Perhaps you should try some spelling variations:
thu sach » tu sach, thuat sach, thuoc sach
hang cao » hoang cao, nang cao, hang ca
thuc day » thuc dan, thuc vat
dan vai » dan va, dan tai, dan vat
thuc va » thuc vat, thuc dan
hieu va » lieu va, hieu qua
sach ty » sach y, sach tu, sach thu
hieu vu » hieu ve, hieu su, dieu vu
cao hoi » cau hoi, co hoi, cao hoc
ty hang » ly hang, ty xang, thi hang
vai va » mai va, dai va, hai va
thiet » thieu

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 ty hang cao hoi. ((hieu vu) or (hieu va)) cham ((thuc va) OR (thuc day)) dan vai va thiet~.
• If you are trying to use Boolean operators, they must be ALL CAPS: thu sach ty hang cao hoi. ((hieu vu) OR (hieu va)) cham ((thuc va) OR (thuc day)) dan vai va thiet.
• The words AND, OR and NOT may confuse the search; try adding quotes: "thu sach ty hang cao hoi. ((hieu vu) or (hieu va)) cham ((thuc va) OR (thuc day)) dan vai va thiet".
• Adding a wildcard symbol may retrieve word variants: thu sach ty hang cao hoi. ((hieu vu) or (hieu va)) cham ((thuc va) OR (thuc day)) dan vai va thiet*.