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61.
We present relations between growth, growth of diameters and the rate of vanishing of the spectral gap in Schreier graphs of automaton groups. In particular, we introduce a series of examples, called Hanoi Towers groups since they model the well known Hanoi Towers Problem, that illustrate some of the possible types of behavior. To cite this article: R. Grigorchuk, Z. ?unik´, C. R. Acad. Sci. Paris, Ser. I 342 (2006). 相似文献
62.
Carlos Lodeiro Jose´ Luis Capelo 《Journal of inclusion phenomena and macrocyclic chemistry》2004,49(3-4):249-258
The synthesis of two new tritopic crown ligands (L1 and L2) bearing two benzo-15-crown-5 lateral moieties linked through a dibenzo-trioxa chain together with their interaction with metal ions, in acetonitrile and acetonitrile–water (50%, v/v) solutions is reported. The influence of K+, Na+, Li+, Ca2+, Ba2+, Cu2+, Zn2+, Cd2+, Pb2+ and Al3+, on the spectroscopic properties of these diaza-polyoxa ligands was investigated by absorption spectrophotometry and in some cases by fluorescence emission spectroscopy. Coordination with alkaline (Na+, K+ and Li+) and alkaline earth (Ca2+and Ba2+) metal ions is assumed to be weak with both macrobicyclic ligands, while the interaction with both imine and amine derivatives causes a minor effect in the absorption spectra. Coordination with Cu2+, Zn2+ and Pb2+ in acetonitrile solution causes a major change in the absorption spectra of the chromophores. In the case of Cu2+, addition of the metal to L1 or L2 leads to a blue–violet complex in solution with an absorbance maximum centred at 590 nm. Interaction of the Schiff-base L1 with Pb2+ leads to a short wavelength shift in the absorption bands, comparable with the ZnL1 complex. Presence of transition metal ions such as Co2+, Ni2+and Cd2+ do not remarkably affect the absorption spectra of L1 and L2 in solution. Trivalent aluminium has a modest effect in the absorption bands of both N2O13 donor set bismacrocyclic ligands. The fluorescence study of L2 in the presence of Na+, K+, Ca2+, Ba2+, Co2+, Cu2+, Ni2+, Pb2+ and Al3+shows that Cu2+, Pb2+ and Al3+ complexes form non-fluorescent complexes. 相似文献
63.
64.
A. N. Araújo Joan Gracia Jose´ L. F. C. Lima Manel Poch M. Lu´cia M. F. S. Saraiva 《Analytical and bioanalytical chemistry》1997,357(8):1153-1156
A procedure is described for the colorimetric determination of iron in infant fortified formulas based on sequential injection
analysis (SIA). Iron(III) complexation with thiocyanate is used as colour developing reaction. The system enables the determination
of iron in the samples (after digestion by dry ashing and treatment with 0.2 mol/L nitric acid in the range of 0.50–20.0 mg/L,
consuming 140 μL of the sample and 8 mg thiocyanate per determination. The reactor geometry and the adjustment of the ionic
content of the calibration solutions is important for the accuracy of the results. A regression line according to the equation
[Fe(III) (mg/L)]SIA=−0.3(±0.4)+1.03(±0.04) [Fe(III) (mg/L)]FAAS was obtained after comparative analysis of a set of 12 samples. The measurement rate was 34 s, thus allowing to analyze 100
samples per hour with a relative standard deviation lower than 2%.
Received: 30 July 1996/Revised: 1 October 1996/Accepted: 4 October 1996 相似文献
65.
The molecular structure of methane sulphonyl fluoride in the vapour state was studied by electron diffraction. Assuming a value of 2.480A?for the distance between the oxygen atoms from a microwave determination, the following geometrical parameters (ra structure) have been obtained: r(C-H) = 1.093±0.010Å, r(S-O) = 1.410±0.003Å, r(S-F) = 1.561 ±0.004Å, r(S-C) = 1.759±0.006Å, ∠F-S-C = 98.2±1.5°, ∠-S-F = 106.2±0.4°, ∠-O-S-O = 123.1 ±1.5° and ∠H-C-H = 112.9±1.9°. All the observed variations in the molecular geometries of (CH3)2SO2, CH3SO2Cl, CH3SO2F and SO2F2 may be accounted for by the valence shell electron pair repulsion theory. It is particularly advantageous to combine electron diffraction and microwave data in studying sulphone molecular geometries. 相似文献
66.
The solutions of various problems in the theories of queuing processes, branching processes, random graphs and others require the determination of the distribution of the sojourn time (occupation time) for the Brownian excursion. However, no standard method is available to solve this problem. In this paper we approximate the Brownian excursion by a suitably chosen random walk process and determine the moments of the sojourn time explicitly. By using a limiting approach, we obtain the corresponding moments for the Brownian excursion. The moments uniquely determine the distribution, enabling us to derive an explicit formula. 相似文献
67.
68.
69.
We have recently developed a global optimization methodology for solving combinatorial problems with either deterministic or stochastic performance functions. This method, the Nested Partitions (NP) method has been shown to generate a Markov chain and with probability one to converge to a global optimum. In this paper, we study the rate of convergence of the method through the use of Markov Chain Monte Carlo (MCMC) methods, and use this to derive stopping rules that can be applied during simulation-based optimization. A numerical example serves to illustrate the feasibility of our approach. 相似文献
70.
M. Violante de Paz Ba´ñez Jose´ A. Aznar Moreno 《Journal of carbohydrate chemistry》2013,32(2):120-140
Biodegradable polymers obtained from renewable natural sources are currently receiving increasing attention because they are an alternative to the traditional petroleum‐based plastics. In the present communication we describe the synthesis of the diol monomers 2,3,4‐tri‐O‐benzyl‐L‐arabinitol (ABnOH) and 2,3,4‐tri‐O‐benzylxylitol (XBnOH), and the diamino monomers 1,5‐diamino‐1,5‐dideoxy‐2,3,4‐tri‐O‐benzyl‐L‐arabinitol (ABnNH 2 ) and 1,5‐diamino‐1,5‐dideoxy‐2,3,4‐tri‐O‐benzylxylitol (XBnNH 2 ), which can be used in the preparation of new potentially biodegradable sugar‐based polymers. As an example, we describe the synthesis and characterization of a polyurethane [PU‐(ABnOH‐HMDI)] and a polyurea [PUR‐(ABnNH2‐HMDI)] by poly addition reaction of ABnOH and ABnNH 2 with 1,6‐hexamethylene diisocyanate. 相似文献