Perhaps you should try some spelling variations:
can thiet » dan thiet, cac thiet, cad thiet
van thiet » va thiet, dan thiet, van thien
hieu van » hieu va, thien van, lieu va
cac bac » cac bai, cac ban, cac cach
tinh vi » trinh vi, tinh voi, tinh va
va tinh » may tinh
vu sach » vu bach, su sach, vu khach
ly nang » ky nang, ly hang, ly vang
van cac » van hac, van cau, van bac
y nang » ky nang, v nang, may nang
bac va » ban va, bac ha, bao 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: vu sach ((y nang) or (ly nang)) x hoi. hieu van cac bac va tinh vi ((van thiet) OR (can thiet))~.
• If you are trying to use Boolean operators, they must be ALL CAPS: vu sach ((y nang) OR (ly nang)) x hoi. hieu van cac bac va tinh vi ((van thiet) OR (can thiet)).
• The words AND, OR and NOT may confuse the search; try adding quotes: "vu sach ((y nang) or (ly nang)) x hoi. hieu van cac bac va tinh vi ((van thiet) OR (can thiet))".
• Adding a wildcard symbol may retrieve word variants: vu sach ((y nang) or (ly nang)) x hoi. hieu van cac bac va tinh vi ((van thiet) OR (can thiet))*.