请问such that和such as引导定从时有什么区别啊?特别是句中缺少什么的时候用as引导?

要明白这两种定语从句,首先得从词性和用法说起.
一、such
1.形容词：这样的,如此的,用于修饰名词,如：
* He has a single parent,one of many such people in the neighborhood.他是单亲,这地区附近有许多这样的人.
* He has never dreamed of such wealth.他从未梦想过这样的财富.
2.不定代词：象这样的人或物,直接用来作主语或宾语,如：
* He expected difficulties,and such occurred.预期会有困难,而这样的困难果然出现了.
* Such are the fortunes of war.这些就是战争的机会.
二、as 用作关系代词指代下面或前面提到的一句话,如：
* The statemant reads in full As follows:...声明全文如下:...
（As 作从句谓语动词 follows 的主语,指代 The statemant reads in full,也可以改写为：The statemant reads in full,which follows:...）
* As you well know,English is an importan tool in communication.众所周知,英语是交流的重要工具.（as 是从句中 know 的宾语,指代 English is an importan tool in communication这件事）
三、that 也是关系代词,但是与 as 不同的是它只指代先行词,而不能指代句子（例句略）.
四、明白上述道理,such that 和 such as 的区别就会迎刃而解,如：
* He expected difficulties,and such that could be avoided occurred at last.预期会有困难,而这种可以避免的困难最终还是出现了.（such 是不定代词,指代 difficulties,关系代词指代 such）
* He expected difficulties,and such avoided occurred as well know to everyone.预期会有困难,而众所周知,这样的困难果然出现了.
说得比较罗嗦,不知道能否解决你的问题.

such……as 和 such……that 的区别
such...as用于引导定语从句，such...that 用于引导结果状语从句。如：
I’ve never heard such stories as he tells. 我从未听过他讲那样的故事。
It was such a cold day that there was nobody on the street. 天...