Perhaps you should try some spelling variations:
"partial differential equation" » "partial differential equations", "partial difference equations"
"racial differences equations" » "racial difference equations", "racial difference equation", "racial differential equations", "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: (("partial differential equation") OR ("racial differences equations")).
• Removing quotes may allow a broader search: (( partial differential equation ) or ( racial differences equations )).
• Adding a wildcard symbol may retrieve word variants: (("partial differential equation") or ("racial differences equations"))*.