A multidisciplinary or general database is one which covers a wide range of topics across multiple academic disciplines. You may want to use a multidisciplinary database if your topic is cross-disciplinary, or if you are not yet sure of the subject area into which your topic falls.
Web of Science: Large multidisciplinary database offering citation linking and citation counts.
A subject-specific database focuses on a single discipline (e.g., Mathematics) or a group of related disciplines (e.g., Mathematics, Physics, and Chemistry) and usually provide comprehensive coverage of that specific field. Using a subject-specific database is ideal if you know a particular subject area is appropriate for your search topic.
Compendex: Compendex is the most comprehensive bibliographic database of scientific and technical engineering research available, covering all engineering disciplines. It includes millions of bibliographic citations and abstracts from thousands of engineering journals and conference proceedings. When combined with the Engineering Index Backfile (1884-1969), Compendex covers well over 120 years of core engineering literature.
Environmental Engineering Abstracts: Covers technological and engineering aspects of air, water and soil quality, environmental safety, sustainability and energy production. Other areas such as mines and quarry equipment, nuclear power plants, thermoelectric energy, tidal and wind power, treatment of sewage and industrial wastes, water analysis and treatment techniques are included.
IET Digital Library: Holds more than 190,000 technical papers from 1994 onwards for all Institution of Engineering and Technology (IET) journals, magazines, books, conference publications and seminar digests.
SciFinder: The most comprehensive database for coverage of chemistry & chemical engineering. It has the world's largest collection of organic and inorganic substance information. The web version of SciFinder provides integrated access to CAPlus, CAS Registry, CASREACT, CHEMLIST, and CHEMCATS which are produced by Chemical Abstracts Service, and to MEDLINE which is produced by the U.S. National Library of Medicine. Sources covered in SciFinder include 10,000 journals, patents from 61 patent authorities, book chapters, conference proceedings, dissertations, evaluated reference works, technical reports, as well as book reviews and biographical information.