the first time,for the first time,by the first time用法区别

the first time
第一次 相当于连词,
The very first time you said my name当你第一次叫我名字的时候
for the first time
首次；第一次
副词,做时间状语.
For the first time,we find portraits that really look like us.
有史以来第一次,肖像画看起来真的就像你我一样鲜活.
World trade may well shrink this year for the first time since 1982.
世界年贸易量也许本年度就要经历1982年来的首次下降.
by the first time 严格来说不存在.
是by +the first time.
Because love isn't finish by the first time you see the one.
因为爱情不是第一眼就能完成的.