Perhaps you should try some spelling variations:
thu sach » tu sach, thuat sach, thuoc sach
cam thuc » am thuc, cam thu, can thuc
hanh tai » thanh tai, hang tai, han tai
day hanh » day nhanh, day thanh, dao hanh
nam thuc » nam thuoc, am thuc, nam thu
su hien » su kien, su tien, thu hien
hieu ve » hieu va, hieu van
lang xa » lang ha, dang xay, lang van
mang xa » mang may, dang xay, mang cua
tai su » tai so, tai tu, lai su

You may be able to get more results by adjusting your search query.

• Performing a fuzzy search may retrieve terms with similar spellings: thu sach y ((mang xa) or (lang xa)) hoi. hieu ve ((cam thuc) OR (nam thuc)) day hanh tai su hien~.
• If you are trying to use Boolean operators, they must be ALL CAPS: thu sach y ((mang xa) OR (lang xa)) hoi. hieu ve ((cam thuc) OR (nam thuc)) day hanh tai su hien.
• The words AND, OR and NOT may confuse the search; try adding quotes: "thu sach y ((mang xa) or (lang xa)) hoi. hieu ve ((cam thuc) OR (nam thuc)) day hanh tai su hien".
• Adding a wildcard symbol may retrieve word variants: thu sach y ((mang xa) or (lang xa)) hoi. hieu ve ((cam thuc) OR (nam thuc)) day hanh tai su hien*.