全文获取类型
收费全文 | 163篇 |
免费 | 8篇 |
专业分类
化学 | 157篇 |
数学 | 7篇 |
物理学 | 7篇 |
出版年
2023年 | 1篇 |
2022年 | 8篇 |
2021年 | 9篇 |
2020年 | 3篇 |
2019年 | 3篇 |
2018年 | 2篇 |
2017年 | 5篇 |
2016年 | 5篇 |
2015年 | 7篇 |
2014年 | 8篇 |
2013年 | 10篇 |
2012年 | 6篇 |
2011年 | 6篇 |
2010年 | 5篇 |
2009年 | 5篇 |
2008年 | 7篇 |
2007年 | 12篇 |
2006年 | 15篇 |
2005年 | 9篇 |
2004年 | 13篇 |
2003年 | 4篇 |
2002年 | 6篇 |
2001年 | 5篇 |
2000年 | 2篇 |
1999年 | 1篇 |
1998年 | 2篇 |
1996年 | 1篇 |
1994年 | 2篇 |
1993年 | 1篇 |
1990年 | 1篇 |
1984年 | 2篇 |
1983年 | 2篇 |
1977年 | 2篇 |
1976年 | 1篇 |
排序方式: 共有171条查询结果,搜索用时 15 毫秒
71.
I Vayá T Gustavsson T Douki Y Berlin D Markovitsi 《Journal of the American Chemical Society》2012,134(28):11366-11368
Transfer of the electronic excitation energy in calf thymus DNA is studied by time-resolved fluorescence spectroscopy. The fluorescence anisotropy, after an initial decay starting on the femtosecond time scale, dwindles down to ca. 0.1. The in-plane depolarized fluorescence decays are described by a stretched exponential law. Our observations are consistent with one-dimensional transfer mediated by charge-transfer excited states. 相似文献
72.
Ruthenium complexes containing 4,7-diphenyl-1,10-phenanthroline disulfonate (bathophenanthroline disulfonate; BPS) ligands, Ru(BPS)34−, Ru(BPS)2(bipy)2− and Ru(BPS)(bipy)2, were compared to tris(2,2′-bipyridine)ruthenium(II) (Ru(bipy)32+), including examination of the wavelengths of maximum absorption and corrected emission intensity, photoluminescence quantum yield, stability of their oxidised ruthenium(III) form, and relative chemiluminescence intensities and signal-to-blank ratios with cerium(IV) sulfate and six analytes (codeine, morphine cocaine, potassium oxalate, furosemide and hydrochlorothiazide) in acidic aqueous solution. The presence of BPS ligands in the complex increased the photoluminescence quantum yield, but decreased the stability of the oxidised form of the reagent. In contrast to previous evidence showing much greater electrochemiluminescence intensities using Ru(BPS)2(bipy)2− and Ru(BPS)(bipy)2, these complexes did not provide superior chemiluminescence signals than their homoleptic analogues. 相似文献
73.
74.
Gustavsson T Bányász A Lazzarotto E Markovitsi D Scalmani G Frisch MJ Barone V Improta R 《Journal of the American Chemical Society》2006,128(2):607-619
The excited-state properties of uracil, thymine, and nine other derivatives of uracil have been studied by steady-state and time-resolved spectroscopy. The excited-state lifetimes were measured using femtosecond fluorescence upconversion in the UV. The absorption and emission spectra of five representative compounds have been computed at the TD-DFT level, using the PBE0 exchange-correlation functional for ground- and excited-state geometry optimization and the Polarizable Continuum Model (PCM) to simulate the aqueous solution. The calculated spectra are in good agreement with the experimental ones. Experiments show that the excited-state lifetimes of all the compounds examined are dominated by an ultrafast (<100 fs) component. Only 5-substituted compounds show more complex behavior than uracil, exhibiting longer excited-state lifetimes and biexponential fluorescence decays. The S(0)/S(1) conical intersection, located at CASSCF (8/8) level, is indeed characterized by pyramidalization and out of plane motion of the substituents on the C5 atom. A thorough analysis of the excited-state Potential Energy Surfaces, performed at the PCM/TD-DFT(PBE0) level in aqueous solution, shows that the energy barrier separating the local S(1) minimum from the conical intersection increases going from uracil through thymine to 5-fluorouracil, in agreement with the ordering of the experimental excited-state lifetime. 相似文献
75.
Despina Kosseoglou Rebecca Kokkinofta Dimitra Sazou 《Journal of Solid State Electrochemistry》2011,15(11-12):2619-2631
Nafion?–polyaniline (PAn) composite films deposited by a two-step process on a stainless steel (SS) substrate were characterized in this study using Fourier transform infrared (FTIR) spectroscopy under various conditions employed to evaluate their anticorrosion properties. The SS|Nafion? electrode was first prepared by placing a certain amount of Nafion? on the SS substrate, and then polymerization of aniline was carried out potentiodynamically on the SS|Nafion? electrode. The SS|Nafion?–PAn electrodes subjected to both potentiodynamic polarization and open-circuit conditions in sulfuric acid solutions without and with chlorides appeared to have distinct differences in their FTIR spectra. It is proposed that under the electrochemical conditions used in this study, the PAn is mostly formed inside the Nafion? membrane with a high proportion of oligomers influencing the ionic transport through the membrane. The inhibition of pitting corrosion arises primarily from the enhanced permselectivity of the composite film due to the Nafion? membrane that prevents chloride transport. An essential beneficial effect comes also from the PAn redox properties on the growth of the passive oxide film. Even under severe corrosion conditions, Nafion???/em>PAn films retain their redox activity and chemical stability, whereas the membrane crystallinity seems to be enhanced. 相似文献
76.
Dimitra Kourti Anastasia Kanioura Theodore Manouras Maria Vamvakaki Panagiotis Argitis Margarita Chatzichristidi Sotirios Kakabakos Panagiota Petrou 《Macromolecular bioscience》2023,23(1):2200301
Surfaces for guided cell adhesion and growth are indispensable in several diagnostic and therapeutic applications. Towards this direction, four diblock copolymers comprising polyethylene glycol (PEG) and poly(2-tetrahydropyranyl methacrylate) (PTHPMA) are synthesized employing PEG macroinitiators of different chain lengths. The copolymer with a 5000 Da PEG block and a PEG-PTHPMA comonomers weight ratio of 43–57 provides a film with the highest stability in the culture medium and the strongest cell repellent properties. This copolymer is used to develop a positive photolithographic material and create stripe patterns onto silicon substrates. The highest selectivity regarding smooth muscle cell adhesion and growth and the highest fidelity of adhered cells for up to 3 days in culture is achieved for stripe patterns with widths between 25 and 27.5 µm. Smooth muscle cells cultured on such patterned substrates exhibit a decrease in their proliferation rate and nucleus area and an increase in their major axis length, compared to the cells cultured onto non-patterned substrates. These alterations are indicative of the adoption of a contractile rather than a synthetic phenotype of the smooth muscle cells grown onto the patterned substrates and demonstrate the potential of the novel photolithographic material and patterning method for guided cell adhesion and growth. 相似文献
77.
A simple and reliable sample methodology based on simultaneous ultrasonic extraction, sulfuric acid clean-up and headspace solid-phase microextraction (SPME)-gas chromatography-mass spectrometry has been developed as an advantageous analytical tool for the determination of seven polychlorinated biphenyl congeners in bird livers at low levels. The influence of several parameters on the efficiency of the proposed method was systematically investigated. The clean-up efficiency of sulfuric acid treatment was tested and compared with those of column chromatography (Flosiril, silica gel and alumina) and solid-phase extraction (SPE) (Supelclean ENVI-Carb cartridge) procedures. The use of sulfuric acid in the clean-up step prior to headspace solid-phase microextraction analysis allows the removal of interfering matrix compounds present in the liver extracts that would otherwise cause severe ionization suppression of the polychlorinated biphenyls (PCBs) during the ionization process. The optimized method had good linearity (R2>0.99) over the range studied (5-500 ng/g wet weight) and showed satisfactory level of precision, with RSD values lower than 10.6%. The obtained relative recoveries ranged between 63 and 94%. The limits of detection (0.06-0.63 ng/g wet weight) were low enough to check for harmful levels of polychlorinated biphenyls in biological samples, and were well below most of the restrictive limits established by European Union regulations. The method was found to be reliable under the operational conditions proposed and was applied successfully to the analysis of individual polychlorinated biphenyls in liver tissues. The results obtained from five bird species from Greece revealed the presence of the target compounds in all samples analyzed, at levels ranging between 0.54 and 39.45 ng/g wet weight. 相似文献
78.
Dimitra Kovala-Demertzi 《Transition Metal Chemistry》1990,15(1):23-26
Summary Platinum(II) and platinum(IV) complexes of 2-amino-4, 6-dimethylpyrimidine, ADMPY, have been prepared. Solids of formula Pt(ADMPYH+)Cl3, Pt(ADMPY)2Cl4 and Pt(ADMPY)2Cl4·2HCl have been isolated and characterized by elemental analyses in conjuction with i.r. and n.m.r. spectra. A paramagnetic tan to reddishbrown complex has been reproducibly prepared from the direct reaction of K2PtCl4 and ADMPY at pH 6. 相似文献
79.
Dimitra Kovala-Demertzi 《Journal of organometallic chemistry》2006,691(8):1767-1774
An overview is given of the results of organotin-NSAIDs interactions. Several organotin complexes with NSAIDs, derivatives of the carboxylic acid family and oxicam family, have been synthesized and characterized by spectroscopy and X-ray crystallography at the University of Ioannina. Results concerning the biological activity of these organotin complexes will be referred. 相似文献
80.
Dimitra Kovala‐Demertzi Aglaia Koutsodimou Angeliki Galani Sotiris K. Hadjikakou Mavroudis A. Demertzis Marianna Xanthopoulou John R. Miller Christopher S. Frampton 《应用有机金属化学》2004,18(9):501-502
The crystal structure of complex [Ph2Sn(Hpir)2 ·CH3CN] shows for the first time chelation to a metal atom of piroxicam through the keto‐enolate oxygen atoms. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献