Perhaps you should try some spelling variations:
ppm decrease » _ decrease (Expand Search), a decrease (Expand Search), nn decrease (Expand Search)
na decrease » a decrease (Expand Search), nn decrease (Expand Search), pa decreased (Expand Search)
n decrease » nn decrease (Expand Search), _ decrease (Expand Search), a decrease (Expand Search)
50 ppm » 5 ppm (Expand Search)
40 na » 40 nm (Expand Search), 40 pa (Expand Search), 40 ns (Expand Search)
50 n » 50 ns (Expand Search), 50 ng (Expand Search), 50 μ (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 ((( 40 na decrease ) OR ( 50 n decrease ))))~".
• Adding a wildcard symbol may retrieve word variants: (( 50 ppm decrease ) OR ((( 40 na decrease ) OR ( 50 n decrease ))))*.