Perhaps you should try some spelling variations:
"resources research theories" » "research research theories", "resources research theory", "resources research themes", "resources research three"
"tissue research topics" » "issues research topics", "pressure research topics", "disease research topics"

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

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