Perhaps you should try some spelling variations:
"code research theories" » "code research theory", "code research themes", "code research topics", "codes research theories", "mode research theories", "code search theories"
"cure research studies" » "cure research study", "curve research studies", "core research studies", "fire research studies"
"care research studies" » "care research study", "life research studies"

You may be able to get more results by adjusting your search query.

• If you are trying to use Boolean operators, they must be ALL CAPS: (((("cure research studies") OR ("care research studies"))) OR ("code research theories"))*.
• The words AND, OR and NOT may confuse the search; try adding quotes: "((((\"cure research studies\") OR (\"care research studies\"))) or (\"code research theories\"))*".
• Removing quotes may allow a broader search: (((( cure research studies ) OR ( care research studies ))) or ( code research theories ))*.