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排序方式: 共有407条查询结果,搜索用时 15 毫秒
311.
Brice H Gill DM Goldie L Keegan PS Kerr WJ Svensson PH 《Chemical communications (Cambridge, England)》2012,48(40):4836-4838
A range of chiral, optically-enriched bicyclic oxabispidines were prepared from (S)-(-)-2,3-epoxypropylphthalimide using an efficient sequence featuring a stereocontrolled intramolecular Mannich reaction as the key transformation. 相似文献
312.
F. Lindberg S.Ya. Istomin G. Svensson P. Svedlindh A. Wannberg E.V. Antipov 《Journal of solid state chemistry》2006,179(5):1434-1444
The effect of replacing Co3+ by Ga3+ and Fe3+ in the perovskite-related tetragonal phase Sr0.75Y0.25CoO2.625 with unit cell parameters: a=2ap, and c=4ap (314 phase) has been investigated. The 314 phase is formed by Sr0.75Y0.25Co1−xMxO2.625+δ, with x?0.375 for M=Ga and x?0.625 for M=Fe. High-resolution transmission electron microscopy and electron diffraction revealed frequent microtwinning in the iron-containing compounds, in contrast to the Ga-substituted 314 phases. Diffraction experiments and electron microscope images indicated that at higher Fe contents, 0.75?x?0.875, a disordered cubic perovskite structure forms. The crystal structures of Sr0.75Y0.25Co0.75Ga0.25O2.625 and Sr0.75Y0.25Co0.5Fe0.5O2.625+δ were refined using neutron powder diffraction data. It was found that the oxygen content of Sr0.75Y0.25Co0.5Fe0.5O2.625+δ is higher than in Fe-free 314 phase, so that δ corresponds to 0.076, whereas δ=0 in Sr0.75Y0.25Co0.75Ga0.25O2.625+δ. Magnetization measurements on the unsubstituted Sr0.7Y0.3CoO2.62 and Ga-substituted Sr0.75Y0.25Co0.75Ga0.25O2.625 compounds indicate the presence of a ferromagnetic-like contribution to the measured magnetization at 320 and 225 K, respectively, while replacing Co by Fe leads to the suppression of this contribution. A neutron diffraction study shows that the Sr0.75Y0.25Co0.5Fe0.5O2.625+δ compound is G-type antiferromagnetic at room temperature, whereas Sr0.75Y0.25Co0.75Ga0.25O2.625 does not exhibit magnetic ordering at room temperature. 相似文献
313.
Bonhommeau S Ottosson N Pokapanich W Svensson S Eberhardt W Björneholm O Aziz EF 《The journal of physical chemistry. B》2008,112(40):12571-12574
The local electronic structure of Fe(III) and Fe(II) ions in different alcohol solutions (methanol, ethanol, propan-1-ol) is investigated by means of soft X-ray absorption spectroscopy at the iron L 2,3-edge. The experimental spectra are compared with ligand field multiplet simulations. The solvated Fe(III) complex is found to exhibit octahedral symmetry, while a tetragonal symmetry is observed for Fe(II). A decrease in the solvent polarity increases the charge transfer from the oxygen of the alcohol to the iron ions. This conclusion is supported by Hartree-Fock calculations of the Mulliken charge distribution on the alcohols. A larger charge transfer is further observed from the solvent to Fe(III) compared to Fe(II), which is connected to the higher positive charge state of the former. Finally, iron ions in solution are found to prefer the high-spin configuration irrespective of their oxidation state. 相似文献
314.
The new compound, Ba4Nb14O23, has been prepared by heating mixtures of Ba5Nb4O15, Nb2O5 and Nb at 1 450°C under Ar. Ba4Nb14O23 has been studied by means of high resolution electron microscopy and X-ray powder diffraction techniques. It has a C-centered orthorhombic unit cell with a=20.782(4), b=12.448(3), c=4.148(1) Å and Z=2. The structure of Ba4Nb14O23 can be considered as being an intergrowth between BaNbO3 and NbO. Characteristic building units are triple chains of corner sharing Nb6 octahedra which are connected via columns of the perovskite type structure to a three dimensional network. 相似文献
315.
Annika K. Eriksson Gunnar Svensson Paul F. Henry Christopher S. Knee 《Journal of solid state chemistry》2008,181(8):2031-2040
A series of oxygen-deficient Sr0.85Bi0.15Co1−xFexO3−δ (0.0?x?1.0) perovskite phases were prepared using solid-state reaction. Results of neutron powder diffraction analyses show that the introduction of Fe onto the B-site severely effects the long range coherence of the oxygen vacancy ordered, I4/mmm supercell, observed for the x=0.0 sample. For x=0.1 a smaller, a=b≈ap, c≈2ap, P4/mmm supercell gives the best agreement to the diffraction data, whilst phases in the range 0.2?x?0.6 adopt disordered cubic perovskite structures. Pseudo-cubic, a=b≈ap, c≈ap, structures are found for x?0.8. Evidence of weak superstructures, reflecting local oxygen ordering, is also obtained from electron diffraction. For all oxygen-annealed phases the average structure reverts to cubic Pm3¯m. The as-prepared samples show G-type antiferromagnetic order at room temperature. The oxygen annealed x=0.10, 0.25 and 1.0 samples display low-temperature spin-glass transitions. 相似文献
316.
A. P. Tyutyunnik V. G. Zubkov V. N. Krasil’nikov I. F. Berger L. A. Perelyaeva I. V. Baklanova M. Yu. Skripkin G. Svensson 《Journal of Structural Chemistry》2011,52(2):350-357
By the hydration of MVO(SeO4)2 with saturated water vapors at room temperature a series of isostructural complex compounds of vanadium(V) of the composition
M[VO2(SeO4)(H2O)2]·H2O (K, Rb, NH4) are synthesized and their physicochemical properties are studied. Based on the X-ray and neutron diffraction data, it is
found that their crystal structure is composed of VO6 octahedra linked in infinite chains by bridging SeO4 tetrahedra. Each of the VO6 octahedra has two short terminal V-O bonds forming a bent dioxovanadium group VO2+. Two water molecules are coordinated by vanadium and one molecule is out of the first coordination sphere in the interchain
space. The vibrational spectra of the studied compounds are completely consistent with their structural features. 相似文献
317.
Stephan Whlbrandt Ole Beyer Helge Reinsch A. Ken Inge Erik Svensson Grape Ulrich Lüning Norbert Stock 《无机化学与普通化学杂志》2019,645(10):732-739
The bifunctional linker molecule [5‐(phosphonomethyl)‐2,4‐bis(sulfonomethyl)phenyl]methanesulfonic acid (HO3S‐CH2)3‐C6H2‐CH2PO3H2 (abbreviated as H5L4) was employed in systematic high‐throughput investigations in order to discover new coordination polymers (CPs). Employing 27 metal salts of 17 different metals in this investigation, five new compounds [Mg2(HL4)(H2O)6] ( 1 ), [Pb4(L4)(OH)3] ( 2 ), [Ba2(H2L4)(OH)(H2O)] ( 3 ), [Ba2(HL4)(H2O)4] ( 4 ), and [Cd2,5(L4)(H2O)7] ( 5 ) were discovered and their crystal structures were determined. In all compounds, the sulfonate and phosphonate groups could not be resolved since the P and S atoms are statistically occupying the atom site with a ratio of 0.25 to 0.75. This is reflected in the P–O and S–O bond lengths. Four of the structures were determined from single‐crystal X‐ray diffraction data, whereas the structure of 4 was solved ab initio from powder data using real‐space methods and refined using Rietveld methods. 相似文献
318.
S Svedhem C A Hollander J Shi P Konradsson B Liedberg S C Svensson 《The Journal of organic chemistry》2001,66(13):4494-4503
A strategy for the synthesis of a series of closely related oligo(ethylene glycol)-terminated alkanethiol amides (principally HS(CH(2))(m)CONH(CH(2)CH(2)O)(n)H; m = 2, 5, 11, 15, n = 1, 2, 4, 6, 8, 10, 12) and analogous esters has been developed. These compounds were made to study the structure and stability of self-assembled monolayers (SAMs) on gold in the prospect of designing new biosensing interfaces. For this purpose, monodisperse heterofunctional oligo(ethylene glycols) with up to 12 units were prepared. Selective monoacylation of the symmetrical tetra- and hexa(ethylene glycol) diols as their mesylates with the use of silver(I) oxide was performed. The synthetic approach was based on carbodiimide couplings of various oligo(ethylene glycol) derivatives to omega-(acetylthio) carboxylic acids via a terminal amino or hydroxyl function. SAM structures on gold were studied with respect to thickness, wettability (water contact angles approximately 30 degrees ), and conformation. A good fit was obtained for the relation between monolayer thickness (d) and the number of units in the oligo(ethylene glycol) chain (n): d = 2.8n + 21.8 (A). Interestingly, the corresponding infrared spectroscopy analysis showed a dramatic change in conformation of the oligomeric chains from all-trans (n = 4) to helical (n > or = 6) conformation. A crystalline helical structure was observed in the SAMs for n > 6. 相似文献
319.
High-resolution S2p photoelectron spectra have been measured for sulfur dichloride and dimethyl sulfide. By means of efficient fitting procedures and theoretical analyses, the vibrational fine structure has been disentangled from the molecular-field induced splitting of the S2p3/2 core-ionized level. The resulting molecular-field splitting is determined to be 177 meV in the case of SCl2 and 104 meV for (CH3)2S. Ab initio calculations that include core–valence electron correlation are able to reproduce these values to within 3 meV. Theoretical predictions of the molecular-field splitting are presented for a series of related sulfur compounds, SX2, where X=H, NH2, CN, and F. 相似文献
320.
Th. Andersson D. Rudolph C. Baktash J. Eberth C. Fahlander D. Haslip D.R. LaFosse S.D. Paul D.G. Sarantites C.E. Svensson H.G. Thomas J.C. Waddington W. Weintraub J.N. Wilson B.A. Brown 《The European Physical Journal A - Hadrons and Nuclei》1999,6(1):5-8
High-spin states of the mass A= 39 mirror pair 39K and 39Ca were investigated via the fusion-evaporation reaction 28Si +16O at 125 MeV beam energy. The Gammasphere array in conjunction with the 4π charged-particle detector array Microball and neutron detectors was used to detect γ rays in coincidence with evaporated light particles. The results of the first
high-spin study of the T
z=−1/2 nucleus 39Ca are discussed in terms of mirror symmetry and compared to spherical shell-model calculations in the 1d
3/2–; 1f
7/2 configuration space.
Received: 18 August 1999 相似文献