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