Perhaps you should try some spelling variations:
"structural foundations" » "structural conditions", "structural fluctuations", "structural equations"
"structures functions" » "structure function", "structure functional", "structural functional"
"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 foundations") OR ((("structures functions") OR ("structure functions")))).
• Removing quotes may allow a broader search: (( structural foundations ) or ((( structures functions ) or ( structure functions )))).
• Adding a wildcard symbol may retrieve word variants: (("structural foundations") or ((("structures functions") or ("structure functions"))))*.