他总不能专心于正题而尽想着愚蠢的事情.His mind kept branching off into the contemplation of silly things.他们专心于实验.They are absorbed in the experiment.他专心于他的业务.He bent his mind to his business....

“专心于”的英语可以翻译为：e absorbed in，pay attention to，devote oneself to，settle down，apply one's mind to ...