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71.
2R-(-)-6-Hydroxytremetone (C13H14O3) is a bioactive metabolite isolated from Xenophyllum poposum (Phil.) V.A. Funk. (ex. Werneria poposa Phil.), a member of the Asteraceae. Various pharmacological properties attributed by popular medicine to benzofurane derivatives prompted their physical and chemical characterization. The obtained substance was characterized by melting point, optic rotation, ultraviolet spectrum, 1HRMN, 13CRMN, infrared spectroscopy, and thermo-analytical techniques. The molecular structure of 2R-(-)-6-hydroxytremetone was determined by single crystal X-rays diffraction methods. The substance crystallizes in the monoclinic space group P2(1) with a = 8.767(2) A, b = 5.423(1) A, c = 24.301(4) A, beta = 90.52(2) degrees , and two independent but very similar molecules of the same handedness per asymmetric unit (Z = 4). Both molecules have the phenyl ring and its attached oxydryl and methyl ketone groups nearly co-planar to one another and are stabilized by a strong OH ... Oketone intra-molecular bond (Ohydroxyl ... Oketone distances of 2.529 and 2.536 A; O-H ... Oketone angles of 146.4 and 143.9 degrees , respectively). 相似文献
72.
Monica Marras Stella Vernier Piro 《Zeitschrift für Angewandte Mathematik und Physik (ZAMP)》2008,59(5):766-779
We investigate the behavior of the solution of a nonlinear heat problem, when Robin conditions are prescribed on the boundary
∂Ω × (t > 0), Ω a bounded R
2 domain. We determine conditions on the geometry and data sufficient to preclude the blow up of the solution and to obtain
an exponential decay bound for the solution and its gradient.
Supported by the University of Cagliari. 相似文献
73.
Gregory March S. Reisberg B. Piro M.-C. Pham M. Delamar V. Noel K. Odenthal D.B. Hibbert J.J. Gooding 《Journal of Electroanalytical Chemistry》2008,622(1):37-43
Electroactive 5-hydroxy-3-hexanedithiol-1,4-naphthoquinone (JUGthio) has been self-assembled on gold. Electrochemical results show the surface coverage is 2.2 × 10−10 mol cm−2, which is consistent with a dense monolayer. The JUGthio shows one quasi-reversible and stable voltametric wave in aqueous buffered solution. A kinetic analysis of the redox reactions involving both electron and proton transfer has revealed an unusual behaviour of this molecule due to the presence of the hydroxyl function in the vicinity of the quinone group. The apparent kinetic rate constant and the anodic coefficient transfer of this reaction depend on the pH. In acid medium, a classical concerted 2e−/2H+ mechanism is obtained. In basic medium (pH > 7), strong intramolecular hydrogen interactions between the quinone and the hydroxyl function have a strong influence on the redox kinetics. These results show that JUGthio electroactivity is very sensitive to hydrogen interactions in neutral and basic pH solution and is able to act as sensitive layer for electrochemical biosensing. 相似文献
74.
75.
Susana H. Tarulli Oscar V. Quinzani Oscar E. Piro Enrique J. Baran Eduardo E. Castellano 《Monatshefte für Chemie / Chemical Monthly》2001,29(5):779-787
The crystal structure of the title complex, [Cd(tsac)2(H2O)], has been determined by single crystal X-ray diffraction methods. It crystallizes in the monoclinic space group C2/c (a = 12.236(3), b = 8.919(3), c = 16.655(3) ?, β = 96.18(2)°, Z = 4). The molecular structure was solved from 1705 independent reflections with I > σ(I) and refined to R 1 = 0.0489. Infrared and Raman spectra of the complex were recorded and are briefly discussed. Its thermal behaviour was investigated by thermogravimetry and differential thermal analysis. 相似文献
76.
G. A. Philippin V. Proytcheva S. Vernier‐Piro 《Mathematical Methods in the Applied Sciences》2009,32(3):330-345
In this paper, we derive bounds for the solutions of a quasilinear heat equation in a finite cylindrical region if the far end and the lateral surface are held at zero temperature, and a nonzero temperature is applied at the near end. Some continuous dependence inequalities are also obtained. We also investigate the case in which a given heat flux is prescribed at the near end, instead of a given temperature. Copyright © 2008 John Wiley & Sons, Ltd. 相似文献
77.
Figueroa JS Piro NA Clough CR Cummins CC 《Journal of the American Chemical Society》2006,128(3):940-950
The transformation of acid chlorides (RC(O)Cl) to organic nitriles (RC[triple bond]N) by the terminal niobium nitride anion [N[triple bond]Nb(N[Np]Ar)3]- ([1a-N]-, where Np = neopentyl and Ar = 3,5-Me2C6H3) via isovalent N for O(Cl) metathetical exchange is presented. Nitrido anion [1a-N]- is obtained in a heterodinuclear N2 scission reaction employing the molybdenum trisamide system, Mo(N[R]Ar)3 (R = t-Bu, 2a; R = Np, 2b), as a reaction partner. Reductive scission of the heterodinuclear bridging N2 complexes, (Ar[R]N)3Mo-(mu-N2)Nb(N[Np]Ar)3 (R = t-Bu, 3b; R = Np, 3c) with sodium amalgam provides 1 equiv each of the salt Na[1a-N] and neutral N[triple bond]Mo(N[R]Ar)3 (R = t-Bu, 2a-N; R = Np, 2b-N). Separation of 2-N from Na[1a-N] is readily achieved. Treatment of salt Na[1a-N] with acid chloride substrates in tetrahydrofuran (THF) furnishes the corresponding organic nitriles concomitant with the formation of NaCl and the oxo niobium complex O[triple bond]Nb(N[Np]Ar)3 (1a-O). Utilization of 15N-labeled 15N2 gas in this chemistry affords a series of 15N-labeled organic nitriles establishing the utility of anion [1a-N]- as a reagent for the 15N-labeling of organic molecules. Synthetic and computational studies on model niobium systems provide evidence for the intermediacy of both a linear acylimido and niobacyclobutene species along the pathway to organic nitrile formation. High-yield recycling of oxo 1a-O to a niobium triflate complex appropriate for heterodinuclear N2 scission has been developed. Specifically, addition of triflic anhydride (Tf2O, where Tf = SO2CF3) to an Et2O solution of 1a-O provides the bistriflate complex, Nb(OTf)2(N[Np]Ar)3 (1a-(OTf)2), in near quantitative yield. One-electron reduction of 1a-(OTf)2 with either cobaltocene (Cp2Co) or Mg(THF)3(anthracene) provided the monotriflato complex, Nb(OTf)(N[Np]Ar)3 (1a-(OTf)), which efficiently regenerates complexes 3b and 3c when treated with the molybdenum dinitrogen anions [N2Mo(N[t-Bu]Ar)3]- ([2a-N2]-) or [N2Mo(N[Np]Ar)3]- ([2b-N2]-), respectively. 相似文献
78.
79.
The crystal structure of NH4[tsac]·H2O (tsac = anion of the thiosaccharin molecule) has been determined by single crystal X‐ray diffractometry. It crystallizes in the orthorhombic space group Pbca with Z = 8. The infrared spectrum of the compound was also recorded and its most important features discussed on the basis of its structural peculiarities. 相似文献
80.
Sun Y Bigi JP Piro NA Tang ML Long JR Chang CJ 《Journal of the American Chemical Society》2011,133(24):9212-9215
A set of robust molecular cobalt catalysts for the generation of hydrogen from water is reported. The cobalt complex supported by the parent pentadentate polypyridyl ligand PY5Me(2) features high stability and activity and 100% Faradaic efficiency for the electrocatalytic production of hydrogen from neutral water, with a turnover number reaching 5.5 × 10(4) mol of H(2) per mole of catalyst with no loss in activity over 60 h. Control experiments establish that simple Co(II) salts, the free PY5Me(2) ligand, and an isostructural PY5Me(2) complex containing redox-inactive Zn(II) are all ineffective for this reaction. Further experiments demonstrate that the overpotential for H(2) evolution can be tuned by systematic substitutions on the ancillary PY5Me(2) scaffold, presaging opportunities to further optimize this first-generation platform by molecular design. 相似文献