Perhaps you should try some spelling variations:
cac thoi » cac toi, cac hop, cac tro
danh doi » danh di, thanh doi, dung doi
hieu van » hieu va, thien van, lieu va
su sach » so sach, vu sach
cac toc » cac toi, cac nuoc
doi cua » dai cua, hoi cua
xa danh » va danh, dia danh, nam danh
sach ky » sac ky, sach y, sach ty
tang ma » mang may, tang van
nang ma » sang ma, nang cao, mang may
cua tre » cua te, cuu tre, cua triet

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 ky ((nang ma) or (tang ma)) hoi. hieu van ((cac toc) OR (cac thoi)) xa danh doi cua tre~.
• If you are trying to use Boolean operators, they must be ALL CAPS: su sach ky ((nang ma) OR (tang ma)) hoi. hieu van ((cac toc) OR (cac thoi)) xa danh doi cua tre.
• The words AND, OR and NOT may confuse the search; try adding quotes: "su sach ky ((nang ma) or (tang ma)) hoi. hieu van ((cac toc) OR (cac thoi)) xa danh doi cua tre".
• Adding a wildcard symbol may retrieve word variants: su sach ky ((nang ma) or (tang ma)) hoi. hieu van ((cac toc) OR (cac thoi)) xa danh doi cua tre*.