Perhaps you should try some spelling variations:
thu sach » tu sach, thuat sach, thuoc sach
hieu van » hieu va, thien van, lieu va
cau tren » cu tren, dau tren, ca tren
sach ky » sac ky, sach y, sach ty
va hanh » van hanh, va thanh, va danh
vi cau » va cau, ve cau, di cau
o hoi » co hoi, o hai, o hoa
o hoc » co hoc, mo hoc, so hoc

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

• If you are trying to use Boolean operators, they must be ALL CAPS: thu sach ky nang ((o hoi) OR (o hoc)). hieu van ((cam xuc) OR (cham soc)) va hanh vi cau tren~.
• The words AND, OR and NOT may confuse the search; try adding quotes: "thu sach ky nang ((o hoi) OR (o hoc)). hieu van ((cam xuc) or (cham soc)) va hanh vi cau tren~".
• Adding a wildcard symbol may retrieve word variants: thu sach ky nang ((o hoi) OR (o hoc)). hieu van ((cam xuc) or (cham soc)) va hanh vi cau tren*.