Perhaps you should try some spelling variations:
"partial difference equations" » "partial differential equations", "partial differential equationss", "racial differences equations"
"potential difference equations" » "potential differential equations", "potential differential equationss"
"racial difference equation" » "racial differential equation", "racial differential equations", "racial differences equation", "facial difference equation", "social difference equation"

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