Fetching details from the dictionary...

intently; single-mindedly; devotedly; solely; earnestly; with all one's heart
彼は只管仕事に打ち込んでいる毎日だ。
He spends every day single-mindedly devoted to his work.
只管練習を続けて上達できた。
I was able to improve by continuously practicing.
目標達成のために只管努力を重ねた。
I made single-minded efforts to achieve my goal.