Perhaps you should try some spelling variations:
dang khoa » dung khoa, hang khoa, dang khoi
hieu van » thien van, lieu va, hieu ve
thu sach » thuat sach, thuoc sach, thu hoach
vat hanh » vat thanh, van hanh, va hanh
khoa hoi » khoan hoi, khoa hoc, khoa doi
tu sach » su sach, te sach, tu cach
hanh ki » hanh vi, hanh ky, hanh kien
hieu va » lieu va, hieu qua
su tien » su kien, su hien, tu tieng
y dang » ky dang, 2 dang, _ dang
ki su » ky su

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 (thu sach)) y dang khoa hoi. ((hieu va) 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) OR (thu sach)) y dang khoa hoi. ((hieu va) 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) OR (thu sach)) y dang khoa hoi. ((hieu va) or (hieu van)) am thuc vat hanh ki su tien".
• Adding a wildcard symbol may retrieve word variants: ((tu sach) OR (thu sach)) y dang khoa hoi. ((hieu va) or (hieu van)) am thuc vat hanh ki su tien*.