Perhaps you should try some spelling variations:
"function systems a tools" » "equation systems a tools", "function spaces a tools", "pension systems a tools", "function system a tools", "function systems via tools", "function system _ tools", "function systems a tool"
"function systems _ tools" » "equation systems _ tools", "function spaces _ tools", "pension systems _ tools"
"fusion system based tools" » "diffusion systems based tools", "fusion system based tool", "fusion system coated 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 systems a tools") OR ("function systems _ tools"))) or ("fusion system based tools"))~.
• If you are trying to use Boolean operators, they must be ALL CAPS: (((("function systems a tools") OR ("function systems _ tools"))) OR ("fusion system based tools")).
• The words AND, OR and NOT may confuse the search; try adding quotes: "((((\"function systems a tools\") OR (\"function systems _ tools\"))) or (\"fusion system based tools\"))".
• Removing quotes may allow a broader search: (((( function systems a tools ) OR ( function systems _ tools ))) or ( fusion system based tools )).
• Adding a wildcard symbol may retrieve word variants: (((("function systems a tools") OR ("function systems _ tools"))) or ("fusion system based tools"))*.