Perhaps you should try some spelling variations:
hieu van » hieu va, thien van, lieu va
su sach » so sach, vu sach
sach ky » sac ky, sach y, sach ty
doi cua » dai cua, hoi cua
va danh » va dinh, va dan, va hanh
xa danh » dia danh, nam danh, van danh
cac toc » cac toi, cac nuoc, cac thoi
van cac » van hac, van cau, van bac
tang ma » mang may, tang van
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 cao) or (tang ma)) hoi. hieu van cac toc ((xa danh) OR (va danh)) doi cua tre~.
• If you are trying to use Boolean operators, they must be ALL CAPS: su sach ky ((nang cao) OR (tang ma)) hoi. hieu van cac toc ((xa danh) OR (va danh)) doi cua tre.
• The words AND, OR and NOT may confuse the search; try adding quotes: "su sach ky ((nang cao) or (tang ma)) hoi. hieu van cac toc ((xa danh) OR (va danh)) doi cua tre".
• Adding a wildcard symbol may retrieve word variants: su sach ky ((nang cao) or (tang ma)) hoi. hieu van cac toc ((xa danh) OR (va danh)) doi cua tre*.