at the beginning和in the beginning根本区别,at.后面一定加of吗

区别不太大,一般情况下,at the beginning后加of,但偶尔也可以单独使用.如：
But,before we get into the openness issues,let's start at the beginning with you and the data you're just dying to share.不过,在探讨开放问题之前,让我们先来看看你渴望分享的数据吧
in the beginning常单独使用,如：
And I spent 30 days eating nothing but this -- fun in the beginning,little difficult in the middle,very dangerous in the end.我曾经在30十天里只吃这一种食品--一开始很有意思到了中间,有一点艰苦,而最后,相当危险.
但也可加OF,如：
Stock levels will increase in the beginning of each month until the orders are full so that consumptions are higher than order intake.在每月月初库存量将会增加,直到定单全部下完,从而消耗量大于入库量.
Pay particularattention in the beginning of the film:at least two clues are revealed beforethe credits?特别要注意影评的开头:在致谢名单开始之前就已经出现两个暗示了