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131.
Differential pulse polarography (d.p.p.) is used to study the degradation of cephalexin. Hydrogen sulphide, evolved during the degradation of cephalexin solutions, was removed continuously in a stream of nitrogen and determined periodically. Other electroactive degradation products were observed by d.p.p. of the degraded sample solutions. The degradation mechanism is highly dependent on pH, the initial concentration of cephalexin, temperature, the particular buffer used, and the presence of dissolved oxygen. The formation and degradation of the diketopiperazine derivative formed by intramolecular aminolysis, particularly at neutral pH, can be followed by means of its polarographic peak at -0.9 V (pH 7.4). Approximately half the total sulphur originally present in cephalexin is liberated as hydrogen sulphide at pH 7.4 at 37°C. Increasing the degradation temperature to 80°C and sweeping out the hydrogen sulphide with nitrogen increases the yield of a major product which gives a peak at -1.26 V. At pH 8.5 (80°C. 100 μg cephalexin ml-1) the percentage of the sulphur evolved as hydrogen sulphide increases with time, and a peak appears at -0.96 V (probably 2-hydroxy-3-phenyl-6-methylpyrazine) which increases as the peak at -1.26 V becomes smaller. Other products formed under different conditions (concentration, pH, temperature) are reported. At pH 3 (80°C) only 8% conversion via intramolecular aminolysis and 5% evolution of total sulphur is indicated after four hours. 相似文献
132.
Abdel-Khalek Ahmed A. Ewais Hassan A. Khaled Eman S.H. Abdel-Hamied Anwar 《Transition Metal Chemistry》2004,29(1):7-11
The kinetics of oxidation of [CoIINM(H2O)]3– (N = nitrilotriacetate, M = malonate) by N-bromosuccinimide (NBS) in aqueous solution have been found to obey the equation: d[CoIII]/dt = k
1
K
2[NBS][CoII]T/{1 + K2[NBS] + (H+/K1)} where k
1 is the rate constant for the electron transfer process, K
1 the equilibrium constant for dissociation of [CoIINM(H2O)]3– to [CoIINM(OH)]4– + H+, and K
2 the pre-equilibrium formation constant. Values of k
1 = 1.07 × 10–3 s–1, K
1 = 4.74 × 10–8 mol dm–3 and K
2 = 472 dm3 mol–1 have been obtained at 30 °C and I = 0.2 mol dm–3. The thermodynamic activation parameters have been calculated. The experimental rate law is consistent with a mechanism in which the deprotonated [CoIINM(OH)]4– is considered to be the most reactive species compared to its conjugate acid. It is assumed that electron transfer takes place via an inner-sphere mechanism. 相似文献
133.
Complexes of 5-(phenylazo)-2-thiohydantoin (L1) and 5-(2-hydroxyphenylazo)-2-thiohydantoin (HL2) with Co(II), Ni(II) and Cu(II) salts have been synthesised and characterized by elemental analysis, conductivity, magnetic susceptibility, UV-Vis, IR, ESR and TG studies. The magnetic and spectral data suggested octahedral geometry for [L1M(OAc)2(H2O)2]·xH2O {M=Nill and Cull} and [L1CuCl2(H2O)]·H2O (dimeric form for the latter), trigonal bipyramidal geometry for [L2Co(OAc)(H2O)]·2H2O, square pyramidal geometry for [L2Ni(OAc)(H2O)]·H2O and square planar geometry for [L2CuCl]·2H2O. TG studies confirmed the chemical formulations of these complexes and showed that their thermal degradation takes place in three to five steps, depending on the type of the ligand and the geometry of the complex. The kinetic parameters (n, E#, A, ΔH#, ΔS# and ΔG#) of the thermal decomposition stages were computed using the Coats-Redfern and other standard equations and are discussed. 相似文献
134.
New complexes of N-2-[3-methylpyridyl]-N-phenylthiourea (HMPyPT) have been prepared from NiII, CuII, ZnII, PdII, PtIV and AuIII chlorides. Three types, containing 1:1, 1:2 and 1:3 metal–ligand ratios, were isolated and characterized. In every case the ligand behaves in a monodentate manner coordinating via the pyridyl nitrogen. Attempts to isolate complexes containing the deprotonated ligand by raising the pH of the reaction mixture from 1.6–5.5 to 8.5 were unsuccessful. The bonding modes and the stereochemistry of the metal complexes have been determined from spectral (i.r., u.v.–vis., 1H-n.m.r.) and magnetic measurements. The results suggest a square-planar structure for the PdII and AuIII complexes, but octahedral geometry for the other metal complexes. Thermal analysis (d.t.a., t.g.a.) measurements on the solid complexes have also been conducted. 相似文献
135.
Mohamed M. Shoukry Ihsan M. Kenawy Afkar K. Abdel Hadi Eman M. Shoukry 《Journal of Chemical Sciences》1988,100(5):381-388
The formation constants of salicyl-4-amino-2,3-dimethyl-1-phenyl-3-pyrazoline-5-one (SAAP) complexes with 3d transition metal
ions [Cu(II), Ni(II), Co(II), Zn(II) and Mn(II)] have been determined in 60% ethanol-water medium ofμ = 0.1M (NaCl) at 25°C. It is observed that the formation constants for chelates with 3d transition metals follow the order
Mn(II) < Co(II) < Ni(II) < Zn(II) < Cu(II). The effects of metal ions, ionic radii, electronegativities and ionization potentials
on chelate formation constants are discussed.
Complexes of UO2(II) and Pd(II) have been synthesized and characterised by elemental analysis, electrolytic conductance, IR spectra and magnetic
measurements. The ligand forms the complexes PdLCl and UO2L2,2H2O, where L is a uninegatively charged tridentate ligand (ONO donor sets). 相似文献
136.
The Role of Order in the Amplification of Light‐Energy Conversion in a Dye‐Sensitized Solar Cell Coupled to a Photonic Crystal
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We investigate the cause of amplification of light‐energy conversion when coupling a nc‐TiO2 film to a TiO2 inverse opal by comparing it to an inverse TiO2 glass (i‐TiO2‐g) fabricated with the exact monodisperse air–hole size as an inverse opal with a stop band at 600 nm (600‐i‐TiO2‐o). A significant twofold average gain in the photon‐to‐current conversion efficiency is measured to the red of the stop band at the 600‐i‐TiO2‐o/nc‐TiO2 bilayer under front‐wall and back‐wall illumination, greater than the gain within the stop band. A smaller amplification is measured under front‐wall illumination—and no gain is measured under back‐wall illumination—for i‐TiO2‐g/nc‐TiO2 at these energies. The photonic crystal therefore causes trapping of light through the bilayer, not only within the gap but also to the red, at frequencies within its dielectric band. This light‐trapping effect is found to be dependent on structural order, as a highly disordered inverse glass film with the same air–hole size and thickness does not yield the same gain. A drop in the transmission of light is measured within the same frequencies to the red of the stop band upon adding nc‐TiO2 to 600‐i‐TiO2‐o, consistent with light trapping in the bilayer. 相似文献
137.
Magda A. Barsy Eman A. El Rady Fawi M. Abd El Latif 《Journal of heterocyclic chemistry》2008,45(3):773-778
138.
Sayed S. Metwally Reham S. Hassan Eman H. El-Masry Emad H. Borai 《Journal of Radioanalytical and Nuclear Chemistry》2018,315(1):39-49
Gamma radiation polymerization method was used for the modification of kaolin to produce (poly acrylamide-acrylic acid)-Kaolin (PAM-AA-K). Monazite ore is one of the main resources of uranium and lanthanide elements, therefore, this work focused on sorption of uranium, lanthanum and europium ions from low grade monazite leachate. The removal percent for Eu3+, La3+ and UO2 2+ are 94.6, 91.6 and 73.4%, respectively. Monolayer capacity of Eu3+, La3+ and UO2 2+ were found to be 54.64, 45.87 and 37.59 mg/g, respectively. The sorption mechanism of lanthanum and europium ions on PAM-AA-K composite mainly takes place as Ln(OH)2+, and for uranium as uranyl ion, UO2 2+. 相似文献
139.
Francesca Mirabella Eman Zaki Dr. Francisco Ivars‐Barceló Xiaoke Li Joachim Paier Joachim Sauer Shamil Shaikhutdinov Hans‐Joachim Freund 《Angewandte Chemie (International ed. in English)》2018,57(5):1409-1413
The initial stages of water adsorption on magnetite Fe3O4(111) surface and the atomic structure of the water/oxide interface remain controversial. Herein, we provide experimental results obtained by infrared reflection–absorption spectroscopy (IRAS) and temperature‐programmed desorption (TPD), corroborated by density functional theory (DFT) calculations showing that water readily dissociates on Fetet sites to form two hydroxo species. These act as an anchor for water molecules to form a dimer complex which self‐assembles into an ordered (2×2) structure. Water ad‐layer ordering is rationalized in terms of a cooperative effect induced by a hydrogen‐bonding network. 相似文献
140.
Methods are described for the determination of amitriptyline, imipramine and orphenadrine in some antidepressant drugs. They are based on a prior reaction with ammonium reineckate to form 11 water-insoluble drugreineckate ion-pair complexes. These complexes are (i) used as ion-exchangers in liquid-membrane electrodes responsive to the drug cations, (ii) extracted with nitrobenzene or dissolved in acetonitrile and spectrophotometrically measured at 525 nm and (iii) dissolved in 90% acetone followed by nebulization in an air-acetylene flame for atomic absorption spectrometric measurements of Cr at 358.6 nm. The reaction and monitoring conditions are optimized to permit determination of as little as 10 g/ml of the drugs. Determination of the drugs in some pharmaceutical preparations shows an average recovery of 98.8% of the nominal and a mean standard deviation of 0.8%. The results compare favorably with data obtained by the United States and British Pharmacopoeia methods. 相似文献