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科学定律与理论
In science, a law is defined as a concise, verbal or mathematical, statement that summarizes a vast number of experimental observations. It…
科学方法
Chemistry is an empirical science. Scientists often pose questions to understand the chemistry in everyday life and seek answers to these questions.…
将物质按状态分类
Chemistry is the study of matter and the changes it undergoes. Matter is anything that has mass and occupies space. Matter is all around us; the air,…
将物质按成分分类
According to its composition, the matter can be classified into two broad categories — pure substances and mixtures.  A pure substance…
物质的物理与化学性质
The characteristics that enable us to distinguish one substance from another are called properties. A physical property is a characteristic of…
什么是能量?
The universe is composed of matter in different forms, and all forms of matter contain energy.  The different forms of energy on Earth originate…
测量:标准单位
Every measurement provides three kinds of information: the size or magnitude of the measurement (a number), a standard of comparison for the…
测量:衍生单位
The International System of Units or SI system, by international agreement, has fixed measurement units for seven fundamental properties: length,…
测量的不确定度:准确性和精确度
Scientists typically make repeated measurements of a quantity to ensure the quality of their findings and to evaluate both the precision and the…
测量不确定度:阅读仪器
Counting is the type of measurement that is free from uncertainty, provided the number of objects being counted does not change during the process.…
测量不确定度:有效数字
All the digits in a measurement, including the uncertain last digit, are called significant figures or significant digits. Note that zero may be a…
量纲分析
Dimensional analysis, also known as the factor label method, is a versatile approach for mathematical operations. The main principle behind this…
设计和全流采样系统(FFS)的使用甲烷排放的量化
The use of natural gas continues to grow with increased discovery and production of unconventional shale resources. At the same time, the natural gas…
用亚硫酸氢萃取协议分离混合物中的醛和反应性酮
The purification of organic compounds is an essential component of routine synthetic operations. The ability to remove contaminants into an aqueous…

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