but,though,however 有什么区别

but 是连词，连接两个并列句，中间用逗号隔开。表示转折

如： I wanted to buy a book, but I don't have enough money.

though 是副词，但在句中的成分相当于连词。引导从句，不能与but 连用，可以放句首或者句中。意思是尽管

如：Though it is so hot I have to go outside.

I have to go outside though it is so hot.

however 也是副词，剧中成分相当于连词。可以放在句首或句中，后面一定要用逗号。表转折。放句首时，与前面的句子是转折的连接。放句首时，前后用逗号隔开
如：I wanted to buy a book, however, i do not have enough money.

but:但是,语气要比however 强
however:可是,然而.语气较弱,通常位于句中.
"I'd like to go with you; however, my hands are full.
He hasn't arrived. He may, however, come later.
though:尽管，虽然．可以位于句首，句中．
I'll call to see you this evening though I can stay only a few minutes．
Though it was raining, he went there.

but = 但是
最平常的用法，与汉语的“但是”用法差不多
例：
I wish I could sleep in but it was Monday.

though = 虽然
一般用于一个句子的中间或句末（区别于although——此词用于句首或句中）
例：
I didn't like the lecturer even though sh