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)
"1 a decrease" » "1 _ decrease" (Expand Search), "1 _ decreased" (Expand Search), "1 _ decreases" (Expand Search), "19 a decrease" (Expand Search)
"_ e decrease" » "_ _ decrease" (Expand Search), "_ _ decreased" (Expand Search), "_ _ 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 (((\"1 a decrease\") OR (((\"_ e decrease\") OR (\"_ fe decrease\"))))))~".
• Removing quotes may allow a broader search: (( 50 ppm decrease ) OR ((( 1 a decrease ) OR ((( _ e decrease ) OR ( _ fe decrease ))))))~.
• Adding a wildcard symbol may retrieve word variants: (("50 ppm decrease") OR ((("1 a decrease") OR ((("_ e decrease") OR ("_ fe decrease"))))))*.