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