全文获取类型
收费全文 | 2166篇 |
免费 | 387篇 |
国内免费 | 391篇 |
专业分类
化学 | 1432篇 |
晶体学 | 31篇 |
力学 | 104篇 |
综合类 | 16篇 |
数学 | 104篇 |
物理学 | 1257篇 |
出版年
2024年 | 4篇 |
2023年 | 29篇 |
2022年 | 39篇 |
2021年 | 56篇 |
2020年 | 62篇 |
2019年 | 54篇 |
2018年 | 53篇 |
2017年 | 57篇 |
2016年 | 107篇 |
2015年 | 75篇 |
2014年 | 132篇 |
2013年 | 210篇 |
2012年 | 150篇 |
2011年 | 144篇 |
2010年 | 138篇 |
2009年 | 169篇 |
2008年 | 176篇 |
2007年 | 174篇 |
2006年 | 150篇 |
2005年 | 130篇 |
2004年 | 134篇 |
2003年 | 103篇 |
2002年 | 85篇 |
2001年 | 72篇 |
2000年 | 63篇 |
1999年 | 58篇 |
1998年 | 47篇 |
1997年 | 39篇 |
1996年 | 37篇 |
1995年 | 32篇 |
1994年 | 21篇 |
1993年 | 43篇 |
1992年 | 23篇 |
1991年 | 15篇 |
1990年 | 14篇 |
1989年 | 10篇 |
1988年 | 6篇 |
1987年 | 7篇 |
1986年 | 3篇 |
1985年 | 7篇 |
1984年 | 3篇 |
1983年 | 3篇 |
1982年 | 2篇 |
1981年 | 2篇 |
1980年 | 2篇 |
1979年 | 1篇 |
1975年 | 1篇 |
1974年 | 2篇 |
排序方式: 共有2944条查询结果,搜索用时 15 毫秒
91.
Jorge Pavez Maritza Páez Armelle Ringuedé Fethi Bedioui José H. Zagal 《Journal of Solid State Electrochemistry》2005,9(1):21-29
We studied the electrocatalytic activity of cobalt tetra-aminophthalocyanine (CoTAPc) for the reduction of molecular oxygen (O2) on adsorbed monomeric and on electropolymerized films of different thicknesses on glassy carbon (GC) electrode. The polymeric films, denoted poly-CoTAPc, were first characterized by electrochemical impedance spectroscopy and it appears that the types of phenomena revealed to be occurring depend less on the film thickness in basic than in acid media. For O2 reduction, the results showed that poly-CoTAPc is more active than the monomeric CoTAPc adsorbed on GC. Indeed, rotating ring-disk electrode data showed that polymeric CoTAPc promotes the four-electron reduction of O2 to water in parallel to a two-electron reduction to give peroxide. On monomeric and thin films of poly-CoTAPc, a two-electron reduction mechanism predominates. In basic media the activity increases very slightly with thickness, whereas in acid media this increase is more pronounced. This parallels the observed behavior revealed by electrochemical impedance spectroscopy. 相似文献
92.
The nickel–iron alloy electrodeposition is affected by a superimposed magnetic field. Some previous papers [Msellak et al.,
Magnetohydrodynamics, 39:487–493, 2003 and Msellak et al., J Magn Magn Mat, 281:295–304, 2004] have exhibited some dramatic changes in iron amount and morphology of these deposits. As it is usual for a magnetic field
up to 1 T, no charge transfer effect can be expected, and the observed modifications can be explained by the magnetohydrodynamic
convection that controls the iron species flux during the electrochemical reaction. By electrochemical impedance spectroscopy
and physical investigations (scanning electron microscopy, X-ray diffraction, and inductively coupled plasma), the reduction
process is analyzed, the characteristic parameters of the mechanism are determined, and the magnetic field effects can be
quantified.
Contribution to special issue on “Magnetic field effects in Electrochemistry”. 相似文献
93.
Production of palladium nanoparticles supported on multiwalled carbon nanotubes by gamma irradiation
J.V. Rojas C.H. Castano 《Radiation Physics and Chemistry》2012,81(1):16-21
Palladium nanoparticles were produced and supported on multiwalled carbon nanotubes (MWCNT) by gamma irradiation. A solution with a specific ratio of 2:1 of water-isopropanol was prepared and mixed with palladium chloride and the surfactant sodium dodecyl sulfate (SDS). The gamma radiolysis of water ultimately produces Pd metallic particles that serve as nucleation seeds. Isopropanol is used as an ion scavenger to balance the reaction, and the coalescence of the metal nanoparticles was controlled by the addition of SDS as a stabilizer. The size and distribution of nanoparticles on the carbon nanotubes (CNT) were studied at different surfactant concentrations and radiation doses. SEM, STEM and XPS were used for morphological, chemical and structural characterization of the nanostructure. Nanoparticles obtained for doses between 10 and 40 kGy, ranged in size 5-30 nm. The smaller nanoparticles were obtained at the higher doses and vice versa. Histograms of particle size distributions at different doses are presented. 相似文献
94.
The dissolution behavior of carbon steel in ammonium chloride (NH4Cl) solution containing sodium thiosulfate (Na2S2O3) of various concentrations (0.01 and 0.1 M) was investigated using electrochemical impedance spectroscopy (EIS) and other nonelectrochemical techniques. The weight loss and polarization measurements indicate a significant increase in the NH4Cl corrosion rate of carbon steel on addition of Na2S2O3. The EIS measurements exhibited two capacitive loops at multiple direct current (dc) potentials for both the concentrations. Electrical equivalent circuit (EEC) and reaction mechanism analysis (RMA) were employed to analyze the impedance data. A four-step mechanism with two intermediate adsorbate species of same charge was proposed to explain the dissolution behavior of carbon steel in the given system. The surface coverage values enumerated that the surface was entirely covered with adsorbed species unlike in the pure NH4Cl system. Charge transfer resistance and polarization resistance values estimated from RMA parameters indicate the increase in a dissolution rate with dc potential. The surface morphology was inspected via field emission scanning electron microscopy, and the corrosion products including surface state of carbon steel electrode were analyzed using energy dispersive X-ray spectroscopy and X-ray photoelectron spectroscopy. 相似文献
95.
《Analytical letters》2012,45(4):644-657
The variables affecting determination of ultra trace levels of uranium (VI) in aqueous samples by differential pulse cathodic stripping voltammetry using chloranilic acid as the complexing agent have been examined in detail. Effect of organic surfactants on the voltammetric behavior has been studied. Electrochemical impedance measurements reveal the effect of adsorption of different surfactants on the adsorption pre-concentration step of uranium-chloranilic acid complex. Additionally, to better understand the analytical feature of the method, physicochemical aspects of the preconcentration process has been studied. Adsorption of uranium-chloranilic acid complex follows the Langmuir adsorption isotherm. Analysis results on sea water samples from India are reported. 相似文献
96.
Trivalent osmium ions are substitutionally incorporated into aqueous precipitates and melt-grown single crystals of AgBr and AgC1. The ions are distributed between three structurally inequivalent lattice sites in both salts. From epr studies, we have inferred that these sites are distinguished by the arrangement of charge-compensating silver ion vacancies in the two closest cation subshells. The most reasonable dopant-vacancy configurations have been deduced from the epr data. These configurations persist up to at least 300 K, and are compared with those observed in other trivalent metal ion doped systems. 相似文献
97.
The main factor in the propagation of traffic noise is the road surface, where the vehicles generate noise due to the contact between tire and pavement, in addition to the noise produced by the engine. 相似文献
98.
99.
Hasan M. El Ghanem Saa’Di Abdul Jawad Yazan A. Hussain Adnan S. Abu-Surrah 《Journal of Macromolecular Science: Physics》2014,53(5):878-892
Impedance spectroscopy was utilized to investigate the dielectric properties, ac conductivity and charge transport mechanisms in propylene-alt-CO/ethylene-alt-CO (EPEC) random terpolymer filled with multi-walled carbon nanotubes (MWCNT) as a function of nanofiller content, frequency, and temperature. Equivalent resistor-capacitor (RC) circuit models were proposed to describe the impedance characteristics of the unfilled terpolymer and the nanocomposite at different temperatures. For the nanocomposites, the ac conductivity tended to be frequency independent at low frequencies. At high frequencies, the ac conductivity increased with frequency. The dc conductivity (i.e., plateau of the ac conductivity at low frequencies) at room temperature increased from 10?9 (Ω·m)?1 for the unfilled polymer to l0?3 (Ω·m)?1 for the 6 wt% MWCNT/EPEC nanocomposite. At low temperatures, the equivalent RC model for EPEC-0 and EPEC-2 was found to consist of a parallel RC circuit. However, for 6 wt% MWCNT/EPEC nanocomposite, an RC model consisting of an R/constant phase element (CPE) circuit and a resistor in series was required to describe the impedance behavior of the nanocomposite. 相似文献
100.
Single‐Walled Carbon Nanotubes in Highly Viscous Media: A Comparison between the Dispersive Agents [BMIM][BF4], L121, and Triton X‐100
下载免费PDF全文
![点击此处可从《Chemistry (Weinheim an der Bergstrasse, Germany)》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Dr. Carla Gasbarri Prof. Fausto Croce Dr. Ida Meschini Christopher H. Bowen Dr. Lisa Marinelli Prof. Antonio Di Stefano Dr. Guido Angelini 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(2):546-549
Dispersions of single‐walled carbon nanotubes (SWNTs) have been prepared by using the room‐temperature ionic liquid [BMIM][BF4] (1‐butyl‐3‐methylimidazolium tetrafluoroborate), the triblock copolymer Pluronic L121 [poly(ethylene oxide)5‐poly(propylene oxide)68‐poly(ethylene oxide)5] and the non‐ionic surfactant Triton X‐100 (TX100) in the pure state. The size of the SWNTs aggregates and the dispersion degree in the three viscous systems depend on the sonication time, as highlighted by UV/Vis/NIR spectroscopy and optical microscopy analysis. A nonlinear increase in conductivity can be observed as a function of the SWNTs loading, as suggested by electrochemical impedance spectroscopy. The generation of a three‐dimensional network of SWNTs showing a viscoelastic gel‐like behavior above a critical percolation concentration has been found at 25 °C in all the investigated systems by oscillatory rheology measurements. 相似文献