可以放在句中。但是：1.并非所有的句子都可以句中；2.并非放在句中的任何地方都可以。

这些时间副词所放的位置，前提是不能破坏句子的结构。

1. The sky is full of gray clouds today.

    The sky today is full of gray clouds.

2. Yesterday a state dinner was given in honor of the visiting president.

    A state dinner was given yesterday in honor of the visiting president.

1. 并非所有的句子都可以，我们不能说：

He is today ill.

He today is ill.

2.并非放在任何地方都可以，我们也不能说：

The sky is today full of gray clouds.

A state dinner was yesterday given in honor of the visiting president.