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