比较和对比是科学研究的主要方法之一，因而也是其中的一个主要写作手段。严格意义上讲，比较是指出同类事物之间的相同或相似之处，而对比则是指出他们的不同之处。但在实际写作中，比较和对比经常同时出现，因为我们所比较的事物往往在某些方面相似，而在另一些方面却可能截然不同。

例：

In his 1976 study of slavery in the United States，Herbert Gutman，like Fogel，Eenerman，and Genovese，has rightly stressed the slaves'achievements.But unlike these historians，Gutman gives plantation owners little credit for these achievements.Rather，Gutman argues that one must look to the Black family and the slaves'extended kinship system to understand how crucial achievements，such as the maintenance of a cultural heritage and the development of a communal consciousness，were possible，his findings compel attention.

在该段中，作者首先指出Gutman和Fogel等历史学家在对奴隶制的研究中有相似之处，然后又通过对比重点突出Gutman与他们的不同。

1.表示比较时的常用结构

（1）表示比较目的

The purpose of the comparison is...

...be compared with...for the purpose of（to/in order to/so that/etc.）

...comparisons were performed in order to determine（for the purpose of determining/so that we could determine/etc.）

（2）表示比较对象

...is（are）compared with（among/between/etc.）

by comparison with.../compared to.../In comparison with...

（3）表示比较依据

...is used as the basis for comparing...

Comparisons were based on...

The basic criterion for comparison is...

例1：

A series of comparisons were performed in order to determine the difference between quantitatively measured and predicted temperatures...

例2：

Most animals live primarily in one horizontal“layer”of the forest but a few are able to forage right through its height.Yet，by comparison with that of the plants，animal biomass is very small indeed.

例3：

When compared with concentrations in samples of soft tissues，the levels of lead in kidneys were two or three times higher than those in livers.

例4：

The best result was then used as the basis for comparing the accuracies estimated using Equations 1 and 2....

例5：

The basic criterion for comparison is the absolute value of this ratio

2.比较和对比的结果

（1）表示比较对象都具备某特点

...are...for both...

...common to both...

...is not part of either...

...just like/as...，has/have/is/are...

...are more similar when compared to...

Either of the...

Both...were（share）...

From both...and...，it can be seen that...

All of these（Any one of/Either of/None of/Neither of these）...

例1：

Both p28 sis as well as PDGF share dimeric structure and susceptibility to proteolysis.Functionally both exert pleiotropic effects on cellular metabolism and can induce sustained cell replication.“Sis”oncogene activation thus has been implicated as a step on oncogenesis.

例2：

Just as electrons with certain energies cannot move through a semiconductor because of an energy band gap，so too，light of certain frequencies cannot propagate through photonic band-gap crystals because of an optical frequency（of wavelength）band gap.In semiconductors，the gap is due to a material's electronic structure.In photonic crystals，it is due to the crystal structure，which strongly scatters certain wavelengths.

（2）表一致或相同、相似

①表示一致/对应/吻合

...matches...

...agrees with...

...coincides with...

...are consistent with...

...and...correspond...

...and...are in agreement

There is a very good fit between...and...

The agreement between...and...is better than...

A comparison of...with...reveals that...are equivalent

例1：

Bachtold et al.attached metal leads to individual multi-walled tubes，and found conductance oscillations consistent with the metallic cylinder theory....The electron-beam paths in the Aharonov-Bohm experiment have effectively been replaced by molecular orbitals.Bachtold et al.were also surprised to find extra oscillations with a smaller period，corresponding to electron paths that revolve several times around the cylinder before interfering.

例2：

This partially agrees with the results of El-Hakim［1981］who concluded that the checkpoint discrepancies were consistent with the 95 percent confidence ellipsoids using real data.(www.daowen.com)

②表示相同/相似

...are...equivalent

...a strong analogy exists...

...resemble.../is analogous to...

...in（exactly/roughly/etc.）the same way...

...have shown closer similarity to...than to...

...and...are nearly the same/alike/identical/similar

is almost similar to（like/the same as/identical with）...

There is no significant difference in...

Equally important...

Among...there is a good deal of similarity...

A similar relationship exists between...and...

在表示相同或相似的程度时，常常要用到以下一些副词：about，almost，just，exactly，precisely，nearly，approximately，more or less，strong，practically，essentially，basically等。

例3：

A strong analogy exists between European composers like Ralph Vauhgan Williams，Edvard Grieg，and Anton Dvorak who combined folk tunes and their own original materials in larger compositions and the pioneer ragtime composers in the United States....

例4：

Just as light，heat，and moisture can degrade many materials，biotechnology relies on naturally occurring，living bacteria to perform a similar function....

例5：

Sometimes，however，the crystal form of the silicate inclusions is observed to resemble more closely the internal structure of diamond than that of other silicate minerals.It is not known how rare this resemblance is，or whether it is most often seen in inclusions of silicates such as garnet，whose crystallography is generally somewhat similar to that diamond；but when present，the resemblance is regarded as compelling evidence that the diamonds and inclusions are truly congenetic.

（3）比较大小和通过对比表差异

①表示大小比较

A is（are/does/do）not as（so）adj.（adv）.as B.

根据程度的不同，上句中的not还可用以下词代替：nearly，quite，almost，nowhere，near，half。

A is（are/does/do）（very）much adj.（比较级）than B.

A has（have/contain）a little adj.（比较级）名词than B.

根据程度的不同，上两句中的副词还可用以下词代替：substantially，significantly，generally，considerably，a great deal，rather，（quite）a lot，somewhat，a bit，slightly，scarcely，hardly，only，just，minimally，数量词。

例1：

The highest concentrations of iron were found in the tissues of voles from Dulowa，which were significantly higher than relevant concentrations determined for animals from other sites.The mean concentrations of zinc were generally lower than those of iron and its distribution in various tissues was more uniform.Only in the kidneys and bones of animals from Dulowa was there significantly less zinc than in corresponding tissues of voles from Niepolomice and Bialowieza.

例2：

In the 1940's ENIAC，an early electronic computer，filled a room with its banks of vacuum tubes and miles of wiring.Today one can hold in the hand a computing device costing about$200 that is twenty times faster than ENIAC，has more components and a larger memory，is thousands of times more reliable，costs 1/10，000 the price，and consumes the power of a light bulb rather than that of a locomotive.

例3：

Compare these projections with those for the typical flat-panel solar-cell array，which typically achieves 15 milliwatts per square centimeter.Whereas these estimates derive from computer models，and actual power outputs will undoubtedly be smaller，prototypes have exhibited power densities greater than one watt per square centimeter.

②表示对比和差异

rather than...

on the other hand...

distinguish/tell...from...

in some...，while in others...

A is inconsistent with B...

A can be distinguished from B by...

whereas（while/though/even when）

...presents quite contrasting features

...is（in）opposite to.../conversely

in contrast（with/to）.../by contrast/contrary to.../on the contrary

A，quite unlike/as distinct from/as against B，has（have/is/are）...

A totally/completely/entirely/quite differs from（is different from）B in...

The difference（discrepancy/inconsistency/etc.）between...and...is（indicates）...

例4：

Quite unlike templated self-assembly processes，some researchers use a procedure of repetitive material deposition and etching to prepare ordered structures that function as photronic crystals.This past summer，researcher Shawn Y.Lin made a stacked structure of micrometersized silicon rods using such methods.

例5：

However，they present quite contrasting features with regard to their intensity of infection in adaptively immunized host.Sensitized thymus and bone marrow cells employed separately gave an intensity of 2.39%and 3.10%respectively in the cestode model in contrast to 14.0%and 16.3%respectively in nematode model at 96 hours.

例6：

Nuclear medicine differs from existing angiography procedures in that nuclear imaging is an emission effect caused by the emission of gamma rays from the decaying isotope.In comparison，angiography is a transmission effect caused by the transmission of X-rays through the patient，to be imaged on the opposite side.

例7：

Their present high standing is due to a different，more democratic political climate and to different aesthetic values:we no longer require artists to provide ideal images of humanity for our moral education but rather regard such idealization as a falsification of the truth.