Perhaps you should try some spelling variations:
"hoc sach ky thuat co khi" » "hoc sinh ky thuat co khi", "hoc cac ky thuat co khi", "hoc anh ky thuat co khi", "hoc sach ky thuat do khi", "hoc sach ky thuat o khi", "hoc sach y thuat co khi", "hoc sach ty thuat co khi", "hoc sach kem thuat co khi"
"so sac ky thuat co khi" » "so sac ky thuat do khi", "so sac ky thuat o khi", "so sach ky thuat co khi", "so dac ky thuat co khi", "so cac ky thuat co khi", "so sai ky thuat co khi"
"bo sach ky thuat co khi" » "bo sach ky thuat do khi", "bo sach ky thuat o khi", "co sach ky thuat co khi", "bo sach y thuat co khi", "bo sach ty thuat co khi", "bo sach kem thuat co khi"

Try widening your search to All Fields.

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

• Performing a fuzzy search may retrieve terms with similar spellings: (("so sac ky thuat co khi") or ((("bo sach ky thuat co khi") or ("hoc sach ky thuat co khi"))))~.
• If you are trying to use Boolean operators, they must be ALL CAPS: (("so sac ky thuat co khi") OR ((("bo sach ky thuat co khi") OR ("hoc sach ky thuat co khi")))).
• Removing quotes may allow a broader search: (( so sac ky thuat co khi ) or ((( bo sach ky thuat co khi ) or ( hoc sach ky thuat co khi )))).
• Adding a wildcard symbol may retrieve word variants: (("so sac ky thuat co khi") or ((("bo sach ky thuat co khi") or ("hoc sach ky thuat co khi"))))*.