Please find some of my sources below.

For scientific articles, I have tried to give links to PubMed or Europe PubMed, where available.

Google Scholar    http://scholar.google.de/

CiteSeerX               http://citeseerx.ist.psu.edu/

PubMed Central                    http://www.ncbi.nlm.nih.gov/pubmed

Europe PubMed Central     http://europepmc.org/

The Cochrane Library           http://www.thecochranelibrary.com/

ResearchGate      http://www.researchgate.net/publicliterature.PublicLiteratureSearch.html

Ingentaconnect   http://www.ingentaconnect.com/

JournalAgent        http://www.journalagent.com/

Wiley Online Library                                http://onlinelibrary.wiley.com/

Springer Link                                              http://link.springer.com/

ScienceDirect (Elsevier)                         http://www.sciencedirect.com/

Taylor and Francis Online                      http://www.tandfonline.com/

Oxford Journals                                        http://www.oxfordjournals.org/

Cambridge Journals Online                  http://journals.cambridge.org/

Ammons Scientific (AmSci)                  http://www.ammonsscientific.com/

Nature Publishing Group (NPG)         http://www.nature.com/

Sage Journals                                             http://online.sagepub.com/

Informa Healthcare                                 http://informahealthcare.com/

De Gruyter                                                  http://www.degruyter.com/

Karger                                                           http://www.karger.com/

CSIRO Publishing                                      http://www.publish.csiro.au/

Endocrine Press                                        http://press.endocrine.org/

The International Society for
Magnetic Resonance in Medicine
(ISMRM)                                                      http://www.ismrm.org/

International Journal
of Transgenderism (IJT)                                         http://www.tandfonline.com/action/journalInformation?journalCode=wijt20

The International Journal
of Transgenderism                                                  http://www.iiav.nl/ezines/web/ijt/97-03/numbers/symposion/ijtc0502.htm

PLOS One                                                                    http://www.plosone.org/

Psychoneuroendocrinology                                 http://www.psyneuen-journal.com/

The British Journal of Psychiatry                        http://bjp.rcpsych.org/

European Neuropsychopharmocology           http://www.europeanneuropsychopharmacology.com/

Journal of psychiatric research                           http://www.journalofpsychiatricresearch.com/

Clinical EEG and Neuroscience                            http://eeg.sagepub.com/

European Journal of Endocrinology (EJE)       http://www.eje-online.org/

The Journal of Neuroscience                               http://www.jneurosci.org/

Biology of Reproduction                                        http://www.biolreprod.org/

Environmental Health Perspectives (EHP)     http://ehp.niehs.nih.gov/

Fondazione Carlo Molo                             http://www.fondazionecarlomolo.it                                                                             http://www.fondazionecarlomolo.it/index.php/en/archives/neuroscience