first和at first的区别?

first有四个词形：adj.adv.n.pron.这里主要谈adj.和adv.
first adj.序数词 第一的
Example:He was the first student who arrived at the classroom.
adv.首先
First I fed the baby.Then I made myself a sandwich.
at first是一个介词短语在句中充当状语
首先
At first I was nervous,but I soon started to relax.
补充一个firstly 修饰句子的副词 首先
The plan was not practical,firstly because of the cost,and secondly because local people did not support it.
通常可互用,但有差别,需查词典体会.

一般没什么区别，都可以做状语，可以用at first的地方都可以用first，但可以用first的地方不一定可以用at first，比如first和second连用的时候

first 第一
at first 一开始