Perhaps you should try some spelling variations:
trinh doc » trinh do, trinh hoa, trinh co
thu sach » tu sach, thuat sach, thuoc sach
hieu van » hieu va, thien van, lieu va
tinh doi » trinh do, tinh hoc, tinh son
sach ky » sac ky, sach y, sach ty
van cac » van hac, van cau, van bac
co hoi » co hoc
dan va » doan va, dan ca, ban va

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

• Performing a fuzzy search may retrieve terms with similar spellings: thu sach ky nang ((co hoi) or (co loi)). hieu van cac dan va ((tinh doi) OR (trinh doc)) cua vat~.
• If you are trying to use Boolean operators, they must be ALL CAPS: thu sach ky nang ((co hoi) OR (co loi)). hieu van cac dan va ((tinh doi) OR (trinh doc)) cua vat.
• The words AND, OR and NOT may confuse the search; try adding quotes: "thu sach ky nang ((co hoi) or (co loi)). hieu van cac dan va ((tinh doi) OR (trinh doc)) cua vat".
• Adding a wildcard symbol may retrieve word variants: thu sach ky nang ((co hoi) or (co loi)). hieu van cac dan va ((tinh doi) OR (trinh doc)) cua vat*.