首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   204篇
  免费   11篇
化学   137篇
晶体学   1篇
力学   9篇
数学   26篇
物理学   42篇
  2023年   1篇
  2022年   4篇
  2021年   6篇
  2020年   6篇
  2019年   2篇
  2018年   7篇
  2017年   9篇
  2016年   10篇
  2015年   10篇
  2014年   13篇
  2013年   12篇
  2012年   9篇
  2011年   14篇
  2010年   19篇
  2009年   10篇
  2008年   14篇
  2007年   11篇
  2006年   13篇
  2005年   6篇
  2004年   5篇
  2003年   10篇
  2002年   4篇
  2001年   6篇
  1999年   3篇
  1998年   2篇
  1997年   2篇
  1996年   1篇
  1995年   2篇
  1994年   1篇
  1992年   1篇
  1991年   1篇
  1988年   1篇
排序方式: 共有215条查询结果,搜索用时 15 毫秒
71.
An anthracene‐containing poly(arylene‐ethynylene)‐alt‐poly(arylene‐vinylene) (PAE‐PAV) of general constitutional unit (? Ph? C?C? Anthr? C?C? Ph? CH?CH? Anthr? CH?CH)n bearing two 2‐ethylhexyloxy solubilizing side chains on each phenylene (Ph) unit has been synthesized and characterized. The basic electrochemical characterization was done, showing the existence of two non‐reversible oxidation and one reversible reduction peaks. The optical properties, the real and imaginary part of the dielectric function, were probed using spectroscopic ellipsometry (SE). The vibrational structure of the undoped/doped polymer was investigated using Fourier transformed infrared spectroscopy. A strong change in the polaronic absorption was observed during the doping, which after modeling revealed the existence of two separated transitions. The optical changes upon doping were additionally recorded using the SE technique. Similar to the results from FT‐IR spectroscopy, two new in‐the‐gap absorptions were found. Moreover, the electrical conductivity as well as the mobility of positive carriers were measured. In the undoped state, the conductivity of the polymer was found to be below the detection limit (<μS cm?1), after doping the conductivity increased to 0.69 S cm?1. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2014 , 52, 338–346  相似文献   
72.
Summary.  We report the synthesis and the spectroscopic properties of a novel soluble thiophene-based copolymer carrying pendant fullerene moieties (donor–acceptor double-cable polymer). Photoinduced absorption (PIA) experiments on spin cast films reveal a photoinduced electron transfer from the polythiophene chain onto the fullerene moieties. The performance of photovoltaic devices produced with this copolymer is also discussed. Corresponding author. E-mail: antonio.cravino@jku.at Received August 16, 2002; accepted (revised) August 26, 2002  相似文献   
73.
74.
Cadmium sulfide (CdS) nanoparticles (NPs) capped with poly(acrylic acid) (PAA) were prepared in aqueous solutions from Cd(NO3)2 and Na2S. Influence of the COOH/Cd ratio (0.8-12.5), reaction pH (5.5 and 7.5), and PAA molecular weight (2100 and 5100 g/mol) on the particle size, colloidal stability, and photoluminescence were investigated. A Cd/S ratio of <1 causes ineffective passivization of the surface with the carboxylate and therefore results in a red shift of the absorption band and a significant drop in photoluminescence. Therefore, the Cd/S ratio was fixed at 1.1 for all experiments studying the mentioned variables. PAA coating provided excellent colloidal stability at a COOH/Cd ratio above 1. Absorption edges of PAA-coated CdS NPs are in the range of 460-508 nm. The size of the NPs increases slightly with increasing PAA molecular weight and COOH/Cd ratio at pH 7.5. It is demonstrated that there is a critical COOH/Cd ratio (1.5-2) that maximizes the photoluminescence intensity and quantum yield (QY, 17%). Above this critical ratio, which corresponds to smaller crystal sizes (3.7-4.1 nm) for each reaction set, the quantum yield decreases and the crystal size increases. Moreover, CdS NPs prepared at pH 7.5 have significantly higher QY and absorb at lower wavelengths in comparison with those prepared at pH 5.5. Luminescence quenching has not been observed over 8 months.  相似文献   
75.
The most widely used method to determine the level of tritium in humans is testing urine. Tritium concentrations in urine samples of 100 persons aged 18–66 years selected randomly from a pilot region in Turkey were analysed. The average activity concentration of urine samples was 4.66?±?1.94?Bq?L?1 and the maximum activity concentration was 27.91?Bq?L?1. The minimum detectable activity was 2.38?Bq?L?1. The annual effective dose from tritium was also evaluated on the basis of the measurement results and reference values recommended by the International Commission on Radiological Protection. The effective doses for males and females were 4.56 and 3.54?nSv, respectively. These results were lower than the permissible annual effective dose for members of the public.  相似文献   
76.
The solvatochromic and spectral properties of oxazolone derivatives in various solvents were reported. Fluorescence spectra clearly showed positive and negative solvatochromism depending on substituents. The solvatochromic plots and quantum chemical computations at DFT-B3LYP/6-31?+?G(d,p) level were used to assess dipole moment changes between the ground and the first excited singlet-states. The electron accepting nitro substituent at the para-position increased the π-electron mobility, however, the 3,5-dinitro substituent decreased the π-electron mobility as a result of inverse accumulation of the electronic density as compared with that of its ground state. Experimental and computational studies proved that the photoinduced intramolecular electron transfer (PIET) is responsible for the observed solvatochromic effects. We demonstrate that PIET can be finely tailored by the position of the electron accepting and donating substituents in the phenyl ring of the oxazolone derivatives. We propose that the photoactive CPO derivatives are new molecular class of conjugated push-pull structures using azlactone moiety as the π-conjugated linker and may find applications in photovoltaic cells and light emitting diodes.  相似文献   
77.
Long QT syndrome, LQTS, results in serious cardiovascular disorders, such as tachyarrhythmia and sudden cardiac death. A promiscuous binding of different drugs to the intracavitary binding site in the pore domain (PD) of human ether-a-go-go related gene (hERG) channels leads to a similar dysfunction, known as a drug-induced LQTS. Therefore, an assessment of the blocking ability for potent drugs is of great pragmatic value for molecular pharmacology and medicinal chemistry of hERGs. Thus, we attempted to create an in silico model aimed at blinded drug screening for their blocking ability to the hERG1 PD. Two distinct approaches to the drug blockage, ligand-based QSAR and receptor-based molecular docking methods, are combined for development of a universal pharmacophore model, which provides rapid assessment of drug blocking ability to the hERG1 channel. The best 3D-QSAR model (AAADR.7) from PHASE modeling was selected from a pool consisting of 44 initial candidates. The constructed model using 31 hERG blockers was validated with 9 test set compounds. The resulting model correctly predicted the pIC(50) values of test set compounds as true unknowns. To further evaluate the pharmacophore model, 14 hERG blockers with diverse hERG blocking potencies were selected from literature and they were used as additional external blind test sets. The resulting average deviation between in vitro and predicted pIC(50) values of external test set blockers is found as 0.29 suggesting that the model is able to accuretely predict the pIC(50) values as true unknowns. These pharmacophore models were merged with a previously developed atomistic receptor model for the hERG1 PD and exhibited a high consistency between ligand-based and receptor-based models. Therefore, the developed 3D-QSAR model provides a predictive tool for profiling candidate compounds before their synthesis. This model also indicated the key functional groups determining a high-affinity blockade of the hERG1 channel. To cross-validate consistency between the constructed hERG1 pore domain and the pharmacophore models, we performed docking studies using the homology model of hERG1. To understand how polar or nonpolar moieties of inhibitors stimulate channel inhibition, critical amino acid replacement (i.e., T623, S624, S649, Y652 and F656) at the hERG cavity was examined by in silico mutagenesis. The average docking score differences between wild type and mutated hERG channels was found to have the following order: F656A > Y652A > S624A > T623A > S649A. These results are in agreement with experimental data.  相似文献   
78.
The effects of W doping on the characteristical properties of SnO2 thin films prepared by sol–gel spin coating method were investigated. The SnO2 thin films were deposited at various W doping ratios and characterized by various measurements. XRD studies indicated that the undoped and W doped SnO2 films had cubic and tetragonal phases. The SEM images of WTO thin films showed cubic shaped nanocubes corresponding to cubic phase and the smaller particles corresponding to tetragonal phase were formed on the film surfaces, and their distributions and sizes were dependent on the W doping ratio. EDX spectroscopy analyses showed that the calculated and participated atomic ratios of W/(W + Sn) (at.%) in the starting solution and in the WTO thin films were almost close. It was found that the sheet resistance depended on W doping ratio and 2.0 at.% W doped SnO2 (WTO) exhibited lowest value of sheet resistance (7.11 × 103 Ω/cm2).  相似文献   
79.
When X-ray structure of a ligand-bound receptor is not available, homology models of the protein of interest can be used to obtain the ligand-binding cavities. The steroelectronic properties of these cavities are directly related to the performed molecular model coordinates. Thus, the use of different template structures for homology may result in variation of ligand-binding modes. We have recently reported the MD simulations of a potent CB ligand at bovine rhodopsin-based CB1 and CB2 receptors (Durdagi et al., Bioorg Med Chem 16:7377–7387, 2008). In this present study, a homology modeling study based on the β2-adrenergic receptor for both CB1 and CB2 receptors was performed, and the results were compared with rhodopsin-based models. In addition, the role of membrane bilayers to the adopted conformations of potent AMG3 CB ligand has been analyzed for receptor-free and membrane-associated receptor systems. The performed MD trajectory analysis results have shown that gauche conformations at the terminal segment of the alkyl side chain of AMG3 are not favored in solution. Different adopting dihedral angles defined between aromatic and dithiolane rings at the active sites of the CB1 and CB2 receptors, which are adapted lead to different alkyl side chain orientations and thus, may give clues to the medicinal chemists to synthesize more selective CB ligands. The binding sites of receptors derived by rhodopsin-based models have been regenerated using the β2-adrenergic based template receptors. The re-obtained models confirmed the ligand-binding pockets that were derived based on rhodopsin.  相似文献   
80.
The non–linear inelastic response of glassy polymers is highly influenced by the three–dimensional deformation state, the temperature and the strain rate at which they are deformed. The contribution presents new experiments for different deformation modes which are carried out at different temperatures and rates on commercial bis–phenol A polycarbonate. Emphasis is put not only on the experimental results by themselves but also on the setup and the technique employed in the obtention of the data. The effect of temperature on the velocity with which the neck propagates along the gaged section of a flat specimen under tension is studied means a facility based on photogrammetry. From the homogeneous compression experiments a single set of material parameters appearing in a constitutive model based on the distributed free volume theory under the frame work of additive kinematics will be identified. The inhomogeneous experimental results serve then as a validation for 3–D simulations since the non–uniform strain distribution on the surfaces of both, simulations and experiments, can be compared. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号