网友所问是传统语法规定的定语从句。先行词前有 as, so, such, the same 修饰时，都用as 引导定语从句，the same 可以用 that引导，区别见解答。as 和 which 引导的非限制性定语从句之间的区别，也一并解答。
一、as 引导定语从句主要用于两种情况：一种是限制性定语从句, 先行词有as, so, such, the same 修饰；一种是非限制性定语从句, 其先行词是整个主句, 即 as 指代整个主句的意思。
(1) as 引导限制性定语从句, 先行词前有 as, so, such, the same 修饰
当先行词前有as, so, such, the same 等修饰时, 关系代词常用 as, 它在从句中作主语或宾语。
Such people as have made great contributions to the world should be greatly respected.那些对世界做出巨大贡献的人应受到极大的尊重。（as作从句的主语）
You may take asmany chairs as you need.你需要多少椅子就拿走多少椅子。（as作need的宾语）
My parents have not somuch money as I want.我父母没有我需要的那么多钱。（as作want的宾语）
He made the same mistake as you made in the last exam. 在上次考试中, 他犯了跟你相同的一个错误。（as作made的宾语）
【重要提示】
1. 在so/such...that...引导的结果状语从句中, that不作任何成分, 只起引导作用。要注意区别这两种不同的结构。如：
They had such a fierce dog that no one dared to go near their house.他们家有一条凶狗, 没人敢靠近他们家。（that引导结果状语从句, 在句中不作成分）
2. the same后有时用that, 它表示“同一个, 就是那一个”的意思, 而as则表示“与……一样”, 但不是同一个。如：
This is the same cell phone that I lost yesterday.这就是我昨天丢的那部手机。
This is the same cell phone as I lost yesterday.这是与我昨天丢的相同的一部手机。
(2) as 引导非限制性定语从句, 其先行词是整个主句
as 也可以引导非限制性定语从句, 先行词就是整个主句, 它在定语从句中作主语、宾语。它引导的从句可以位于主句前, 也可以位于主句后, 还可以位于主句中间。
As everybody knows, Shakespeare was a great English writer.众所周知, 莎士比亚是伟大的英国作家。（从句在主句之前, as作从句的宾语）
Tom is a brave boy, as is described in the report.汤姆是一个勇敢的男孩, 这正如在报道中描述的那样。（从句在主句之后, as作从句的主语）
The project, as we had expected, got along well.正如我们所预料的那样, 工程进展顺利。（从句在主句中间, as作从句的宾语）
as 引导非限制性定语从句时, 常见的固定表达：
as we all know 众所周知
as I can remember 正如我所记得的
as often happens 这经常发生
as we expect 正如我们预料的那样
as you see 这一点你明白
as has been said before 如前所述
as is well known 众所周知
as was expected 正如预料的那样
as can be seen 看得出来
as may be imagined 正如可以想象出来的那样
as has been said above 如上所述
as we all can see 正如我们都能看到的那样
as is often the case 像常规那样
as everybody can do 正想人人都能做到的那样
二、as 与 which 引导的非限制性定语从句的区别
关系代词as与which引导的非限制性定语从句，其先行词都可以是整个主句，指代主句整个意思。但as和which具有不同的词义和用法。
（1）as 引导的定语从句，表示说话人的看法、态度、解释或评论。
引导定语从句时，as仍具有“正如，像，由……可知”等意思，这些字眼翻译时可不必译出。as 定语从句中常含有这些动词：see, know, hear, watch, remember, say, tell, show, expect, guess等，这类动词与as连用几乎成了一种固定搭配。as 引导的定语从句可以置于句首、句中或句尾。
Respecting the old and taking care of the young, as we all know, is a good Chinese tradition. 众所周知，尊老爱幼是中国人的优良传统。
There is a net bar around here, as I remember. 我记得这儿附近有一家网吧。
As is often the case, girls like dolls while boys like guns. 女孩子喜欢玩具而男孩子喜欢枪，这是常见的情况。
（2）which引导的从句对主句所叙述的事情进行补充说明，表明事物的状态或结果。
which此时指前面主句所提到的这件事，常译为“这一点，这件事”等。这时它所引导的从句与主句之间常表示并列意义或状语意义。注意它引导的从句不像as那样位置灵活，它只能位于主句的后面。
He changed his mind again, which (=and it) made us all angry.他又改变了主意，这使我们大家都生气了。
She tore up my photos, which (=and it) upset me.她撕碎了我的照片，这使我很不安。
（3）在从句中作定语或介词的宾语时，要用which。
Jenny might come, in which case I'll ask her.詹妮可能会来，要是那样的话我就去问她。
She graduated from a local middle school, after which she went to Beijing University.她毕业于当地的一所中学，之后她去了北京大学。
（4）当从句的谓语动词是否定形式或含着一个复合宾语时，一般用which而不用as。
He pretended not to know me, which I didn't understand.他假装不认识我，这是我搞不明白的。
He admires everyone in his class, which I find quite strange.他羡慕班里的每个学生，我认为太奇怪了。
