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排序方式: 共有369条查询结果,搜索用时 15 毫秒
361.
362.
Antoine Villesuzanne Werner Paulus Alain Cousson Shoichi Hosoya Lo?c Le Dr��au Olivier Hernandez Carmelo Prestipino Mohamed Ikbel Houchati Juerg Schefer 《Journal of Solid State Electrochemistry》2011,15(2):357-366
The structure of oxygen-intercalated La2CuO4.07 has been investigated at 20 and 300?K by neutron diffraction on an electrochemically oxidized single crystal. At 20?K, reconstruction of the nuclear density by maximum entropy method shows strong displacements of the apical oxygen atoms towards [100] with respect to the F-centred unit cell, whilst displacements towards [110] and [100] were both found to be present at ambient temperature. Combining structural studies with first-principles lattice dynamical calculations, we interpret the displacements of the apical oxygen atoms to be at least partially of dynamic origin already at ambient temperature. Strong displacements of the apical oxygen atoms of stoichiometric and oxygen-doped $ {\hbox{L}}{{\hbox{a}}_{{2}}}{\hbox{Cu}}{{\hbox{O}}_{{{4} + \delta }}} $ and corresponding associated lattice instabilities, i.e. low-energy phonon modes, are considered as a general prerequisite of low-temperature oxygen diffusion mechanisms. Lattice dynamical calculations on $ {\hbox{L}}{{\hbox{a}}_{{2}}}{\hbox{Cu}}{{\hbox{O}}_{{{4} + \delta }}} $ suggest that the oxygen species diffusing at low temperature are not the interstitial but, more prominently, the apical oxygen atoms. The presence of interstitial oxygen atoms is, however, important to amplify via specific, low-energy phonon modes, a dynamic exchange mechanism between apical and vacant interstitial oxygen sites, thus allowing a dynamically triggered, shallow potential oxygen diffusion pathway. The crucial role of lattice dynamics to enable low-temperature oxygen mobility in K2NiF4-type oxides is discussed on a microscopic scale and compared to similar low-temperature oxygen diffusion mechanisms, recently proposed for non-stoichiometric oxides with Brownmillerite-type structure. 相似文献
363.
364.
Erk C Hammerschmidt L Andrae D Paulus B Schlecht S 《Physical chemistry chemical physics : PCCP》2011,13(13):6029-6035
A precursor-based approach to the cubic β-phase of PbF(2) was developed and allowed the preparation of this high-temperature phase well below the temperature for transition from the orthorhombic α- to the cubic β-phase. The formation of β-PbF(2) from the molecular precursors Pb[Se(C(6)H(2)(CF(3))(3))](2) and Pb(C(6)H(2)(CF(3))(3))(2) is facilitated by the presence of several short PbF contacts in these molecules. The cubic form of PbF(2) was obtained as macroscopic crystals as well as nanoparticulate powder. Its formation at relatively low temperature suggested a theoretical re-investigation of the phase stabilities of the two polymorphs. The theoretical results from the Kohn-Sham density functional theory indicate that the energy content for the β-phase is slightly lower than the one for the α-phase, by 0.5-1.7 kJ mol(-1) depending on the density functional used (zero-point vibrational energy correction included). 相似文献
365.
Patrick Degen D. C. Florian Wieland Michael Paulus Martin A. Schroer Metin Tolan Heinz Rehage 《Colloid and polymer science》2013,291(3):653-659
This study focuses on the preparation and characterization of magnetic switchable thin iron oxide–polymer films. In a series of experiments, the formation and growth of iron oxide under ultrathin polysiloxane layers was controlled by changing the concentration of iron ions in the aqueous subphase or by varying the residence time of ammonia in the gas phase above the liquid sample. The growth of the combined film structures is studied in situ by interfacial rheology, optical microscopy, and x-ray scattering experiments and ex situ by scanning electron microscopy. Different stages of iron oxide aggregation, from a very thin layer of amorphous iron oxide with thickness of a few nanometers up to micrometer thick coatings of crystalline maghemite (γ-Fe2O3) were investigated. The specific interactions between the inorganic iron oxide and the polymer membranes cause the creation of new composite materials which are sensitive to magnetic forces. Figure
Magnetic switchable membranes should be achieved by the combination of an ultrathin polymer network with the in-situ formation of iron oxide at the interface. (Left) After completing the polymerization the creation of iron oxide was induced by adding NH3 gas. (Right) SEM investigations clearly approve the formation of a thin composite layer as well as the growth of iron-oxide under this layer 相似文献
366.
Quantum chemical study of Co<Superscript>3+</Superscript> spin states in LaCoO<Subscript>3</Subscript> 总被引:1,自引:0,他引:1
L. Siurakshina B. Paulus V. Yushankhai E. Sivachenko 《The European Physical Journal B - Condensed Matter and Complex Systems》2010,74(1):53-61
Ab initio quantum-chemical cluster calculations are
performed for the perovskite LaCoO3. The main concern is to
calculate the energy level ordering of different spin states of
Co3+, which is an issue of great controversy for many years.
The calculations performed for the trigonal lattice structure at
T = 5 K and 300 K, with the structural data taken from experiment,
display that the low-spin (LS, S = 0) ground state is separated from
the first excited high-spin (HS, S = 2) state by a gap <100 meV,
while the intermediate-spin (IS, S = 1) state is located at much
higher energy ≈0.5 eV. We suggest that the local lattice
relaxation around the Co3+ ion excited to the HS state and the
spin-orbit coupling reduce the spin gap to a value ~10 meV.
Coupling of the IS state to the Jahn-Teller local lattice distortion
is found to be rather strong and reduces its energy position to a
value of 200 ?\div 300 meV. Details of the quantum-chemical
cluster calculation procedure and the obtained results are
extensively discussed and compared with those reported earlier by
other authors. 相似文献
367.
Leimeng Zhuang Marcel Hoekman Willem Beeker Arne Leinse Ren Heideman Paulus van Dijk Chris Roeloffzen 《Laser \u0026amp; Photonics Reviews》2013,7(6):994-1002
In this paper, novel photonic delay lines (DLs) using Vernier/non‐identical ring resonators (VRRs) are proposed and demonstrated, which are capable of simultaneous generation of multiple different delays at different wavelengths (frequencies). The simple device architectures and full reconfigurability allow the DLs to be integrated with other functional building blocks in photonic integrated circuits to realize on‐chip, complex multi‐λ microwave photonic signal processors with reduced system complexity. To prove the concept, DLs using VRRs in cascaded and coupled configurations have been fabricated in TriPleXTM waveguide technology, which enables a very low delay‐induced loss of approximately 0.18 dB/100 ps. The fabricated DLs demonstrated simultaneous generation of four incremental delays, where a maximum incremental step of 550 ps and a corresponding top delay of 1650 ps were measured for a bandwidth up to 1 GHz. To our knowledge, this is the first report on VRRs for delay generation functionalities. 相似文献
368.
The gelation rate of poly(vinylidene fluoride) (PVF2)/glyceryl tributyrate (GTB) system has been measured. It has been analysed with the help of an equation which contains φn and f(T) term where φ is a reduced overlapping concentration and n is analogous to the percolation exponent β in a three-dimensional lattice. f(T) is related to the temperature function of the coil-to-helix transition. Analysis of the gelation rates supports that the three-dimensional percolation is a suitable mechanism in this gelation process and it also indicates that the gelation is caused by coil-to-helix transition followed by their association. 相似文献
369.
Dr. Arsh S. Hazrah Dr. Aran Insausti Jiarui Ma Mohamad H. Al-Jabiri Prof. Dr. Wolfgang Jäger Prof. Dr. Yunjie Xu 《Angewandte Chemie (International ed. in English)》2023,62(44):e202310610
Two competing solvation pathways of 3-methylcatechol (MC), an atmospherically relevant aromatic molecule, with up to five water molecules were explored in detail by using a combination of broadband rotational spectroscopy and computational chemistry. Theoretically, two different pathways of solvation emerge: the commonly observed droplet pathway which involves preferential binding among the water molecules while the solute serves as an anchor point for the formation of a water cluster, and an unexpected wetting pathway which involves interactions between the water molecules and the aromatic face of MC, i.e., a wetting of the π-surface. Conclusive identification of the MC hydrate structures, and therefore the wetting pathway, was facilitated by rotational spectra of the parent MC hydrates and several H218O and 13C isotopologues which exhibit splittings associated with methyl internal rotation and/or water tunneling motions. Theoretical modelling and analyses offer insights into the tunneling and conversion barriers associated with the observed hydrate conformers and the nature of the non-covalent interactions involved in choosing the unusual wetting pathway. 相似文献