Perhaps you should try some spelling variations:
"tissue research theories" » "tissue research theory", "tissue research themes", "tissue research topics", "issues research theories", "disease research theories"
"pressure research theories" » "pressure research theory", "pressure research themes", "pressure research topics", "present research theories", "pressure release theories"
"residue research studies" » "residues research studies", "residual research studies", "rescue research studies", "residue research study"

Try widening your search to All Fields.

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: (((("tissue research theories") OR ("pressure research theories"))) OR ("residue research studies")).
• The words AND, OR and NOT may confuse the search; try adding quotes: "((((\"tissue research theories\") OR (\"pressure research theories\"))) or (\"residue research studies\"))".
• Removing quotes may allow a broader search: (((( tissue research theories ) OR ( pressure research theories ))) or ( residue research studies )).
• Adding a wildcard symbol may retrieve word variants: (((("tissue research theories") OR ("pressure research theories"))) or ("residue research studies"))*.