what is periodic sentence?(the definition of periodic senten

According to the periodic table,______ still some elements undiscovered.
选这个选项的原因
答案为什么是 there seem to be

英语翻译
therefore,a periodic sentence is likely to be more emphatic than a sentence with a loose construction.
notice the difference between the loose and periodic construcions in the fllowing examples
the history of english words is the history of our civilization in many ways

When the cabin crew is making its periodic
checks,the passenger will often have questions
about service,schedules,routes and weather.
这个句子的主句和从句各使用的是什么时态?

it is the periodic abnormal warming of the sea surface off Peru
我想知道那个秘鲁前面的off是怎么样个说法.该怎么从句子中理解这个off.
这是一个例句！

According to the periodic table ,( )still some elements undicovered.
A.there seem to be B.it seems to be
C.it seems that D.here seem
答案是什么,为什么?

英语翻译
If the force is periodic,it can be decomposed into a combination of harmonic ones on use of Fourier series.
The machine and foundation can vibarate with much greater independence above a resonance frequency of the system.Here take the transverse excitation and motion into account.

Elements in the upper right corner of the Periodic table form acid anhydrides because nonmetallic oxides react with water to form acid solution.这句话对吗 中文：因为非金属氧化物与水反应生成酸溶液,所以在元素周期表最右上方的元素会形成酸酐

Elements in the upper right corner of the Periodic table form acid anhydrides.
Nonmetallic oxides react with water to form acid solution.
第二句话为什么可以构成第一句话的explanation啊?

When the cabin crew is making its periodic
checks,the passenger will often have questions
about service,schedules,routes and weather.
这个句子的从句为什么用现在进行时?

英语翻译
语境：Regularly schedule housekeeping tours and periodic self assessments are conducted

英语翻译
Examples of periodic sources and broadband sources are,respectively,rotating machinery such as turbines,fans,etc.,and aerodynamic noise associated with jets or flow past a solid surface.In fact,the two types often occur together with a series of pure tone peaks above a broadband spectrum.An example is where a large machine with several random sources has a strong periodic mode of operation.For more specific detail on the frequency spectra and appropriate analysis required for different kinds of sources see section 3.3.3.
图2.4及其说明
2.1.3 Wavelength
A wavelength is defined as the distance between analogous points on successive waves of a pure tone signal; it is most easily assessed by measuring the distance between adjacent maxima or minima on the pressure spatial distribution (see figure 2.3a,above).Wavelength is denoted by the symbol X and is numerically equal to the ratio of the speed of sound in a medium to the frequency:
公式
where c is the speed of sound,m/s
f is the frequency,Hz.
2.1.4 Speed
For very high amplitude waves,which occur either when the ambient speed of sound is exceeded (see section 7.1.1) or with strong source radiation as in certain severe impact situations,shock formation occurs,and the waveform is distorted into nonlinear behavior.Essentially,this means that sounds of different frequencies propagate at different speeds through the transmitting medium.However,for most commonplace situations in industry this will not be so,and the speed of sound can be regarded as being the same for all frequencies.
For propagation in a gas,the general expression for the velocity of sound waves,c,is given by
c = _fTrT m/s
where
λ is the ratio of specific heat of gas at constant pressure to that at constant volume
r is the constant dependent on gas involved and equal to the ratio of the gas constant and molecular weight of the gas,J/kg.K
T is the absolute temperature,K.
The velocity is directly proportional to the square root of the absolute temperature,the other terms being constant.Pressure changes and nonuniformity of gas composition are of much less significance in affecting the velocity.For air at atmospheric pressure,the relationship simplifies to
公式：c = 20.05x/T m/s
More complex relationships exist for liquids and solids 1:
Liquids:公式
Solids:公式
(large cross section)
Solids公式
(small cross section)
where
Bbt is the isothermal bulk modulus,N/m 2
0o is the density,kg/m 3

已知名义利率是10%,利息每半年复利一次.5年后终值为1000,求定期利率.就是periodic interest rate.
我算出来实际年利率了,是10.25%

英语翻译
Tracking Customer Experience:Persistent,Periodic,Pulsed
客户体验的追踪：持续追踪、定期追踪、
Companies can monitor various patterns of interaction with customers to gain a better understanding of the customer experience they are providing.Depending on the precise information a company is seeking,it may choose to analyze past patterns,present patterns,potential patterns,or a combination.Each pattern requires a distinct method of generating and analyzing data and will yield different types of insights.
公司可以通过监测与客户多种不同的交易模式从而进一步了解他们为客户提供的体验.根据公司正在寻找的精确信息,公司可以选择分析以往的交易模式、当前的交易模式和潜在的交易模式,或者是多种模式的结合.每一种模式都需要各自独特的方法来产生数据和分析数据,并且会产生不同类别的深刻见解.

英语翻译
since the first publications of the periodic law,both by dimitri mendeleev and lothar meyer in the 1870s,there have been a large number of forms proposed for the periodic table.
the version easiest to use and most closely related to the electronic structures of the atoms is so-called long-form in table 1.
the elements fall into 18 vertical columns that define the chemical families,or
groups.the members of each group have valence-electron configurations that are the same,except for principal numbers.the only exceptions to this rule involve nearby and electrons.
while chemical similarties are most often strongest among elements in same column,there is some resemblance between elements that are not in the same column but which do have the same number of valence electrons.
r example,members of the scandium group have the configuration(n-1)d1ns2 and are in some respects similar to the elements below boron,which have the configurations ns2np1.
consequently the elements under scandium in the third column are said to be members of group iiib ,while the boron family is labeled group iiia.
other groups in the perodic table are related and labeled in asimilar manner.
the elements in the three columns designated group viii resemble each other in many respects and separate the a subgroups from the b subgroups in periodic table.