Perhaps you should try some spelling variations:
tinh dieu » trinh dieu, tinh dien, vinh dieu
khoa hoi » khoan hoi, khoa hoc, khoa doi
dieu tra » dieu tri, kiem tra, dieu cua
thuc may » thuc day, truc may, phuc may
nam thuc » nam thuoc, am thuc, nam thu
hieu ve » hieu va, hieu van
tu sach » thu sach, te sach, tu cach
hoa hoi » hoa hoc, hoa doi, hoc hoi
ky tang » ky nang, ky dang, kho tang
su sach » so sach, vu sach
tra tre » tran tren, tran tri, tran tro
ve nam » he nam, va nam, le nam

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 (su sach)) ky tang ((hoa hoi) OR (khoa hoi)). hieu ve nam thuc may tinh dieu tra tre~.
• If you are trying to use Boolean operators, they must be ALL CAPS: ((tu sach) OR (su sach)) ky tang ((hoa hoi) OR (khoa hoi)). hieu ve nam thuc may tinh dieu tra tre.
• The words AND, OR and NOT may confuse the search; try adding quotes: "((tu sach) or (su sach)) ky tang ((hoa hoi) OR (khoa hoi)). hieu ve nam thuc may tinh dieu tra tre".
• Adding a wildcard symbol may retrieve word variants: ((tu sach) or (su sach)) ky tang ((hoa hoi) OR (khoa hoi)). hieu ve nam thuc may tinh dieu tra tre*.