在日常的學習、工作、生活中，肯定對各類范文都很熟悉吧。相信許多人會覺得范文很難寫？下面是小編為大家收集的優(yōu)秀范文，供大家參考借鑒，希望可以幫助到有需要的朋友。
cet4閱讀理解 四級閱讀理解2233篇一
現(xiàn)在，2017年的下半年就要到來，有的考生已經(jīng)在進行2017年下半年pets4的備考了。小編認為考生可以在復(fù)習時候，進行一些pets4閱讀文章預(yù)測，更充分地備考。下面是小編為大家整理的一篇2017pets4閱讀理解預(yù)測文章，供大家參考，還有更多精彩內(nèi)容盡在應(yīng)屆畢業(yè)生考試網(wǎng)。
chemistry did not emerge as a science until after the scientific revolution in the seventeenth century and then only rather slowly and laboriously. but chemical knowdedge is as old as history, being almost entirely concerned with the practical arts of living. cooking is essentially a chemical process; so is the melting of metals and the administration of drugs and poisons. this basic chemical knowledge, which was applied in most cases as a rule of thumb, was nevertheless dependent on previous experiment. it also served to stimulate a fundamental curiosity about the processes themselves. new information was always being gained as artisans improved techniques to gain better results. the development of a scientific approach to chemistry was, however, hampered by several factors. the most serious problem was the vast range of material available and the consequent difficulty of organizing it into some system. in addition, there were social and intellectual difficulites, chemistry is nothing if not practical; those who practice it must use their hands, they must have a certain practical flair. yet in many ancient civilizations, practical tasks were primarily the province of a slave population. the thinker or philosopher stood apart from this mundane world, where the practical arts appeared to lack any intellectual content or interest. the final problem for early chemical science was the element of secrecy. experts in specific trades had developed their own techniques and guarded their knowledge to prevent others from stealing their livelihood. another factor that contributed to secrecy was the esoteric nature of the knowledge of a alchemists, who were trying to transform base metals into gold or were concerned with the hunt for the elixir that would bestow the blessing of eternal life. in one sense, the second of these was the more serious impediment because the records of the chemical processes that early alchemists had discovered were often written down in symbolic language intelligible to very few or in symbols that were purposely obscure.
化學在17 世紀的科技革命后才成為一門科學，其發(fā)展是緩慢而艱難的。但化學知識卻象人類歷史一樣古老，與人們實際生活密切相關(guān)。做飯基本上是一個化學過程。同樣，金屬熔煉、使用藥品或毒劑也是如此。人們在大多數(shù)情況下只是粗糙地運用這些基本化學知識，但這些基本知識的確是來自于前人的實驗。它們同時也激發(fā)了人們對化學本身的興趣。 匠人們利用新技術(shù)來改良工藝，就增加了對化學的了解。但是，化學科學方法的發(fā)展卻有許多阻礙的因素。其中最嚴重的問題就是要把浩如煙海的物質(zhì)歸納為若干系統(tǒng)確實很困難。此外，還有社會和知識的原因。離開實際用途，化學就毫無價值;研究化學的.人必須親自動手，這就要求他們要有很強的動手能力。 但在許多古代文明中，動手的活都是奴隸的行當。思想家與哲學家與此勞碌決不沾邊，因為在他們看來，實際操作技能低智而乏味。最后，還有一個原因妨礙早期化學的發(fā)展，那就是保密。某個行家一旦發(fā)現(xiàn)了新技術(shù)，就竭力保密以防被人偷了飯碗。另一個原因加劇了知識封鎖這是因為煉金術(shù)士的知識的神秘性。這些術(shù)士們要么想他便宜的金屬變成黃金，要么期望找到一種長生不老藥。從某種意義上說，這第二個因素帶來了更嚴重的阻礙，因為早期術(shù)士們的研究成果記載于鮮為人知的或故意讓人不懂的符號中。
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