Although there are many scientific search engines available on the web, Google is a very powerful search engine that manages to dominate and hide these specific search engines.
I recently came across a list of search engines that can be used to find specific information on a wide range of topics.
Here's the list I recently discovered and I'd like to share it with you:
www.refseek.com - Academic Resource Search. RefSeek is a web search engine for students and researchers that aims to make academic information easily accessible to everyone. RefSeek searches more than five billion documents, including web pages, books, encyclopedias, journals, and newspapers. RefSeek's unique approach offers students comprehensive subject coverage without the information overload of a general search engine—increasing the visibility of academic information and compelling ideas that are often lost in a muddle of sponsored links and commercial results.
www.worldcat.org - WorldCat is a great resource for locating unique, trustworthy materials that you often can’t find anywhere except in a library. And by connecting thousands of libraries’ collections in one place, WorldCat.org makes it easy for you to browse the world’s libraries from one easy search box. During the past 50+ years, thousands of libraries have entered their information about millions of books, magazines, movies, songs, maps, genealogical records, research theses and so much more into WorldCat. And not just the physical items you could find when you visit a library, but many kinds of digital content like open-source e-books, articles, downloadable audiobooks, and photos. You can also find article citations with links to full text, authoritative research materials, one-of-a-kind documents and photos of local or historic significance, and digital versions of rare items that aren’t generally available to the public.
https://link.springer.com - Springer Nature advances discovery by publishing robust and insightful research, supporting the development of new areas of knowledge, making ideas and information accessible around the world, and leading the way on open access. Key to this is our ability to provide the best possible service to the whole research community.
www.bioline.org.br - Bioline International is a pioneer in the provision of open access to peer-reviewed bioscience journals published in developing countries. These journals contain timely research on public health, international development, tropical medicine, food and nutritional security, and biodiversity. Bioline increases the visibility of this research by making it readily available to researchers across the world. Bioline is not a publisher, but an aggregator that provides a free platform for journals who wish to participate in the global open access movement.
http://repec.org - The RePEc bibliographic data is in the public domain and thus used by other services as well. Over 2,200 archives from 103 countries have contributed about 4.5 million research items from 4,000 journals and 5,500 working paper series. Over 65,000 authors have registered and 75,000 email subscriptions are served every week. RePEc is entirely based on the contributions of volunteers.
www.science.gov - Science.gov is an official website of the U.S. government providing ready access to the massive stores of federally funded scientific research results, without needing to know which agency funded the research. Research results include scientific and technical reports, peer-reviewed scholarly publications, digital data, software, conference presentations and proceedings, and other scientific and technical information that federal agencies publish resulting from their research investments. Originally launched in 2002, Science.gov searches content from across multiple federal agencies that fund scientific research and provides top-level results from those agencies, where users get the most relevant results for the information they search. Unlike typical web-based search engines that crawl and index web content at unknown frequencies, Science.gov uses a search technology that retrieves results in real-time. This ensures that the most recent content is available for search and retrieval by Science.gov.
www.base-search.net - BASE is one of the world's most voluminous search engines especially for academic web resources. BASE provides more than 340 million documents from more than 11,000 content providers. You can access the full texts of about 60% of the indexed documents for free (Open Access). BASE is operated by Bielefeld University Library. We are indexing the metadata of all kinds of academically relevant resources – journals, institutional repositories, digital collections etc. – which provide an OAI interface and use OAI-PMH for providing their contents (see our Golden Rules for Repository Managers).