亚洲一区欧美在线,日韩欧美视频免费观看,色戒的三场床戏分别是在几段,欧美日韩国产在线人成

The variation of heavy metal content in soils has important influence on cultivation security of crops. The concentrations of Pb, Hg, Cd, Cr, Cu and similar heavy metal As in arable soil were quarterly recorded in Binzhou of Shandong during the period from January 2010 to January 2013. The methods of periodic analysis and fast Fourier transform (FFT) spectral analysis were applied to calculate the principal component cycle of heavy metals, and to make further periodic test. The results showed that there was a different degree of accumulation trends in metals between the periods. The principal component cycle of Pb was two quarters in a year, Cd and As had four quarters as the main component cycle, and other heavy metals major cycle characteristics was not obvious.