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排序方式: 共有217条查询结果,搜索用时 15 毫秒
91.
Sol-gel deposition of an ultrasonically atomized aerosol has been proven to be a convenient thin film deposition method. Flexibility of the ultrasonic process allows the use of a large range of source solutions. In this paper we describe and discuss the deposition conditions of SiO2 films. The chemical parameters are contemplated and we discuss the influence of ultrasonic waves on the reliability of our process. Source solutions and SiO2 film properties are studied by viscosimetry, Fourier Transform IR spectroscopy and spectroscopic ellipsometry. 相似文献
92.
Single crystals of CaCu3Mn4O12, a new ferromagnetic perovskite-like compound (Tc ? 160°C), have been synthesized at 50 kbar and 1000°C. By X-ray analysis it was found to be cubic (a = 7.241Å), space groupIm3 with two molecules per unit cell. The two Ca2+ and six Cu2+ cations occupy theA sites of the ideal perovskite structure, while the eight Mn4+ cations occupy theB sites. In theIm3 space group the sites occupied by the calcium and copper cations have different point symmetry and therefore the 12-oxygen polyhedra have different distortions. The Ca cations are surrounded by slightly distorted icosahedra, the CaO distance is 2.562Å. The twelve oxygens around the copper cations are arranged as three mutually perpendicular rectangles of different size, the smallest and the largest of which are almost squares. The three sets of Cu0 distances are 1.942, 2.707, and 3.181Å, respectively. The octahedral Mn0 distance is 1.915Å. This arrangement is similar to that found in NaMn3Mn4O12. A comparison between the two structures and a discussion of their thermal data are given. 相似文献
93.
G. M. Dongho Nguimdo George S. Manyali Mahmud Abdusalam Daniel P. Joubert 《The European Physical Journal B - Condensed Matter and Complex Systems》2016,89(4):90
We employ state-of-the-art ab initio density functional theory techniques to investigatethe structural, dynamical, mechanical stability and electronic properties of the ternaryAgInS2 compoundsunder pressure. Using cohesive energy and enthalpy, we found that from the six potentialphases explored, the chalcopyrite and the orthorhombic structures were very competitive aszero pressure phases. A pressure-induced phase transition occurs around 1.78 GPa from the low pressure chalcopyritephase to a rhombohedral RH-AgInS2 phase. The pressure phase transition around 1.78 GPa isaccompanied by notable changes in the volume and bulk modulus. The calculations of thephonon dispersions and elastic constants at different pressures showed that thechalcopyrite and the orthorhombic structures remained stable at all the selected pressure(0, 1.78 and 2.5 GPa), where detailed calculations were performed, while the rhombohedralstructure is only stable from the transition pressure 1.78 GPa. Pressure effect on thebandgap is minimal due to the small range of pressure considered in this study. Themeta-GGA MBJ functional predicts bandgaps which are in good agreement with availableexperimental values. 相似文献
94.
The isomorphism of borates CaLn3+BO4 where Ln3+ stands for a small rare earth cation of Y3+, with the mineral warwickite (Fe,Mg)3Ti(BO4)2 is demonstrated. The octahedral sites of the warwickite structure seem thus to accommodate rather large cations, like trivalent Y3+ or Dy3+ and bivalent Ca2+. The synthesis of several new transition-metal borates with this structure is reported. From a survey of all the warwickite-type compounds one comes to the conclusion that the structure is only stable when the size of the divalent cation M2+ is larger than that one of the trivalent M3+. 相似文献
95.
96.
Association of symmetrical alkane diols with pyridine: DFT/GIAO calculation of 1H NMR chemical shifts 下载免费PDF全文
John S. Lomas Laurent Joubert François Maurel 《Magnetic resonance in chemistry : MRC》2016,54(10):805-814
Proton nuclear magnetic resonance (NMR) shifts of the free diol and of its 1 : 1 and 1 : 2 hydrogen‐bonded complexes with pyridine have been computed for five symmetrical alkane diols on the basis of density functional theory, by applying the gauge‐including atomic orbital method to geometry‐optimized conformers. For certain conformers, intramolecular OH ···OH interactions, evidenced by high NMR OH proton shifts, are further enhanced on going from the free diol to the corresponding 1 : 1 diol/pyridine complex. This is confirmed by atoms‐in‐molecules and non‐covalent interaction plots. The computed OH and CH proton shifts for the diol and the two complexes correlate well with values obtained by analysing data from the NMR titration of the diols in benzene against pyridine. Shift values for the diols in neat pyridine are calculated by weighting the shifts of the various protons in the three forms (free diol, 1 : 1 and 1 : 2 diol/pyridine complexes) according to the experimentally determined association constants. The results are in good agreement with those observed, and after empirical scaling, the root mean square difference is 0.18 ppm. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献
97.
Mathieu Joubert Christelle Delaite Elodie Bourgeat‐Lami Philippe Dumas 《Macromolecular rapid communications》2005,26(8):602-607
Summary: The grafting of poly(ethylene oxide) (PEO) onto silica nanoparticles was performed in situ by the ring‐opening polymerization of the oxirane monomer initiated from the mineral surface using aluminium isopropoxide as an initiator/heterogeneous catalyst. Alcohol groups were first introduced onto silica by reacting the surfacic silanols with prehydrolyzed 3‐glycidoxypropyl trimethoxysilane. The alcohol‐grafted silica played the role of a coinitiator/chain‐transfer agent in the polymerization reaction and enabled the formation of irreversibly bonded polymer chains. Silica nanoparticles containing up to 40 wt.‐% of a hairy layer of grafted PEO chains were successfully produced by this technique.
98.
J. Hussong R. Lückerath W. Stricker X. Bruet P. Joubert J. Bonamy D. Robert 《Applied physics. B, Lasers and optics》2001,73(2):165-172
This work describes a further step towards the determination of the temperature accuracy of H2 Q-branch CARS (Coherent Anti-Stokes Raman Scattering) at high pressure with regard to the influence of the H2 line widths. In laminar steady H2/air flames in the pressure range 1–15 bar and at fuel-rich conditions with stoichiometries between two and four, quasi-simultaneous
temperature measurements were performed with H2 and N2 CARS. The temperature values deduced from H2 CARS are in good agreement with the reference temperature from N2 CARS. The influence of different line-width contributions on the accuracy of H2 Q-branch thermometry was investigated in detail.
Received: 10 April 2001 / Revised version: 22 May 2001 / Published online: 18 July 2001 相似文献
99.
New efficient mechanisms of long-wavelength excitation of short-wavelength luminescence in a system of rare-earth impurity ions are proposed. The model studied involves a multilevel system of electronic states of a rare-earth ion interacting with the long-wavelength emission that is in resonance with one or several transitions between the excited levels. The concentration of impurity ions is assumed to be sufficiently high, so that the interionic cross-relaxation and the up-conversion play a significant role. Moreover, the model includes processes similar to photon avalanche, in which the photoinduced excitation of a single ion is converted into lower-level excitations of several ions, each of them reentering the process after photon absorption. Numerical solutions of the system of balance equations for a multilevel system are obtained with calculated and semiempirical parameters of self-quenching and up-conversion. It is shown that, in a system of Tm3+ impurity ions, short-wavelength luminescence at λ≥0.29 μm can be efficiently excited by radiation at λ?1.11 or 0.649 μm with a moderate intensity. 相似文献
100.
Comparison of classical, semiclassical and quantum methods in hydrogen broadening of acetylene lines
Franck Thibault Sergey V. Ivanov Laura Gomez Pierre Joubert 《Journal of Quantitative Spectroscopy & Radiative Transfer》2011,112(9):1429-1437
Quantum close coupling (CC) calculations of H2-broadening coefficients of infrared and isotropic Raman lines of acetylene (C2H2) are performed for temperatures between 77 and 2000 K. They are used to test three more approximate methods, the quantum coupled states (CS) theory, the semiclassical Robert-Bonamy (RB) formalism and the full classical (FC) model of Gordon. In order to allow a clear and well founded comparison, all the dynamical calculations were performed employing the same ab initio potential energy surface free of any adjustable parameters. It is shown that below room temperature both the coupled states method and full classical method fail at reproducing the close coupling pressure broadening coefficients while above room temperature they are correct and predict comparable accurate values for temperatures greater than about 1000 K. The values provided by the RB method are clearly not satisfactory even at the highest temperature examined. However, the temperature dependence of the RB results follows the functional form used for interpolating and extrapolating CC, CS and FC pressure broadening coefficients. 相似文献