Perhaps you should try some spelling variations:
hoc thiet » hoc thieu, hoc thuyet, toc thieu
dung cong » dung trong
tram xay » tra xay, pham xay, tap xay
thau xay » thuat xay, tu xay, phan xay
cong tan » cong tac, cong san, cong thanh
tan chan » dan chan, ban chan, can chan
chan cau » phan cau, can cau, chinh cau

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: ((hoc thiet) OR (hoc hien)) tach - hanh ((tram xay) OR (thau xay)) dung cong tan chan cau~.
• The words AND, OR and NOT may confuse the search; try adding quotes: "((hoc thiet) or (hoc hien)) tach - hanh ((tram xay) OR (thau xay)) dung cong tan chan cau~".
• Adding a wildcard symbol may retrieve word variants: ((hoc thiet) or (hoc hien)) tach - hanh ((tram xay) OR (thau xay)) dung cong tan chan cau*.