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11.
12.
The electron paramagnetic resonance (EPR) parameters (the anisotropic g factors, the hyperfine structure parameters and the quadrupole coupling constant Q) and local structure for Cu2+ in BeO are theoretically investigated from the perturbation formulas of these parameters for a 3d9 ion under trigonally distorted tetrahedra. The ligand orbital and spin-orbit coupling contributions are included in the basis of the cluster approach, in view of the strong covalency of the [CuO4]6? cluster. From the calculations, the impurity Cu2+ is suggested not to occupy exactly the ideal Be2+ site but to suffer a slight inward displacement (≈0.024 Å) toward the ligand triangle along the C3 axis. The theoretical EPR parameters show good agreement with the experimental data. 相似文献
13.
Let G = (V, E) be a simple graph. A subset S ⊆ V is a dominating set of G, if for any vertex u ∈ V-S, there exists a vertex v ∈ S such that uv ∈ E. The domination number, denoted by γ(G), is the minimum cardinality of a dominating set. In this paper we will prove that if G is a 5-regular graph, then γ(G) ⩽ 5/14n. 相似文献
14.
Jing Wang Xi Chen Xiu Wang Wei-Qiang Zhang Hua-Ming Sun Guo-Fang Zhang Ya Wu Zi-Wei Gao 《Transition Metal Chemistry》2016,41(7):731-738
Tunable organometallic Lewis acid catalysts were developed by combining salicylic acid (H2-Sal) with benzoic acid (H-Ben), 4-fluorobenzoic acid (H-BenF) and 3-thiophenic acid (H-Th), as coligands for mixed bis-carboxylate titanocene complexes. Three air-stable complexes [Cp2Ti(η1-HSal)(η1-Ben)] (1), [Cp2Ti(η1-HSal)(η1-BenF)] (2) and [Cp2Ti[η1-HSal][(η1-Th)] (3) were prepared in high yields by the reaction of salicylato titanocene chelate with carboxylate ligands. The mixed bis-carboxylate titanocene complexes were fully characterized by physicochemical and spectroscopic methods. Single-crystal X-ray diffraction studies revealed Ti–O(H-Sal) bond distances in 1, 2 and 3 of 1.972(3), 1.9245(18) and 1.912(5) Å, respectively, while the bond distances involving the coligands of 1, 2 and 3 are 1.908(3) Å (Ti–OBen), 1.9296(19) Å (Ti–OBenF) and 1.945(5) Å (Ti–OTh), respectively. These bis-carboxylate titanocene complexes showed satisfactory activities and selectivities in Mannich and cross-aldol reactions. Notably, complex 3 bearing the labile thiophene carboxylate ligand gave high yields with a diastereomer ratio (d.r.) as high as 1:99 for the direct Mannich reactions of benzaldehyde, cyclohexanone and aniline. In cross-aldol reaction of benzaldehyde and cyclohexanone, 1 and 2 successfully catalyzed the formation of double-aldol products in up to 99 % yield. 相似文献
15.
A rapid and sensitive capillary electrophoresis (CE) method has been developed for profiling organic metabolites containing
amine functional groups in mammalian biofluids. Metabolites containing an amine group were derivatized with 4-fluoro-7-nitrobenzo-2,1,3-oxadiazol
(NBD-F), separated by micellar electrokinetic chromatography (MEKC), and detected by argon-ion (488 nm) laser-induced fluorescence
detection. The optimized MEKC background electrolyte conditions were: 50 mmol L−1 sodium cholate, 5 mmol L−1 β-cyclodextrin, and 20 mmol L−1 Brij 35 in 20 mmol L−1 aqueous borate buffer, pH 9.3, containing 7% methanol. Under these conditions all the amine compounds in mammalian biofluids,
for example plasma, saliva, and urine, were derivatized directly, without extraction, in a minimum volume of 100 nL and the
derivatives could be separated within 16 min. Up to 90% of the amine-containing metabolites in plasma and saliva could be
identified by reference to standard compounds. For twenty amine standards linearity of calibration was better than R
2 = 0.99. Migration-time and peak-area reproducibility were better than RSD 1.5% and 15% respectively. In replicate analysis
of human plasma bioanalytical precision ranged between 0.7 and 3.8 RSD% for a 5.0-μL volume and between 1.7 and 5.5 RSD% for
100-nL volume. The concentrations measured were found to be in agreement with literature values. 相似文献
16.
17.
Chemical sensors based on optical signal detection are of increasing importance. Optical sensors of bulk optodes have the advantage of being robust and showing a highly reversible response explainable by means of the chemical equilibria involved. Therefore, a great number of new ion-selective bulk optodes have reported within a few years. Several sensors for detecting toxicologically revalant ions,such as Pb2+,Ag+,Hg2+ and UO22+ have been developed recently and exhibit the low detection limit required. Although a number of ionophores have been used in optodes and ISEs,the sensors described so far are inadequate for monitoring Ag+ in water, especially in drinking water because of their limited selectivity and/or insufficient sensitivity. More recently Pretsch et al designed and synthesized an improved optical sensor, methylene bis(2-thiobenzothiazole),which was Ag+-selective. Here we report synthesis of another ionophore,1,2-bis(2-thiobenzothiazole) ethane, and its IR, ESI-MS, 1HNMR and UV-Vis. 相似文献
18.
A novel ionic compound [Fe(CN)6(PhCH2NC9H7)4]·12H2O (C70H80FeN10O12, Mr = 1309.29) has been synthesized and its structure was characterized by IR, elemental analysis and X-ray diffraction. The compound crystallizes in triclinic, space group P1, with a = 10.968(7), b = 11.466(7), c = 14.077(8) , α = 87.014(7), β = 78.124(7), γ = 72.708(7)o, V = 1654.1(17) 3, Z = 1, Dc = 1.314 g·cm–3, F(000) = 692, μ = 0.298 mm–1, the final R = 0.0519 and wR = 0.1355. The building unit of the title compound consists of four (PhCH2N+C9H7) ions, one [Fe(CN)6]4– anion, and a dozen water molecules. According to the structural analysis, [Fe(CN)6]4– ions are linked together by O–H···O and O–H···N hydrogen bonds, while (PhCH2N+C9H7) and [Fe(CN)6]4– ions interact with each other by electrostatic force to form an ionic compound. 相似文献
19.
A simple and sensitive sweeping micellar electrokinetic chromatography method coupled with UV laser-induced native fluorescence detection has been developed for quantitative analysis of biogenic amines in biofluids. The background electrolyte comprised 30 mmol L−1 phosphoric acid and 20 mmol L−1 sodium dodecyl sulfate. The concentration limits of detection of analytes using sweeping-micellar electrokinetic chromatography (sweeping-MEKC) were in the range 7–100 nmol L−1, which were 250–3600-fold improvement for dopamine, DOPA and epinephrine compared with conventional capillary zone electrophoresis. An improvement of approximately 20-fold was observed for all analytes compared with typical micellar electrokinetic chromatography conditions. Baseline separation was achieved for the all analytes within 12 min and migration-time and peak-area repeatability were better than RSD 0.35% and 5.68%, respectively. The developed method was applied to measure the biogenic amines in biofluids extracted from wheat phloem sap, human plasma and human urine. 相似文献
20.
Hua-Ming Zhang Shao-Yi Wu Yue-Xia Hu Xue-Feng Wang Pei Xu 《Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy》2009,73(5):879-883
The local angular distortions and the spin-Hamiltonian parameters (the g factors and the hyperfine parameters) for Ni+ in ABS2 (ACu, Ag; BAl, Ga) ternary sulfides are theoretically investigated from the perturbation formulas of these parameters for 3d9 ions in a tetragonally distorted tetrahedron. In view of the strong covalency of such systems, the ligand orbital and spin–orbit coupling contributions are taken into account using the cluster approach. The local impurity-ligand bond angles in the Ni+ centers are found to be about 1.4–4.5° smaller than those of the host monovalent A sites in the pure crystals, due to size mismatching substitution. As a result, the ligand tetrahedra exhibit slight elongation in CuBS2:Ni+ and slight compression in AgGaS2:Ni+. The calculated spin-Hamiltonian parameters, optical transitions and the relative intensity ratios show reasonable agreement with the experimental data. 相似文献