which the search engine[推荐]

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[B]Search engines [/B]  are computer programs that automatically collect web sites using "spiders" or "robots". The sites are listed and stored in a database. To query a search engine, you type keywords related to your topic into a search "box." The search engine scans its database and returns a file with links to websites containing the specified keywords. Because search engine databases are very large, your results file may include thousands of websites. It is important to remember that when you are using a search engine you are not searching the Internet "live". Rather, you are searching a fixed database that may be updated dayly, weekly, or even monthly. According to a study reported in Nature (1) no search engine indexes more than 16% of the Web. Even though search engine databases are enormous, they cover very little of what's actually available on the Web.

It is essential to apply each engine's specialized search techniques in order to narrow results and push the most relevant pages to the top of the results list. Relevancy of results also depends on the size of the search engine and how it processes your words. Each engine determines relevancy of results in unique ways. Consult the help file of each engine to learn about these. In Alta Vista, document relevancy is calculated according to frequency, hierarchy (closer to the top of the document gets more points), and adjacency (proximity of words) of search words. In Google, relevancy is determined by how sites link to a site as a measure of popularity and presumed usefulness. Comparison of results between engines, given the same keyword search, yield quite different findings based on search capabilities, size, and updating frequency. Four of the best engines, based on search speed, user interface, and search capabilities, are:
Google: http://www.google.com
Alta Vista: http://www.altavista.com
AllTheWeb: http://www.alltheweb.com/ (also known as FAST)
WiseNut: http://www.wisenut.com/

There are many search engines to choose from and some "meta" search tools are able to search the databases of multiple engines simultaneously, via a single interface. These meta engines are very fast but they do not offer the same level of control over the relationship between keywords as do individual search engines. They can be used as good starting points to compare sites across several databases at once. Recently, the capabilities of meta-tools have been improved to include such useful features as the ability to sort results by site, by type of resource, or by domain, the ability to select which search engines to include, and the ability to modify results. These modifications have greatly increased the effectiveness and utility of the meta-tools. Examples of meta search tools are:
Dogpile: http://www.dogpile.com
Ixquick: http://www.ixquick.com/
Metacrawler: http://www.metacrawler.com
Vivisimo: http://vivisimo.com/

Subject directories are lists compiled by people. They are organized in a hierarchy where each subject includes a list of sub-topics. For example:
Computers and Internet
    World Wide Web
     Tutorials
Subjects lists are usually evaluated but sites are not presented in order of relevancy. In other words, the best sites on a topic are not necessarily listed first. Sites are compiled through submission of URLs by site creators and human selection. One advantage of subject indexes is their browsability, although this feature is only suitable with fairly general topics. Examples of popular subject directories include:


BUBL LINK: http://bubl.ac.uk/link/ (LINK = Libraries of Networked Knowledge)
Infomine: http://infomine.ucr.edu
Librarians' Index to the Internet: http://www.lii.org/
Yahoo: http://www.yahoo.com

[B]Does the Tool Matter? [/B]  

The short answer is "Yes"! There are various ways to begin a Web search. The choice of search tool depends on the nature of your question. Different questions necessitate different types of information to answer them. Are you looking for quick facts (phone numbers, weather, or postal codes), government documents, statistics, pictures, or research papers? For each of these types of information there are recommended starting points that are quite different.

from the http://searchenginewatch.com/