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61.
The cationic complexes with hexacoordinate silicon(IV), tris[1‐oxopyridine‐2‐olato(1–)]silicon(IV) trifluoromethanesulfonate ( 4 ), 4 · 1/2 C5H5NO2, tris[1‐oxopyridine‐2‐olato(1–)]silicon(IV) ethyl sulfate–ethanol ( 5 · EtOH), and tris[1‐oxopyridine‐2‐olato(1–)]silicon(IV) isopropyl sulfate ( 6 ), were synthesized. The identities of 4 , 4 · 1/2 C5H5NO2, 5 · EtOH, and 6 were established by elemental analyses (C, H, N, S), mass‐spectrometric studies (FAB MS) as well as solid‐state (29Si) and solution (1H, 13C, 19F, 29Si) NMR experiments. In addition, 4 · 1/2 C5H5NO2 was structurally characterized by single‐crystal X‐ray diffraction. 相似文献
62.
Bocharova I Karimi R Penka EF Brichta JP Lassonde P Fu X Kieffer JC Bandrauk AD Litvinyuk I Sanderson J Légaré F 《Physical review letters》2011,107(6):063201
The process by which a molecule in an intense laser field ionizes more efficiently as its bond length increases towards a critical distance R(c) is known as charge resonance enhanced ionization (CREI). We make a series of measurements of this process for CO(2), by varying pulse duration from 7 to 200 fs, in order to identify the charge states and time scales involved. We find that for the 4+ and higher charge states, 100 fs is the time scale required to reach the critical geometry ≈ 2.1 ? and <θ(OCO)> ≈ 163° (equilibrium CO(2) geometry is ≈ 1.16 ? and <θ(OCO)> ≈ 172°). The CO(2)(3+) molecule, however, appears always to begin dissociation from closer than 1.7 ? indicating that dynamics on charge states lower than 3+ is not sufficient to initiate CREI. Finally, we make quantum ab initio calculations of ionization rates for CO(2) and identify the electronic states responsible for CREI. 相似文献
63.
Penka Shegunova Ofelia Bercaru Berit Sejerøe-Olsen 《Accreditation and quality assurance》2008,13(1):11-18
Estimation of measurement uncertainty has become a more regularly performed part of the whole analytical process. However,
there is still much on-going discussion in the scientific community about ways of building up the uncertainty budget. This
study describes two approaches for estimation of measurement uncertainty in organic analysis: one which can be used for single
sets of measurements and the other based on validation studies. In both cases the main contributions to the uncertainty are
presented and discussed for the analysis of PCBs in mussel tissue, but the approaches can be extended to other organic pollutants
in environmental/food samples. The main contributions to the uncertainty budget arise from calibration, sample preparation,
and GC–MS measurements. A comparison of the relevant sources and their contributions to the expanded uncertainty is presented. 相似文献
64.
65.
E. Vassileva S. Arpadjan R. Stefanova V. Vassileva 《Fresenius' Journal of Analytical Chemistry》1990,336(7):582-585
Summary Different extraction sytems including long chain quaternary alkylammonium salts and APDC were investigated in order to determine the optimal conditions for extraction separation and preconcentration of traces of Ag, Bi, Cd, Cu, Fe, Mo, Pb, Sb and Zn from high purity NiSO4·6H2O, NiCl2·6H2O, Ni(OOCCH3)2·4H2O and Ni(NO)3)2·6 H2O. Best results for multielement preconcentration were found with the extraction system HCl-trioctylmethylammonium chloride-0,002 mol/l APDC/MIBK. The proposed method permits the flame atomic absorption determination of 5·10–6%, Ag, Cd, Cu and Zn, 1·10–5% Bi, Fe, Pb and 5·10–5% Mo and Sb with good accuracy and precision. 相似文献
66.
The application of a fast program combined with the advantages of the iridium permanent modifier is proposed for trace element analysis of plant samples by electrothermal atomic absorption spectrometry (ETAAS). For two volatile elements (Cd, Pb) and two mid-refractory elements (Cr, Ni) it was demonstrated that coating of the platform or of the tube atomization area with Ir is an efficient means of improving the accuracy and precision of results. A detailed study of interference from individual main matrix components and from composite plant matrices has confirmed the usefulness of the whole approach. The validity of the method has been confirmed by analysis of eight reference plant materials. 相似文献
67.
J.C. Pivin M.A. García H. Hofmeister A. Martucci M. Sendova Vassileva M. Nikolaeva O. Kaitasov J. Llopis 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2002,20(2):251-260
Precipitation of silver clusters in silica is achieved by different methods: ion implantation, ion beam mixing of superimposed
layers and ion irradiation of films deposited by means of co-sputtering or sol-gel technique. Main features of the nanoparticles
depending on the preparation method are investigated by TEM. The optical extinction resonance of these clusters is analysed
in terms of sizes and interaction between the clusters on the basis of calculations. We found that resonances in sputtered
and gel films with low metal concentrations are well described by plasmon polaritons in isolated clusters and calculations
based on Mie theory allow the study of their growth under irradiation. This theory is not appropriate to describe the optical
response of silver clusters in silica implanted with Ag concentrations higher than 5 at.% or in ion beam mixed films, because
of the interaction between clusters. Using an effective medium model, it is demonstrated that the random dispersion of clusters
in implantation films causes fluctuations and, on average, an increase of the clusters polarization. On the contrary, the
particular arrangement of the clusters with a bimodal size distribution in ion beam mixed films induces a screening effect
between the clusters of largest size.
Received 10 January 2002 / Received in final form 26 April 2002 Published online 19 July 2002 相似文献
68.
Mihail Atanasov Claude A. Daul E. Penka Fowe 《Monatshefte für Chemie / Chemical Monthly》2005,52(8):925-963
Metal–ligand bonding in transition metal halide molecules and complexes with different central ions, oxidations states, and coordination numbers: CrIIIX63–, CrIVX4, CrIIX2 (X = F,Cl,Br,I), MIIICl63–(M = Mo,W), MIII(H2O)63+(M = Cr,Co) and Re2Cl82– has been studied in terms of the Extended Transition State (ETS) energy patitioning scheme within the DFT and electron density analysis (the Laplacian of the electron density and the electronic localization function). Bonding is found to be dominated by ionicity in all cases, especially so for complexes with higher coordination numbers. Covalent contributions to the metal–ligand bond are found to be mainly due to the nd-electrons and to lesser extent due to the metal (n+1)s and (n+1)p-orbitals, contributions from (n+1)s increasing when going to lower coordination numbers. Metal–ligand bonding analysis have been used in order to check some concepts emerging from ligand field theory when applied to the spectroscopy and magnetism of transition metal complexes. It is pointed out that for complexes of high symmetry (MX6, Oh, MX4, Td, and MX2, Dh) electron density analyses gain interpretative power when partitioned into contributions from occupied orbitals of different symmetry. 相似文献
69.
Galia Gentscheva Penka Tzvetkova Paunka Vassileva Lako Lakov Ognyan Peshev Elisaveta Ivanova 《Mikrochimica acta》2006,156(3-4):303-306
The sorption behavior of a newly synthesized silica gel sorbent with thioetheric sites (STS) towards microgram levels of Au(III),
Pt(IV) and Pd(II) was studied. Au(III) is quantitatively (>95%) sorbed in the pH region of 1–9. The sorption of Pt(IV) starts
at pH 1 and does not exceed 25% in the entire pH region examined. The sorption of Pd(II) starts at pH 7 and reaches 80% at
pH 9. The sorption of Au(III) on STS at pH 1 is not affected by milligram amounts of Ni(II), Zn(II), Fe(III), Cu(II), Pb(II),
Cd(II) or Co(II). Au(III) is quantitatively eluted with a 5% aqueous solution of thiourea. The adsorption capacity of STS
towards Au(III) is 195 mg g−1. The detection limit (DL) of Au(III) (3σ, n = 9) is 25 ng mL−1. The RSD at a level of 10 × DL is about 2%. Solid-phase extraction of trace amounts of Au(III) on the STS sorbent, followed
by its flame AAS determination in the eluate was applied to the determination of gold in geological samples. The results obtained
for the gold content in the samples were in good agreement with those of the ICP-AES analysis. 相似文献
70.
Michel Boisbrun Elka Vassileva Marion Raoul Jean-Yves Laronze Janos Sapi 《Monatshefte für Chemie / Chemical Monthly》2003,134(12):1641-1649
Summary. In view of finding new 5-HT6 receptor ligands various -acetamido substituted tryptamine and N,N-dimethyltryptamine derivatives were synthesized from a common intermediate. A trimolecular condensation between indole, Meldrums acid and N-phthalimidoacetaldehyde followed by careful deprotection and functional group manipulations were proposed for this purpose.Present address: GEVSM, UMR 7565 CNRS-UHP, Faculté de Pharmacie, F-54001 Nancy Cedex, FrancePresent address: University of Global and National Economy, Studentski Grad Christo Botev, BG-1700 Sofia, Bulgaria 相似文献