Neither a professor nor a doctor, but I have some questions for you:

1) What is the nature of your 'personal improvement'? You state that you are interested in so many things- that can be a problem because it's not easy reading scientific journals if you don't have the training to dissect, understand and analyze them. This can only come from a uni class tutorial or you find someone in uni to guide you through the jargon. Also, people with years of experience reading lengthy papers don't particularly find them appealing.

2)  There are plenty of free journal abstracts/summaries available (Science Direct comes to mind) which have easily digestible information for the layman- they're basically news updates that do the dissecting and summarizing of journals for you.

3) Scientific journals are specialized and people usually read them if they're doing research because they need to cite them in their research. For the casual reader, it's not exactly worth a journal subscription (because they are VERY expensive) unless you know what you're doing and you need to know the details of the research, such as you're an academic looking to keep abreast of the latest research in whatever area of your specialization.

4) "Most people say they're good"- as a scientist (to be or whatever), you're advised to analyze statements like that. What is the nature of this "good"? As opposed to what? How is it 'important'?

It's not a silly question, my dear. Everyone has to start off somewhere, and your quest for knowledge at your age is commendable. Keep it up, we need more intellectually inclined people like yourself. Knowledge is power.

Reading such journals DOES help, but not at your level. Journals can be read by anyone who is able to read them (by read, I mean utilize them) and it's just a waste if you subscribe and can't make use of it. There is no stopping you from downloading them by the truckloads under a free account courtesy of your uni, though *coughs*looksguiltilyaround*coughs*.

Yes, the site you provided looks sound. They're meant for undergrads, but just have a looksee if you are able to understand it. I must emphasize that without a sound understanding of the basics of what you want to read about, it would be immensely tedious and pointless. So brush up on your basic knowledge of terms and jargons in the 3 sciences before investing in something you need to pay cash for.

By influential, they probably mean it contains peer-reviewed journals? If so, then it means that in a way, yes, it is more 'credible', because peer-reviewed journal articles undergo more rigorous scrutiny of their research, and this is important for those who are doing research as it needs to be cited, and peer-reviewed articles have more solid research methodologies. Not so much a concern for you now at this stage.

But always remember: Research is not the gospel truth. They are not facts, they merely shed light on areas that enlightenment.