science vs subject area

science and subject area both are nouns.

Word	Noun	Adjective	Verb	Adverb
science	Yes	No	No	No
subject area	Yes	No	No	No

As nouns, subject area is a hypernym of science; that is, subject area is a word with a broader meaning than science:

Other hypernyms of science include bailiwick, discipline, field, field of study, study, subject, subject field.

science (noun)	subject area (noun)
a particular branch of scientific knowledge	a branch of knowledge
ability to produce solutions in some problem domain