Perhaps you should try some spelling variations:
nam thuc » nam thuoc, am thuc, nam tu
day danh » day manh, dai danh, dao danh
danh vai » danh sai, danh va, doanh van
tu sach » thu sach, su sach, te sach
nang ma » tang ma, sang ma, nang cao
hieu va » lieu va, hieu qua
ca tren » cau tren, cu tren, la tren
vai ca » vai cac, vai cua, bai ca

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) OR (nam thu)) day danh vai ca 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) OR (nam thu)) day danh vai ca 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) OR (nam thu)) day danh vai ca tren".
• Adding a wildcard symbol may retrieve word variants: tu sach y ((nang ma) or (nang x)) hoi. hieu va ((nam thuc) OR (nam thu)) day danh vai ca tren*.