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