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51.
The reactivity of the product believed to be 2-(1-phenyl-2-thiocyanato-ethylidene)malononitrile toward a variety of electrophilic and nucleophilic reagents is reported. 相似文献
52.
Barkleit A Tsushima S Savchuk O Philipp J Heim K Acker M Taut S Fahmy K 《Inorganic chemistry》2011,50(12):5451-5459
Thermodynamic parameters for the complexation of Eu(3+) with pyromellitic acid (1,2,4,5-benzenetetracarboxylic acid, BTC) as a model system for polymerizable metal-complexing humic acids were determined using temperature-dependent time-resolved laser-induced fluorescence spectroscopy (TRLFS) and isothermal titration calorimetry (ITC). At low metal and ligand concentrations (<50 μM Eu(3+), <1 mM BTC), a 1:1 monomeric Eu-BTC complex was identified in the range of 25-60 °C. At elevated concentrations (>500 μM Eu(3+) and BTC) a temperature-dependent polymerization was observed, where BTC monomers are linked via coordinating shared Eu(3+) ions. The two methods lead to comparable thermodynamic data (ΔH = 18.5 ± 1.5/16.5 ± 0.1 kJ mol(-1); ΔS = 152 ± 5/130 ± 5 J mol(-1) K(-1); TRLFS/ITC) in the absence of polymerization. With the onset of polymerization, TRLFS reveals the water coordination number of the lanthanide, whereas calorimetry is superior in determining the thermodynamic data in this regime. Evaluating the heat uptake kinetics, the monomer and polymer formation steps could be separated by "time-resolved" ITC, revealing almost identical binding enthalpies for the sequential reactions. Structural features of the complexes were studied by Fourier-transform infrared (FTIR) spectroscopy in combination with density functional theory (DFT) calculations showing predominantly chelating coordination with two carboxylate groups in the monomeric complex and monodentate binding of a single carboxylate group in the polymeric complex of the polycarboxylate with Eu(3+). The data show that pyromellitic acid is a suitable model for the study of metal-mediated polymerization as a crucial factor in determining the effect of humic acids on the mobility of heavy metals in the environment. 相似文献
53.
Moustafa A. Gouda 《Journal of heterocyclic chemistry》2011,48(1):1-10
This review describe the synthesis and reactions of 3‐amino‐4,6‐dimethyl‐1H‐pyrazolo[3,4‐b]pyridine as building block for the synthesis of polyfunctionalized heterocyclic compounds with pharmacological interest. J. Heterocyclic Chem., 2011. 相似文献
54.
Rabie UM Abou-El-Wafa MH Nassar H 《Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy》2011,78(1):512-517
Thiazolidine-2-thione (T2T) has been studied spectrophotometrically by UV–visible and IR spectra. The spectral studies have indicated that T2T has two tautomeric forms, namely thione and thiole forms, in addition to the dimeric thioamide complex existing as a hydrogen-bonded dimer of two thione forms. Interaction of the T2T as an electron donor with iodine as a typical σ-type acceptor has been studied spectrophotometrically. Electronic absorption spectra of the system T2T–I2 in several organic solvents of different polarities have performed a clear charge transfer (CT) band in each spectrum. Formation constants (KCT) and molar absorption coefficients (?CT) and thermodynamic properties, ΔH, ΔS, and ΔG, of this system in various organic solvents were determined and discussed. The stoichiometric ratio of the T2T–I2 system in solutions was found to be 1:1 T2T:I2, whereas the elemental analysis of the prepared solid CT complex has illustrated the same stoichiometry. The obtained KCT and ?CT values have indicated that T2T is a donor of moderately strength capable of interacting with the iodine just to form the corresponding CT complex with an iodine molecule without further reducing of the iodine to either of the corresponding poly-iodide ions viz. I3?, I5?, etc. This action of spongy trapping of iodine simulates in vitro the chemical scenario of the anti-thyroid action of this compound. 相似文献
55.
Hegazy ME El-Beih AA Moustafa AY Hamdy AA Alhammady MA Selim RM Abdel-Rehim M Paré PW 《Natural product communications》2011,6(12):1809-1812
One new cembrane diterpene, 2R,7R,8R-dihydroxydeepoxysarcophine (1), together with three known compounds, 7alpha,8beta-dihydroxydeepoxysarcophine (2), 7beta-acetoxy-8alpha-hydroxydeepoxysarcophine (3), and sarcophine (4), have been isolated from the Red Sea soft coral Sarcophyton glaucum. Their structures were determined using 1D and 2D NMR spectroscopy. 7beta-Acetoxy-8alpha-hydroxydeepoxysarcophine (3) exhibits cytotoxic activity against HepG2, HCT-116, and HeLa cells with IC50 values of 3.6, 2.3, and 6.7 microg/mL, respectively. 相似文献
56.
New guest dye cations within the channel cavities of supramolecular hosts are studied. The guest organic dyes are intercalated in the supramolecular hosts by a coprecipitation reaction to give new dye‐sensitizer coordination polymers. The absorption spectra for the dye molecules within the supramolecular hosts show intense bands in the region from 500 to 700 nm due to the presence of the dyes within the parallel channels in the monomeric forms. The properties of the resulting colored polymers were investigated by IR, UV–vis, fluorescence spectra and X‐ray powder diffraction, indicating the excitation energy transfer from neutral red or pyronine as donors to methylene blue or thionine as acceptors within a supramolecular system filled with a mixture of both dyes. The wide‐ranging tenability of these highly organized materials offers fascinating new possibilities for exploring excitation energy transfer phenomena, and challenges for developing new photonic devices. Copyright © 2005 John Wiley & Sons, Ltd. 相似文献
57.
Magdi S. Moustafa 《Applied mathematics and computation》1996,80(2-3):245-255
A single server attends to two separate queues. Each queue has Poisson arrivals and exponential service. There is a switching cost whenever the server switches from one queue to another. The objective is to minimize the discounted or average holding and switching costs over a finite or an infinite horizon. We show numerically that the optimal assignment policy is characterized by a switching curve. We also show that the optimal policy is monotonic in the following senses: If it is optimal to switch from queue one to queue two, then it is optimal to continue serve queue two whenever the number of customers in queue one or in queue two decreases or increases, respectively. 相似文献
58.
A method to design a corrugated optical waveguide filter by modulating the corrugation width profile is proposed. This method is based on combined applications of the Fourier transformation and the F-matrix formalism. The method achieves the spatial profile of the corrugation width required to design a filter with any specified spectral profile of the reflection coefficient. The idea of the technique is that the spatial variation of the effective refractive index can be transformed, with the help of the F-matrix formalism, to variation of the corrugation width while maintaining a constant amplitude of the refractive index variation. Two examples are given applying the technique to the design of optical waveguide filters with reflectivity profiles of two- and four-rejection bands. 相似文献
59.
G. Cauquis G. Pierre M. H. Elnagdi H. M. Fahmy 《Journal of heterocyclic chemistry》1979,16(2):413-414
The behaviour of 2-amino-5-ethoxycrbonyl-4-methylthiazole on oxidation at a rotating platinum disc electrode is reported. The mechanism of the formation of the azo and hydraazo dimeric compounds as main oxidation products is discussed. 相似文献
60.
Equilibrium-based computer models using MINIQUAD-75 program were utilized to determine the stoichiometry and formation constants involved in the systems pyridoxamine(Pm)-glycine (Gly)-imidazole (lmd) with CO(II), Ni(II), Cu(II), Zn(II) and Cd(II) metal ions. The data were obtained from potentiometric pH titration of the various binary and ternary quaternary systems under physiological-like conditions (0.15 M NaNO3-37°C). Various composition ratios of metal and ligands were used. The ligand concentrations did not exceed 4 times the concentration of metal ion in the binary systems and 4 times of the metal ions in ternary systems. In case of the quaternary systems only imidazole concentrations were two or four times the concentrations of metal ions keeping those of other ligands equal to that of metal ions. The stability constants of the quaternary species are discussed in terms of binary and ternary constants as are the effect of ring size on the stability of mixed ligand species. In addition, electrostatic as well as statistical effects also are mentioned and the biological implications of these model equilibria are described. 相似文献