Perhaps you should try some spelling variations:
"article and nonlinear chemical" » "article and nonlinear mechanical", "article and nonlinear dynamical", "article and nonlinear numerical"
"article and nuclear medical" » "article and nuclear medicine", "article and nuclear material"

Try widening your search to All Fields.

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

• If you are trying to use Boolean operators, they must be ALL CAPS: (("article and nuclear medical") OR ("article and nonlinear chemical")).
• Removing quotes may allow a broader search: (( article and nuclear medical ) or ( article and nonlinear chemical )).
• Adding a wildcard symbol may retrieve word variants: (("article and nuclear medical") or ("article and nonlinear chemical"))*.