在Jquery中最根本的方法就是jQuery(),它是jquery的根本。
有的朋友可能会奇怪，为什么和你的标题中的工厂方法不一致呢？
呵呵，其实$()是jQuery()的简写形式。但是这个简写形式在给我们带来便利的同时，也会带来一些麻烦：
因为在其它的一些JS框架里，$()是经常被使用的，所以如果你使用了jquery的同时，还引用了其它的JS框架的话，就会产生冲突（据说是有其它的解决方法，我还不知道呢，请各位指正吧），这时你就不能用$()这种简写形式了。
不过签于Jquery的强大功能，把其它的框架都去掉吧：－）
$()方法的参数可以是任何形式的字符，返回值是一个jQuery对象。例如：
$('div')：表示取出页面中的所有div元素，并返回一个jQuery对象。
注：对象可以理解为一个特殊形式的容器，比如一辆宝马汽车，就是汽车的一个具体对象，包含汽车的基本特征。
没想到我这个JQ菜鸟的几句话，引起了大家这么多的意见；－），看来我还是要深入的去学习，下面我把我的参考资料帖出来：
节选自《Learning Jquery》：
The $() Factory Function
No matter which type of selector we want to use in jQuery—be it CSS, XPath, or custom—we always start with the dollar sign and parentheses: $()
As mentioned in Chapter 1, the $() function removes the need to do a for loop to access a group of elements since whatever we put inside the parentheses will be looped through automatically and stored as a jQuery object. We can put just about anything inside the parentheses of the $() function. A few of the more common examples include:
A tag name: $('p') gets all paragraphs in the document.
An ID: $('#some-id') gets the single element in the document that has the corresponding some-id ID.
A class: $('.some-class') gets all elements in the document that have a class of some-class.
Making jQuery Play Well with Other JavaScript Libraries
In jQuery, the dollar sign $ is simply shorthand for jQuery. Because a $()
function is very common in JavaScript libraries, conflicts could arise if more than one of these libraries is being used in a given page. We can avoid such conflicts by replacing every instance of $ with jQuery in our custom jQuery code. Additional solutions to this problem are addressed in Chapter 10.
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•Now that we have covered the basics, we're ready to start exploring some more powerful uses of selectors.