Is a research article the most comprehensive information available about a research project?
Is there usually a more complete documentation available which delineates the whole process of the experiment/research-project?


Typically not all of the details of the research can feasibly be published. Different areas have different methods to cope with this. Some journals will allow supplementary material to be submitted that's made available online through the publisher's site. Some authors will add links to homepages for the project where more details are available. Sometimes authors will publish an extended "technical report" (e.g., with full proofs or full methodologies that would not be feasible under a page limit) and publish it on their institute homepage or a site like arXiv. I believe some biomedical journals allow for publishing databases containing micro-data on experiments ...

So it varies widely. The most generic answer, however, is simply to get in contact with the authors and ask them if more details are available! Their contact details should be provided in the paper.