As far as I know, we have to pay for every good journal sites. But there are certain open access journals. But most of the open access journals are not good and the quality of the work published there are not that good. Do not think that open access journals do not have any good papers. Some papers are really good.
There are different sources available on internet some of my favorite and working websites are listed here
1. libgen.org which allow you access the full text articles articles from sciencdirect, springer etc.
2. You can also access fulltext scientific article from www.freefullpdf.com which allows to download free science papers, patents, theses and posters too.