Perhaps you should try some spelling variations:
khach danh » khach hang, khach san, sach danh
sach ngan » sach ngon, sach nha, sach han
va thuat » ki thuat, va thuc, va thiet
toan hoc » toan khoa, van hoc, hoa hoc
vu khach » vu khanh, vu khac, vay khach
tu sach » thu sach, su sach, te sach
ngan va » ngan van, nhan va, ngay va
danh ky » hanh ky, dan ky, dang ky

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 ngan va thuat toan hoc ) or ( vu khach danh ky thuat toan hoc ))~.
• If you are trying to use Boolean operators, they must be ALL CAPS: (( tu sach ngan va thuat toan hoc ) OR ( vu khach danh ky thuat toan hoc ))*.