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31.
A.S. Nikolov P.A. Atanasov D.R. Milev T.R. Stoyanchov A.D. Deleva Z.Y. Peshev 《Applied Surface Science》2009,255(10):5351-5354
Nanoparticles (NPs) creation by pulsed-laser ablation of targets in a liquid environment has recently become a promising technique, which has several relative advantages, such as simplicity and low cost. This technique was employed in the present work for preparation of TiOx NPs suspension by ablation of metal Ti targets into twice-distilled water. A second harmonic generation (SHG) pulsed Nd:YAG laser was used in the experiments. Preferential formation of spherical NPs and their TiOx nature was established. Aggregation of the created particles during aging was found. Transition of the NPs’ structure from amorphous to crystalline with increasing the laser energy was revealed. A difference was observed in the transmittance of the suspensions obtained depending on the laser intensity. 相似文献
32.
Galabov B Atanasov Y Ilieva S Schaefer HF 《The journal of physical chemistry. A》2005,109(50):11470-11474
Density functional and ab initio methods were applied in examining the possible mechanistic pathways for the reaction of methyl benzoate with ammonia. Transition state structures and energies were determined for concerted and neutral stepwise mechanisms. The theoretical results show that the two possible pathways have similar activation energies. The general base catalysis of the process was also examined. The predictions reveal that the catalytic process results in considerable energy savings and the most favorable pathway of the reaction is through a general-base-catalyzed neutral stepwise mechanism. The structure and transition vectors of the transition states indicate that the catalytic role of ammonia is realized by facilitating the proton-transfer processes. Comparison of the energetics of the aminolysis for methyl benzoate and methyl formate shows the more favorable process to be that for the aliphatic ester. The differing reactivity of the two esters is explained in terms of the electrostatic potential values at the atoms of the ester functionality. 相似文献
33.
Dr. Uttam Chakraborty Dr. Serhiy Demeshko Prof. Dr. Franc Meyer M. Sc. Christophe Rebreyend Prof. Dr. Bas de Bruin Prof. Dr. Mihail Atanasov Prof. Dr. Frank Neese Dr. Bernd Mühldorf Prof. Dr. Robert Wolf 《Angewandte Chemie (International ed. in English)》2017,56(27):7995-7999
The 15 valence-electron iron(I) complex [CpArFe(IiPr2Me2)] ( 1 , CpAr=C5(C6H4-4-Et)5; IiPr2Me2=1,3-diisopropyl-4,5-dimethylimidazolin-2-ylidene) was synthesized in high yield from the FeII precursor [CpArFe(μ-Br)]2. 57Fe Mössbauer and EPR spectroscopic data, magnetic measurements, and ab initio ligand-field calculations indicate an S= 3/2 ground state with a large negative zero-field splitting. As a consequence, 1 features magnetic anisotropy with an effective spin-reversal barrier of Ueff=64 cm−1. Moreover, 1 catalyzes the dehydrogenation of N,N-dimethylamine–borane, affording tetramethyl-1,3-diaza-2,4-diboretane under mild conditions. 相似文献
34.
In this study we present results of the conductivity and resistance to thermooxidative and condensation reactions of a highly phosphonated poly(pentafluorostyrene) (PWN2010) and of its blends with poly(benzimidazole)s (PBI). This polymer, which combines both: (i) a high degree of phosphonation (above 90%) and (ii) a relatively high acidity (pKa (–PO3H2 ↔ –PO3H−) ∼ 0.5) due to the fluorine neighbors, is designed for low humidity operating fuel cell. This was confirmed by the conductivity measurements for PWN2010 reaching σ = 5 × 10−4 S cm−1 at 150 °C in dry N2 and σ = 1 × 10−3 S cm−1 at 150 °C (λ = 0.75). Furthermore, this polymer showed only 48% of anhydride formation when annealing it at T = 250 °C for 5 h and only 2% weight loss during a 96 h Fenton test. These properties combined with the ability of the PWN2010 to form homogeneous blends with polybenzimidazoles resulting in stable and flexible polymer films, makes PWN2010 a very promising candidate as a polymer electrolyte for intermediate- and high-temperature fuel cell applications. 相似文献
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37.
Dr. Stephan Walleck Prof. Dr. Mihail Atanasov Prof. Dr. Jürgen Schnack Dr. Eckhard Bill Anja Stammler Dr. Hartmut Bögge Prof. Dr. Thorsten Glaser 《Chemistry (Weinheim an der Bergstrasse, Germany)》2021,27(61):15240-15251
The first confacial pentaoctahedron comprised of transition metal ions namely ZnIIFeIIIAFeIIIBFeIIIAZnII has been synthesized by using a dinucleating nonadentate ligand. The face-sharing bridging mode enforces short ZnII⋅⋅⋅FeIIIA and FeIIIA⋅⋅⋅FeIIIB distances of 2.83 and 2.72 Å, respectively. Ab-initio CASSCF/NEVPT2 calculations provide significant negative zero-field splittings for FeIIIA and FeIIIB with |DA|>|DB| with the main component along the C3 axis. Hence, a spin-Hamiltonian comprised of anisotropic exchange, zero-field, and Zeeman term was employed. This allowed by following the boundary conditions from the theoretical results the simulation in a theory-guided parameter determination with Jxy=+0.37, Jz=−0.32, DA=−1.21, EA=−0.24, DB=−0.35, and EB=−0.01 cm−1 supported by simulations of high-field magnetic Mössbauer spectra recorded at 2 K. The weak but ferromagnetic FeIIIAFeIIIB interaction arises from the small bridging angle of 84.8° being at the switch from anti- to ferromagnetic for the face-sharing bridging mode. 相似文献
38.
We report here the synthesis and characterization of four dinuclear cyanide-bridged Fe(III)-Cu(II) complexes, based on a tetra- or a pentadentate bispidine ligand (L(1) or L(2), respectively; bispidines are 3,7-diazabiyclo[3.3.1]nonane derivatives) coordinated to the Cu(II) center, and a tridentate bipyridineamide (bpca) coordinated to the low-spin Fe(III) site, with cyanide groups completing the two coordination spheres, one of them bridging between the two metal ions. The four structurally characterized complexes [{Fe(bpca)(CN)(3)}{Cu(L(1)·H(2)O)}]BF(4), [{Fe(bpca)(CN)(3)}{Cu(L(2))}][Fe(bpca)(CN)(3)]·5H(2)O, [{Fe(bpca)(CN)(3)}{Cu(L(2)·MeOH)}]PF(6)·MeOH·H(2)O, and [{Fe(bpca)(CN)(3)}{Cu(L(2))}]PF(6)·2H(2)O belong to different structural isomers. The most important differences are structurally and electronically enforced (direction of the pseudo-Jahn-Teller mode) strong or weak interactions of the copper(II) center with the cyanide bridge. The related strength of the magnetic coupling of the two centers is analyzed with a combination of experimental magnetic, electron paramagnetic resonance (EPR), electronic spectroscopic data together with a ligand-field theory- and density functional theory (DFT)-based analysis. 相似文献
39.
Erbium, and erbium and ytterbium co-doped YVO4 waveguiding films were deposited on MgO/Si substrates by PLD. The samples were post-annealed at two different temperatures in air atmosphere. The influence on the crystalline structure and waveguiding properties of the films at these annealing temperatures for two dopant concentrations was investigated. Layers annealed up to 900 °C are polycrystalline. The dominant fraction of YVO4 crystallites exhibited preferred orientation of the (0 0 1) zone axes parallel to the substrate surface. The polycrystalline samples show difference in the refractive indexes Δn (Δn = nTE − nTM) for TE and TM polarizations. 相似文献
40.
We investigate the effect of curvature on the behaviour of a quantum particle bound to move on a surface shaped as a helical tube. We derive and discuss the governing Schrödinger equation and the corresponding quantum effective potential which is periodic and points to the helical configuration as more energetically favorable as compared to the straight tube. The exhibited periodicity also leads to energy band structure of pure geometrical origin. 相似文献