Perhaps you should try some spelling variations:
dan manh » dang manh, doan manh, van manh
thuc dan » thuc hanh, hoc dan, thuc vat
nam thuc » nam thuoc, am thuc, nam thu
tu sach » thu sach, su sach, te sach
sach ky » sac ky, sach y, sach ty
hieu ve » hieu va, hieu van
hai ca » hai cua, hai ba, hai va
ve nam » he nam, va nam, le nam
o hai » co hai, so hai, o lai
o hoi » co hoi, o hoc, o 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 ky nang ((o hoi) OR (o hai)). hieu ve nam thuc dan manh ((hai ca) or (bai ca)) viet~.
• If you are trying to use Boolean operators, they must be ALL CAPS: tu sach ky nang ((o hoi) OR (o hai)). hieu ve nam thuc dan manh ((hai ca) OR (bai ca)) viet*.
• The words AND, OR and NOT may confuse the search; try adding quotes: "tu sach ky nang ((o hoi) OR (o hai)). hieu ve nam thuc dan manh ((hai ca) or (bai ca)) viet*".