1·Certain stages and periodicities existed in the variation of water resources.
水资源的变化存在一定的阶段性和周期性。
2·The result shows that there exist pronounced lower-frequency periodicities of 31~54 years and higher-frequency variations of 2~4 years.
结果显示，青海南部高原地区春季最高气温的变化存在较明显的31~54年低频和2~4年高频准周期波动特征。
3·Up to now, the Earth's orbital parameters remain the only periodicities in geology subject to precise calculations and, therefore, may provide new scales for geochronology.
迄今为止，地球轨道参数的变化是地质尺度上惟一可以精确定量计算的周期现象，可以用作地质计时的标尺。