英语中哪些句子是部分否定?

英语中哪些句子是部分否定?
比如They are't all happy.是部分否定吗?

是.
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英语中部分否定的几种表示方法
英语中的部分否定（即不完全否定）有如下一些表示方法：
一、 all 的否定式：not all…（或：all…not）表示"并非都……"、"不是所有的都……"例如：
Not all men can be masters.
= All men cannot be masters.
并非人人都能当头头.
Not all bamboo grows tall.
并非所有的竹子都会长得很高.

二、 both 的否定式：not…both (或：both… not) "并非两个……都……"
例如：
I don’t want both the books.
我不是两本书都要.
Both (the) windows are not open.
两扇窗子并不都开着.
三、 every…的否定式："不是每……都……" 例如：
Not every book is educative.
=Every book is not educative.
不是每本书都有教育意义的.
Not everyone likes this book.
并非人人都喜欢这本书.
This flower is not seen everywhere.
这花并不是随处可见的.

四、 always的否定式："并非总是（并非一直）……" 例如：
He is not always so sad.
他并不是一直都这样悲伤.

五、 entirely, altogether, completely 和quite 的否定式："不完全……","并非完全……" 例如：
The businessman is never to be entirely trusted. 不可以完全信任商人.
He felt not altogether satisfied.
他并不完全满意.
I don’t agree completely.
我并不完全同意.
What he did was not quite proper.
他做的不十分妥当.

六、 all the time 的否定式："并非一直……"、"未必老是……" 例如：
A foolish man doesn’t make a mistake all the time. 笨人未必老是犯错误.

七、 not…and…的否定式,被否定的往往是and后面的那一部分. 例如：
He did not speak clearly and correctly. 他讲得清楚但不正确.
This film is not interesting and instructive.
这部电影有趣但无教育意义.
She cannot sing and dance.
她会唱歌但不会跳舞.
如果将and 换成or,not 对其后面的两部分就全盘否定了.
He did not speak clearly or correctly.
他讲的既不清楚也不正确.
如要对上述的all, both, every, always, 以及entirely, altogether, completely, quite 和 all the time 等词作完全否定,那就分别要用与之相对应的全否定词,如no, none, neither, no one, never, not (never)… at all 等.例如：
All of them can do it.--- None of them can do it.
Both are good.---Neither is good.
Everybody likes it. ---Nobody likes it.
He is always late. --- He is never late.
We trust them entirely. --- We never trust them at all.
He was here all the time. --- He was never here.