Perhaps you should try some spelling variations:
nang doc » nang luc
cau tren » cu tren, dau tren, ca tren
doc hoc » duoc hoc, toc hoc, duc hoc
sach ky » sach y, sach ty, sach kem
va hanh » van hanh, va thanh, va danh
hanh ve » hanh vi, hanh va, hanh kem
ve chat » va chat, van chat
sac ky » cac ky, sai ky
ve cac » va cac, vien cac
luc va » duc va, tuc va, loc va
ve cau » ke cau, va cau, le cau

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

• Performing a fuzzy search may retrieve terms with similar spellings: thu ((sach ky) or (sac ky)) nang doc hoc. hieu ((ve chat) or (ve cac)) luc va hanh ve cau tren~.
• If you are trying to use Boolean operators, they must be ALL CAPS: thu ((sach ky) OR (sac ky)) nang doc hoc. hieu ((ve chat) OR (ve cac)) luc va hanh ve cau tren.
• Adding a wildcard symbol may retrieve word variants: thu ((sach ky) or (sac ky)) nang doc hoc. hieu ((ve chat) or (ve cac)) luc va hanh ve cau tren*.