Perhaps you should try some spelling variations:
"fractional difference equation" » "functional differences equation", "fractional differential equation", "national differences equation", "fractional differential equations"
"fractional difference equations" » "functional differences equations", "fractional differential equations", "national differences equations", "fractional differential equationss"
"national difference equation" » "national differences equation", "rational difference equation", "functional difference equation", "national differential equation", "national 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: (("national difference equation") OR ((("fractional difference equation") OR ("fractional difference equations")))).
• The words AND, OR and NOT may confuse the search; try adding quotes: "((\"national difference equation\") or (((\"fractional difference equation\") OR (\"fractional difference equations\"))))".
• Removing quotes may allow a broader search: (( national difference equation ) or ((( fractional difference equation ) OR ( fractional difference equations )))).
• Adding a wildcard symbol may retrieve word variants: (("national difference equation") or ((("fractional difference equation") OR ("fractional difference equations"))))*.