全文获取类型
收费全文 | 1699篇 |
免费 | 70篇 |
国内免费 | 11篇 |
专业分类
化学 | 1197篇 |
晶体学 | 14篇 |
力学 | 56篇 |
数学 | 154篇 |
物理学 | 359篇 |
出版年
2023年 | 9篇 |
2022年 | 28篇 |
2021年 | 35篇 |
2020年 | 36篇 |
2019年 | 38篇 |
2018年 | 29篇 |
2017年 | 26篇 |
2016年 | 55篇 |
2015年 | 49篇 |
2014年 | 51篇 |
2013年 | 78篇 |
2012年 | 125篇 |
2011年 | 133篇 |
2010年 | 94篇 |
2009年 | 95篇 |
2008年 | 145篇 |
2007年 | 106篇 |
2006年 | 83篇 |
2005年 | 85篇 |
2004年 | 75篇 |
2003年 | 58篇 |
2002年 | 67篇 |
2001年 | 21篇 |
2000年 | 39篇 |
1999年 | 29篇 |
1998年 | 22篇 |
1997年 | 15篇 |
1996年 | 10篇 |
1995年 | 10篇 |
1994年 | 10篇 |
1993年 | 11篇 |
1992年 | 8篇 |
1991年 | 8篇 |
1990年 | 3篇 |
1989年 | 4篇 |
1988年 | 6篇 |
1987年 | 4篇 |
1985年 | 7篇 |
1984年 | 8篇 |
1983年 | 6篇 |
1982年 | 8篇 |
1980年 | 4篇 |
1979年 | 4篇 |
1978年 | 4篇 |
1977年 | 5篇 |
1976年 | 4篇 |
1974年 | 4篇 |
1973年 | 4篇 |
1970年 | 4篇 |
1965年 | 3篇 |
排序方式: 共有1780条查询结果,搜索用时 15 毫秒
101.
Jungwoo Moon 《Applied Surface Science》2007,253(18):7554-7558
The adsorption of metal ions, a type of surface reaction on binary mixed self-assembled monolayers (SAMs) on a gold surface composed of 1,6-hexanedithiol (HDT) with 11-mercaptoundecanoic acid (MUA), was monitored by in situ surface plasmon resonance (SPR) measurements. The differential SPR reflectance (ΔR) enables the kinetics of adsorption of Pt2+ on the mixed SAMs to be investigated. Unlike single HDT SAM, kinetic analyses of the mixed SAMs showed that the rate of adsorption of Pt2+ was enhanced and that it was highly dependent on the fraction of MUA present. These SPR measurements suggest that the adsorption rate of metal ions can be readily manipulated simply by using mixed SAMs. 相似文献
102.
Influence of pretreatment methods on adsorption and catalytic characteristics of toluene over heterogeneous palladium based catalysts 总被引:1,自引:0,他引:1
The adsorption and catalytic characteristics of heterogeneous palladium based catalyst and its modified catalysts with gases (air and hydrogen) and acidic aqueous solution (HCl) were studied for evaluating the influence of pretreatment methods for toluene. The structural and energetic adsorption properties of the parent and pretreated catalysts were analyzed by means of nitrogen adsorption isotherms and gravimetric methods. The light-off curve and the XPS investigation were used for analyzing the catalytic activity and the surface state of palladium. It was clearly shown from the experimental results that hydrogen pretreated catalysts having metallic surface state exhibited the highest adsorption capacity and catalytic activity compared to that of parent and modified catalysts. The adsorption equilibrium data for toluene were obtained at three different temperatures and correlated successfully with the two-site Langmuir molecular isotherm model (L2m). It was also found that the palladium phase has more adsorption affinity for toluene molecules than the alumina support. The isosteric heat of adsorption calculated by using the Clausius-Clapeyron equation significantly changed with the coverage and the lateral interactions between the adsorbate-adsorbate molecules control the system. Furthermore, comparative analysis of the adsorption energy distribution revealed that the parent and its modified catalysts have different types of surface energetic heterogeneities. 相似文献
103.
In this paper, we proposed a novel infrared absorbing structure for uncooled infrared detectors. The infrared absorber makes use of a quarter-wavelength structure composed of a dielectric layer, a protecting layer, an active layer, a supporting layer and a reflecting layer. Sputtered amorphous silicon is used as a dielectric layer because of its high refractive index. We fabricated the uncooled microbolometer with the proposed infrared absorbing structure by surface micromachining method. Then we characterized various bolometric properties such as thermal conductance, thermal time constant, responsivity and infrared absorptance. The fabricated bolometer showed the thermal conductance of 6.72 × 10−7 W/K, the thermal mass of 4.43 × 10−9 J/K, the thermal time constant of 6.6 ms and the responsivity of 7.76 × 103 V/W at 10 Hz chopper frequency and 9.22 μA bias current. From the results, the estimated absorptance is about 80%. We expect that the proposed absorbing structure shows high infrared absorption and high performance of uncooled microbolometer. 相似文献
104.
Inae Jang Sun Young Lee Song Hwangbo Dukjin Kang Hookeun Lee Hugh I. Kim Bongjin Moon Han Bin Oh 《Journal of the American Society for Mass Spectrometry》2017,28(1):154-163
The present study demonstrates that one-step peptide backbone fragmentations can be achieved using the TEMPO [2-(2,2,6,6-tetramethyl piperidine-1-oxyl)]-assisted free radical-initiated peptide sequencing (FRIPS) mass spectrometry in a hybrid quadrupole time-of-flight (Q-TOF) mass spectrometer and a Q-Exactive Orbitrap instrument in positive ion mode, in contrast to two-step peptide fragmentation in an ion-trap mass spectrometer (reference Anal. Chem. 85, 7044–7051 (30)). In the hybrid Q-TOF and Q-Exactive instruments, higher collisional energies can be applied to the target peptides, compared with the low collisional energies applied by the ion-trap instrument. The higher energy deposition and the additional multiple collisions in the collision cell in both instruments appear to result in one-step peptide backbone dissociations in positive ion mode. This new finding clearly demonstrates that the TEMPO-assisted FRIPS approach is a very useful tool in peptide mass spectrometry research. 相似文献
105.
John T. Shaw Christine E. Brotherton Robert W. Moon Mark D. Winland Mark D. Anderson Keith S. Kyler 《Journal of heterocyclic chemistry》1980,17(1):11-16
A much improved synthesis of the heretofore difficultly obtainable 2,6-diaminopyrazine (4) was afforded by the low-pressure catalytic hydrogenation (palladium on carbon) of 2,6-diazido-pyrazine (2) ; reaction of 2,6-dichloropyrazine (1) and sodium azide gave 2 in 84% yield. The outcome of the reduction was found to be solvent dependent: 1,2-dimethoxyethane containing aqueous ammonia gave 4 in 83% yield; 1,2-dimethoxyethane alone gave 5-aminotetrazolo[1,5-a]-pyrazine (3) in 26% yield. Additional alternative syntheses of 3 and 4 are described. A number of acyl and azo derivatives of 4 were prepared. Reactions of 2 with dimethyl acetylenedicarboxylate and ethyl acetate (base catalyzed) leading to vic-triazole derivatives are also described. 相似文献
106.
Kyung‐Lae Park Byoung‐Gi Moon Sang‐Hun Jung Jin‐Gyu Kim Il‐Hwan Suh 《Acta Crystallographica. Section C, Structural Chemistry》2000,56(10):1247-1250
The title compound, (S)‐(+)‐4‐[5‐(2‐oxo‐4,5‐dihydroimidazol‐1‐ylsulfonyl)indolin‐1‐ylcarbonyl]anilinium chloride (S)‐(+)‐1‐[1‐(4‐aminobenzoyl)indoline‐5‐sulfonyl]‐4‐phenyl‐4,5‐dihydroimidazol‐2‐one, C24H23N4O4S+·Cl?·C24H22N4O4S, crystallizes in space group C2 from a CH3OH/CH2Cl2 solution. In the crystal structure, there are two different conformers with their terminal C6 aromatic rings mutually oriented at angles of 67.69 (14) and 61.16 (15)°. The distances of the terminal N atoms (of the two conformers) from the chloride ion are 3.110 (4) and 3.502 (4) Å. There are eight distinct hydrogen bonds, i.e. four N—H?Cl, three N—H?O and one N—H?N, with one N—H group involved in a bifurcated hydrogen bond with two acceptors sharing the H atom. C—H?O contacts assist in the overall hydrogen‐bonding process. 相似文献
107.
Jong Seung Kim Moon Hwan Cho Sang Chul Lee Kyung Bok Lee Wonbo Sim Jae Hyung Yoo 《Microchemical Journal》1998,60(3):282-289
The mole transport rate of alkaline earth metal ions through a bulk liquid membrane and a supported liquid membrane using a series of proton diionizable acyclic polyethers was measured. Among alkaline earth metal ions, the calcium ion was observed to be selectively transported in both single and competitive transport experiments. Potentiometric titration and solution calorimetric titration also gave calcium selectivity over other alkaline earth metal ions. Acyclic polyether bearing a diethylene glycol unit andn-tetradecyl lipophilic chain at the α position of carboxylic acid affords the best selectivity for the calcium ion in bulk and supported liquid membranes. 相似文献
108.
Homo-apioneplanocin A was efficiently synthesized via stereoselective hydroxymethylation, regio- and chemoselective hydroboration, and chemoselective oxidation as key steps from d-ribose. 相似文献
109.
Suppose one is given two related generating functionsa(x) = a
n
x
n
andb(x) = b
n
x
n
, often it is of interest to determine the limiting behaviour of the quantitiesa
n
/b
n
We survey some earlier results of this nature and give some new ones 相似文献
110.
Lee SK Cho JM Goo Y Shin WS Lee JC Lee WH Kang IN Shim HK Moon SJ 《Chemical communications (Cambridge, England)》2011,47(6):1791-1793
A highly processable, new semiconducting polymer, PCDTTz, based on alternating thiazolothiazole and carbazole units was synthesized. The new polymer exhibited a field-effect carrier mobility of up to 3.8 × 10(-3) cm(2) V(-1) s(-1) and bulk heterojunction solar cells made from PCDTTz produced a power conversion efficiency of 4.88% under AM 1.5 G (100 mW cm(-2)) conditions. 相似文献