as 在定语从句中的用用法

Answer 1

as 在定语从句中的用法
在限制性定语从句中，as多和such和the same连用，在从句中充当主语宾语或表语。例如，
1. I've never seen such a talented young man as he is. 我从未见过像他这样才华横溢的年轻人。（as作表语）
2. Such books as I have read are classical works.我所读过的书都是些经典著作。（as 作宾语）

区分such...as与such....that的区别
He is such a good teacher as every student likes.(as充当宾语)
He is such a good teacher that every student likes him.（从句中不缺少成分，such...that 引导结果状语从句）

the same...as虽然在结构上与the same...that相同，但有时句意却不一样。比较：
This is the same pen as I uesd last week.这和我上周用的那支笔是一样的。（不是同一支）
This is the same pen that I used last week.这就是我上周用的那支笔。（同一支）
补充
此外，as在非限定定语从句中也有应用，例如
The murderer was finally arrested by the police, as was expected. 如我们所愿，杀人犯最终被警察逮捕了。
其实as更多的是用在句首，有时会用在句中，或句尾，而且多出现在固定搭配中，如
as is well known,.........众所周知
as is often the case,.........情况常常如此
as may be imagined,......可以想象得出
as was said before/mentioned above,....如前面所说的/如上文所提到的

Answer 2

定语从句特殊关系词as的用法

Answer 3

透析which与as在定语从句中的运用
定语从句是高中英语的主要语法项目之一，也是高考英语的常考知识点，尤其是as和which引导的定语从句，更是历年高考试题中的重点和热点。as和which在引导定语从句时既有相同点又存在着很大的区别。
一、相同点
1. as和which都能引导定语从句，并都可以在定语从句中做主语或宾语，代表前面整个句子。
例 1 He married her, as / which was natural. 他跟她结婚了，这是很自然的事。
例 2 He is honest, as we can see. 他很诚实， 这一点我们看得出来。(表示人们从日常主观常识, 经验对某一事情的看法、评价,用as为妥。)
2. 当非限定性定语从句置于句末时，as和which都可用来引导这个定语从句。
例 3 The number of senior high school students is increasing, as is mentioned above. （as引导非限定性定语从句，意思是“正如”。此时也可以换用which引导，但意思有别，意思是：“这一点上面提到了”。）
二、不同点
（一）语义上的区别
as作为关系代词仍多少保留 “理由”“比较” “方式” “等同”等意义，而which没有这些意义。因此，由as引导的定语从句通常在意义上不可与主句相悖，而且一般是肯定的，对主句意义起相辅作用，表示 “正如”等意义；而which引导从句则不受此限制。
例 4 Mother treats me just like a baby，which I can’t bear． 妈妈对我就像小孩，我真受不了。
例 5 She has married again，which was unexpected． 她又结婚了，这是大家没有预料到的。
上面两句中的which都不宜用as。
但当否定的定语从句作正面理解，对主句起相辅作用而不是与其相悖时，仍可用as。
例 6 He turned his eyes on Philip’s face，as he had not done for ten years．他转过身来看着菲利普的脸，他十年来没有这样看过他的脸了。
例 7 He really can’t lend you the money，as you might not realize． 他的确不能把那些钱借给你，这一点你可能意识不到。
（二）用法上的区别
1. which与as引导非限制性定语从句的区别：
（1）which只能放在主句后面，而as引导的从句位置相对比较灵活，可以放在前，也可以放在后，甚至还可以分割主句。另外，as 常常有“正如、正像”的含义。
例 8 As he realized, I was very useful to him.（在前）
例 9 Air, as we know, is a gas. （在中）
例 10 He was a foreigner, as I know from his accent. (在后)
例 11 He came late again, which made his boss angry.（在后）
例 12 As is known to all, China is a developing country. 众所周知，中国是发展中国家。
（2）在which引导的定语从句中，谓语动词若是am, is, are，则这些系动词不能省略，而as后面若是这种情况，则可以省略。
例 13 He is a teacher, as (is) clear from his manner. (is可以省略)
例 14 He said he had never seen her before, which was not true. （was 不可省略）
（3）当which引导的从句在意义上近乎并列关系时，可以用and this, and that代替，意思是“这件事”。
例 15 He changed his mind, which(and this, and that) made me very angry. 他改变了主意，这使我很生气。
而as主要起与上下文连接的作用，表达说话人的看法、观点，并指出主句内容的出处或根据等。
例 16 Einstein, as we know, is a famous scientist.爱因斯坦，众所周知，是一位伟大的科学家。
例 17 As is announced in today’s newspaper, we must improve our style of work. 今天的报纸上说，我们必须改进工作作风。
（4）做主语时，which既可以作系动词be的主语，也可以作实义动词的主语，而这时as 只可以做系动词be的主语。
例 18 He married her, which was natural. （可用as代替which）他和她结婚，这是很自然的事。
例 19 He won a /the Nobel Prize in chemistry, which made him illustrious. (不可用as代替which)他获得了诺贝尔化学奖，这使他名扬天下。
（5）当定语从句位于主句之后，纯粹表示主句所述的内容，不带有“如……那样”的意思时，往往用which, 而不用as。
例 20 They were invited to the state banquet, which(as) was a great honor to them. 他们被邀请参加国宴，这对他们来说是莫大的荣幸。
例 21 We had to sleep in our wet clothes, which was most uncomfortable. 我们不得不穿着湿衣服睡觉，这简直太不舒服了。
（6）当定语从句有“如同……那样”的含义时，用as比用which更常见，而这些从句几乎成为固定说法。
例 22 Things will turn out contrary to one’s wishes, as is often the case. 事与愿违，这是常有的事。

例 23 As was natural, this inordinate hope was followed by an excessive depression.这种过分希望之后，接着是极度的沮丧，是很自然的事。
例 24 The material is elastic, as is show in the figure. 这种材料有弹性，如图所示。

例 25 As we know. 众所周知。
例 26 As has been said above/ before. 正如前文所述 。
（7）当定语从句的关系代词指的是先行词本身时，只能用which。
例 27 These apple trees, which I planted tree years ago, have not borne any fruit.这些苹果树是我三年前种下的，没结出任何果实。
例 28 The Thames, which is now clean enough to swim in, was polluted for over a hundred years.泰晤士河，现在已经很干净，可以在里面游泳，它曾被污染了一百多年。
（8）带介词的典型的定语从句，必须用which，不能用as。
例 29 There is a great deal of oxygen around us, without which we could not live. 我们周围有许多氧气，没有它我们就无法生存。
例 30 The shed in our garden, in which we often played, has lasted for a long time. 我们经常玩耍的花园里的那个棚子，已经有很长时间了。
（9）as常与从句中的know，see， hear，expect等动词连用，也常用于as often happens，as is often the case（常有的事）等句子中；而which一般不用于以上情况。
例 31 As is well known，Shanghai is a big city．
（10）当后置的非限制性定语从句是否定结构时，只能用which引导。
例 32 The result of the experiment was very good, which we hadn’t expected.
2. 引导限制性定语从句时which与as的区别：
(1)先行词如果是表示物的名词或代词，在从句中又做介词的宾语时，只能用which。
例 33 This is the pan in which I boiled the milk. 这就是我煮牛奶的锅。
（2）前面有as时,引导定语从句的关系代词用as, 不用which。
例 34 There are as many dictionaries as are needed.所需要的字典都有了。
（3）前面有such时，引导的定语从句的关系代词用as, 不用which。
例 35 Such women as know Tom thought he was charming. 认识汤姆的女人都认为他很迷人。
例 36 I have never heard such stories as he tells. 他讲的那些故事我从没听过。
（4）前面有the same时，引导定语从句的关系代词用as而不用which。
例 37 We are facing the same problems as we did years ago.我们正面临着和多年以前同样的困难。
例 38 This is the same wallet as I lost. 这只钱包与我丢失的那只相同。
（5）单个词引导限制性定语从句时，一般不用as而用which和that。由于关系词在从句中作宾语，which和that都可以省略。
例 39 The project which/that a British businessman has invested in is under construction at present.
（6）“介词+关系代词”引导定语从句时，只能用which。
例 40 Recently I bought an ancient Chinese vase, the price of which was very reasonable.
注：此时的which不能用as来代替。另外还应注意：引导定语从句时，which不能单独作定语，此时不管先行词是人还是物，都只能用whose引导，但指物时，可以用of which替换。