Merging several bibliographies in one

I want to make a document with several chapters and a merged bibliography at the end. There are 7 different files that I merged  in  one big file. I had thought that the bibliography would be automatically merged and ordered, however this doesnt happen. The bibliography is still separated by chapters and although I asked to actualise fields. It stay the same.

How may I merge all the 7 bibliographies in one ??

Thanks in advance. I cannot finish my phd without this :frowning:

Malva

Reading here I found a response:

"The only way to achieve this, it to keep the two documents separate and format them, and then make a copy and unlink the fields, and then merge the copies.  Go back to the original chapter files to make any changes and repeat the process. "

However it is not clear, how unlink the fields??? :-{