钻研 (zuānyán) means 'to study meticulously, to delve into' and implies deep, painstaking focus over time, often on a narrow or difficult topic. It is more intense and specific than 研究 (yánjiū, general research/study), and more concrete than 深入 (shēnrù, to go deep into, often abstract). Unlike 抠 (kōu, to pick at details, sometimes with a negative connotation), 钻研 is always positive and scholarly.