Perhaps you should try some spelling variations:
"life groups" » "lie groups", "like groups", "line groups", "little groups"
"link groups" » "sink groups", "risk groups", "linear groups"
"disk groups" » "risk groups", "task groups", "risk group"
"life group" » "lie group", "line group", "little group"

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: (((("life groups") OR ("life group"))) OR ((("link groups") OR ("disk groups")))).
• The words AND, OR and NOT may confuse the search; try adding quotes: "((((\"life groups\") or (\"life group\"))) or (((\"link groups\") OR (\"disk groups\"))))".
• Removing quotes may allow a broader search: (((( life groups ) or ( life group ))) or ((( link groups ) OR ( disk groups )))).
• Adding a wildcard symbol may retrieve word variants: (((("life groups") or ("life group"))) or ((("link groups") OR ("disk groups"))))*.