Perhaps you should try some spelling variations:
toc sach » hoc sach, doc sach, thuoc sach
sach cuc » sach cua, sach duoc, sach nuoc
cuc nang » chuc nang, cuu nang, cua nang
hieu va » hieu qua
va danh » va dinh, va dan, va hanh
danh de » hanh de, dan de, dang de
x hoi » xa hoi, o hoi, x ho
de va » de van, te va, ke 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: toc sach cuc nang x hoi. ((hieu va) or (lieu va)) pham duc va danh de va thiet~.
• If you are trying to use Boolean operators, they must be ALL CAPS: toc sach cuc nang x hoi. ((hieu va) OR (lieu va)) pham duc va danh de va thiet.
• Adding a wildcard symbol may retrieve word variants: toc sach cuc nang x hoi. ((hieu va) or (lieu va)) pham duc va danh de va thiet*.