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91.
92.
Christian M. Boily Jean-Julien Fleck Ariane Lançon Florent Renaud 《Astrophysics and Space Science》2009,324(2-4):265-269
We point out a strong time evolution of the mass-to-light conversion factor, η, commonly used to estimate masses of unresolved star clusters from observed cluster spectrophotometric measures. We present a series of gas-dynamical models, coupled with the Cambridge stellar evolution tracks, to compute line-of-sight velocity dispersions and half-light radii weighted by the luminosity. We explore a range of initial conditions, varying in turn the cluster mass and/or density, and the stellar population’s initial mass function. We find that η, and hence the estimated cluster mass, may increase by as much as a factor of three over time-scales of 50 million yr. We apply these results to an hypothetic cluster mass distribution function (d.f.), and show that the d.f. shape may be strongly affected at the low-mass end by this effect. Fitting truncated isothermal (Michie–King) models to the projected light profile leads to over-estimates of the concentration parameter, c, of δ c≈0.3 compared to the same functional fit applied to the projected mass density. 相似文献
93.
94.
Baptiste Mourre Pierre De Mey Yves Ménard Florent Lyard Christian Le Provost 《Ocean Dynamics》2006,56(5-6):473-486
We evaluate in this paper the ability of several altimeter systems, considered separately as well as together with tide gauges,
to control the time evolution of a barotropic model of the North Sea shelf. This evaluation is performed in the framework
of the particular model errors due to uncertainties in bathymetry. An Ensemble Kalman Filter (EnKF) data assimilation approach
is adopted, and observing-systems simulation experiments (OSSEs) are carried out using ensemble spread statistics. The skill
criterion for the comparison of observing networks is, therefore, not based on the misfit between two simulations, as done
in classic twin experiments, but on the reduction of ensemble variance occurring as a consequence of the assimilation. Future
altimeter systems, such as the Wide Swath Ocean Altimeter (WSOA) and satellite constellations, are considered in this work.
A single WSOA exhibits, for instance, similar performance as two-nadir satellites in terms of sea-level correction, and is
better than three satellites in terms of model velocity control. Generally speaking, the temporal resolution of observations
is shown to be of major importance for controlling the model error in these experiments. This result is clearly related to
the focus adopted in this study on the specific high-frequency response of the ocean to meteorological forcing. Altimeter
systems lack adequate temporal sampling for properly correcting the major part of model error in this context, whereas tide
gauges, which provide a much finer time resolution, lead to better global statistical performance. When looking into further
detail, tide gauges and altimetry are demonstrated to exhibit an interesting complementary character over the whole shelf,
as tide gauge networks make it possible to properly control model error in a ∼100-km coastal band, while high-resolution altimeter
systems are more efficient farther from the coast. 相似文献
95.
Late Cenozoic geodynamic evolution of eastern Indonesia 总被引:2,自引:0,他引:2
Florent Hinschberger Jacques-Andr Malod Jean-Pierre Rhault Michel Villeneuve Jean-Yves Royer Safri Burhanuddin 《Tectonophysics》2005,404(1-2):91-118
This paper presents an internally and globally consistent model of plate evolution in eastern Indonesia from Middle Miocene to Present time. It is centered on the Banda Sea region located in the triple junction area between the Pacific–Philippine, Australia and South–East Asia plates. The geological and geophysical data available from Indonesia were until recently insufficient to define a unique plate tectonic model. In this paper, the new data taken into account clearly restrict the possible interpretations. Owing to a great number of geological, geophysical and geochemical studies, the major plate boundaries (the Sunda–Banda subduction zone to the south, the Tarera–Aiduna Fault zone and the Seram Thrust to the east, and the Sorong Fault zone and Molucca Sea collision zone to the north) are now clearly identified. The age of the major tectonic structures is also better known. Geodetic measurements well constrain the Present time plate kinematics. We also consider the deformation history within eastern Indonesia, where numerous short-lived microplates and their related microcontinents successively accreted to the Asiatic margin. Moreover, magnetic anomalies identification of the North and South Banda Sea basins allows a precise kinematic reconstruction of the back-arc opening. We used the Plates software to test the coherency of our model, presented as a series of 4 plate reconstruction maps from 13 Ma to the present. Finally, the origin of oceanic domains restored by our reconstruction is discussed. 相似文献
96.
We propose a process for calculating water vapor absorption in solar radiation transmission through the atmosphere, in order to rebuild a true solar line profile, blended with telluric lines, with very good accuracy. First, we calculated a transmission profile using a spectroscopic data base. We then deduced the corrected line parameters by comparing the computed and observed profiles. An iterative method was applied to a solar spectral region around 1083 nm recorded at Kitt Peak. We showed that a relatively good fit may be obtained using an approximate atmospheric model and a simplifying assumption whereby all atmospheric, instrumental, and spectroscopic uncertainties are artificially assigned to the line parameters. 相似文献
97.
Tree Species Composition in European Pristine Forests: Comparison of Stand Data to Model Predictions 总被引:1,自引:0,他引:1
Franz-W. Badeck Heike Lischke Harald Bugmann Thomas Hickler Karl Hönninger Petra Lasch Manfred J. Lexer Florent Mouillot Jörg Schaber Benjamin Smith 《Climatic change》2001,51(3-4):307-347
The degree of general applicability across Europe currently achieved with several forest succession models is assessed, data needs and steps for further model development are identified and the role physiology based models can play in this process is evaluated. To this end, six forest succession models (DISCFORM, ForClim, FORSKA-M, GUESS, PICUS v1.2, SIERRA) are applied to simulate stand structure and species composition at 5 European pristine forest sites in different climatic regions. The models are initialized with site-specific soil information and driven with climate data from nearby weather stations. Predicted species composition and stand structure are compared to inventory data. Similarity and dissimilarity in the model results under current climatic conditions as well as the predicted responses to six climate change scenarios are discussed. All models produce good results in the prediction of the right tree functional types. In about half the cases, the dominating species are predicted correctly under the current climate. Where deviations occur, they often represent a shift of the species spectrum towards more drought tolerant species. Results for climate change scenarios indicate temperature driven changes in the alpine elevational vegetation belts at humid sites and a high sensitivity of forest composition and biomass of boreal and temperate deciduous forests to changes in precipitation as mediated by summer drought. Restricted generality of the models is found insofar as models originally developed for alpine conditions clearly perform better at alpine sites than at boreal sites, and vice versa. We conclude that both the models and the input data need to be improved before the models can be used for a robust evaluation of forest dynamics under climate change scenarios across Europe. Recommendations for model improvements, further model testing and the use of physiology based succession models are made. 相似文献
98.
Van Ngoc Pham Danièle Boyer Jean-Louis Le Mouël Thi Kim Thoa Nguyen 《Comptes Rendus Geoscience》2002,334(10):733-740
In the Mekong Delta (South Vietnam), the agglomeration of Ho-Chi-Minh (HCM) City, with more than 5 million inhabitants, is confronted with a dramatic shortage of fresh water supply because of the pollution of several aquifers at different depths. The electric tomography, obtained by concurrent inversion of two complementary geoelectrical methods, the Vertical Electrical Sounding (VES) and the Magneto-Telluric Sounding (MTS), turned out to be very efficient to provide a complete electrical image of the underground from the surface until about 800 m depth. This methodology constitutes a very cheap guide for the evaluation of the quality of the groundwater resources in the vast alluvial plain of the Mekong Delta. To cite this article: V.N. Pham et al., C. R. Geoscience 334 (2002) 733–740. 相似文献
99.
100.
In an attempt to more fully understand the dissolved inorganic nitrogen dynamics of the Neuse River estuary, 15NH4 + and 15NO3 ? uptake rates were measured and daily depth-integrated rates calculated for seven stations distributed along the salinity gradient. Measurements were made at 2–3-wk intervals from March 1985 to February 1989. Significant dark NH4 + uptake occurred and varied both spatially and seasonally, accounting for as much as 95% of light uptake with the median being 33%. Apparent NH4 + uptake ranged from 0.001 μmol N 1?1 h?1 to 4.2 μmol N 1?1 h?1, with highest rates occurring during late summer-fall in the oligohaline estuary. Apparent NH4 + uptake was significantly related to NH4 + concentration (p<0.01); however, the regression explained <3% of the variation. Daily-integrated NH4 + uptake ranged from 0.1 mmol N m?2 d?1 to 133 mmol N m?2 d?1 and followed the trend of apparent uptake. Annual NH4 + uptake of the estuary was significantly lower in 1988 than for any other year. Dark uptake of NO3 ? was only 14% of maximum light uptake. Apparent NO3 ? uptake rates ranged from 0.001 μmol N 1?1 h?1 to 1.84 μmol N 1?1 h?1 with highest rates occurring in the oligohaline estuary. Apparent NO3 ? uptake was significantly related to NO3 ? concentration (p<0.01); however, the regression explained <5% of the variation. In general, NO3 ? uptake was only 20% of total dissolved inorganic nitrogen (DIN) uptake. Daily-integrated NO3 ? uptake ranged from 0.1 mmol N m?2 d?1 to 53 mmol N m?2 d?1 and followed similar patterns of apparent uptake. Annual NH4 + uptake was 11.39 mol N m?2 yr?1, 10.28 mol N m?2 Yr?1, 10.93 mol N m?2 yr?1, and 7.38 mol N m?2 yr?1, and 1.84 mol N m?2 yr?1, with the 4-yr mean being 10.0. Annual NO3 ? uptake was 3.12 mol N m?2 yr?1, 3.40 mol N m?2 yr?1, 1.96 mol N m?2 yr?1, and 1.84 mol N m?2 yr?1, with the 4-yr mean being 2.6. The total annual DIN uptake was more than twice published estimates of phytoplankton DIN demand, indicating that there is an important heterotrophic component of DIN uptake occurring in the water column. The extrapolation of nitrogen demand from primary productivity results in serious underestimates of estuarine nitrogen demand for the Neuse River estuary and may be true for other estuaries as well. 相似文献