Perhaps you should try some spelling variations:
toc sach » hoc sach, doc sach, thuoc sach
tinh van » trinh van, dinh van, tinh va
pham duy » pham duc
hieu va » lieu va, hieu qua
van cua » vang cua, ban cua, dan cua
va tinh » may tinh
va pham » van pham, va phat, va phap
ly nang » ly hang, ly vang, ly quang
duy va » duy vat, duy van, day va
cua su » qua su
o hoi » co hoi, o hoc, o hai

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

• Performing a fuzzy search may retrieve terms with similar spellings: ((te sach) OR (toc sach)) ((ly nang) or (ky nang)) o hoi. hieu va pham duy va tinh van cua su~.
• If you are trying to use Boolean operators, they must be ALL CAPS: ((te sach) OR (toc sach)) ((ly nang) OR (ky nang)) o hoi. hieu va pham duy va tinh van cua su.
• The words AND, OR and NOT may confuse the search; try adding quotes: "((te sach) OR (toc sach)) ((ly nang) or (ky nang)) o hoi. hieu va pham duy va tinh van cua su".
• Adding a wildcard symbol may retrieve word variants: ((te sach) OR (toc sach)) ((ly nang) or (ky nang)) o hoi. hieu va pham duy va tinh van cua su*.