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高等数学语言中的时序要素 被引量:5
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作者 龚妙昆 《大学数学》 2003年第6期38-39,共2页
相对来说 ,时间比空间抽象 ,数学中许多概念和定理可以借助于图形和曲线来描述 ,而对于其中的时间因素注意不多 。
关键词 高等数学语言 时序要素 高等数学教学 教学质量
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Regional long-term trend of ground solar radiation in China over the past 50 years 被引量:4
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作者 MA JinYu LUO Yong +2 位作者 SHEN YanBo LIANG Hong LI ShiKui 《Science China Earth Sciences》 SCIE EI CAS 2013年第7期1242-1253,共12页
Based on global solar radiation and related meteorological data from 57 stations in China between 1961 and 2009, we analyze the variation of surface global solar radiation (G) and its relationship to meteorological el... Based on global solar radiation and related meteorological data from 57 stations in China between 1961 and 2009, we analyze the variation of surface global solar radiation (G) and its relationship to meteorological elements using linear-trend estimation, wavelet analysis, and the Mann-Kendall test. The results show that of the 33 stations with time series longer than 45 years, G is significant at the 95% confidence level. G has a decreasing trend at many stations, but results vary across different areas. The decadal departure percentage of G increased from the 1960s to 1970s, declined gradually after the 1970s, and decreased significantly in the 1980s. In the 1990s, the trend at a few sites slightly increased. The trend of cumulative variance is of four types, i.e. rise-fall, rise-fall-slight rise, rise-fall-rise, and not obvious. For changes within a year, the most obvious decline was in winter, and the rest of the year had a slight decrease. The major cycles of annual G were 6-9, 10-13, and 29-33 a. The inflection points were mostly in the 1970s. The reasons for greater changes were complex. Relevant meteorological elements were selected and analyzed by statistical methods. Trends in climatic parameters, such as annual average percentage of sunshine, annual average wind speed, and annual average of low cloud cover, were closely related to G. Thus, this indicated the potential causes of the observed trends in G. The long-term trend for annual G in some regions was also influenced by anthro- pogenic activities. Annual average percentage of sunshine and annual average wind speed were positively correlated with annual G, respectively. 展开更多
关键词 surface global solar radiation linear trend estimation method Mann-Kendall test wavelet analysis
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