Perhaps you should try some spelling variations:
toc sach » hoc sach, doc sach, thuoc sach
hieu va » hieu qua
cam duc » cam xuc, pham duc, nam duoc
cao duc » dao duc, cao suc, giao duc
va hanh » van hanh, va thanh, va danh
hanh de » hanh ve, hanh kem
sach v » sach va, sach y, sach 2
v nang » va nang, vu nang, van nang
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 v nang x hoi. ((hieu va) or (lieu va)) ((cam duc) OR (cao duc)) va hanh de va thiet~.
• If you are trying to use Boolean operators, they must be ALL CAPS: toc sach v nang x hoi. ((hieu va) OR (lieu va)) ((cam duc) OR (cao duc)) va hanh de va thiet.
• The words AND, OR and NOT may confuse the search; try adding quotes: "toc sach v nang x hoi. ((hieu va) or (lieu va)) ((cam duc) OR (cao duc)) va hanh de va thiet".
• Adding a wildcard symbol may retrieve word variants: toc sach v nang x hoi. ((hieu va) or (lieu va)) ((cam duc) OR (cao duc)) va hanh de va thiet*.