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61.
A Simple Method of Estimating Scalar Fluxes Over Forests 总被引:1,自引:0,他引:1
Nelson Luis Dias Jinkyu Hong Monique Y. Leclerc T. Andrew Black Z. Nesic P. Krishnan 《Boundary-Layer Meteorology》2009,132(3):401-414
A simple aerodynamic-variance method is proposed to fill gaps in continuous CO2 flux measurements in rainy conditions, when open-path analysers do not function. The method requires turbulent conditions
(friction velocity greater than 0.1 ms–1), and uses measurements of mean wind speed, and standard deviations of temperature and CO2 concentration fluctuations to complement, and at times replace, eddy-covariance measurements of friction velocity, sensible
heat flux and CO2 flux. Friction velocity is estimated from the mean wind speed with a flux-gradient relationship modified for the roughness
sublayer. Since normalised standard deviations do not follow Monin-Obukhov similarity theory in the roughness sublayer, a
simple classification scheme according to the scalar turbulence scale was used. This scheme is shown to produce sensible heat
and CO2 flux estimates that are well correlated with the measured values. 相似文献
62.
Seventy-five species and lower taxonomic units of rotifers have been identified in Lake Geneva (= lac Léman); seven species and one form are new for the lake. When using indicators of trophic conditions, the qualitative composition of the biocenosis is still dominated by oligo-mesotrophic lake indicators, mixed with eutrophic and oligotrophic ones. However the rotifer biocenosis has not yet reached a steady state. 相似文献
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La présente étude a pour objectif d’analyser la variabilité spatiale multi-échelles de l’équivalent en eau de la neige (EEN). Dans un premier temps, la variabilité spatiale de l’EEN par rapport à la latitude et à la longitude a été analysée. Des indices locaux ont été utilisés pour caractériser les différentes structures spatiales. Par la suite, les structures spatiales homogènes ont été délimitées à l’aide de l’approche de segmentation spatiale multi-résolutions en utilisant des méta-variables physiographiques. La segmentation a été validée à l’aide du test non paramétrique de Kruskal-Wallis appliqué aux données de l’EEN de chaque paire de zones adjacentes. À l’échelle régionale, la segmentation spatiale a permis d’identifier six zones géographiques différenciées par leur position par rapport aux modes de circulations atmosphériques et la disposition du relief. À l’échelle locale, la segmentation spatiale montre le rôle de la pente, de la courbure, etc. dans la variabilité spatiale du couvert nival.
Editeur Z. W. Kundzewicz; Editeur associé E. Gargouri 相似文献
67.
Monique Y. Leclerc Peter H. Schuepp George W. Thurtell 《Boundary-Layer Meteorology》1986,34(4):399-410
This paper reports on forced-convection mass transfer from isolated discs on rectangular plates as well as hemispheres on realistic fluttering leaves. An electrochemical method was used where the convective transfer of ions to the test electrode (the droplet or the wet spot) in an electrolytic flow system was measured as a function of flow rates, sizes of discs and hemispheres. Measurements showed that the local transfer coefficient for uniformly transferring plates varied as expected while the transfer from isolated discs on plates was much less a function of the distance from the leading edge. An expression to describe the transfer coefficient for an isolated disc as a function of distance from the leading edge was determined. An expression describing the transfer from hemispherical drops on fluttering leaves was derived and compared with the predictions from transfer theory for a sphere in free space. 相似文献
68.
The turbulence field obtained using a large-eddy simulation model is used to simulate particle dispersion in the convective
boundary layer with both forward-in-time and backward-in-time modes. A Lagrangian stochastic model is used to treat subgrid-scale
turbulence. Results of forward dispersion match both laboratory experiments and previous numerical studies for different release
heights in the convective boundary layer. Results obtained from backward dispersion show obvious asymmetry when directly compared
to results from forward dispersion. However, a direct comparison of forward and backward dispersion has no apparent physical
meaning and might be misleading. Results of backward dispersion can be interpreted as three-dimensional or generalized concentration
footprints, which indicate that sources in the entire boundary layer, not only sources at the surface, may influence a concentration
measurement at a point. Footprints at four source heights in the convective boundary layer corresponding to four receptors
are derived using forward and backward dispersion methods. The agreement among footprints derived with forward and backward
methods illustrates the equivalence between both approaches. The paper shows explicitly that Lagrangian simulations can yield
identical footprints using forward and backward methods in horizontally homogeneous turbulence. 相似文献
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