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111.
Salmon L Thuéry P Ephritikhine M 《Dalton transactions (Cambridge, England : 2003)》2004,(10):1635-1643
Treatment of U(acac)4 with the hexadentate Schiff base H2L(i) gave the [UL(i)2] complexes 1-4 [H2L1=N,N'-bis(3-methoxysalicylidene)-2-methyl-1,2-propanediamine, H2L2=N,N'-bis(3-methoxysalicylidene)-1,2-phenylenediamine, H2L3=N,N'-bis(3-methoxysalicylidene)-2-aminobenzylamine and H2L4=N,N'-bis(3-methoxysalicylidene)-2,2-dimethyl-1,3-propanediamine for 1-4, respectively]. The [U(L(i))(acac)2] compounds could not be isolated because of their ready disproportionation into [UL(i)2] and U(acac)4. Compounds 2 and 4 adopt a meridional configuration in the solid state and in solution, while exists in solution as the two equilibrating meridional and sandwich isomers and crystallizes in the meridional isomeric form. Reaction of U(acac)4 with H4L5 afforded the expected compound [U(H2L5)(acac)2] (5) [H4L5=N,N'-bis(3-hydroxysalicylidene)-2-methyl-1,2-propanediamine] but, in the presence of H4L6 and H4L7, U(acac)4 was transformed in a serendipitous and reproducible manner into the tri- and tetranuclear U(IV) complexes [U3(L6)(HL6)2(acac)2] (6) and [U4(HL7)4(H2L7)2] (7) [H4L6=N,N'-bis(3-hydroxysalicylidene)-1,2-phenylenediamine and H4L7=N,N'-bis(3-hydroxysalicylidene)-2-aminobenzylamine]. The crystal structures of 6.3thf and 7.5thf show the assembling role of the Schiff-base ligands. 相似文献
112.
Moliner N Muñoz MC Létard S Salmon L Tuchagues JP Bousseksou A Real JA 《Inorganic chemistry》2002,41(26):6997-7005
The suitability of the system [Fe(4,4'-bipy)(H(2)O)(2)(NCX)(2)].(4,4'-bipy), where 4,4'-bipy stands for 4,4'-bipyridine and X = S (1) and Se (2), as a precursor for the synthesis of new polymeric spin-crossover compounds has been studied. The reaction of 1 or 2 with bt (2,2'-bithiazoline) afforded the polymeric compounds of formula [Fe(4,4'-bipy)(bt)(NCX)(2)] (X = S (3), Se (4)). Compounds 3 and 4 are isostructural, but only the crystal structure of 3 has been fully determined. It crystallizes in the orthorhombic system, Fdd2 space group, Z = 24, with a = 38.962(8) A, b = 11.545(2) A, c = 30.889(6) A, V = 13895(5) A(3). The structure consists of linear chains constituted by trans-4,4'-bipy linked iron(II) ions; two cis equatorial positions are occupied by two pseudohalide ligands, and the remaining positions are filled by the bidentate bt ligand. Investigation of their magnetic properties and M?ssbauer spectra has revealed the occurrence of a low-spin (LS) <--> high-spin (HS) conversion involving 12% (3, S) and 20% (4, Se) of the Fe(II) ions. The thermal variation of the HS fraction is gradual with onset temperatures as low as 60 K. A theoretical approach based on the Ising-like model, completed with molecular vibrations, through harmonic oscillators, fits the data successfully, leading to an energy gap of 65 cm(-1) (3) and 86 cm(-1) (4) between the lowest LS and HS levels, and an average vibration frequency ohgrmacr;(LS) of 382 cm(-1) (3) and 365 cm(-1) (4) in the LS state. The ca. 1.05 omega(LS(3))/omega(LS(4)) ratio is close to the ca. 1.09 Se/S molar mass ratio. The simple electrovibrational Ising-like model permits us to explain, for the first time, a mass effect through the molecular vibrations in a spin-crossover complex that is in the unusual situation of equienergy among the HS and LS states. 相似文献
113.
The temperature dependence of the abundance of trapped electrons which absorb in the visible (e?vis) and infrared (e?IR) in crystalline D2O ice has been studied by pulse radiolysis between 77 and 6 k. The yield (G) and decay of e?vis show little dependence on temperature or doping with NH4F. At 6 K G(e?vis) is 0.54 and the electron decays by half within 5 μs. These observations are consistent with e?vis being mainly located in spurs. The yield and decay of e?IR, on the other hand, show a more marked dependence on temperature. In the pure crystal G(e?IR) increases more than tenfold from ≈ 0.1 at 77 K to 1.3 at 6 K and its decay rate is greatly decreased at the lower temperature. Doping with NH4F increases G(e?IR) to 0.85 to 77 K and to 1.8 at 6 K and some decay is observed at 6 K but not at 77 K. These results are interpreted on the basis that geminate recombination between electrons and holes is very fast at 77 K but becomes sufficiently slow for the electrons to be observed at 6 K. It is also inferred that the hole is more mobile than e?IR. The mechanisms causing the decays of e?vis and e?IR are discussed. 相似文献
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115.
Dextran‐Coated Antiferromagnetic MnO Nanoparticles for a T1‐MRI Contrast Agent with High Colloidal Stability
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Herbert R. Neves Rafael A. Bini Jeam H. O. Barbosa Carlos E. G. Salmon Laudemir C. Varanda 《Particle & Particle Systems Characterization》2016,33(3):167-176
A simple approach to synthesize carboxymethyl dextran‐coated MnO nanoparticles (CMDex‐MnONPs) with high colloidal stability in physiological saline solutions is described here for potential applications as a magnetic resonance imaging (MRI) T1 contrast agent. The thermal decomposition methodology is used to produce uniform MnONPs with an average size of around 20 nm, and its hydrophobic surface is modified with CMDex molecules, conferring hydrophilic properties. After CMDex coating, the nanoparticle presents high colloidal stability in concentrations ranging from 10 to 50 μg mL?1, average hydrodynamic size (Z‐average) of 130 nm, polydispersity degree of ≈12%, and negative surface charge in both simulated body fluid solutions and pure water with zeta‐potential of –20 and –40 mV, respectively. The CMDex‐MnONPs with 20 nm show antiferromagnetic behavior at room temperature, and the magnetic properties are found to be strongly dependent of the nanoparticle size, increasing the contribution of the ferromagnetic Mn3O4 phase with decreasing size for nanoparticles about 3 nm. Cytotoxicity evaluation in cancerous and noncancerous cells in the range of 5.0–50.0 μg mL?1 shows low toxicity for cancerous cells and lack of the same for healthy cells lines. Related to the magnetic properties, CMDex‐MnONP presents significant r1 relaxivity and low r2/r1 relaxivity ratio. The results suggest that these nanoparticles display characteristics for potential applications as an MRI T1 contrast agent. 相似文献
116.
Ornelas C Aranzaes JR Salmon L Astruc D 《Chemistry (Weinheim an der Bergstrasse, Germany)》2008,14(1):50-64
"Click" dendrimers containing 1,2,3-triazolyl ligands that coordinate to PdII(OAc)2 have been synthesized in view of catalytic applications. Five of these dendrimers contain ferrocenyl termini directly attached to the triazole ligand in order to monitor the number of PdII that are introduced into the dendrimers by cyclic voltammetry. Reduction of the PdII-triazole dendrimers by using NaBH4 or methanol yields Pd nanoparticles (PdNPs) that are stabilized either by several dendrimers (G0, DSN) or by encapsulation inside a dendrimer (G1 and G2: DEN), as confirmed by TEM. Relative to PAMAM-DENs (PAMAM=poly(amidoamine)), the "click" DSNs and DENs show a remarkable efficiency and stability for olefin hydrogenation under ambient conditions of various substrates. The influence of the reductant of PdII bound to the dendrimers is dramatic, reduction with methanol leading to much higher catalytic activity than reduction with NaBH4. The most active NPs are shown to be those derived from dendrimer G1, and variation of its termini groups (ferrocenyl, alkyl, phenyl) allowed us to clearly delineate, optimize, and rationalize the role of the dendrimer frameworks on the catalytic efficiencies. Finally, hydrogenation of various substrates catalyzed by these PdNPs shows remarkable selectivity features. 相似文献
117.
M.H. Christmann G.H. Dierssen O.N. Salmon A.L. Taylor W.H. Thom 《Journal of Physics and Chemistry of Solids》1975,36(12):1371-1374
Physical properties of selected CdS single crystal platelets as-grown and after vacuum heat treatments at temperatures up to 600°C have been studied using u.v. excited edge emission, mass spectrometry, electrical resistivity and electron paramagnetic resonance (EPR). It was found that sulfur leaves the crystal at temperatures as low as 100°C creating a depletion layer. The native defect changes were monitored by edge emission studies at 4.2°K in combination with etch treatments. The defect structure throughout the crystal is not only dependent upon the temperature and atmosphere of the treatments, but is also strongly dependent upon the cooling rate. 相似文献
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