comb through vs research

comb through

verb
  • To examine scrupulously. 

research

verb
  • To make an extensive investigation into. 

  • To search or examine with continued care; to seek diligently. 

  • To search again. 

noun
  • Diligent inquiry or examination to seek or revise facts, principles, theories, applications, etc.; laborious or continued search after truth. 

  • The research station that houses Wang and his team is outside Lijiang, a city of about 1.2 million people. File:The research station that houses Wang and his team is outside Lijiang.ogg 

How often have the words comb through and research occurred in a corpus of books? (source: Google Ngram Viewer )