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61.
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
62.
63.
Influence of bioturbation by the polychaete Nereis diversicolor on the structure of bacterial communities in oil contaminated coastal sediments 总被引:1,自引:0,他引:1
Cuny P Miralles G Cornet-Barthaux V Acquaviva M Stora G Grossi V Gilbert F 《Marine pollution bulletin》2007,54(4):452-459
Patterns of change in the structure of bacterial communities monitored by ribosomal intergenic spacer analysis (RISA) in oil contaminated sediments inhabited or not by the marine polychaete Nereis diversicolor were studied during 45 days under laboratory conditions. Results supported by principal component analysis showed a marked response of the bacterial communities to the oil contamination and to the presence of N. diversicolor. Phylogenetic affiliation of specific RISA bands showed that, in the contaminated sediments, the presence of the marine polychaetes favoured the development of bacteria which may play an active role in natural bioremediation processes of oil polluted environments. 相似文献
64.
Flux-Variance Method for Latent Heat and Carbon Dioxide Fluxes in Unstable Conditions 总被引:4,自引:0,他引:4
Xiaofeng Guo Hongsheng Zhang Xuhui Cai Ling Kang Tong Zhu Monique Y. Leclerc 《Boundary-Layer Meteorology》2009,131(3):363-384
Applied previously to momentum and heat fluxes, the present study extends the flux-variance method to latent heat and CO2 fluxes in unstable conditions. Scalar similarity is also examined among temperature (θ), water vapour (q), and CO2 (c). Temperature is adopted as the reference scalar, leading to two feasible strategies to estimate latent heat and CO2 fluxes: the first one relies on flux-variance similarity relations for scalars, while the second is based on the parameterization
of relative transport efficiency in terms of scalar correlation coefficient and a non-dimensional quantity. The relationship
between the θ-to-q transport efficiency (λ
θ
q
) and θ-q correlation coefficient (R
θ
q
) is used to describe the intermediate hydrological conditions. We also parameterize the θ-to-c transport efficiency (λ
θ
c
) as a function of the θ-c correlation coefficient (R
θ
c
) by introducing a new non-dimensional ratio (α). The flux-variance method is a viable technique for flux gap-filling, when turbulence measurements of wind velocity are
not available. It is worth noting that the extended method is not exempt from a correction for density effects when used for
estimating water or carbon exchange. 相似文献
65.
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
66.
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
67.
68.
69.
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
70.
Isabelle Larocque-Tobler Roberto Quinlan Monique M. Stewart Martin Grosjean 《Quaternary Science Reviews》2011,30(13-14):1770-1779
Chironomids (non-biting midges) can provide accurate climate reconstructions from the Late Glacial to the present. Until now, anoxic lakes have been avoided for temperature reconstructions since chironomid assemblages are sensitive to changes in oxygen concentrations in the hypolimnion. However, anoxic lakes may have varved sediments, providing the possibility for near-annual climate reconstructions. Here, we tested the applicability of two calibration methods to reconstruct mean July air temperatures from chironomid assemblages preserved in the sediments of the anoxic Seebergsee located in the northern Swiss Alps: a calibration-in-space approach and a calibration-in-time approach. The calibration-in-space approach (i.e. chironomid assemblages from surficial lake sediments (0–1 cm) calibrated against meteorological data) provided accurate inferences (i.e. similar temperature changes as measured at the closest meteorological station, and at regional stations) in the Seebergsee stratigraphy until anoxia increased in the lake. With the increase of anoxia, the chironomid-inferred temperatures were generally colder than measured temperatures. A calibration-in-time approach (i.e. calibration of chironomid assemblages in a time series against instrumental data from the closest meteorological station) provided accurate reconstructions (i.e. similar to the regional records) for the past 100 years, including the time period of inferred anoxia. However, its applicability should be further tested on longer temporal scales. 相似文献