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971.
雷电电磁场对通信局站中的电信设备的危害,主要是通过电源线耦合到电信终端设备。要对其危害进行有效的防护,首先要研究雷电电磁场对通信电源线的耦合机理。文章运用电磁场理论和传输线方程,推导出了大地为均匀非理想导体时,雷电电磁场对通信线的感应电流和感应电压的表达式。 相似文献
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975.
通过简单分析古典自由主义产生的时代背景,以及他本身的理论表达,以此为前提来分析霍布斯 和洛克的政治思想,并分析他们各自理论中的自由主义因素,进而比较他们政治理论表达的不同以及他们的理 论在自由主义历史发展的影响和它们的历史意义。 相似文献
976.
LIUWei SHUWensheng LANChongyu 《科学通报(英文版)》2004,49(1):29-32
This paper reports upon the finding of Viola baoshanensis, a cadmium (Cd) hyperaccumulator through field survey and greenhouse experiments. Average Cd concentration in the shoots and roots of V. baoshanensis growing on Baoshan lead/zinc mine in Hunan Province, China, was 1168 and 981 mg/kg, respectively, varying from 456 to 2310mg/kg in the shoots, and from 233 to 1846 mg/kg in the roots.The ratio of Cd concentration in shoot to root (DW) and that in plant shoots to total concentration in surface soil was 1.32 and 2.38, respectively. Under nutrient solution culture, biomass (DW) of V. baoshanensis exposed to 0-30 mg/L Cd insolution increased with Cd supply increasing and reached a maximum at 30 mg/L Cd. Further increase of Cd concentration (40, 50 mg/L) in solution significantly reduced biomass.Cd concentration in the shoots was positively correlated with Cd concentration in the culture medium. Cd concentration in the shoots reached 4825 mg/kg at 50 mg/L Cd solution. Theratio of Cd concentration of shoots to roots in V. baoshanensis was greater than 1 at all Cd treatments, with an average of 1.67 (1.14-2.22). The results indicate that V. baoshanensis is a Cd hyperaccumulator plant. 相似文献
977.
XIONGZhiyong TANGuangxuan YOUAiqing HEGuangyuan SHEChaowen LILijia SONGYunchun 《科学通报(英文版)》2004,49(6):591-596
Oryza granulata Nees et Arn. ex Watt. is one of the three wild relatives of rice,which are the most valuable for study and utilization in China.In this study,the homology and physical locations of three rice resistance genes,Glh,Bph-3 and xa-5 are comparatively analyzed between O.sativa and O. granulata by Southern blotting and fluorescence in situ hybridization (FISH).The results of Southern blotting indicate that there exist homologous sequences of the tested RFLP markers in O. granulata.By using three bacterial artificial chromosome (BAC) clones scanned by the tested RFLP as probes, FISH signals are detected on both mitotic and pachytene chromosomes in O.sativa and O.granulata.Dual-color FISH demonstrates that two of the three BAC clones (14E16 and 38J9) are located on the short arm of the same chromosome pair in O. granulata. Additionally, colinearity is shown for the two clones between O.sativa and O.granulata. Another BAC clone 44B4 is located on the end of the short arm of other chromosome pair in these two species.Although the phylogenetic relationship between O.sativa and O.granulata is the most distinct in Oryza and these two species have evidently different biological features and ecological habits, the relative lengths and arm ratios of the detected chromosomes and the relative positions of the tested clone signals on chromosomes in O. granulata are quite similar to those in O. sativa. 相似文献
978.
NPP distribution related to the terrains along the North-South Transect of Eastern China 总被引:2,自引:0,他引:2
LI Yan LIAO Shendong CHI Guobin & LIAO Qifang . Spatial Information Research Center South China Normal University Guangzhou China . Guangdong Key Laboratory of RS GIS Applications Guangzhou China 《科学通报(英文版)》2004,49(6):617-624
Vegetation net primary productivity (NPP) is defined as the accumulative amount of organic matters per unit area and time, which is calculated from the difference between accumulative photosynthesis and accumulative autotrophic respiration by green plants. Since the NPP reflects the physiological and ecological characteristics of the plants and the interactive results of the environmental factors, it is an important index to evaluate a structure of ecological system, functional features and … 相似文献
979.
LiYanping ZHANGXin WANGZhimin LUDaru HANGWei JINLi 《科学通报(英文版)》2004,49(16):1777-1778
Imbalance of redox state has been associated with human diseases, such as cardiovascular diseases, Huntington‘s disease and Alzheimer‘s disease. Catalase, an important antioxidant enzyme, decomposes H202 into O2 and H2O, therefore limiting the deleterious effect of the reactive oxygen species (ROS). Previous study showed that a C-T polymorphism, located at -844 bp from the translational start site of catalase, is strongly associated with essential hypertension in an isolated Chinese population of Xiangchang country, Anhui Province. To explore the impact of SNP-844C/T on the expression of catalase, human catalase promoters containing either SNP-844C or T variant were subcloned into the pGL3Basic luciferase vector. 相似文献
980.
LIUZhifei TUOShouting ZHAOQuanhong CHENGXinrong HUANGWei 《科学通报(英文版)》2004,49(20):2190-2197
The most prominent cooling event of the Earth surface during Cenozoic in the long-term transition from a non-glaciated planet, or “green-house world”, to a polar, glaciated planet, or “ice-house world”, is the Earliest Oligocene Glacial Maximum (EOGM) above the Eocene/Oligocene boundary at about 33.7 Ma. Planktonic and benthic foraminiferal oxygen and carbon isotopes, carbonate content, and coarse fraction, along with high-resolution color reflectance and magnetic susceptibility records during 35-30 Ma, from deep-water Sites 1262 and 1265, Ocean Drilling Program (ODP) Leg 208 in South Atlantic, reveal the global cooling event occurring in both surface and deep oceans. The results show that the earliest Oligocene δ^18O values during 33.5-33.1 Ma represent the magnitude of continental ice sheets on east Antarctica and indicate the large decrease in both surface and deep water temperatures of worldwideoceans. The δ^13C records show the large excursion during the period of EOGM event and indicate some types of shift in global carbon reservoir, probably demonstrating the sudden increase in organic carbon burial rates and the changes in the distribution and timing of production. At the same time, lithologic composition, carbonate content, color reflectance, and coarse fraction brought about significant changes close to the Eocene/Oligocene boundary, reflecting the abrupt deepening in the carbonate compensation depth (CCD). Changes in carbonate content were revealed from the color reflectance identify periodicities associated with eccentricity of the Earth‘s orbit (100 and 400 ka), further indicating orbitally forced global climate variations in the Early Oligocene. 相似文献