Perhaps you should try some spelling variations:
toc sach » hoc sach, doc sach, thuoc sach
vuc nang » cuc nang, chuc nang, van nang
vu nang » va nang, vu dang, v nang
hieu va » hieu qua
cam duc » cam xuc, cao duc, pham duc
va hanh » van hanh, va thanh, va danh
hanh de » hanh ve, hanh kem
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 ((vu nang) OR (vuc nang)) x hoi. ((hieu va) or (lieu va)) cam duc va hanh de va thiet~.
• If you are trying to use Boolean operators, they must be ALL CAPS: toc sach ((vu nang) OR (vuc nang)) x hoi. ((hieu va) OR (lieu va)) cam duc va hanh de va thiet.
• The words AND, OR and NOT may confuse the search; try adding quotes: "toc sach ((vu nang) OR (vuc nang)) x hoi. ((hieu va) or (lieu va)) cam duc va hanh de va thiet".
• Adding a wildcard symbol may retrieve word variants: toc sach ((vu nang) OR (vuc nang)) x hoi. ((hieu va) or (lieu va)) cam duc va hanh de va thiet*.