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71.
Electrical and dielectric properties of Al/p-Si and Al/perylene/p-Si type diodes in a wide frequency range 下载免费PDF全文
The perylene(C20H12) layer effect on the electrical and dielectric properties of Al/p-Si(MS) and Al/perylene/p-Si(MPS) diodes have been investigated and compared in the frequency range of 0.7 kHz–2 MHz. Experimental results show that C–V characteristics give an anomalous peak for two structures at low frequencies due to interface states(Nss) and series resistance(Rs). The increases in C and G/ω at low frequencies confirm that the charges at interface can easily follow an ac signal and yield excess capacitance and conductance. The frequency-dependent dielectric constant(ε) and dielectric loss(ε) are subtracted using C and G/ω data at 1.5 V. The ε and ε values are found to be strongly dependent on frequency and voltage, and their large values at low frequencies can be attributed to the excess polarization coming from charges at traps. Plots of ln(σac)–ln(ω) for two structures have two linear regions, with slopes of 0.369 and 1.166 for MS, and of 0.077 and 1.061 for MPS, respectively. From the C 2–V characteristics, the doping acceptor atom concentration(NA) and barrier height(ΦB) for Schottky barrier diodes(SBDs) of MS and MPS types are also obtained to be 1.484 × 1015 and 1.303 × 1015cm 3, and 1.10 and 1.13 eV, respectively. 相似文献
72.
Spectroscopic Investigation of the Adsorption of Nitrophenol Isomers on Ammonium Zeolite of Type “Y”
In this study, nitrophenol isomers were adsorbed on synthetic ammonium Y zeolite and the samples acquired were examined with infrared spectroscopy and scanning electron microscopy. The aim of the work is to investigate whether isomeric effects can be monitored after adsorption process. Theoretical calculations of isomers had been performed and the data acquired show that adsorption occurred via bonding from the sites of zeolite. 相似文献
73.
Anniyev T Kaya S Rajasekaran S Ogasawara H Nordlund D Nilsson A 《Angewandte Chemie (International ed. in English)》2012,51(31):7724-7728
Scratching beneath the surface: Pt-M(3d)-Pt(111) (M(3d) = Co, Ni) bimetallic subsurface alloys have been designed to show the ligand effect tunes reactivity in oxygen and hydrogen adsorption systems. The platinum-oxygen bond order was investigated by oxygen atom projection in the occupied and unoccupied space using X-ray emission spectroscopy (XES) and X-ray absorption spectroscopy (XAS). 相似文献
74.
The aim of this study was to investigate the pressure drop coefficient and the static pressure difference related to the natural vortex length and to evaluate the results for gas-particle applications. CFD simulations were carried out using a numerical technique which had been verified previously. Results obtained from the numerical simulations were compared with the experimental data. Analysis of the results showed that the pressure drop coefficient decreases with the increasing inlet velocity, becoming almost constant above a certain value of the inlet velocity. The reason is that the effect of viscous forces decreases at high Reynolds numbers. The pressure drop coefficient also decreases with the increasing exit pipe diameter and decreasing exit pipe length. 相似文献
75.
Hybrid agents which combine potent DNA-photocleavers with tunable amino acids or small peptides were designed to improve selectivity of Nature's most potent class of antibiotics towards cancer cells. The ability of these compounds to photocleave DNA is controlled by their incorporation into hybrid architectures with functional elements derived from natural amino acids. These conjugates are highly effective at inducing double-strand DNA cleavage and, in some cases, rival or even surpass both naturally occurring DNA cleavers and anticancer agents that are currently in clinical use. The possibility of triggering their activity in a photochemical and pH-sensitive fashion allows for a high degree of selectivity over activation. The conjugates were shown to penetrate cell membranes and induce efficient intracellular DNA cleavage. Initial in vitro tests against a variety of cancer cell lines confirm the potential of these compounds as anticancer agents at low nanomolar concentrations. 相似文献
76.
Solans-Monfort X Chow C Gouré E Kaya Y Basset JM Taoufik M Quadrelli EA Eisenstein O 《Inorganic chemistry》2012,51(13):7237-7249
DFT(B3PW91) calculations have been carried out to propose a pathway for the N(2) cleavage by H(2) in the presence of silica-supported tantalum hydride complexes [(≡SiO)(2)TaH(x)] that forms [(≡SiO)(2)Ta(NH)(NH(2))] (Science 2007, 317, 1056). The calculations, performed on the cluster models {μ-O[(HO)(2)SiO](2)}TaH(1) and {μ-O[(HO)(2)SiO](2)}TaH(3), labelled as (≡SiO)(2)TaH(x) (x = 1, 3), show that the direct hydride transfers to coordinated N-based ligands in (≡SiO)(2)TaH(η(2)-N(2)) and (≡SiO)(2)TaH(η(2)-HNNH) have high energy barrier barriers. These high energy barriers are due in part to a lack of energetically accessible empty orbitals in the negatively charged N-based ligands. It is shown that a succession of proton transfers and reduction steps (hydride transfer or 2 electron reduction by way of dihydride reductive coupling) to the nitrogen-based ligands leads to more energetically accessible pathways. These proton transfers, which occur by way of heterolytic activation of H(2), increase the electrophilicity of the resulting ligand (diazenido, N(2)H(-), and hydrazido, NHNH(2)(-), respectively) that can thus accept a hydride with a moderate energy barrier. In the case of (≡SiO)(2)TaH(η(2)-HNNH), the H(2) molecule that is adding across the Ta-N bond is released after the hydride transfer step by heterolytic elimination from (≡SiO)(2)TaH(NH(2))(2), suggesting that dihydrogen has a key role in assisting the final steps of the reaction without itself being consumed in the process. This partly accounts for the experimental observation that the addition of H(2) is needed to convert an intermediate, identified as a diazenido complex [(≡SiO)(2)TaH(η(2)-HNNH)] from its ν(N-H) stretching frequency of 3400 cm(-1), to the final product. Throughout the proposed mechanism, the tantalum remains in its preferred high oxidation state and avoids redox-type reactions, which are more energetically demanding. 相似文献
77.
Mixed convection heat transfer about a semi-infinite inclined plate in the presence of magneto and thermal radiation effects
is studied. The fluid is assumed to be incompressible and dense. The nonlinear coupled parabolic partial differential equations
governing the flow are transformed into the non-similar boundary layer equations, which are then solved numerically using
the Keller box method. The effects of the mixed convection parameter R
i, the angle of inclination α, the magnetic parameter M and the radiation–conduction parameter R
d on the velocity and temperature profiles as well as on the local skin friction and local heat transfer parameters. For some
specific values of the governing parameters, the results are compared with those available in the literature and a fairly
good agreement is obtained. 相似文献
78.
Alkan A Kutlu R Hallac T Sigirci A Emul M Pala N Altinok T Aslan M Sarac K Ozcan C 《Magnetic resonance imaging》2004,22(5):707-713
Our purpose was to investigate, by magnetic resonance (MR) spectroscopy, the metabolite changes in the brains of subjects in the shoemaking industry who had been chronically exposed to organic solvents. A total of 49 male subjects and 30 age-matched healthy volunteers underwent detailed neurological and psychiatric examinations. All subjects had long-echo [repetition time (TR) 2000 ms, echo time (TE) 136 ms] single-voxel MR spectroscopy. Voxels (15 x 15 x 15 mm(3)) were placed in the parietal white matter, thalamus, and basal ganglia. N-acetylaspartate (NAA)/creatine (Cr) and choline (Cho)/Cr ratios were calculated. There was no significant difference between the study subjects and the control group in NAA/Cr ratios obtained from thalamus, basal ganglia, and parietal white matter. Cho/Cr ratios in thalamus, basal ganglia, and parietal white matter were found to be significantly increased compared to controls. There was a positive correlation between basal ganglia Cho/Cr ratio and duration of exposure (r = 0.63). MR spectroscopy should be performed to reveal metabolite changes and determine the degree of brain involvement in solvent-related industry workers. 相似文献
79.
Fully automated liquid chromatography-mass spectrometry determination of 17beta-estradiol in river water 总被引:1,自引:0,他引:1
Watabe Y Kubo T Nishikawa T Fujita T Kaya K Hosoya K 《Journal of chromatography. A》2006,1120(1-2):252-259
Surface modified molecularly imprinted polymers (SM-MIPs) for 17beta-estradiol (E2), utilizing 6-ketoecradiol as a pseudo template were prepared. MIPs for E2 were synthesized using 4-vinyl pyridine and ethylene dimethacrylate as a functional monomer and cross-linking agent, respectively. MIPs selectively retained E2 and provided excellent chromatographic resolution from interfering compounds inherent in river water sample matrices. Therefore, freshly prepared MIPs were applied to quantitative mass spectrometric (negative electrospray ionization mode) detection of low levels of E2 in river water sample. In order to pre-concentrate the target compound for HPLC analysis, column switching was coupled with a pretreatment column packed with the MIPs. The repeatability of actual determinations of river water sample, in which background E2 was not detected, spiked with 50 ng/L of E2 was 2.2% RSD with a detection limit and qualification limit of 1.8 and 5.4 ng/L, respectively. Surface modification of MIP particlefs packed in the pretreatment column provided selective affinity and on-line concentration of low levels of E2 while simultaneously eliminating sample matrix interference, resulting in a significant increase in sensitivity and reproducibility for liquid chromatography-mass spectrometry analysis of E2 in river water sample. 相似文献
80.
Enthalpies (Δisom
H
(g)o), Gibbs free energies (Δisom
G
(g)o), and equilibrium constants (log K
isom) for the trans → cis isomerization of various 3,3′-, 4,4′-, and 5,5′- disubstituted 2,2′-diphenoquinones with a range of electron withdrawing
and releasing moieties (methyl, fluoro, chloro, bromo, trifluoromethyl, and amino) were calculated in the gas phase and in
the solvent phase (n-hexane, benzene, n-octanol, acetonitrile, and water). In the gas phase, the trans isomer of the parent and all substituted 2,2′-diphenoquinones is predicted to be more thermodynamically stable than the cis configuration, with log K
isom ranging from −2.8 to −7.0. For all compounds, increasing solvent polarity/proticity progressively favors shifting the cis/trans equilibrium towards greater contributions of the cis configuration and substantially increases the log K
isom by up to 5.1 units relative to the gas phase. In polar protic and polar aprotic solvents, the estimated log K
isom ranges as low as −0.4, indicating significant populations of the cis isomers should be present. The findings support the polar solvent phase mechanistic predictions for a cis configuration of 2,2′-diphenoquinones participating in the thermal transformation of trans-2,2′-diphenoquinones to oxepino[2,3-b]benzofurans. With limited exceptions for some amino derivatives, the cis-2,2′-diphenoquinone to oxepino[2,3-b]benzofuran isomerization is expected to be thermodynamically favorable for all substituents/phases
under consideration. The cis-2,2′-diphenoquinone to oxepino[2,3-b]benzofuran rearrangement is predicted to become less thermodynamically favored with
increasing solvent polarity/proticity. 相似文献