Perhaps you should try some spelling variations:
dau tren » dau tien, dat tren, dau tieng
cam thuc » am thuc, nam thuc, cam thu
hanh dua » hanh sua, hanh cua, hanh qua
hieu van » hieu va, thien van, lieu va
hanh da » hanh dao, hanh va, hanh de
su sach » so sach, vu sach
hieu ve » hieu va
y nang » ky nang, ly nang, v nang
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: su sach y nang x hoi. ((hieu ve) OR (hieu van)) cam thuc vat ((hanh da) or (hanh dua)) dau tren~.
• If you are trying to use Boolean operators, they must be ALL CAPS: su sach y nang x hoi. ((hieu ve) OR (hieu van)) cam thuc vat ((hanh da) OR (hanh dua)) dau tren.
• The words AND, OR and NOT may confuse the search; try adding quotes: "su sach y nang x hoi. ((hieu ve) OR (hieu van)) cam thuc vat ((hanh da) or (hanh dua)) dau tren".
• Adding a wildcard symbol may retrieve word variants: su sach y nang x hoi. ((hieu ve) OR (hieu van)) cam thuc vat ((hanh da) or (hanh dua)) dau tren*.