Perhaps you should try some spelling variations:
"tu sach kxy thuat doc khi" » "tu sach kxy thuat duoc khi", "tu sach kxy thuat doi khi", "tu sach kxy thuat don khi", "tu sach ki thuat doc khi", "tu sach my thuat doc khi", "tu sach ky thua doc khi", "tu sach kxy thuat oc khi", "tu sach xa thuat doc khi", "tu sach kem thuat doc khi", "tu sac ky thuat doc khi", "thu sach kxy thuat doc khi", "su sach kxy thuat doc khi", "te sach kxy thuat doc khi", "tu sach kxy thuat hoc khi", "tu sach kxy thuat hoc khoi"
"tu sach ky thuat do thi" » "tu sach ky thuat o thi", "thu sach ky thuat do thi", "su sach ky thuat do thi", "te sach ky thuat do thi", "tu sac ky thuat do thi", "tu sach y thuat do thi", "tu sach ty thuat do thi"

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: (("tu sach ky thuat do thi") or ("tu sach kxy thuat doc khi"))~.
• If you are trying to use Boolean operators, they must be ALL CAPS: (("tu sach ky thuat do thi") OR ("tu sach kxy thuat doc khi")).
• Removing quotes may allow a broader search: (( tu sach ky thuat do thi ) or ( tu sach kxy thuat doc khi )).
• Adding a wildcard symbol may retrieve word variants: (("tu sach ky thuat do thi") or ("tu sach kxy thuat doc khi"))*.