Perhaps you should try some spelling variations:
"chemical mechanical" » "chemical mechanisms", "chemo mechanical", "chemical biochemical"
"physical mechanical" » "physico mechanical", "physical mechanisms"
"thermal mechanical" » "thermo mechanical"

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: (((("chemical mechanical") OR ("thermal mechanical"))) OR ("physical mechanical")).
• The words AND, OR and NOT may confuse the search; try adding quotes: "((((\"chemical mechanical\") OR (\"thermal mechanical\"))) or (\"physical mechanical\"))".
• Removing quotes may allow a broader search: (((( chemical mechanical ) OR ( thermal mechanical ))) or ( physical mechanical )).
• Adding a wildcard symbol may retrieve word variants: (((("chemical mechanical") OR ("thermal mechanical"))) or ("physical mechanical"))*.