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121.
A Robust Set-Inversion via Interval Analysis method in a bounded-error framework is used to compute three-dimensional location zones in real time, at a given confidence
level. This approach differs significantly from the usual Gaussian error model paradigm, since the satellite positions and
the pseudorange measurements are represented by intervals encompassing the true value with a particular level of confidence.
The method computes a location zone recursively, using contractions and bisections of an arbitrarily large initial location
box. Such an approach can also handle an arbitrary number of erroneous measurements using a q-relaxed solver and allows the integration of geographic and cartographic information such as digital elevation models or
three-dimensional maps. With enough data redundancy, inconsistent measurements can be detected and even rejected. The integrity
risk of the location zone comes only from the measurement bounds settings, since the solver is guaranteed. A method for setting
these bounds for a particular location zone confidence level is proposed. An experimental validation using real L1 code measurements
and a digital elevation model is also reported in order to illustrate the performance of the method on real data. 相似文献
122.
ARGO hydrographic profiles, two hydrographic transects and satellite measurements of air–sea exchange parameters were used
to characterize the properties and seasonal heat budget variations of the Surface Mixed Layer (SML) south of Africa. The analysis
distinguishes the Subtropical domain (STZ) and the Subantarctic Zone (SAZ), Polar Frontal Zone (PFZ) and Antarctic Zone (AZ)
of the Antarctic Circumpolar Current. While no Subantarctic Mode Water forms in that region, occurrences of deep SML (up to
∼450 m) are observed in the SAZ in anticyclones detached from the Agulhas Current retroflection or Agulhas Return Current.
These are present latitudinally throughout the SAZ, but preferentially at longitudes 10–20° E where, according to previous
results, the Subtropical Front is interrupted. Likely owing to this exchange window and to transfers at the Subantarctic Front
also enhanced by the anticyclones, the SAZ shows a wide range of properties largely encroaching upon those of the neighbouring
domains. Heat budget computations in each zone reveal significant meridional changes of regime. While air–sea heat fluxes
dictate the heat budget seasonal variability everywhere, heat is mostly brought through lateral geostrophic advection by the
Agulhas Current in the STZ, through lateral diffusion in the SAZ and through air–sea fluxes in the PFZ and AZ. The cooling
contributions are by Ekman advection everywhere, lateral diffusion in the STZ (also favoured by the ∼10° breach in the Subtropical
Front) and geostrophic advection in the SAZ. The latter likely reflects an eastward draining of water warmed through mixing
of the subtropical eddies. 相似文献
123.
Jenny A. U. Nilsson Srdjan Dobricic Nadia Pinardi Vincent Taillandier Pierre-Marie Poulain 《Ocean Dynamics》2011,61(10):1475-1490
The Mediterranean Forecasting System (MFS) has been operational for a decade, and is continuously providing forecasts and
analyses for the region. These forecasts comprise local- and basin-scale information of the environmental state of the sea
and can be useful for tracking oil spills and supporting search-and-rescue missions. Data assimilation is a widely used method
to improve the forecast skill of operational models and, in this study, the three-dimensional variational (OceanVar) scheme
has been extended to include Argo float trajectories, with the objective of constraining and ameliorating the numerical output
primarily in terms of the intermediate velocity fields at 350 m depth. When adding new datasets, it is furthermore crucial
to ensure that the extended OceanVar scheme does not decrease the performance of the assimilation of other observations, e.g.,
sea-level anomalies, temperature, and salinity. Numerical experiments were undertaken for a 3-year period (2005–2007), and
it was concluded that the Argo float trajectory assimilation improves the quality of the forecasted trajectories with ~15%,
thus, increasing the realism of the model. Furthermore, the MFS proved to maintain the forecast quality of the sea-surface
height and mass fields after the extended assimilation scheme had been introduced. A comparison between the modeled velocity
fields and independent surface drifter observations suggested that assimilating trajectories at intermediate depth could yield
improved forecasts of the upper ocean currents. 相似文献
124.
David Washington Daniel Rodriguez Vincent Ogunro 《Geotechnical and Geological Engineering》2011,29(1):13-17
The monitoring operation of an older impoundment (such as dams and waste barrier materials) during the service life of the
structure cannot be overemphasized. Since older infrastructures seem to be more susceptible to piping and seepage failure,
their construction design should be analyzed and monitored at places where a potential problem could occur. Once an impoundment
is constructed without adequate filters layers and foundation treatments, then the prevention of piping or seepage may require
an effective approach to constructing a cut-off wall to prevent eventual failure. In order to identify and understand theses
failure modes, it is important to identify the physical parameters of the impoundment system, such as the zones of various
soil gradations, the compaction of these zones, the hydraulic conductivity, the compatibility of the soil formations within
and beneath the core or liner, as well as the cohesive and dispersive properties of soils at various location within the structure.
Once these parameters are known and quantified, an adequate assessment of the structure’s susceptibility to piping or contaminant
transport can be established. This type of an analysis will enable the proper design of a cut-off wall and predetermine the
effectiveness of its long-term performance. The Vermont Waterbury Dam (built in 1938) is example of seepage related problem
that implemented a cut-off wall design to prevent piping paths from undermining the structure. In this case, some forensic
sampling had to be performed and the parameters of the soils as just mentioned were key factors in determining the wall design.
In this paper, the Waterbury dam rehabilitation is investigated as case studies, in order to better understand how older designs
and poor construction of impoundments can lead to piping condition in dams as well as failures in waste barrier systems. The
Secant Cut-off wall (constructed at Waterbury Dam) is mentioned as a corrective measure taken for this dam and there is a
brief discussion as to how this construction rehabilitation technique can be applied to waste barrier impoundments. 相似文献
125.
Natesan Usha Rajalakshmi P. R. Ramana Murthy M. V. Ferrer Vincent A. 《Natural Hazards》2013,69(3):1751-1766
Natural Hazards - Data from satellites are invaluable for applications including long-term climate studies and engineering design. Most present applications of wind-wave research for coastal... 相似文献
126.
K. Deepthi Usha Natesan A. L. Muthulakshmi Vincent A. Ferrer V. P. Venugopalan S. V. Narasimhan 《Environmental Earth Sciences》2013,69(7):2357-2364
Sediments from Kalpakkam, southeast coast of India were geochemically analyzed to document the provenance, tectonic setting, and role of chemical weathering. The sediments are dominated by quartz (Si), and the higher concentration of Si suggests the presence of quartz (±feldspar) dominated terrigenous sands. The study demonstrates that the sediments are derived from the granitic to gneissic or from a sedimentary source. Beach sediments are deposited in a passive continental margin setting and seabed sediments are deposited in active continental margin. In the A–CN–K diagram, most of the samples fall in the lower part, i.e., below the plagioclase feldspar joint which indicates a low degree of alteration. Only S6 falls just above the plagioclase feldspar joint, close to the AK boundary suggesting a slightly advanced weathering of sediment and source. Beach and seabed sediments lie close to CNK and FM region suggesting the presence of ferromagnesian minerals (likely to be pyroxene) except S6 which falls in the inner triangle of the minerals feldspar, garnet, and biotite in A-CNK-FM diagram. Both CIA and CIW values depict the unweathered nature of the sediments under humid to semi-humid climatic conditions. 相似文献
127.
D. A. Holdsworth Rupa Vuthaluru Iain M. Reid Robert A. Vincent 《Journal of Atmospheric and Solar》2002,64(18)
The differential absorption experiment (DAE) was first proposed in the 1950s for the estimation of mesospheric and lower thermospheric electron density using MF/HF radars. The technique was used extensively until the late 1970s, when interest in the technique declined, due to experimental limitations and questions regarding the assumptions of the technique. This paper describes the application of the DAE within the online observations of the Buckland Park MF (BPMF) radar. The experimental limitations of the technique for the BPMF radar are discussed, with particular attention paid to effects of complex gain differences between receiving channels used to decompose the linearly received signals into circular components. Hourly and monthly averaged midday DAE electron densities are presented, revealing good agreement with IRI model estimates. Monthly averaged midnight DAE electron densities are also presented, revealing good qualitative agreement with the IRI model estimates. 相似文献
128.
Multivariate statistical analysis of geochemical data as indicative of the hydrogeochemical evolution of groundwater in a sedimentary rock aquifer system 总被引:15,自引:0,他引:15
Vincent Cloutier Ren Lefebvre Ren Therrien Martine M. Savard 《Journal of Hydrology》2008,353(3-4):294-313
The study of groundwater hydrogeochemistry of the Paleozoic Basses-Laurentides sedimentary rock aquifer system in Québec produced a large geochemical dataset. Groundwater samples were collected at 153 sites over a 1500 km2 study area and analyzed for major and minor ions. The large number of data can lead to difficulties in the integration, interpretation and representation of the results. Two multivariate statistical methods, hierarchical cluster analysis (HCA) and principal components analysis (PCA), were applied to a subgroup of the dataset to evaluate their usefulness to classify the groundwater samples, and to identify geochemical processes controlling groundwater geochemistry. This subgroup consisted of 144 samples and 14 parameters (Ca2+, Mg2+, Na+, K+, , Cl−, , Fe2+, Mn2+, Br−, Sr2+, F−, Ba2+, HS−). Seven geochemically distinct clusters, C1–C7, resulted from the HCA. Samples from clusters C3, C4, C6 and C7 are mostly located in preferential recharge areas. The majority of these samples have Ca–Mg–HCO3 recharge groundwater (C3, C6, C7) and Na–HCO3 evolved groundwater (C4). Samples from the other three clusters (C1, C2, C5) are characteristic of an aquifer system under confined conditions. The majority of these samples have Na–HCO3 evolved groundwater (C1, C5) and Na–Cl ancient groundwater that exhibits elevated concentrations in Br− (C2). In addition to recognizing the importance of hydrogeological conditions on groundwater geochemistry, the distribution of clusters also showed the importance of the geological formations on minor and trace elements, such as Fe2+, Mn2+, Sr2+, F− and Ba2+. The first five components of the PCA account for 78.3% of the total variance in the dataset. Component 1 is defined by highly positive loadings in Na+, Cl− and Br− and is related to groundwater mixing with Champlain Sea water and solute diffusion from the marine clay aquitard. The high positive loadings in Ca2+ and Mg2+ of component 2 suggest the importance of dissolution of carbonate rocks in this aquifer system. From their characteristic loadings, the first two components are defined as the “salinity” and “hardness” components, respectively. Components 3–5 are related to more local and geological effects. The integration of the HCA and the PCA, with conventional classification of groundwater types, as well as with the hydrogeological and geological contexts, allowed the division of the region into four main geochemical areas, providing an improved regional picture of the aquifer system dynamics and hydrogeochemical evolution of groundwater. The following factors were recognized as influencing the evolution of groundwater identified in every geochemical area: (1) geological characteristics including sedimentary rock type and till mineralogy; (2) hydrogeological characteristics represented by the level of confinement and the hydraulic gradient; and (3) the geological history including the latest glaciation and the Champlain Sea invasion. With its integrated approach, this hydrogeochemical study contributes to the characterization and understanding of complex groundwater flow systems, and provides an example of the long-term geochemical evolution of hydrogeological systems after a major perturbation, in this case seawater invasion. 相似文献
129.
130.
Bethany N. Deshpande Roxane Tremblay Reinhard Pienitz Warwick F. Vincent 《Journal of Paleolimnology》2014,52(3):171-184
Lac Saint-Augustin is an urban lake located on the outskirts of Quebec City, one of North America’s oldest cities. Anthropogenic inputs from land clearing, agriculture, highway development and urbanization in the surrounding catchment have resulted in strong impacts on the limnology of the lake throughout the past three centuries. In recent years, this lake has experienced severe eutrophication, including persistent cyanobacterial blooms. In winter 2011, a sediment core was extracted from the deepest area of the lake. A detailed paleopigment analysis was used to assess eutrophication processes in the lake and to determine the timing and appearance of cyanobacterial blooms and their subsequent variability. Extracted chlorophyll a, its degradation products and 11 carotenoid pigments were identified and quantified via reverse-phase high performance liquid chromatography to examine relative changes in the phytoplankton. The results revealed large variations in the phytoplankton community structure of Lac Saint-Augustin over the past 356 years. Chlorophyll a concentrations per unit organic matter (OM) increased significantly from the base of the core to present day, rising more than 15-fold from 18.4 µg (g OM)?1 at the base of the core to 287 µg (g OM)?1 in the most recent strata. Biostratigraphical analysis revealed three major periods of enrichment, with episodes of cyanobacterial abundance from the 1890s onwards. The greatest changes occurred in the most recent period (from the 1960s to the present) relative to earlier periods, with pigment increases for all phytoplankton groups. The cyanobacterial pigments canthaxanthin, echinenone and zeaxanthin (also a marker for green algae) showed concentrations in the surface sediments that were significantly above values at the bottom of the core, and these differences were large, even giving consideration to the lesser pigment degradation near the surface. Overall, the results indicate that cyanobacterial blooms are not a recent feature of Lac Saint-Augustin but began to occur soon after catchment modification 150 years ago. The pigment records also imply that cyanobacterial and associated algal populations have risen to unprecedented levels over the last few decades of ongoing development of the Lac Saint-Augustin catchment. This study highlights the utility of multiple pigment analysis of lake sediments for identifying the timing and magnitude of anthropogenic impacts. 相似文献