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61.
Amo-Ochoa P Rodríguez-Tapiador MI Castillo O Olea D Guijarro A Alexandre SS Gómez-Herrero J Zamora F 《Inorganic chemistry》2006,45(19):7642-7650
The direct reaction between 6-mercaptopurine (6-MP) and Cd(II) under different conditions yields either [Cd2(6-MP)4(NO3)2](NO3)2 (1) or [Cd(6-MP-)2.2H2O]n (4). Compound 1 behaves as the building block of the polymer [Cd(6-MP2-)2]n[Ca(H2O)6]n (3), by deprotonation of 6-MP ligand. In the reaction of 1 to give 3, the dinuclear compound [Cd2(6-MP)4(H2O)2](NO3)4.2H2O (2) can be isolated as an intermediate. Polymers 3 and 4 convert into each other in water via deprotonation-protonation reactions. The structures of compounds 1-3 have been determined by X-ray diffraction. Given the small differences in the arrangement shown in the crystal structures of the polymer 4 and the polyanion of 3, the stabilities and energetics of the two arrangements have been examined by DFT calculations to determine the possibility of identifying new conformations of both polymers. In addition, the two polymers have been characterized on surfaces by means of AFM. The direct reaction between 6-MP and Cd(II) and the deprotonation of the polymer 4 have proven to be useful routes for the isolation of one-dimensional systems on surfaces. The development of new strategies to characterize these types of polymers on surfaces opens the possibility to perform nanoscale studies on their properties and their potential use as nanomaterials. 相似文献
62.
The flow injection spectrophotometric determination of cysteine was carried out by reaction with cobalt(II) ions entrapped in a polymeric material and filling a packed-bed reactor; the released cobalt(II) complexed with the amino acid was monitored at 360 nm. The method worked with a high repeatability, even with independent reactors, days and solutions. Selectivity of the procedure was tested with twenty different foreign compounds found in pharmaceutical formulations containing cysteine, parent amino acids included; no serious interferences were observed. The calibration graph for cysteine was linear over the range 1-90 micrograms ml-1 with a relative standard deviation of 0.8% at 60 micrograms ml-1 (n = 158). The calculated sample throughput was 90 h-1. The method was applied to determine the content of cysteine in pharmaceutical formulations. 相似文献
63.
Gómez-Taylor Corominas B Catalá Icardo M Lahuerta Zamora L García Mateo JV Martínez Calatayud J 《Talanta》2004,64(3):618-625
A direct chemiluminescent procedure for determination of hydroquinone based on the emergent flow methodology known as multicommutation or tandem-flow is presented for first time. The manifold was based on a set of three channels and three solenoid valves; and, the determination was performed at 60 °C and at flow-rate of 7.5 ml min−1. The complete cycle lasted 35 s, which resulted in a sample flow trough of 103 h−1. The chemical process was the hydroquinone oxidation with the system sulphuric acid-potassium permanganate; and the light emission was clearly enhanced by the presence of quinine sulphate and benzalkonium chloride reaching a detection limit of 30 μg l−1. The dynamic interval was over the range 0.1-15.0 mg l−1 and a large list of interferents were assayed; the chemical robustness was also tested. The method was applied to different type of samples: namely, pharmaceutical formulations, a photographic solution and irrigation and residual superficial waters. 相似文献
64.
65.
A. Garrido Frenich D. Picón Zamora M. Martínez Galera J. L. Martínez Vidal 《Analytical and bioanalytical chemistry》2003,375(7):974-980
The application of the generalised rank annihilation method (GRAM) and the trilinear decomposition (TLD) method to the resolution and quantitation of fluorescence excitation-emission matrices of a ternary mixture of pesticides, carbendazim, fuberidazole, and thiabendazole, with overlapped spectra is described. The results obtained with both methods are compared and evaluated using measures of similarity (correlation coefficients) between the real and estimated spectra. Both approaches have been tested using augmented data matrices containing only two samples, but none of these methods succeeded completely in resolution of the system. When TLD was applied to augmented data matrices containing more than two samples better performance was achieved. To illustrate the application of both algorithms to real samples, they were used in the analysis of water samples containing the target pesticides. Again, TLD had an advantage over GRAM because the ability to analyse data from multiple (more than two) samples simultaneously allowed the resolution of the mixtures. 相似文献
66.
67.
D. Oyola Lozano L. E. Zamora G. A. Pérez Alcázar Y. A. Rojas H. Bustos J. M. Greneche 《Hyperfine Interactions》2006,169(1-3):1253-1258
In this work the magnetic and structural properties are investigated by Mössbauer spectrometry, Vibrating Sample Magnetometry and X-ray diffraction of Nd2(Fe100?x Nb x )14B powdered alloys with x?=?0, 2 and 4 prepared by arc melting. The Mössbauer spectra of the samples were fitted with several contributions from: Nd2Fe14B, α-Fe and a paramagnetic phase associated with Nd1.1Fe4B4 for x?=?0 and additionally from NbFeB and Nd2Fe17 for x?=?2 and x?=?4. The relative fractions of α-Fe and Nd2Fe14B are smaller for x?=?4 than for x?=?0, indicating that the amount of these two phases is reduced with increasing Nb content, while the relative fraction of Nd2Fe17 increases. The α-Fe grain size slightly decreases while that of the Nd2Fe14B phase is increasing, when the Nb content increases. The hysteresis loops indicate that these samples behave as hard ferromagnets, with a coercive field which decreases when the Nb content increases, but with rather low remanent magnetization. 相似文献
68.
An affine graph is a pair (G,σ) where G is a graph and σ is an automorphism assigning to each vertex of G one of its neighbors. On one hand, we obtain a structural decomposition of any affine graph (G,σ) in terms of the orbits of σ. On the other hand, we establish a relation between certain colorings of a graph G and the intersection graph of its cliques K(G). By using the results we construct new examples of expansive graphs. The expansive graphs were introduced by Neumann-Lara in 1981 as a stronger notion of the K-divergent graphs. A graph G is K-divergent if the sequence |V(Kn(G))| tends to infinity with n, where Kn+1(G) is defined by Kn+1(G)=K(Kn(G)) for n?1. In particular, our constructions show that for any k?2, the complement of the Cartesian product Ck, where C is the cycle of length 2k+1, is K-divergent. 相似文献
69.
García-Couceiro U Olea D Castillo O Luque A Román P de Pablo PJ Gómez-Herrero J Zamora F 《Inorganic chemistry》2005,44(23):8343-8348
The compound [Mn(mu-ox)(4atr)2]n (1) (ox = oxalato and 4atr = 4-amine-1,2,4-triazole) has been synthesized and characterized by FT-IR spectroscopy, thermal analysis, variable-temperature magnetic measurements, and X-ray single-crystal diffraction methods. The crystal structure of compound 1 consists of one-dimensional linear chains in which trans-[Mn(4atr)2]2+ units are sequentially bridged by centrosymmetric bis-bidentate oxalato ligands. Cryomagnetic measurements show an overall antiferromagnetic behavior of the compound. Isolated chains of this polymer have been obtained by sonication of 1 in ethanol or treatment of the polymer with NaOH and morphologically characterized on highly oriented pyrolitic graphite and mica surfaces by atomic force microscopy and scanning tunneling microscopy. The procedures employed to obtain single chains of this coordination polymer open a route for future nanotechnological applications of these types of materials. 相似文献
70.
In this short note we give a characterization of extremal principally polarized abelian varieties determining an isolated point in Sing
The case g = 5 is treated in depth.Received: 14 June 2004 相似文献