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711.
Ramanuj Mishra Jayanta Hazarika Anil Hazarika Binod Gogoi Ragini Dubey Debanjan Bhattacharjee 《Liquid crystals》2018,45(11):1661-1671
This study focuses on the electrical characteristics of a strongly polar nematic liquid crystal, Hexyloxy-cyanobiphenyl (6OCB), doped with a low concentration (2% by weight) of citrate buffer stabilised gold nanoparticles (GNPs) at low frequencies between 20 Hz and 35 MHz. The doped samples have lower values of nematic–isotropic transition temperature, permittivity (both parallel and perpendicular to the field direction) and dielectric anisotropy; however, relaxation time and activation energy were increased. The observed results could be explained on the basis of weakly anisotropic nature of GNPs and a local rearrangement of liquid crystal molecules surrounding the nanoparticles. Moreover, a complimentary suggestion on a possible change in the dipole–dipole correlation is made to explain the difference in changes (qualitative and quantitative) observed for permittivity of the host nematic liquid crystal doped with GNP. Temperature dependent dielectric relaxation studies indicate an increase in viscosity and potential barrier; and hence a change in strength of inter-molecular and intra-molecular interactions is suggested. 相似文献
712.
《中国化学》2018,36(3):199-205
We report a new small molecular acceptor, ITIC‐OEG, which is based on indacenodithieno[3,2‐b]thiophene and 1,1‐(dicyanomethylene)‐3‐ indanone including oligoethyleneglycol (OEG) side‐chains. ITIC‐OEG was found to have higher dielectric constant (εr=5.6) than that of a reference molecule of ITIC with normal alkyl substituents (εr=3.9). The dielectric constant of medium influences significantly the exciton binding energy and the resulting charge separation and recombination. The optical, electrochemical and morphological properties of ITIC‐OEG and its photovoltaic characteristics were investigated by blending with a semi‐crystalline donor polymer, PPDT2FBT, with comparison to those of ITIC. ITIC‐OEG shows more red‐shifted absorption and stronger crystalline packing than ITIC. However, the lower photovoltaic performance (with 1.58% power conversion efficiency, PCE) was measured for PPDT2FBT:ITIC‐OEG, compared to PPDT2FBT:ITIC (5.52% PCE). The incompatibility between PPDT2FBT and ITIC‐OEG (due to high hydrophilic nature of OEG chains) resulted in poor intermixing with large domain separation over 300 nm, showing inefficient charge separation and significant charge recombination. Therefore, to investigate the effect of dielectric constant of the materials on the charge separation and recombination, the blend morphology of the PPDT2FBT:ITIC‐OEG should be optimized first by improving their miscibility and phase separation. 相似文献
713.
《先进技术聚合物》2018,29(7):1974-1987
The ac‐impedance of bulk‐like films of pure polyethylene oxide (PEO) polymer was measured as a function of frequency f in the range 0.1 to 107 Hz at various constant temperatures T (155 − 330 K ). The as‐measured data were analyzed by electric permittivity and modulus formalisms to unveil which dielectric and conductive relaxation processes were responsible for their relaxation behavior below/above glass transition temperature Tg of pure PEO polymer. At T > Tg , none of the α ‐, β ‐, or γ ‐relaxations could be inferred for studied pure PEO films from frequency variation of measured imaginary part ε′′(f, T) of complex dielectric permittivity , as low‐frequency losses masked real dielectric contribution to the measured ε′′(f, T) at low frequencies and high temperatures. However, at T < Tg , a broad, relaxation process has been observed in the high‐frequency part of their isothermal ε′′(f, T) − f spectra, which can be related to the β ‐ or γ ‐dielectric relaxation process. Nonlinear regressions of the measured ε′′(f, T) − f data for T < Tg yielded moral fits to a simple addition of a Havriliak‐Negami function, and a Bergman‐loss Kohlrausch‐Williams‐Watts‐type function, with the relaxation time τmax(T) obtained from Havriliak‐Negami‐fitting parameters, was found to follow a thermally activated Arrhenius‐like relaxation behavior. Conversely, representation of the imaginary part M′′(f, T > Tg) − f spectra of complex electric modulus was found to depict 2 overlapped relaxation processes, which were detached well by a nonlinear regression of a simple superposition of 2 different M′′(f) expressions having the form of the universal Bergman loss function, where it was found that the relaxation time is also thermally activated. 相似文献
714.
A. Jurlewicz 《Journal of statistical physics》1995,79(5-6):993-1003
This paper provides the frequency domain analysis of the probabilistic representation of the cluster model for dielectric relaxation in dipolar systems. It is proved that the restriction (0.1) experimentally found for both the powerlaw coefficientsn andm is the necassary and sufficient condition to obtain the low- and high-frequency power-law behavior. Consequently, in both frequency regions the Kramers-Krönig-compatible frequency-independent rules are fulfilled. Moreover, in contrast to the empirical functions proposed to fit the experimental data, the dielectric susceptibility derived from the stochastioc considerations does cover the full range of the observed dielectric responses. 相似文献
715.
Dina Bresenden A. S. Carlson P. J. Partain Graciela Reynoso Bobbie Oudinarath K. A. Martin A. M. Nishimura 《Journal of fluorescence》1995,5(4):377-381
The extent to which energy transfer occurs in electronically excited organic adlayer films on dielectric surfaces is investigated. Migration and subsequent trapping of the energy in the film are observed by pumping the singlet state of an organic adlayer of benzophenone and by monitoring the phosphorescence and fluorescence lifetimes. To observe the effects of adsorption, benzophenone was chosen as the adlayer because the energies of its well characterizedn, carbonyl states are remarkably sensitive to solvent interactions. Upon excitation with a nitrogen laser, the perturbation on the electronic states of benzophenone by the substrate caused the emergence of the normally absent fluorescence from the adlayer traps at the interface between the surface of the dielectric substrate and the adlayer. Energy transfer to this interface was observed as a function of film thickness. On the surface of a single crystal of an organic crystal, naphthalene, energy transfer from the adlayer to the substrate was observed, whereas such transfer was not energetically possible with the other dielectric surfaces. 相似文献
716.
A mean spherical model of classical dipoles on a simple cubic lattice of sideM=2N+1 sites is considered. Exact results are obtained for finite systems using periodic boundary conditions with an external dielectric constant and using reaction field boundary conditions with a cutoff radiusR
c
N and an external dielectric constant. The dielectric constant in the disordered phase is calculated using a variety of fluctuation formulas commonly implemented in Monte Carlo and molecular dynamics simulations of dipolar systems. The coupling in the system is measured by the parametery=4
2/9kT, where
2 is the fixed mean square value of the dipole moments on the lattice. The system undergoes a phase transition aty2.8, so that very high dielectric constants cannot be obtained in the disordered phase. The results show clearly the effects of system size, cutoff radius, external dielectric constant, and different measuring techniques on a dielectric constant estimate. It is concluded that with periodic boundary conditions, the rate of approach of the dielectric constant estimate to its thermodynamic limit is asN
–2/3 and depends only weakly on. Methods of implementing reaction field boundary conditions to give rapid convergence to the thermodynamic limit are discussed. 相似文献
717.
Shirafuji Tatsuru Nakagami Yuko Hayashi Yasuaki Nishino Shigehiro 《Plasmas and Polymers》1998,3(2):115-127
Fluorinated amorphous carbon films were prepared from tetrafluoroethylene (TFE; C2F4) and tetraisocyanatesilane (TICS; Si(NCO)4) using an RF plasma enhanced chemical vapor deposition method for the purpose of application to inter layer low permittivity films used in large scale integrated circuits. Structure of the deposited films was investigated by X-ray photoelectron spectroscopy and Fourier transform infrared spectroscopy. Adhesion characteristics were examined by a tape-peel method. Permittivity of the films was investigated from capacitance measurement on metal-insulator-semiconductor structure. The structural analysis revealed that the deposited films contained imide-like group
in spite of the fact that TICS molecules contained isocyanate group
. The films deposited under the flow ratio TICS/(TFE + TICS) = 70% showed permittivity of 2.3, good adhesion on silicon substrates, and higher thermal stability than the films deposited without TICS. 相似文献
718.
David A. Babb Bob R. Ezzell Katherine S. Clement W. Frank Richey Alvin P. Kennedy 《Journal of polymer science. Part A, Polymer chemistry》1993,31(13):3465-3477
Novel polymers containing alternating perfluorocyclobutane and aromatic ether subunits are prepared from aryl poly(trifluorovinyl ether) monomers via the thermal [2π + 2π] dimerization of the trifluorovinyl ether functionality. A model study is described, which probes the nature of the perfluorocyclobutane rings formed during the polymerization reaction. The bifunctional monomer 4,4′-bis(trifluorovinyloxy) biphenyl and the trifunctional monomer 1,1,1-tris(4-trifluorovinyloxyphenyl)ethane are prepared and polymerized to provide thermoplastic and thermoset polymers, respectively. Characterization of the mechanical and dielectric properties of these new polymers is presented. © 1993 John Wiley & Sons, Inc. 相似文献
719.
用密度泛函方法研究了ZrO2在羟基预处理的Si(100)-2×1表面原子层淀积(ALD)初始反应过程的反应机理, ZrO2的ALD过程包括两个前体反应物ZrCl4和H2O交替的半反应. 两个半反应都经历一个相似的吸附中间体反应路径. 比较单羟基Si表面反应的反应焓变, 可以发现双羟基Si表面反应, 由于相邻羟基的存在, 对ZrCl4的半反应影响较大, 尤其是化学吸附能增加明显. 而对于H2O的半反应, 单、双羟基Si表面反应的能量变化不是很明显. 使用内禀反应坐标(IRC)方法, 验证了两个半反应存在相似的过渡态结构和反应机理. 另外, 发现随着温度的升高, 吸附络合物的稳定性降低, 其向反应物方向的解吸附变得容易, 而向产物方向的解离难度增加. 相似文献
720.
Nd2O3添加量对BaTiO3陶瓷介电性能的影响 总被引:4,自引:0,他引:4
BaTiO3 ceramics doped with Nd2O3(the additive content was respectively 0.001,0.002,0.003,0.005,0.01,0.03mol)were prepared by Sol-Gel method. Effects of Nd2O3 contents on the dielectric constant (ε), the dielectric loss (tanδ) ,the Curie-temperature (TC) and the resistivity (ρ) of BaTiO3 ceramic were studied. When Nd2O3 content was 0.001mol and 0.002mol, the dielectric constant was increased obviously, but the dielectric loss was also increased. When Nd2O3 content was 0.003mol, the dielectric constant was increased, and the dielectric loss was decreased, which was suitable for application in condenser. The resistivity was decreased obviously with the increasing of Nd2O3 contents, the resistivity was the smallest when Nd2O3 content was 0.001mol. The Curie-temperature was also decreased with the increasing of Nd2O3 contents. 相似文献