! calls out to a shell (in a new process), while % affects the process associated with the notebook (or the notebook itself; many % commands have no shell counterpart).
!cd foo, by itself, has no lasting effect, since the process with the changed directory immediately terminates.
%cd foo changes the current directory of the notebook process, which is a lasting effect.
!调用 shell（在新进程中），而 % 影响与笔记本（或笔记本本身;许多 % 命令没有 shell 对应项）关联的进程。
！cd foo 本身没有持久的影响，因为更改目录的进程会立即终止。
%cd foo 更改笔记本进程的当前目录，这是一个持久的效果。