be industrious/diligent/assiduous vs buckle down

be industrious/diligent/assiduous

buckle down

verb
  • To put forth the needed effort; to focus; become serious; apply oneself (e.g. to work or study). 

How often have the words be industrious/diligent/assiduous and buckle down occurred in a corpus of books? (source: Google Ngram Viewer )