BeginOfDay 获取一天的起始时间.

BeginOfHour begin of hour.

BeginOfMinute begin of minute.

BeginOfMonth 获取月的起始时间.

BeginOfWeek 获取一周的起始时间.

BeginOfYear beginning of year.

EndOfDay 获取一天的结束时间.

EndOfHour end of hour.

EndOfMinute end of minute.

EndOfMonth 获取月的结束时间.

EndOfWeek 获取一周的结束时间.

EndOfYear end of year.