Perhaps you should try some spelling variations:
cau tren » cu tren, dau tren, ca tren
nam thuc » nam thuoc, am thuc, nam thu
qua nam » quan nam, cua nam, quang nam
va danh » va dinh, va dan, dia danh
va hanh » van hanh, va thanh, ban hanh
nang ma » tang ma, sang ma, nang cao
vai cau » va cau, van cau, vai cac
tu sach » thu sach, su sach, te sach

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