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975.
广州市蔬菜生产布局与“渡淡”问题探讨 总被引:1,自引:1,他引:1
本文分析了广州市蔬菜供应出现淡季的主要原因,指出现行蔬菜生产布局的不合理性,并提出合理调整生产布局,改善淡季蔬菜供应的基本设想。 相似文献
976.
何兴刚 《中国地理科学(英文版)》1993,(3)
Metropolises are centers of politics, economy, culture and information, and also economic growth poles in comparatively large areas. After 1949, China's urban structure have changed greatly, from original "pyramid" shape into "upside -down pyramid" shape, that is, more megalopolises and metropolises, fewer medium-sized and small cities. The most distinguishing feature of urban population growth was the remarkable increase of population in megalopolises and metropolises. The key reason for urban population expansion is to want to obtain the benefits of scale -agglomeration economy of metropolises. The number of urban functions directly determines the quality and quantity of urban population. Metropolises appeal not only agricultural population but also the population of medium-sized and small cities, which put much more population pressure on metropolises. The ideal goals of scale-control of metropolitan population are discussed in terms of economy, society and ecollogy. In order to control the metropoli 相似文献
977.
地下介质横向变化的地震多尺度边缘检测技术 总被引:10,自引:3,他引:10
本文提出的地震多尺度边缘检测技术以坎尼最佳边缘检测准则和小波变换的多分辨分析为理论基础,能在地震记录上较方便而可靠地识别地下介质的横向变化。这些横向变化包括不能用肉眼在地震同相轴上直接发现而又实际存在的隐蔽特征。对地层尖灭,透镜体、岩性变化和孔洞、裂缝发育带均可进行识别。模型计算和实际地震资料的处理结果显示该方法具有实际应用价值 相似文献
978.
采用了单柱离子色谱法测MnO2产品中无机离子杂质;提出了消除干扰的可行途径,将La(OH)3加入后能同时消除进样峰的干扰和溶剂峰的出现。选用1.75mmol/L邻苯二甲酸1.75mmol/L三羟甲基氨基甲烷为混合淋洗剂测定F^-,Cl^-,NO3^和SO^2-4,其标准加入回收率为95%-105%;RSD(n=7)为2.47%-8.08%。 相似文献
979.
Two semi-asymmetric flow patterns of typhoons are chosen to qualitatively determine the effect of exchange of horizontal momentum between inflow and outflow layers and the environment on the motion of typhoons. The results show that only the asymmetric flow component (residual after azimuthal mean flow has been removed) could cause a net momentum input into or output from a typhoon and therefore contribute to the changes in speed and direction of the typhoon movement. A typhoon with major inflow and/or outflow channels on its right (left) side would tend to accelerate and turn left (decelerate and turn right); On the other hand, a typhoon with major inflow and/or outflow channels in the rear (front) semicircle would tend to accelerate and turn right (decelerate and turn left). 相似文献
980.
The shales of the Qiongzhusi Formation and Wufeng–Longmaxi Formations at Sichuan Basin and surrounding areas are presently the most important stratigraphic horizons for shale gas exploration and development in China. However, the regional characteristics of the seismic elastic properties need to be better determined. The ultrasonic velocities of shale samples were measured under dry conditions and the relations between elastic properties and petrology were systemically analyzed. The results suggest that 1) the effective porosity is positively correlated with clay content but negatively correlated with brittle minerals, 2) the dry shale matrix consists of clays, quartz, feldspars, and carbonates, and 3) organic matter and pyrite are in the pore spaces, weakly coupled with the shale matrix. Thus, by assuming that all connected pores are only present in the clay minerals and using the Gassmann substitution method to calculate the elastic effect of organic matter and pyrite in the pores, a relatively simple rock-physics model was constructed by combining the self-consistent approximation (SCA), the differential effective medium (DEM), and Gassmann’s equation. In addition, the effective pore aspect ratio was adopted from the sample averages or estimated from the carbonate content. The proposed model was used to predict the P-wave velocities and generally matched the ultrasonic measurements very well. 相似文献