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111.
Nicolas Fritier Nicolas MasseiBenoit Laignel Alain DurandBastien Dieppois Julien Deloffre 《Comptes Rendus Geoscience》2012,344(8):396-405
The inter-annual to multi-decadal winter variability (DJFM) of precipitation on the Seine River watershed (France) was analysed using continuous wavelet transform analysis and compared to the winter North Atlantic Oscillation Index (NAOI). Nine weather stations were used over the 1951 to 2004 period and confirmed the homogeneity of inter-annual fluctuations for all stations but one. Wavelet coherence between SLP over the Icelandic and Azores regions and precipitation highlighted coherence for different scales of variability according to the centre of action considered. Segmentation and wavelet analysis and coherence between precipitation and NAOI over a long period of time (1873–2004) showed: i) increasing variability across the last century at most time scales, especially for NAOI; ii) the existence of change points for the mean and variance of both signals; iii) overall discontinuity of the coherence whatever the scale considered, especially between ∼1910 and ∼1955 for inter-decennial to pluri-decennial scales. 相似文献
112.
Pierre Boszczuk Li Zhen Cheng Hanafi Hammouche Patrice Roy Sylvain Lacroix Alain Cheilletz 《Journal of Applied Geophysics》2011,75(1):77-86
Two inversions, unconstrained and constrained, of a gravity survey of the Matagami mining camp (Abitibi Archaean Subprovince, Canada) have been performed in order to identify the downward extension of a rhyolitic horizon hosting VMS-type base metals deposit and the morphologies of the major felsic plutons. A comparative study exhibits the similarities between measured and calculated densities from chemical compositions of the Matagami lithologies. This allows building an initial 3D geodensity model which integrates densities and available structural and geological surface mapping data. This model is integrated during the iteration process of the constrained inversion in the objective function. The resulting true density model and two derived cross-sections upgrade the 3D imaging of this area. Also, the model gives new insight for regional geological interpretation exposing possible shapes of the main geological units at depth and suggests the potential existence of deep fertile geological bodies. 相似文献
113.
Daniele L. Pinti Catherine Béland-Otis Alain Tremblay Chris M. Hall Jean-Yves Lavoie 《Geochimica et cosmochimica acta》2011,75(15):4228-4243
Brines in Cambrian sandstones and Ordovician dolostones of the St-Lawrence Lowlands at Bécancour, Québec, Canada were sampled for analysis of all stable noble gases in order to trace their origin and migration path, in addition to quantifying their residence time. Major ion chemistry indicates that the brines are of Na-Ca-Cl type, possibly derived from halite dissolution. 87Sr/86Sr ratios and Ca excess indicate prolonged interactions with silicate rocks of the Proterozoic Grenville basement or the Cambrian Potsdam sandstone. The brines constrain a 2-3% contribution of mantle 3He and large amounts of nucleogenic 21Ne∗ and 38Ar∗ and radiogenic 4He and 40Ar∗. 4He/40Ar∗ and 21Ne∗/40Ar∗ ratios, corrected for mass fractionation during incomplete brine degassing, are identical to their production ratios in rocks. The source of salinity (halite dissolution), plus the occurrence of large amounts of 40Ar∗ in brines constrain the residence time of Bécancour brines as being older than the Cretaceous. Evaporites in the St-Lawrence Lowlands likely existed only during Devonian-Silurian time. Brines might result from infiltration of Devonian water leaching halite, penetrating into or below the deeper Cambrian-Ordovician aquifers. During the Devonian, the basin reached temperatures higher than 250 °C, allowing for thermal maturation of local gas-prone source rocks (Utica shales) and possibly facilitating the release of radiogenic 40Ar∗ into the brines. The last thermal event that could have facilitated the liberation of 40Ar∗ into fluids and contributed to mantle 3He is the Cretaceous Monteregian Hills magmatic episode. For residence times younger than the Cretaceous, it is difficult to find an appropriate source of salinity and of nucleogenic/radiogenic gases to the Bécancour brines. 相似文献
114.
Alain Genty Christophe Le Potier Stéphane Gounand 《Geotechnical and Geological Engineering》2011,29(4):537-554
Numerical simulations of the transport of radionuclide from high-level radioactive waste stored in geological repositories
often do not take into account construction defects in the repository. The potential impact of drilling and excavation deviation
from the engineer planned design is a priori considered negligible. We conducted computations on repository geometries that
contain deviations from horizontal of a few degrees. The analysis of the results shows that the impact of deviation defects
varies from 9 to 16%. A perfect control of the galleries and waste repository cell orientations is then of concern for radioactive
waste repository construction, failing which numerical simulations must be conducted on the worst geometric configuration
or margin errors added. On the other hand, if the orientation control is precise enough, a modification of the repository
design including controlled deviations from the horizontal may be of interest. 相似文献
115.
Jean-Baptiste Saulnier Alain Clément Teresa Pontes Pierpaolo Ricci 《Ocean Engineering》2011,38(1):130-147
To date the estimation of long-term wave energy production at a given deployment site has commonly been limited to a consideration of the significant wave height Hs and mean energy period Te. This paper addresses the sensitivity of power production from wave energy converters to the wave groupiness and spectral bandwidth of sea states. Linear and non-linear systems are implemented to simulate the response of converters equipped with realistic power take-off devices in real sea states. It is shown in particular that, when the converters are not much sensitive to wave directionality, the bandwidth characteristic is appropriate to complete the set of overall wave parameters describing the sea state for the purpose of estimating wave energy production. 相似文献
116.
Margaret Armstrong Aziz Ndiaye Rija Razanatsimba Alain Galli 《Mathematical Geosciences》2013,45(2):165-182
Having a large number of geostatistical simulations of a mineral or petroleum deposit provides a better idea of its upside potential and downside risk; however, large numbers of simulated realizations of a deposit may pose computational difficulties in subsequent decision-making phases. Hence, depending on the specific case, there can be a need to select a representative subset of conditionally simulated deposit realizations. This paper examines and extends an approach developed by the stochastic optimization community based on stochastic mathematical programming with recourse and is discussed here in the context of mineral deposits while it is possibly suitable for other earth science applications. The approach is based on measuring the “distance” between simulations and the introduced distance measure between simulated realizations of a mineral deposit is based on the metal above a given set of cutoff grades while a pre-existing mine design is available. The approach is tested on 100 simulations of the Walker Lake data with promising results. 相似文献
117.
Agnès Mazot Alain Bernard Tobias Fischer Salvatore Inguaggiato Igan S. Sutawidjaja 《Journal of Volcanology and Geothermal Research》2008
Papandayan is a stratovolcano situated in West Java, Indonesia. Since the last magmatic eruption in 1772, only few hydrothermal explosions have occurred. An explosive eruption occurred in November 2002 and ejected ash and altered rocks. The altered rocks show that an advanced argillic alteration took place in the hydrothermal system by interaction between acid fluids and rocks. Four zones of alteration have been defined and are limited in extension and shape along faults or across permeable structures at different levels beneath the active crater of the volcano. 相似文献
118.
Caroline Bouvet de Maisonneuve Olivier Bachmann Alain Burgisser 《Bulletin of Volcanology》2009,71(6):643-658
Silicic pumices formed during explosive volcanic eruptions are faithful recorders of the state of the magma in the conduit,
close to or at the fragmentation level. We have characterized four types of pumices from the non-welded rhyolitic Kos Plateau
Tuff, which erupted 161,000 years ago in the East Aegean Arc, Greece. The dominant type of pumice (>90 vol.%) shows highly
elongated tubular vesicles. These tube pumices occur throughout the eruption. Less common pumice types include: (1) “frothy”
pumice (highly porous with large, sub-rounded vesicles), which form 5–10 vol.% of the coarsest pyroclastic flow deposits,
(2) dominantly “microvesicular” and systematically crystal-poor pumices, which are found in early erupted, fine-grained pyroclastic
flow units, and are characterized by many small (<50 μm in diameter) vesicles and few mm-sized, irregular voids, (3) grey
or banded pumices, indicating the interaction between the rhyolite and a more mafic magma, which are found throughout the
eruption sequence and display highly irregular bubble shapes. Except for the grey-banded pumices, all three other types are
compositionally identical and were generated synchronously as they are found in the same pyroclastic units. They, therefore,
record different conditions in the volcanic conduit leading to variable bubble nucleation, growth and coalescence. A total
of 74 pumice samples have been characterized using thin section observation, SEM imagery, porosimetry, and permeametry. We
show that the four pumice types have distinct total and connected porosity, tortuosity and permeability. Grey-banded pumices
show large variations in petrophysical characteristics as a response to mingling of two different magmas. The microvesicular,
crystal-poor, pumices have a bimodal bubble size distribution, interpreted as reflecting an early heterogeneous bubble nucleation
event followed by homogeneous bubble nucleation close to fragmentation. Finally, the significant differences in porosity,
tortuosity and permeability in compositionally identical tube and frothy pumices are the result of variable shear rates in
different parts of the conduit. Differential shear rates may be the result of either: (1) pure shear, inducing a vertical
progression from frothy to tube and implying a relatively thick fragmentation zone to produce both types of pumices at the
same time or (2) localized simple shear, inducing strongly tubular vesicles along the wall and near-spherical bubbles in the
centre of the conduit and not necessarily requiring a thick fragmentation zone. 相似文献
119.
Estelle Asseo Alain Riazuelo 《Monthly notices of the Royal Astronomical Society》2000,318(4):983-1004
The properties of waves able to propagate in a relativistic pair plasma are at the basis of the interpretation of several astrophysical observations. For instance, they are invoked in relation to radio emission processes in pulsar magnetospheres and to radiation mechanisms for relativistic radio jets. In such physical environments, pair plasma particles probably have relativistic, or even ultrarelativistic, temperatures. Besides, the presence of an extremely strong magnetic field in the emission region constrains the particles to one-dimensional motion: all the charged particles strictly move along magnetic field lines.
We take anisotropic effects and relativistic effects into account by choosing one-dimensional relativistic Jűttner–Synge distribution functions to characterize the distribution of electrons and/or positrons in a relativistic, anisotropic pair plasma. The dielectric tensor, from which the dispersion relation associated with plane wave perturbations of such a pair plasma is derived, involves specific coefficients that depend on the distribution function of particles. A precise determination of these coefficients, using the relativistic one-dimensional Jűttner–Synge distribution function, allows us to obtain the appropriate dispersion relation. The properties of waves able to propagate in anisotropic relativistic pair plasmas are deduced from this dispersion relation. The conditions in which a beam and a plasma, both ultrarelativistic, may interact and trigger off a two-stream instability are obtained from this same dispersion relation. Two astrophysical applications are discussed. 相似文献
We take anisotropic effects and relativistic effects into account by choosing one-dimensional relativistic Jűttner–Synge distribution functions to characterize the distribution of electrons and/or positrons in a relativistic, anisotropic pair plasma. The dielectric tensor, from which the dispersion relation associated with plane wave perturbations of such a pair plasma is derived, involves specific coefficients that depend on the distribution function of particles. A precise determination of these coefficients, using the relativistic one-dimensional Jűttner–Synge distribution function, allows us to obtain the appropriate dispersion relation. The properties of waves able to propagate in anisotropic relativistic pair plasmas are deduced from this dispersion relation. The conditions in which a beam and a plasma, both ultrarelativistic, may interact and trigger off a two-stream instability are obtained from this same dispersion relation. Two astrophysical applications are discussed. 相似文献
120.