文献