Perhaps you should try some spelling variations:
"partial difference equations" » "partial different equations"
"racial differences equationss" » "racial differents equationss", "facial differences equationss", "racial differences equationis", "racial differences equationsy", "racial differences equationists"

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 equations"))) OR ("racial differences equationss"))*.
• The words AND, OR and NOT may confuse the search; try adding quotes: "((((\"partial differential equation\") OR (\"partial difference equations\"))) or (\"racial differences equationss\"))*".
• Removing quotes may allow a broader search: (((( partial differential equation ) OR ( partial difference equations ))) or ( racial differences equationss ))*.