Perhaps you should try some spelling variations:
co thiet » so thiet, ho thiet, cuu thiet
hieu van » hieu va, thien van, lieu va
hanh tai » thanh tai, hang tai, han tai
van hanh » van thanh, ban hanh, van anh
pham duy » pham duc
duy van » duy vat, dung van
tu sach » thu sach, su sach, te sach
sach ty » sach y, sach tu, sach thu
hieu ve » hieu va
nang ma » tang ma, sang ma, nang cao
tai co » mai co, tai so, tri co

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

• Performing a fuzzy search may retrieve terms with similar spellings: tu sach ty ((nang ma) or (nang x)) hoi. ((hieu ve) or (hieu van)) pham duy van hanh tai co thiet~.
• If you are trying to use Boolean operators, they must be ALL CAPS: tu sach ty ((nang ma) OR (nang x)) hoi. ((hieu ve) OR (hieu van)) pham duy van hanh tai co thiet.
• Adding a wildcard symbol may retrieve word variants: tu sach ty ((nang ma) or (nang x)) hoi. ((hieu ve) or (hieu van)) pham duy van hanh tai co thiet*.