Perhaps you should try some spelling variations:
doc sach » hoc sach, toc sach, nuoc sach
hieu sau » hieu su, hieu suat, tieu su
cham loc » cham soc, chon loc, cham o
hieu vu » hieu va, hieu ve, hieu su
sach vu » sach va, sach tu, sach uu
va hanh » van hanh, va thanh, va danh
vu nang » vuc nang, va nang, vu dang
dau cuu » dau cuoi
dau cua » dai cua, day cua, cau cua
loc va » hoc va, luc va
x hoi » xa hoi, o hoi, x ho

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

• Performing a fuzzy search may retrieve terms with similar spellings: doc sach vu nang x hoi. ((hieu vu) or (hieu sau)) cham loc va hanh ((dau cuu) OR (dau cua)) tre~.
• If you are trying to use Boolean operators, they must be ALL CAPS: doc sach vu nang x hoi. ((hieu vu) OR (hieu sau)) cham loc va hanh ((dau cuu) OR (dau cua)) tre.
• The words AND, OR and NOT may confuse the search; try adding quotes: "doc sach vu nang x hoi. ((hieu vu) or (hieu sau)) cham loc va hanh ((dau cuu) OR (dau cua)) tre".
• Adding a wildcard symbol may retrieve word variants: doc sach vu nang x hoi. ((hieu vu) or (hieu sau)) cham loc va hanh ((dau cuu) OR (dau cua)) tre*.