Perhaps you should try some spelling variations:
khoan hoi » khoan nhoi, khoa hoc, khoa doi
khoa hoi » khoa hoc, khoa doi, khoa noi
vat hanh » vat thanh, van hanh, va hanh
hieu van » hieu va, thien van, lieu va
tu sach » thu sach, su sach, te sach
hanh ki » hanh vi, hanh ky, hanh kien
hieu ve » hieu va
sach ty » sach y, sach tu, sach thu
ty dang » ty xang, ky dang, ty hang
su tien » su kien, su hien, tu tieng
ki su » ky su
thuc » thu

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 ty dang ((khoa hoi) OR (khoan hoi)). ((hieu ve) or (hieu van)) am thuc vat hanh ki su tien~.
• If you are trying to use Boolean operators, they must be ALL CAPS: tu sach ty dang ((khoa hoi) OR (khoan hoi)). ((hieu ve) OR (hieu van)) am thuc vat hanh ki su tien.
• The words AND, OR and NOT may confuse the search; try adding quotes: "tu sach ty dang ((khoa hoi) OR (khoan hoi)). ((hieu ve) or (hieu van)) am thuc vat hanh ki su tien".
• Adding a wildcard symbol may retrieve word variants: tu sach ty dang ((khoa hoi) OR (khoan hoi)). ((hieu ve) or (hieu van)) am thuc vat hanh ki su tien*.