Hi,

It seems the scientific journals are using mostly recommendations from reviewers, and other scientists who know the subject and its sources.

In Elsevier they use CrossCheck

https://www.elsevier.com/editors/perk/plagiarism-complaints/plagiarism-detection

Different anti plagiarism softwares are used to check the copied portion of any published article present in internet.

But it can not check the immoral mentality of the particular section of researchers who copy other's publication.

All anti plagiarism softwares can be bypassed if all the words of the copied portion are completely changed by using similar words.

It require good control over the language and subject, and immoral researchers are not having such amount of patience or efficiency to do it.

They check it using ithenticate or plagrism checker

Mostly By Turnitin/iThenticate softwares. However, Some fewer journals recommend the reviewers to check the plagrism.

Turnitin,ithenticate,plagrism checker x

Below are the popular ones,

Plagiarism checker,

ithenticate,

Turnitin,