请问as在定语从句中的用法？是什么意思？

请问as在定语从句中的用法？是什么意思？

as引导定语从句时的用法
①as引导限制性定语从句通常用于the same … as, such … as结构中。
e.g. I want the same shirt as my friend’s. 我要一件跟我朋友一样的衬衫。
Such machines as are used in our workshop are made in China. 我们车间使用的这种机器是中国制造的。
②as引导非限制性定语从句既可放在主句之前，也可放在主句之后，用来修饰整个句子。通常用下列句型：as is known to all, as is said, as is reported, as is announced, as we all know, as I expect 等。
e.g. As I expected, he got the first place again in this mid-term examination. 正如我所预料的那样，他在这次期中考试中又获得了第一名。
as 引导非限制性定语从句时与which的区别
①当主句和从句语义一致时，用as；反之，用which来引导非限制性定语从句。
e.g. He made a long speech, as we expected.
He made a long speech, which was unexpected.
②当非限制定语从句为否定时，常用which引导。
e.g. Tom drinks a lot every day, which his wife doesn’t like at all.

as 可以理解为兼词。即既有介词的性质“像”， 又有名词的性质。
比如as引导非限制性定语从句既可放在主句之前，也可放在主句之后，用来修饰整个句子。通常用下列句型即可按兼词理解：as（like what ) is known to all, as is said, as is reported, as is announced, as we all know, as I expect 等。

as引导定语从句时的用法也可以
①as引导限制性定语从句通常用于the same … as, such … as结构中。
e.g. I want the same shirt as my friend’s. 我要一件跟我朋友一样的衬衫。
Such machines as are used in our workshop are made in China. 我们车间使用的这种机器是中国制造的。

e.g. As I expected, he got the first place again in this mid-term examination. 正如我所预料的那样，他在这次期中考试中又获得了第一名。
as 引导非限制性定语从句时与which的区别
①当主句和从句语义一致时，用as；反之，用which来引导非限制性定语从句。
e.g. He made a long speech, as we expected.
He made a long speech, which was unexpected.
②当非限制定语从句为否定时，常用which引导。
e.g. Tom drinks a lot every day, which his wife doesn’t like at all.
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