PHRASAL VERB (尤指前期不努力之后)开始努力工作(或学习) If someone knuckles down, they begin to work or study very hard, especially after a period when they have done very little work. (尤指前期不努力之后)开始努力工作(或学习) [informal]
The only thing to do was knuckle down and get on with some serious hard work. [VERBPREP.]
唯一能做的就是开始努力工作,好好干出点儿成绩来。
He managed to knuckle down to his lessons long enough to pass his examination. [VERBPREP. + to]