Perhaps you should try some spelling variations:
"potential differential equations" » "potential differentiation equations", "polynomial differential equations", "partial differential equations"
"racial differences equations" » "racial difference equation", "racial differentes situations", "racial differences variations", "regional differences equations", "national differences equations"

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: (("racial differences equations") OR ((("potential difference equations") OR ("potential differential equations")))).
• The words AND, OR and NOT may confuse the search; try adding quotes: "((\"racial differences equations\") or (((\"potential difference equations\") OR (\"potential differential equations\"))))".
• Removing quotes may allow a broader search: (( racial differences equations ) or ((( potential difference equations ) OR ( potential differential equations )))).
• Adding a wildcard symbol may retrieve word variants: (("racial differences equations") or ((("potential difference equations") OR ("potential differential equations"))))*.