Perhaps you should try some spelling variations:
van hanh » van thanh, ban hanh, van anh
thuc van » thuc vat, thuc dan, thuc va
cam thuc » am thuc, nam thuc, cam thu
tai cua » thai cua, tai cuc, tri cua
tai sua » dai sua, tai su, tan sua
tu sach » thu sach, su sach, te sach
tang ma » mang may, tang van
ky tang » ky nang, ky dang, kho tang
vu sach » vu bach, su sach, vu khach
hieu va » lieu va, hieu qua
va cam » va cham, va cac, va cao
ma hoi » mai hoi, xa hoi, ma hoa

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 (vu sach)) ky tang ma hoi. hieu va cam thuc van hanh ((tai sua) OR (tai cua)) viet~.
• If you are trying to use Boolean operators, they must be ALL CAPS: ((tu sach) OR (vu sach)) ky tang ma hoi. hieu va cam thuc van hanh ((tai sua) OR (tai cua)) viet.
• The words AND, OR and NOT may confuse the search; try adding quotes: "((tu sach) or (vu sach)) ky tang ma hoi. hieu va cam thuc van hanh ((tai sua) OR (tai cua)) viet".
• Adding a wildcard symbol may retrieve word variants: ((tu sach) or (vu sach)) ky tang ma hoi. hieu va cam thuc van hanh ((tai sua) OR (tai cua)) viet*.