I've been in a weird craze of editing wikipedia pages, specifically the portuguese pages. But when it comes to History, I try to follow the strict guidelines about providing good and reliable sources. Which is pretty hard! We don't really have a lot of academic historians to help around, and in general, we don't have a lot of anonymous volunteers like the English Wikipedia.
One thing that is kind of common knowledge is that the historians in Brazil are pretty left-leaning. I tried to find some of the books they use, and a lot of it is about class struggle. Now, don't get me wrong, I know some of it is valid, but when most of the bibliography is talking about that, we have a bias. Basically, I'm trying to bring different views in the sources, so as to maintain the neutral point of view in the article.
I've been poking around with Google Books and Scholar Google for now, but that's about it. I'm in a small college for IT, History is more of a hobby. I just want to help my fellow brazilians, and by extension, all the lusophones, with more in-depth knowledge, but help them not only with sources in english, which I can simply copy-paste, but also sources in portuguese.
At the risk of starting some kind political war, I'd say that at least in the Western world, most historians are politically left-leaning. While "bias" is at times at work here, the field and its sub-fields do, in their best peer-reviewed forms, aim at a kind of objectivity, at really trying to figure out the most reasonable way to interpret historical data, to find a truth that's as close as possible to the past. And that data overwhelmingly shows that those in power have exploited those who don't have it, whether it's about class, race, or gender (and actually all of these are always intermingled). So when historians state that there has been oppression, that women and minorities have been historically disenfranchised, that colonialism was about the strong taking advantage of the weak, these typically are not pre-existing notions that we're just pasting onto the past. It's what the data says.
A huge issue at work here is that for centuries the practice of history was fundamentally slanted towards the narrative of 'great men doing great things.' Historians were scholars who were employed by the elites, and their job was to heroicize those elites. While this shifted slowly, it's only in the middle of the 20th century that this assumption that 'great men' - kings, dukes, high-ranking scholars themselves, etc - were the only proper subjects of history came to be widely challenged. Historians began to look at Marx (not Communism as a political system practiced by Stalin, Mao, etc, but at Marx in terms of his emphasis on the worker), for insight into who (here, the worker, common people, stretching out later into women and minorities) was worthy of study. I don't know much at all about Brazilian historiography, but from what you're saying it sounds rooted still in that 1960s-80s turn towards class as a foundational methodology. Every country's historical fields have their own trajectories and quirks, and they're not all in the same place.
In any case, to your real question. Great that you're looking at Google books and Google scholar. Another very large database is Worldcat.org, though they skew more to books than articles. Jstor is better for articles, but they skew Amercan/English language. What I'd advise for finding specifically Portuguese sources is to go to the university libraries of Portuguese-speaking countries, i.e. start maybe with the Uni. of Lisbon, which possibly has the best resources (as I said, this isn't my area so it may not be the absolute best) and just search their catalogs using Portuguese keywords for the subjects you want to know about. Depending on what your college has paid for, you may or may not be able to access the actual journals but you should be able to find a lot of titles. You may also find that there are integrated catalogs for the educational institutes in that country, which saves a lot of time.
Then, when you're evaluating the quality of the individual article or book, the question is: how respected is the press/journal? For the presses, if they have 'University' in their name that's a good sign, though cultural institutes can be great too. For journals, again, it's kind of difficult because every national and language sphere has their own rankings and they shift depending on who's doing the ranking. For English-language history the SJR works ok: http://www.scimagojr.com/journalrank.php?category=1202 You can try googling in Portuguese for something similar for that area. Good luck!!
Brazilian historiography is much more than class strugle!
In my University (Universidade Federal do Paraná) I heard more criticism than apology to marxist methods. And this is the trend in the most important institutions of our country.
This is not refuse marxist works, or Marx theory by himself. And yeah, most part of Brazilian historians are left-wingers, as well our colleagues of ocidental countries. ANPUH (Associação Nacional dos Professores Universitários de História) published more than one note agains Dilma Roussef's impeachment. By that reason, the average of historian speeches can sound marxist for some people.
Give us an chance =). I know we are living an tense political moment, and some is hard to hear some staff, our heads are full of social media crap. But in Brazil there's an large number of competent historians and serious ressearches.
What theme you're looking for? Perhaps I can help you to found something.
Suggestion for you, we have the privilege to live in an country that the most part of relevant jobs are free to download.
Look at the theme of your interess in SciELO (http://search.scielo.org/advanced/?lang=pt)
Just type "Independência do Brasil" or anything you want, and you find a lot about of it.
If you really refuses marxist method, just look for the "key words" or down to bibliography and check it before the read!