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131.
Some numerical urban boundary-layer studies 总被引:2,自引:0,他引:2
Two types of models, describing respectively the thermal and the dynamic structure of the urban boundary layer are presented. The influence of density and height of urban buildings, urban traffic, man-made heat flux, changes of albedo and existence of an aerosol layer are tested. The models give a possibility of explaining the influence of selected factors on the atmospheric state over an urban area.On sabbatical at Meteorological Department, University Uppsala, Sweden. 相似文献
132.
133.
Zbigniew Sorbjan 《Boundary-Layer Meteorology》1997,82(3):503-517
Results of a large-eddy simulation of a decaying convective mixed layer over land are presented. The time evolution of the mixed layer is forced by the surface heat flux gradually decreasing with time. The results obtained show that the decay of the turbulent kinetic energy is governed by two scales, the external time scale controlling the surface heat flux changes, and the convective time scale. During the simulation, large eddies persist even when the heat flux at the surface becomes negative. A decoupled residual layer of active turbulence is developed above the stable surface layer. The residual layer is marked by large-scale updrafts that are able to penetrate the capping inversion layer and induce entrainment. 相似文献
134.
Anna Worobiec E. Anna Stefaniak Sanja Potgieter-Vermaak Zbigniew Sawlowicz Zoya Spolnik René Van Grieken 《Applied Geochemistry》2007
The effectiveness of electrostatic separation of zircon and TiO2 phases during the processing of heavy mineral concentrates derived from heavy mineral sands depends upon the chemical, physical and mineralogical characteristics of the concentrates. Here the authors’ demonstrate the use of combined micro-Raman spectrometry (MRS), scanning electron microscopy (SEM) and computer controlled scanning electron microscopy coupled with an energy-dispersive X-ray detector (CC-SEM/EDX), followed by hierarchical cluster analysis (HCA) to determining these characteristics on samples from the non-magnetic fraction of the Richards Bay (South Africa) heavy mineral concentrate. All samples were found to be predominately comprised a heterogeneous population of grains of zircon and rutile and other TiO2 polymorphs with diverse physicochemical properties. Combined MRS and CC-SEM/EDX enabled the identification of textural characteristics which impacted on the efficiency of electrostatic separation of zircon and rutile concentrate streams. 相似文献
135.
Zbigniew Sorbjan 《Boundary-Layer Meteorology》2007,123(1):143-157
Effects of wind on quasi-steady, shallow convection in the Martian boundary layer are studied using a large-eddy simulation
model. Convection in the model is generated by the radiative flux divergence and the strength of the surface heat flux, which
do not vary in time. The resulting convective boundary layer exhibits transient, irregular, horizontal cellular structures,
transported by wind, and a lack of well-pronounced regular horizontal rolls, observed for analogous conditions on Earth. The
dimensionless statistics of turbulence are generally similar to those generated in the windless conditions, and depend on
the ratio F, defined in terms of the integrated radiative and turbulent heating rates in the boundary layer. The simulations show that
variations of the radiative heating influence the temperature statistics, while their effects on the wind velocity are relatively
small. The horizontal velocity variances do not show a strong dependence on parameter F, in contrast with the vertical velocity variances, which are strongly dependent on F. 相似文献
136.
137.
While rockbursts from underground copper mining in Western Poland normally produce surface peak ground accelerations (PGA) and velocities of 0.05–0.1 g and 1–3 cm/s, occasionally these peak motions may exceed 0.15 g and 10 cm/s, respectively. These larger motions are of considerable concern and an investigation has been undertaken to define the nature of these larger induced ground motions. This paper compares these rockburst motions with low intensity earthquakes. Various strong motion parameters such as PGA, peak ground velocity (PGV) and displacements as well as strong motion duration, Arias intensity, Fourier and response spectra are compared with those from earthquakes. It is concluded that although short duration is the most obvious parameter that differentiates rockbursts from earthquakes, in fact their high dominant frequencies, which result in high PGA/PGV ratios differentiate them the most. Two types of rockburst-induced ground motions are indicated in this paper: typical—with 3–6 months return period and characteristic, high frequency content—as well as rare events similar to shallow, low intensity earthquakes. 相似文献
138.
Emília Juhsov Milan Hurk Zbigniew Zembaty 《Soil Dynamics and Earthquake Engineering》2002,22(9-12):1193-1197
The paper is devoted to the investigation of seismic response of the masonry structure and describes experiences with modelling of boundary conditions during the test of large heavy model on 6DOF shaking table. The main aim of the research was how to increase dynamic resistance capacity of old masonry buildings including the medium and strong seismic effects. The results of theoretical and numerical analyses are compared including initial forecasting calculations made before any test started. The emphasis is given to the boundary conditions reached during the excitation of the large masonry model via shaking table. Strengthening and retrofitting procedures and their effects are discussed when special fibre mortar is used for repair and strengthening of masonry parts of structure. 相似文献
139.
Anna Swiatek Iwona Stanislawska Zbigniew Zbyszynski Beata Dziak-Jankowska 《Acta Geophysica》2014,62(1):259-269
Ionosphere coverage is likely to be a driver for the EGNOS coverage area. Hence, a study considering a dedicated ionosphere algorithm to improve the ionosphere coverage area has been conducted. The logic of the study is the following: the accuracy of the GPS signal depends mainly on the total electron content (TEC). At two close points, TEC changes in time in a very similar way; these are region dependent variables. This correlation decreases with growing distance between the observation points and is anisotropic. Based on TEC variogram analysis, the specific algorithm has been developed. This specific algorithm is presented and discussed. 相似文献
140.