”“但是”、“可是”、“不过”these Chinese words use like'but' 。 1、但是 dànshì [but;yet;however] 用在后半句,表示转折的语气;可是 虽然困难很多,但是他一点也不怕 2、 可是 kěshì (1) [but]——连接分句、句子或段落,表示转折关系,常和前面的“虽然”相呼应;先由“虽然”引出一层意思,后用“可是”一转,引出相反或不一致的意思。相当于“但是” 他虽然有病,可是仍继续工作 (2) [yet;however;nevertheless]∶然而 可是他错了 (3) [really;truly;indeed]∶真是;实在是 要论人家姚大叔,老成持重,又有骨气,可是百里挑一。—— 杨朔《三千里江山》 (4) [in fact;the fact is]∶却是 现在可是换了一个说法了 (5) [whether;whether or not;if]∶是否 [青蝇]却从鼻尖跑下,又用冷舌头来舐我的嘴唇了,不知道可是表示亲爱。——鲁迅《野草》 (6) [or]∶还是 你这鱼是卖的,可是博的?——元· 李文蔚《燕青博鱼》 3、 不过 bùguò (1) [cannot be better] ——用在形容词性的词组或双音形容词后面,表示程度很高 那就再好不过了 (2) [but;however;only] ——作连词,表示转折,只是 然亦不过增一倍而止矣。——清·洪亮吉《治平篇》 病人精神还不错,不过胃口还不好 (3) [only;just;merely;nothing but;no more than]∶副词,指明范围;只,仅仅 不过是个小孩子

但是 or 但 means exactly but 不过 or 然而 means however en francais we say par contre (but means mais en francais) "but" means the meaning will change, for example, I could have finished this job, BUT(但是) I didnt, because u were not there. 只是 means but too, but its meaning is weak, normally we use 只是 to supply something (ofc the meaning is opposite, like "but") example: I have finished this job, 只是 I forgot giving the rapport of this job to my boss. if u say like this, u want to highlight "finish this job", "forget giving the rapport" is not a big problem, but if u use but : I have finished this job, but(但是) I forgot giving the rapport to my boss, it means that "forgot giving the rapport to my boss" is a big problem (even if "I have finished this job") so if u use but, it means "give the rapport" is as important as "finish this job" OR "give the rapport" is more important than "finish this job"

Just check out "然而", but pls note that it is a formal expression. Informal one can be "可是". Good luck.