Perhaps you should try some spelling variations:
thang mua » thang cua, than cua, thang va
cau tren » cu tren, dau tren, ca tren
sach thu » sach thue, sach thieu, sach tham
hieu van » hieu va, thien van, lieu va
than ma » than man, than va, khan ma
van cau » van dau, van hau, van chat
truc va » thuc va, thuc vat, trung va
va hanh » van hanh, va thanh, va danh
cuu tre » cua tre, cau treo
tu sach » thu sach, su sach, te sach

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 thu ((than ma) or (thang mua)) hoi. hieu van cau truc va hanh vi ((cuu tre) OR (cau tren))~.
• If you are trying to use Boolean operators, they must be ALL CAPS: tu sach thu ((than ma) OR (thang mua)) hoi. hieu van cau truc va hanh vi ((cuu tre) OR (cau tren)).
• The words AND, OR and NOT may confuse the search; try adding quotes: "tu sach thu ((than ma) or (thang mua)) hoi. hieu van cau truc va hanh vi ((cuu tre) OR (cau tren))".
• Adding a wildcard symbol may retrieve word variants: tu sach thu ((than ma) or (thang mua)) hoi. hieu van cau truc va hanh vi ((cuu tre) OR (cau tren))*.