Perhaps you should try some spelling variations:
vao thiet » va thiet, tao thiet, van thiet
hieu van » hieu va, thien van, lieu va
nam thuc » nam thuoc, nam thu, nam tu
vu sach » vu bach, su sach, vu khach
sach va » sach xa, sach ha, sach dao
va nang » van nang, da nang, cam nang
cao hoi » cau hoi, co hoi, cao hoc
va hanh » van hanh, va thanh, va danh
hanh di » hanh vi, hanh de, hang di

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

• Performing a fuzzy search may retrieve terms with similar spellings: vu sach va nang cao hoi. hieu van ((am thuc) or (nam thuc)) va hanh di vao thiet~.
• If you are trying to use Boolean operators, they must be ALL CAPS: vu sach va nang cao hoi. hieu van ((am thuc) OR (nam thuc)) va hanh di vao thiet.
• Adding a wildcard symbol may retrieve word variants: vu sach va nang cao hoi. hieu van ((am thuc) or (nam thuc)) va hanh di vao thiet*.