pandas 的日期/时间类型有如下几种：
Concept
Scalar Class
Array Class
pandas Data Type
Primary Creation Method
Date times
Timestamp
DatetimeIndex
datetime64[ns] or datetime64[ns, tz]
to_datetime or date_range
Time deltas
Timedelta
TimedeltaIndex
timedelta64[ns]
to_timedelta or timedelta_range
Time spans
