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1.
在对中国农村剩余劳动力现状描述的基础上 ,对剩余劳动力形成的原因进行了分析与阐述 ;结合目前形势 ,指出未来农村剩余劳动力的转移前景不容乐观 ;并在此基础上阐述了中国剩余劳动力转移途径和主要措施 相似文献
2.
Pollen collected from snow samples on the Quelccaya Ice Cap in 2000 and 2001 reveals significant interannual variability in pollen assemblage, concentration, and provenance. Samples from 2000, a La Niña year, contain high pollen concentrations and resemble samples from the Andean forests (Yungas) to the east. Samples from 2001, an El Niño year, contain fewer pollen and resemble those from the Altiplano. We suggest that varying wind patterns under different El Niño/Southern Oscillation (ENSO) conditions may affect the processes of pollen transport over the Altiplano and on the ice cap, although confounding variables such as flowering phenology and sublimation should also be considered 相似文献
3.
Analysis of village accessibility and its impact on land use dynamics in a mountainous province of northern Vietnam 总被引：5，自引：0，他引：5
Jean-Christophe Castella Pham Hung Manh Suan Pheng Kam Lorena Villano Nathalie Rachel Tronche 《Applied geography (Sevenoaks, England)》2005,25(4):308-326
Surveys carried out in mountainous areas of northern Vietnam at research sites selected across a gradient of market integration, revealed strong relationships between the location of the village with respect to the national road network and the nature of its land-use systems, its poverty level and more generally its potential for development. We developed and tested in Bac Kan province a method to give an objective and quantitative definition of accessibility over a large geographic area. Accessibility maps integrated in a provincial GIS showed that despite recent improvements to the road network, some remote areas do not benefit from recent development. 相似文献
4.
Geotechnical and Geological Engineering - Elastic constants and crack propagation stress thresholds of brittle rocks are important mechanical properties for engineering applications. However, these... 相似文献
5.
Geotechnical properties of a chemically stabilized soil from Malaysia with rice husk ash as an additive 总被引：1，自引：0，他引：1
Summary The stabilization of Malaysian soil by mixing with rice husk ash, a locally available waste material, to improve its engineering properties is described. Stabilizing agents, i.e. cement and lime, were added to produce the reaction products which are responsible for the enhancement of the engineering properties. Based on the strength development, it seems that lime is the more effective stabilizing agent. However, the cheap waste material can be used as partial replacement for the more expensive cement in the cement-treatment of the soil. A durability study was carried out to evaluate the effectiveness of this stabilization method. 相似文献
6.
Ayugi Brian Shilenje Zablon Weku Babaousmail Hassen Lim Kam Sian Kenny T. C. Mumo Richard Dike Victor Nnamdi Iyakaremye Vedaste Chehbouni Abdelghani Ongoma Victor 《Natural Hazards》2022,113(2):1151-1176
Natural Hazards - The ongoing global warming has caused unprecedented changes in the climate system, leading to an increase in the intensity and frequency of weather and climate extremes. This... 相似文献
7.
This paper presents an innovative set of high‐seismic‐resistant structural systems termed Advanced Flag‐Shaped (AFS) systems, where self‐centering elements are used with combinations of various alternative energy dissipation elements (hysteretic, viscous or visco‐elasto‐plastic) in series and/or in parallel. AFS systems is developed using the rationale of combining velocity‐dependent with displacement‐dependent energy dissipation for self‐centering systems, particularly to counteract near‐fault earthquakes. Non‐linear time‐history analyses (NLTHA) on a set of four single‐degree‐of‐freedom (SDOF) systems under a suite of 20 far‐field and 20 near‐fault ground motions are used to compare the seismic performance of AFS systems with the conventional systems. It is shown that AFS systems with a combination in parallel of hysteretic and viscous energy dissipations achieved greater performance in terms of the three performance indices. Furthermore, the use of friction slip in series of viscous energy dissipation is shown to limit the peak response acceleration and induced base‐shear. An extensive parametric analysis is carried out to investigate the influence of two design parameters, λ1 and λ2 on the response of SDOF AFS systems with initial periods ranging from 0.2 to 3.0 s and with various strength levels when subjected to far‐field and near‐fault earthquakes. For the design of self‐centering systems with combined hysteretic and viscous energy dissipation (AFS) systems, λ1 is recommended to be in the range of 0.8–1.6 while λ2 to be between 0.25 and 0.75 to ensure sufficient self‐centering and energy dissipation capacities, respectively. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
8.
本文提出一种结构紧凑且固有倾斜辐射波束的圆极化天线.通过使用一对正交的互补源,将在俯仰面的倾角方向上产生圆极化波.为了验证方法的可行性,该天线主要由扇形的单极子、短路钉和L型的接地板组成.短路钉一端连接单极子天线,另一端连接接地板的水平部分,从而形成一个环路辐射单元.研究结果表明：该天线的最大辐射增益在θ=60°,φ=90°的方向上,具有6.2%左右的3 dB轴比工作带宽.同时,相较于现有的倾斜波束圆极化天线,它的结构更加紧凑,适用于小型化的设计需求. 相似文献
9.
We generalized experimental data on the structural group composition and macrostructural characteristics of high-molecular compounds (HMCs)—hydrocarbons, resins, and asphaltenes—from more than 180 crude oil samples extracted from different oil fields of Eurasia. Most of oil resin molecules contain 1–3 structural blocks, each consisting of 0–3 aromatic and 0–5 naphthenic rings in different combinations, with the total number of rings in each block not exceeding 5–6. The average molecular weights of resins are no more than 100–1500 a.m.u. Asphaltenes differ from resins from the same source in the larger number of structural blocks (mainly tri- or tetracyclic aromatic) in molecule (up to five), lower degrees of substitution of aromatic cores, and smaller portions of carbon atoms in saturated fragments. The average molecular weights of asphaltenes measured by naphthalene cryoscopy do not exceed 2500 a.m.u. Owing to intermolecular interactions, HMCs form various associates and polymolecular particles, including quasi-crystalline “batches” and multibatch aggregates. Spontaneous disintegration and formation of such particles make the oils dynamically equilibrium polydisperse systems. We have developed the main regularities of compositional and structural changes of HMCs depending on the depth of occurrence, age, and lithologic composition of oil-bearing deposits. Being chemically labile heteroatomic substances, petroleum HMCs are more rapidly subjected to compositional and structural transformations than hydrocarbons, i.e., are more responsive to changes in strata conditions. 相似文献
10.
A Galerkin Finite Element formulation for the dynamic stability analysis of liquid-filled shells is given in this paper. The coupling among the axial and circumferential modes is investigated. The dynamic stability characteristics of two liquid-filled storage tanks subjected to vertical, horizontal and rocking seismic excitations are presented. It is shown that a tall tank tends to buckle at distinct frequencies; and for cos θ-type ground excitation, cos 2θ, cos 3θ and cos 4θ are the dominant modes of failure. On the other hand, in a broad tank, buckling regions overlap each other. In particular, for cos θ-type ground excitation, the dominant buckling modes are cos 6θ to cos 9θ, and also cos 12θ to cos 14θ. 相似文献