全文获取类型
收费全文 | 521篇 |
免费 | 40篇 |
专业分类
化学 | 433篇 |
晶体学 | 1篇 |
力学 | 11篇 |
数学 | 24篇 |
物理学 | 92篇 |
出版年
2023年 | 15篇 |
2022年 | 7篇 |
2021年 | 18篇 |
2020年 | 25篇 |
2019年 | 13篇 |
2018年 | 10篇 |
2017年 | 10篇 |
2016年 | 22篇 |
2015年 | 20篇 |
2014年 | 27篇 |
2013年 | 31篇 |
2012年 | 56篇 |
2011年 | 59篇 |
2010年 | 26篇 |
2009年 | 18篇 |
2008年 | 29篇 |
2007年 | 32篇 |
2006年 | 27篇 |
2005年 | 28篇 |
2004年 | 23篇 |
2003年 | 14篇 |
2002年 | 11篇 |
2001年 | 4篇 |
2000年 | 3篇 |
1999年 | 5篇 |
1998年 | 2篇 |
1997年 | 1篇 |
1996年 | 3篇 |
1995年 | 3篇 |
1994年 | 2篇 |
1992年 | 3篇 |
1991年 | 1篇 |
1990年 | 1篇 |
1983年 | 1篇 |
1978年 | 1篇 |
1975年 | 1篇 |
1974年 | 1篇 |
1973年 | 2篇 |
1972年 | 2篇 |
1971年 | 1篇 |
1970年 | 1篇 |
1969年 | 1篇 |
1967年 | 1篇 |
排序方式: 共有561条查询结果,搜索用时 46 毫秒
151.
Galen L. Eakins Joshua S. Alford Brandon J. Tiegs Bryan E. Breyfogle Chad J. Stearman 《Journal of Physical Organic Chemistry》2011,24(11):1119-1128
Highest occupied molecular orbital–lowest unoccupied molecular orbital (HOMO–LUMO) tuning is an important consideration in the development of organic‐based semiconducting materials. A study of the specific effects and overall trends for the HOMO–LUMO tuning of a diverse series of 9‐fluorenones by means of extended conjugation and substituent effects is described. Trends were explored in a range of compounds, beginning with structures having highly electron‐withdrawing substituents and progressing to structures having highly electron‐donating substituents. Compounds with an incremental increase in conjugation were also examined. Electrochemical and optical measurements were used to calculate the HOMO–LUMO levels and HOMO–LUMO bandgap (HLG) for each structure. Results from both methods were compared and correlated with the differences in molecular structure. Increasing the electron‐donating character of the substituents was observed to decrease the HLG and increase the energy levels of the HOMO and the LUMO, whereas an increase in the electron‐withdrawing character produced the opposite results. Increasing conjugation decreased the HLG, increased the HOMO energy level, but decreased the LUMO energy level. Spectroscopic evidence of substituent influence on the carbonyl suggests that substituents directly impact the HLG by influencing the availability of nonbonding electrons within the carbonyl, which impacts the probability of an nπ* transition. The data presented not only elaborate on the HOMO–LUMO tuning of 9‐fluorenone systems but also enable the consideration of 9‐fluorenones as analogous models for HOMO–LUMO tuning in other more complex polyaromatic systems such as bifluorenylidenes. These trends may provide insight into developing materials with specifically tuned HLGs and HOMO–LUMO levels for a variety of applications. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
152.
We experimentally studied the spatial coherence of random laser emission from dye solutions containing nanoparticles. The spatial coherence, measured in a double slit experiment, varied significantly with the density of scatterers and the size and shape of the excitation volume. A qualitative explanation is provided, illustrating the dramatic difference from the spatial coherence of a conventional laser. This work demonstrates that random lasers can be controlled to provide intense, spatially incoherent emission for applications in which spatial cross talk or speckle limit performance. 相似文献
153.
SrTaxTi1−xO3 (STT) with x = 0.01, 0.05, and 0.10, has been investigated as a potential electron conductor for solid oxide fuel cell (SOFC) anodes. STT was found to be chemically stable under oxidizing and reducing conditions and chemically compatible with yttria-stabilized zirconia (YSZ). The coefficient of thermal expansion (CTE) was near that of YSZ, ranging from 11.3 to 11.8 × 10−6 K−1. The conductive properties of bulk STT and porous STT-YSZ composites were studied under relevant SOFC operating temperatures and redox cycling conditions. In order to achieve reasonable conductivities, samples were initially reduced at 1673 K. Conductivity after redox cycling was higher for lower dopant concentrations. The redox stable conductivity of a porous composite with x = 0.01 was 1.1 S/cm at 1073 K in humidified H2 (3% H2O). Fuel cell tests indicated an anode impedance of 0.4 Ω cm2 at 973 K in humidified H2 for STT-YSZ anodes infiltrated with 3 wt.% CeO2 and 1 wt.% Pd. 相似文献
154.
Li FF Pinzón JR Mercado BQ Olmstead MM Balch AL Echegoyen L 《Journal of the American Chemical Society》2011,133(5):1563-1571
The [2 + 2] cycloaddition reaction of Sc(3)N@I(h)-C(80) with benzyne was successfully conducted for the first time. The reaction affords both the [5,6]- and [6,6]-monoadducts with a four-membered ring attached to the cage surface on 5,6- and 6,6-ring fusions, respectively. The compounds were characterized by MALDI-TOF, NMR, UV-vis-NIR spectroscopy and single-crystal X-ray structure determination. The electrochemical behavior of both monoadducts was investigated. The [5,6]-regioisomer displays reversible cathodic behavior similar to that observed for the fulleropyrrolidines with a 5,6-addition pattern. Surprisingly, the [6,6]-regioisomer also exhibits reversible cathodic behavior. The interconversion reaction of the isomers was also explored, and the results showed that both monoadducts are thermally very stable. 相似文献
155.
We demonstrate how a single-crystal to single-crystal transformation resulting from bridging-linker replacement is possible in extended 2D and 3D metal-organic frameworks (MOFs) by introducing pillared paddlewheel MOF structures into a solution containing dipyridyl linkers. No lateral movement of the layers was observed during this transformation, creating a templating effect from the "parent" structure to the "daughter" structure. A previously unattainable structure was obtained by a two-step synthetic method utilizing the bridging-linker replacement transformation method. Additionally, a bridging-linker insertion was observed when excess linker was used with the 2D MOF structure, inducing an overall 2D to 3D transformation. 相似文献
156.
Jais Abdul Azim Ali S. A. Muhammed Anwar Mustafa Somalu Mahendra Rao Muchtar Andanastuti Isahak Wan Nor Roslam Wan Baharudin Nurul Akidah Lim Kean Long Brandon Nigel P. 《Journal of Solid State Electrochemistry》2020,24(3):711-722
Journal of Solid State Electrochemistry - Nickel/scandia-ceria-stabilized-zirconia (Ni/10Sc1CeSZ) cermet is a potential anode for solid oxide fuel cells. The anode powder is prepared through a... 相似文献
157.
Changfei He Peter R. Christensen Trevor J. Seguin Eric A. Dailing Brandon M. Wood Rebecca K. Walde Kristin A. Persson Thomas P. Russell Brett A. Helms 《Angewandte Chemie (International ed. in English)》2020,59(2):735-739
Control of equilibrium and non‐equilibrium thermomechanical behavior of poly(diketoenamine) vitrimers is shown by incorporating linear polymer segments varying in molecular weight (MW) and conformational degrees of freedom into the dynamic covalent network. While increasing MW of linear segments yields a lower storage modulus at the rubbery plateau after softening above the glass transition (Tg), both Tg and the characteristic time of stress relaxation are independently governed by the conformational entropy of the embodied linear segments. Activation energies for bond exchange in the solid state are lower for networks incorporating flexible chains; the network topology freezing temperature decreases with increasing MW of flexible linear segments but increases with increasing MW of stiff segments. Vitrimer reconfigurability is therefore influenced not only by the energetics of bond exchange for a given network density, but also the entropy of polymer chains within the network. 相似文献
158.
Using first‐principles calculations with predictive capability we show that organic molecules having negative electron affinity can be transformed to superhalogens with electron affinities far exceeding that of chlorine, once its core and ligand atoms are suitably replaced. The discovery of organic superhalogens could have significant impact in chemistry, allowing the synthesis of new materials and compounds. 相似文献
159.
In this paper, effects of ethylene glycol (EG) and indium tin oxide (ITO) solution on the morphology, porosity, and roughness of TiO2 film prepared by sol‐gel process were investigated and discussed. Initially, the addition of EG were used to control the viscosity of the solution and it was found to increase the pore size of TiO2 film. The various TiO2 films were investigated and characterized by scanning electron microscopy (SEM) and atomic force microscopy (AFM) and then assembled to dye‐sensitized solar cell (DSSC) to measure the photoelectric conversion efficiency. The optimum efficiencies of 1.32% with Jsc and Voc of 2.99 mA/cm2 and 0.80 V, respectively, were obtained by the TiO2 film prepared from a solution containing 20 wt% EG. 相似文献
160.