Perhaps you should try some spelling variations:
thu sach » tu sach, thuat sach, thuoc sach
kho tang » cao tang
cau tren » cu tren, dau tren, ca tren
lai hoi » dai hoi, lai hoa, lai roi
ky sang » ky nang, ky dang, ky tang
dau vai » dau va, dau hai, dau tai
vai cau » va cau, van cau, vai cac
hieu ve » hieu va, hieu van
ve cam » ve cham, ve cac, va cam
luc va » tuc va, loc va

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

• Performing a fuzzy search may retrieve terms with similar spellings: thu sach ((ky sang) or (kho tang)) lai hoi. hieu ve cam ((luc va) OR (duc va)) dau vai cau tren~.
• If you are trying to use Boolean operators, they must be ALL CAPS: thu sach ((ky sang) OR (kho tang)) lai hoi. hieu ve cam ((luc va) OR (duc va)) dau vai cau tren.
• The words AND, OR and NOT may confuse the search; try adding quotes: "thu sach ((ky sang) or (kho tang)) lai hoi. hieu ve cam ((luc va) OR (duc va)) dau vai cau tren".
• Adding a wildcard symbol may retrieve word variants: thu sach ((ky sang) or (kho tang)) lai hoi. hieu ve cam ((luc va) OR (duc va)) dau vai cau tren*.