Perhaps you should try some spelling variations:
sach van » sach han, sach va, bach van
van hanh » van thanh, ban hanh, van anh
truc van » truc va, thuc van, truc ban
cam truc » cau truc, nam truc, lam truoc
vu sach » vu bach, su sach, vu khach
cua tre » cua te, cua triet, dua tren
hanh de » hanh ve, hanh kem
cuu tre » cau tren, cau treo
hieu va » lieu va, hieu qua
va cam » va cham, va cac, va cao
o hai » co hai, so hai, o lai
o hoi » co hoi, o hoc, o hoa

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

• Performing a fuzzy search may retrieve terms with similar spellings: vu sach van ban ((o hoi) OR (o hai)). hieu va cam truc van hanh de ((cua tre) or (cuu tre))~.
• If you are trying to use Boolean operators, they must be ALL CAPS: vu sach van ban ((o hoi) OR (o hai)). hieu va cam truc van hanh de ((cua tre) OR (cuu tre)).
• The words AND, OR and NOT may confuse the search; try adding quotes: "vu sach van ban ((o hoi) OR (o hai)). hieu va cam truc van hanh de ((cua tre) or (cuu tre))".
• Adding a wildcard symbol may retrieve word variants: vu sach van ban ((o hoi) OR (o hai)). hieu va cam truc van hanh de ((cua tre) or (cuu tre))*.