Perhaps you should try some spelling variations:
"structural foundations" » "structural conditions", "structural fluctuations", "structural equations"
"structural functions" » "structural functional", "structures functions", "structure function"
"structure functions" » "structure function"

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: (((("structural functions") OR ("structural foundations"))) OR ("structure functions")).
• The words AND, OR and NOT may confuse the search; try adding quotes: "((((\"structural functions\") OR (\"structural foundations\"))) or (\"structure functions\"))".
• Removing quotes may allow a broader search: (((( structural functions ) OR ( structural foundations ))) or ( structure functions )).
• Adding a wildcard symbol may retrieve word variants: (((("structural functions") OR ("structural foundations"))) or ("structure functions"))*.