Perhaps you should try some spelling variations:
vat danh » va danh, van danh, luat danh
nam thuc » nam thuoc, am thuc, nam thu
vai cau » van cau, vai cac, lai chau
tu sach » thu sach, su sach, te sach
hieu va » lieu va, hieu qua
nang ma » tang ma, sang ma, nang cao
va cau » van cau, va cac, va dau
va nam » van nam, ha nam, va nay

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 y ((nang ma) or (nang x)) hoi. hieu va nam thuc vat danh ((vai cau) OR (va cau)) tren~.
• If you are trying to use Boolean operators, they must be ALL CAPS: tu sach y ((nang ma) OR (nang x)) hoi. hieu va nam thuc vat danh ((vai cau) OR (va cau)) tren.
• The words AND, OR and NOT may confuse the search; try adding quotes: "tu sach y ((nang ma) or (nang x)) hoi. hieu va nam thuc vat danh ((vai cau) OR (va cau)) tren".
• Adding a wildcard symbol may retrieve word variants: tu sach y ((nang ma) or (nang x)) hoi. hieu va nam thuc vat danh ((vai cau) OR (va cau)) tren*.