Perhaps you should try some spelling variations:
sach thu » sach thue, sach thieu, sach tham
van hanh » van thanh, ban hanh, van anh
vai cua » dai cua, hai cua, lai cua
hieu su » hieu sau, tieu su, hieu so
so sach » so sanh, bo sach, co sach
nang ma » tang ma, sang ma, nang cao
lang ha » long ha
su nam » sung nam
nam vo » nam bo, nam so, nam va
vi cua » di cua

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

• Performing a fuzzy search may retrieve terms with similar spellings: so sach thu ((nang ma) or (lang ha)) hoi. hieu su nam vo van hanh ((vi cua) or (vai cua)) tre~.
• If you are trying to use Boolean operators, they must be ALL CAPS: so sach thu ((nang ma) OR (lang ha)) hoi. hieu su nam vo van hanh ((vi cua) OR (vai cua)) tre.
• Adding a wildcard symbol may retrieve word variants: so sach thu ((nang ma) or (lang ha)) hoi. hieu su nam vo van hanh ((vi cua) or (vai cua)) tre*.