it is no wonder写全了是it is no wonder that...后面接一个从句.在非正式英语中that通常都可以省略.No wonder是省略说法.
正式英语指的是：论文,法律法规,文件,商业往来信件等.例：
It is no wonder he is not hungry.
No wonder he is not hungry.
都是一个意思.