Perhaps you should try some spelling variations:
nham thuc » nhan thuc, nam thuc, nham thu
cham thuc » pham thuc, tham thuc, pham thuoc
cua viet » ca viet, hoa viet, cua vat
danh vai » danh sai, danh va, doanh van
hieu van » hieu va, thien van, lieu va
lai hoi » dai hoi, lai hoa, lai roi
mai doi » moi doi, mai hoi, mai khoi
va danh » va dinh, va dan, va hanh
vai cua » dai cua, hai cua, lai cua
so sach » so sanh, bo sach, co sach
y nang » ky nang, ly nang, v nang

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

• Performing a fuzzy search may retrieve terms with similar spellings: so sach y nang ((mai doi) or (lai hoi)). hieu van ((cham thuc) OR (nham thuc)) va danh vai cua viet~.
• If you are trying to use Boolean operators, they must be ALL CAPS: so sach y nang ((mai doi) OR (lai hoi)). hieu van ((cham thuc) OR (nham thuc)) va danh vai cua viet.
• The words AND, OR and NOT may confuse the search; try adding quotes: "so sach y nang ((mai doi) or (lai hoi)). hieu van ((cham thuc) OR (nham thuc)) va danh vai cua viet".
• Adding a wildcard symbol may retrieve word variants: so sach y nang ((mai doi) or (lai hoi)). hieu van ((cham thuc) OR (nham thuc)) va danh vai cua viet*.