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

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