Perhaps you should try some spelling variations:
tham thuc » nham thuc, pham thuc, tam thuc
tu sach » thu sach, te sach, tu cach
su sach » so sach
vu sach » vu bach, vu khach
ky tang » ky nang, ky dang, kho tang
tang ma » mang may, tang van
hieu ve » hieu va, hieu van
ve tham » va tham, ve cham, vi tham
thuc va » thuc vat, thuc dan, thuc day
dao va » dao van, tao va, do 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: ((tu sach) or (((su sach) or (vu sach)))) ky tang ma hoa. hieu ve tham thuc va van dao va thiet~.
• If you are trying to use Boolean operators, they must be ALL CAPS: ((tu sach) OR (((su sach) OR (vu sach)))) ky tang ma hoa. hieu ve tham thuc va van dao va thiet.
• Adding a wildcard symbol may retrieve word variants: ((tu sach) or (((su sach) or (vu sach)))) ky tang ma hoa. hieu ve tham thuc va van dao va thiet*.