as ... as

句式

as + 形容词/副词原级 + as

“和 ... 一样”

I think foreign languages are as difficult as science subjects.
我认为外语和自然科学课程一样难。

句式

not as + 形容词/副词原级 + as

“不如 ... ”

Computers are very popular now and they are not as expensive as before. 电脑现在非常普及，并且也不如以前那么昂贵。