look up 一般指在字典里查找單詞什么的,
look up the word in the dictionary.
look for 指尋找,更傾向于找的過(guò)程,動(dòng)作,（順便提一下）
find也是尋找,但更傾向于結(jié)果.
I looked (look的過(guò)去式）for my shoes ,but I couldn't find them .
look over 多指檢查,考試檢查之類的
Please look over your exam paper carefully.
look at 看,瞧.更傾向于看的動(dòng)作,（順便提一下）,see也是看,但傾向于結(jié)果.
I look at the blackboard,but I can't see anything.
順便提一下,所有的詞組百度里查一下都能找到,我的是中小學(xué)生經(jīng)常用的,常見(jiàn)的簡(jiǎn)單語(yǔ)法點(diǎn).