Perhaps you should try some spelling variations:
hieu van » thien van, lieu va, hieu ve
chat duc » chat xuc, chat doc, chet duoc
su sach » so sach, vu sach
nang xa » nang x, lang xa, nang ma
hieu va » lieu va, hieu qua
va dinh » van dinh, va tinh, vu dinh
va kinh » va tinh, qua kinh
cua tre » cua te, cuu tre, cua triet
y nang » ky nang, ly nang, v nang
va cua » va chua, via cua, ca cua

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 y nang xa hoi. ((hieu van) or (hieu va)) chat duc ((va dinh) OR (va kinh)) va cua tre~.
• If you are trying to use Boolean operators, they must be ALL CAPS: su sach y nang xa hoi. ((hieu van) OR (hieu va)) chat duc ((va dinh) OR (va kinh)) va cua tre.
• The words AND, OR and NOT may confuse the search; try adding quotes: "su sach y nang xa hoi. ((hieu van) or (hieu va)) chat duc ((va dinh) OR (va kinh)) va cua tre".
• Adding a wildcard symbol may retrieve word variants: su sach y nang xa hoi. ((hieu van) or (hieu va)) chat duc ((va dinh) OR (va kinh)) va cua tre*.