Perhaps you should try some spelling variations:
"50 ppm decrease" » "50 _ decrease" (Expand Search)
"_ fe decrease" » "_ _ decrease" (Expand Search), "_ f_ decrease" (Expand Search), "_ f_ decreased" (Expand Search), "_ f_ decreases" (Expand Search), "_ e decrease" (Expand Search)
"50 a decrease" » "50 _ decrease" (Expand Search), "50 _ decreased" (Expand Search), "50 _ decreases" (Expand Search), "5 a decrease" (Expand Search), "50 i decrease" (Expand Search)
"5 e decrease" » "5 _ decrease" (Expand Search), "5 _ decreased" (Expand Search), "5 _ decreases" (Expand Search)

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

• The words AND, OR and NOT may confuse the search; try adding quotes: "((\"50 ppm decrease\") OR (((\"50 a decrease\") OR (((\"5 e decrease\") OR (\"_ fe decrease\"))))))~".
• Removing quotes may allow a broader search: (( 50 ppm decrease ) OR ((( 50 a decrease ) OR ((( 5 e decrease ) OR ( _ fe decrease ))))))~.
• Adding a wildcard symbol may retrieve word variants: (("50 ppm decrease") OR ((("50 a decrease") OR ((("5 e decrease") OR ("_ fe decrease"))))))*.