Perhaps you should try some spelling variations:
tu sach » thu sach, su sach, te sach
hieu va » lieu va, hieu qua
cac tuc » cac tu, cac tac, cac nuoc
cac toc » cac toi, cac nuoc, cac thoi
va hanh » van hanh, va thanh, va danh
hanh ca » hanh cac, hanh cat, hanh cua
cua tre » cua te, cuu tre, cua triet
y nang » ky nang, ly nang, v nang
ca cua » co cua

You may be able to get more results by adjusting your search query.

• Performing a fuzzy search may retrieve terms with similar spellings: tu sach y nang ((le hoi) or (ma hoa)). hieu va ((cac tuc) OR (cac toc)) va hanh ca cua tre~.
• If you are trying to use Boolean operators, they must be ALL CAPS: tu sach y nang ((le hoi) OR (ma hoa)). hieu va ((cac tuc) OR (cac toc)) va hanh ca cua tre.
• The words AND, OR and NOT may confuse the search; try adding quotes: "tu sach y nang ((le hoi) or (ma hoa)). hieu va ((cac tuc) OR (cac toc)) va hanh ca cua tre".
• Adding a wildcard symbol may retrieve word variants: tu sach y nang ((le hoi) or (ma hoa)). hieu va ((cac tuc) OR (cac toc)) va hanh ca cua tre*.