Perhaps you should try some spelling variations:
"function systems a tool" » "equation systems a tool", "function spaces a tool", "fusion system a tool", "fusion systems a tool", "function systems _ tool", "function systems via tool", "function system _ tool"
"function system a tool" » "fusion system a tool", "function system _ tool", "function systems _ tool"
"function layer using tools" » "function layer being tools", "function paper using tools", "function cancer using tools"

You may be able to get more results by adjusting your search query.

• Performing a fuzzy search may retrieve terms with similar spellings: (((("function system a tool") OR ("function systems a tool"))) OR ("function layer using tools"))~.
• The words AND, OR and NOT may confuse the search; try adding quotes: "((((\"function system a tool\") OR (\"function systems a tool\"))) OR (\"function layer using tools\"))".
• Removing quotes may allow a broader search: (((( function system a tool ) OR ( function systems a tool ))) OR ( function layer using tools )).
• Adding a wildcard symbol may retrieve word variants: (((("function system a tool") OR ("function systems a tool"))) OR ("function layer using tools"))*.