knock at和knock on的区别：中文含义不同、用法不同。knock at中文翻译为“打”、“捶”、“敲”，作为固定词组，只可用于表示敲门；而knock on意为不停地工作、以敲击通知演员上场、使增加，后面可接名词和动名词。
一、knock at的基本含义及用法介绍
knock at作为固定词组，意为打；捶；敲。例句：
1、Late that evening, there was a knock at the door.
那天深夜，有人敲过门。
2、Knock at my window at eight o'clock and I'll be ready
8点钟敲我的窗，我会准备好的。
3、I was wakened by a knock at the door.
敲门声把我吵醒了。
4、I wish you wouldn't knock at the table again.
我希望你不要再敲桌子了。
5、He was scarcely awake when he heard the knock at the door.
他刚醒来就听见有人敲门。
6、Just when she was going to bed, there was a knock at the door.
就在她准备睡觉的时候，传来了敲门声。
二、knock on的基本含义及用法介绍
knock on意为以敲击通知演员上场;不停地工作;〈非正〉（使）增加。例句有：
1、He got a nasty knock on the head.
他头部遭到重重一击。
2、He went up the garden path to knock on the door.
他穿过花园小径去敲门。
3、While he was half asleep, he seemed to hear a knock on the door.
矇胧中他仿佛听到有人敲门。
4、She got a nasty knock on the head when she fell.
她跌倒时头部受到严重碰撞。
5、Someone will knock on your door at midnight tonight.
今晚午夜时分会有人敲你的门。
6、They knock around on weekends in grubby sweaters and pants
他们周末穿着邋遢的毛衫和裤子到处闲逛。
