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

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: "((\"partial difference equations\") OR (\"racial differences equations\"))".
• Removing quotes may allow a broader search: (( partial difference equations ) OR ( racial differences equations )).
• Adding a wildcard symbol may retrieve word variants: (("partial difference equations") OR ("racial differences equations"))*.