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排序方式: 共有190条查询结果,搜索用时 15 毫秒
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2.
Laura Bader Nicola Durante Maska Law Guglielmo Lunardon Tim Penttila 《Designs, Codes and Cryptography》2003,29(1-3):41-50
We do the tentative beginnings of a study of BLT-sets of generalised quadrangles via their symmetries. In particular, the study of whorls about a line leads us to hyperbolic reflections preserving a BLT-set of Q(4, q). 相似文献
3.
Roy L. Whistler Guglielmo Ruffini Richard E. Pyler 《Journal of polymer science. Part A, Polymer chemistry》1968,6(9):2501-2510
Grafting of 1,2-O-isopropylidene-α-D -xylofuranose to commercial cellulose diacetate has been accomplished by using a boron trifluoride catalyst. The reaction proceeds quickly at 25 and 40°C, resulting in degrees of molar substitution (MS) of 0.37 and 0.34, respectively. If monomer and catalyst are added over an extended period of time to maintain low concentrations, MS values as high as 0.89 and 0.85 are obtained at 25 and 40°C, respectively. Major side reactions are depolymerization of the cellulose acetate backbone and grafted D -xylose and the homopolymerization of the monomer. These side reactions may be minimized by conducting the reaction at 40°C for a short time or by adding monomer and catalyst over an extended period of time. Grafting has also been accomplished by using D -xylose derivatives with various reactive groups at the anomeric carbon atom. The grafted material of MS greater than 0.7 is insoluble in acetone and after deacetylation is soluble in water under alkaline, neutral and acidic conditions. Oxalic acid hydrolysis of the deacetylated material indicates that most of the grafted D -xylose units are in the furanose form. Methylation and hydrolysis of the methylated material shows that 75% of the D -xylose residues are terminal units and indicates the presence of many singly grafted D -xylose residues and a few di-and trisaccharide grafts. 相似文献
4.
Kurt Burdeska Hermann Fuhrer Guglielmo Kabas Adolf Emil Siegrist 《Helvetica chimica acta》1981,64(1):113-152
Preparation of Styryl and Stilbenyl Derivatives of Pyrimidines 2- and 4-(p-Tolyl)-substituted pyrimidines react with anils of hetero-aromatic aldehydes in the presence of dimethylformamide and potassium hydroxide or potassium t-butoxide to yield the corresponding 2- and 4-[4″-(heteroaryl)stilben-4′-yl]pyrimidines or the 2- and 4-[a-(heteroaryl)-4′-styryl]pyrimidines respectively (‘Anil synthesis’). Furthermore, the Schiff′s bases derived from p-chloroaniline and 4-(pyrimidine-2-yl and 4-yl)benzaldehydes give, with methyl- and with p-tolyl-substituted heterocycles, the corresponding heterocyclic substituted styryl and stilbenyl derivatives. Alkyl-, alkoxy- or phenyl-substituted pyrimidines undergo also the ‘Anil synthesis’. 相似文献
5.
Dr. Guglielmo Monaco Prof. Emeritus Lawrence T. Scott Prof. Riccardo Zanasi 《ChemistryOpen》2020,9(5):616-622
The three-fold HOMO-LUMO gap oscillation, typical of finite length armchair carbon nanotubes (CNT), has a major effect on the magnetic response of ultrashort, single-end-capped [5,5] carbon nanotubes to a perturbing magnetic field parallel to the main symmetry axis. For the CNT's containing 40, 70, and 100 carbon atoms, for which 100 % of the C=C double bonds can be grouped into aromatic-sextets, i. e., fully or complete Clar networks, large paratropic (antiaromatic) global circulations around the cylindrical axis are predicted at the DFT level of calculation. Local and semi-global diatropic (aromatic) currents of strengths not larger than that of the benzene molecule are determined for a perpendicular perturbing magnetic field. CNTs of intermediate lengths do not display this enhanced antiaromatic response. The paratropic current flow clearly shows that these complete Clar networks can be viewed as stacked cycloparaphenylene belts, each providing a double annulene circuit as a consequence of the quinoidal resonance structure that results from their closure. Paradoxically, the fully aromatic Clar structure itself is responsible for the enhanced global antiaromaticity. 相似文献
6.
7.
Rosace G Giuffrida G Saitta M Guglielmo G Campagna S Lanza S 《Inorganic chemistry》1996,35(23):6816-6822
Tight contact ion pairs of general formula {Pt(H(2)-R(2)-dto)(2)(2+),(X(-))(2)} have been prepared, and their absorption spectra and luminescence properties (at room temperature in dichloromethane fluid solution and at 77 K in butyronitrile rigid matrix) have been studied (dto = dithiooxamide; R = methyl, X = Cl (1); R = butyl, X = Cl (2); R = benzyl, X = Cl (3); R = cyclohexyl, X = Cl (4); R = cyclohexyl, X = Br (5); R = cyclohexyl, X = I (6)). The absorption spectra of all the compounds are dominated by moderately strong Pt(dpi)/S(p) to dithiooxamide (pi) charge transfer (Pt/S --> dto CT) bands in the visible region (epsilon in the 10(4)-10(5) M(-)(1) cm(-)(1) range). Absorption features are also present at higher energies, due to pi-pi transitions centered in the dto ligands (ligand centered, LC). All the compounds exhibit a unstructured luminescence band in fluid solution at room temperature, with the maximum centered in the 700-730 nm range. The luminescence bands are blue-shifted about 4000 cm(-)(1) on passing to the rigid matrix at 77 K. Luminescence lifetimes are on the 10(-)(8)-10(-)(7) s time scale at room temperature and 1 order of magnitude longer at 77 K. Luminescence is assigned to triplet Pt/S --> dto CT excited states in all cases. Compounds 3-6 also exhibit a second higher-energy luminescence band at room temperature, centered at about 610 nm, attributed to a LC excited state. Charge transfer interactions between halides and dto ligands destabilize dto-centered orbitals, affecting the energy of Pt/S --> dto CT transitions and states. The X counterions and X --> dto CT levels are proposed to play a role in promoting excited state conversion between LC and Pt/S --> dto CT levels. The R substituents on the nitrogen atoms of the dto ligands influence the absorption and photophysical properties of the compounds, by affecting proximity of the ion pairs. The possibility to functionalize the R substituents may open the way to interface these luminescent compounds with desired substrates and to construct supramolecular assemblies. 相似文献
8.
Vladimir S. Koroliuk Raimondo Manca Guglielmo D’Amico 《Journal of Mathematical Sciences》2014,196(5):644-651
The storage impulsive processes given by a sum of random variables on a superposition of two renewal processes are considered on increasing time intervals. The averaging, diffusion approximation, and large deviation problem are studied in the series scheme with a small parameter series under suitable scaling. 相似文献
9.
Guglielmo D’Amico 《Applications of Mathematics》2014,59(5):571-588
Markov chain usage models were successfully used to model systems and software. The most prominent approaches are the so-called failure state models Whittaker and Thomason (1994) and the arc-based Bayesian models Sayre and Poore (2000). In this paper we propose arc-based semi-Markov usage models to test systems. We extend previous studies that rely on the Markov chain assumption to the more general semi-Markovian setting. Among the obtained results we give a closed form representation of the first and second moments of the single-use reliability. The model and the validity of the results are illustrated through a numerical example. 相似文献
10.
Depending on their relative orientation, coupled oscillating carbonyl groups provide a VCD spectrum with a characteristic CO bond stretching region showing a strong bisignate VCD feature, which can be readily predicted adopting long available semiempirical methods. The extended coupled oscillator (ECO) formalism has been used to assign the absolute configuration of a recently synthesized chiral 3-substituted isoindolinone. The prediction of (S) configuration for the (−) enantiomer has been confirmed by quantum mechanical calculations. 相似文献