asとlikeについて

as もlike もsimilarity を表現します。その場合、asは接続詞で　like は前置詞であり。
like ＋名詞（noun,pronoun)
as　＋節（cluase)
as ＋　前置詞句（preposition phrase)

なので、
He ran like the wind.は言いえても、
He ran as the wind. とは言えない。
She's good at scientific subjects, like mathematics.は言えても
She's good at scientific subjects, as mathematics.は言えない。

as の使い方の代表例は、
We often drink tea with the meal,as they do in China.
In 1933, as in 1914, everybody seemed to want war.

ところで最近の英語で、特にinformalなstyleでは、like が接続詞のように使われる。すなわち、
Nobody loves you like I do.
You look exactly like your mother did when she was 20.

as があとに名詞を伴うのは、人又は物事がどのような機能（function,role)を果たすかを表現するもので、similarity を表現するものではない。この場合のasは前置詞。

以上は、like が接続詞として使われる説明以外では、当たり前のことを言ってるにしかすぎにのかもしれない。

like が否定形の節の後に来るか、先に来るかで意味が違ってくる。

I don't smoke,like Jane.(Jane smokes.)
節の後に来たときは、前の節の肯定部分のみにlike はかかる。

Like Mary,I don't smoke.(Mary doesn't smoke.)
節の前に来たときは、全ての節の意味に、like はかかる。

from today's Nikkei

時価総額2000兆円目減り　金融危機直撃　ＧＤＰの4割　世界の株、ピークから1年で

Aggregate market value of the stocks in the world's major markets has been sharply declining. It seems that at the end of September the total market value of the stocks in the major stock exchanges in the world decreased by more than 2000 trillion yen, comapared with that at the end of October,2007,when the highest-ever total value was recorded. This means that the U.S.-originated financial crisis has accelerated stock prices declining and the loss of the value this time is equivalent to more than 40% of nominal gross domestic product(GDP) combined in the world's all nations.