基本含义相同，但使用场合不同。year after year 含有“年年重复，毫无变化”之意。而year by year含有“年年发生变化”之意。
Year after year I have a birthday present from my parents. 我年年都从父母那里得到一份生日礼物。
Year by year we grow a little older. 我们会逐年变老一些。
They liked the cool wet weather there and their number increase year by year. 它们喜欢那儿凉爽而潮湿的气候，因此它们的数目逐年增加。
上面的解释也适用于day after day 和day by day:
Day after day the mouse came back. 老鼠天天都回来。
Day by day the situation is improving. 情况每天都在改善着。
