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