Perhaps you should try some spelling variations:
hieu van » hieu va, thien van, lieu va
nam thuc » nam thuoc, nam thu, nam tu
su sach » so sach, vu sach
sach va » sach xa, sach ha, sach dao
va nang » van nang, da nang, cam nang
nang co » nang cao, nang doc, nang noi
va hanh » van hanh, va thanh, va danh
hanh di » hanh vi, hanh de, hang di
co hoi » co hoc, co loi
di va » dai va, di vao, doi va
thiet » thieu

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

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