Perhaps you should try some spelling variations:
mach tinh » mach tich, manh tinh, trach tinh
thuyet so » thuyet co, thuyet do, thuyet mo
tinh son » tinh toan, dinh so, tinh hoc
toan cao » toan ban, toan tap
thiet so » thieu so, thiet ke, thiet bi
tu mach » tu cach, tu manh, tu hach
tu hanh » du hanh, lu hanh, thuc hanh
so giao » so giai, hoc giao

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: (( tu mach tinh son - toan cao ) OR ( tu hanh ((thiet so) OR (thuyet so)) - so giao ))~.
• The words AND, OR and NOT may confuse the search; try adding quotes: "(( tu mach tinh son - toan cao ) or ( tu hanh ((thiet so) OR (thuyet so)) - so giao ))~".
• Adding a wildcard symbol may retrieve word variants: (( tu mach tinh son - toan cao ) or ( tu hanh ((thiet so) OR (thuyet so)) - so giao ))*.