Perhaps you should try some spelling variations:
van hanh » van thanh, ban hanh, van anh
tu sach » thu sach, su sach, te sach
cam tuc » cam xuc, cam tu, nam thuc
tai cua » thai cua, tai cuc, tri cua
tai cuu » tai cuc, tai buu, thai cua
tuc van » thuc van, truc van, tuc va
sach ty » sach y, sach tu, sach thu
hieu ve » hieu va, hieu van
nang ma » tang ma, sang ma, nang cao
ve cam » ve cham, ve cac, va cam

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

• Performing a fuzzy search may retrieve terms with similar spellings: tu sach ty ((nang ma) or (nang x)) hoi. hieu ve cam tuc van hanh ((tai cuu) OR (tai cua)) tre~.
• If you are trying to use Boolean operators, they must be ALL CAPS: tu sach ty ((nang ma) OR (nang x)) hoi. hieu ve cam tuc van hanh ((tai cuu) OR (tai cua)) tre.
• The words AND, OR and NOT may confuse the search; try adding quotes: "tu sach ty ((nang ma) or (nang x)) hoi. hieu ve cam tuc van hanh ((tai cuu) OR (tai cua)) tre".
• Adding a wildcard symbol may retrieve word variants: tu sach ty ((nang ma) or (nang x)) hoi. hieu ve cam tuc van hanh ((tai cuu) OR (tai cua)) tre*.