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91.
92.
J. O. Liimatta B. Lfgren M. Miettinen M. Ahlgren M. Haukka T. T. Pakkanen 《Journal of polymer science. Part A, Polymer chemistry》2001,39(9):1426-1434
Dynamic mechanical thermoanalysis showed that polyethene, prepared under suitable polymerization conditions with the Brookhart‐type catalyst dibromo‐N,N′‐1,2‐acenaphthylenediylidenebis[2,6‐bis(1‐methylethyl)benzeneamine]Ni(II)/methylaluminoxane (MAO), behaved like an elastomer, even though no comonomer was added. A structural characterization showed that the polymers contained methyl to hexyl branches and some longer branches. The effect of the polymerization conditions on branching was investigated through variations in the pressure and temperature of the polymerization. Depending on the degree and type of branching, polyethene was either quite amorphous or highly crystalline with a high melting temperature. The solid‐state structure of the catalyst dibromo‐N,N′‐1,2‐acenaphthylenediylidenebis[2,6‐bis(1‐methylethyl)benzeneamine]Ni(II) consisted of two centrosymmetrically related monomeric moieties, where Ni atoms were bridged by two bromide ligands. The Ni atom was five‐coordinated, with a square pyramidal coordination polyhedron. The sixth coordination site of the octahedral geometry was effectively blocked by the isopropyl groups of the 2,6‐C6H3(i‐Pr) substituents of the diimine ligand. In solution in the presence of MAO, the longer bridging Ni? Br bonds broke, and the complex dissociated to a monomeric species. © 2001 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 39: 1426–1434, 2001 相似文献
93.
Patrí cia Pinto Maria Jos Calhorda Thomas Straub Ville Miikkulainen Jarkko R ty Mika Suvanto Tapani A. Pakkanen 《Journal of molecular catalysis. A, Chemical》2001,170(1-2):209-218
The effects of preparation process and starting material on hydrodesulfurization (HDS) activity of alumina supported ruthenium, molybdenum and ruthenium–molybdenum hydrotreating catalysts were investigated. Conventional impregnation method and gradual gas phase adsorption were compared as a preparation route. The HDS tests showed that controlled gas phase deposition is advantageous in the preparation of the monometallic catalyst systems. The most promising HDS activity was achieved with the RuMo/Al2O3 catalyst prepared from binuclear organometallic complex. This suggests that the direct ruthenium–molybdenum bond in the structure of the catalyst precursor favors the formation of highly active surface phase. The oxidation and reduction behavior of the catalysts was studied by oxygen pulse chemisorption (PCO) and temperature programmed reduction (TPR). A clear relationship was observed between the method of preparation and the reactivity of the surface species. 相似文献
94.
95.
Scott Ahlgren 《Proceedings of the American Mathematical Society》2000,128(5):1333-1338
In his Lost Notebook, Ramanujan claimed that the ``circular' summation of the -th powers of the symmetric theta function satisfies a factorization of the form . Moreover, Ramanujan recorded identities expressing , , , , and in terms of his theta functions , , and . Ramanujan's claims were proved by Rangachari, and later (via elementary methods) by Son. In this paper we obtain similar identities for , , , and .
96.
I. Simonsen P. T.H. Ahlgren M. H. Jensen R. Donangelo K. Sneppen 《The European Physical Journal B - Condensed Matter and Complex Systems》2007,57(2):153-158
The value of stocks, indices and other assets, are examples of stochastic processes with unpredictable dynamics. In this paper,
we
discuss asymmetries in short term price movements that can not be
associated with a long term positive trend. These empirical
asymmetries predict that stock index drops are more common on a
relatively short time scale than the corresponding raises. We
present several empirical examples of such asymmetries. Furthermore,
a simple model featuring occasional short periods of synchronized
dropping prices for all stocks constituting the index is introduced
with the aim of explaining these facts. The collective negative
price movements are imagined triggered by external factors in our
society, as well as internal to the economy, that create fear of the
future among investors. This is parameterized by a “fear factor”
defining the frequency of synchronized events. It is demonstrated
that such a simple fear factor model can reproduce several empirical
facts concerning index asymmetries. It is also pointed out that in
its simplest form, the model has certain shortcomings. 相似文献
97.
Matero S Pajander J Soikkeli AM Reinikainen SP Lahtela-Kakkonen M Korhonen O Ketolainen J Poso A 《Analytica chimica acta》2007,595(1-2):190-197
The amounts of drug and excipient were predicted from ATR-FTIR spectra using two multi-way modelling techniques, parallel factor analysis (PARAFAC) and multi-linear partial least squares (N-PLS). Data matrices consisted of dissolved and undissolved parallel samples having different drug content and spectra, which were collected at axially cut surface of the flat-faced matrix tablets. Spectra were recorded comprehensively at different points on the axially cut surface of the tablet. The sample drug concentrations varied between 2 and 16% v/v. The multi-way methods together with ATR-FTIR spectra seemed to represent an applicable method for the determination of drug and excipient distribution in a tablet during the release process. The N-PLS calibration method was more robust for accurate quantification of the amount of components in the sample whereas the PARAFAC model provided approximate relative amounts of components. 相似文献
98.
Ruusunen J Tapanainen M Sippula O Jalava PI Lamberg H Nuutinen K Tissari J Ihalainen M Kuuspalo K Mäki-Paakkanen J Hakulinen P Pennanen A Teinilä K Makkonen U Salonen RO Hillamo R Hirvonen MR Jokiniemi J 《Analytical and bioanalytical chemistry》2011,401(10):3183-3195
Several studies have shown that combustion-derived fine particles cause adverse health effects. Previous toxicological studies on combustion-derived fine particles have rarely involved multiple endpoints and a detailed characterization of chemical composition. In this study, we developed a novel particle sampling system for toxicological and chemical characterization (PSTC), consisting of the Dekati Gravimetric Impactor (DGI) and a porous tube diluter. Physico-chemical and toxicological properties of the particles emitted from various combustion sources were evaluated in two measurement campaigns. First, the DGI was compared with the High-Volume Cascade Impactor (HVCI) and to the Dekati Low-Pressure Impactor (DLPI), using the same dilution system and the same sampling conditions. Only small differences were observed in the mass size distributions, total particulate matter (PM), and particulate matter with diameter smaller than 1 um (PM(1)) concentrations and geometric mass mean diameters (GMMD) between these three impactors. Second, the PSTC was compared with the HVCI sampling system, which has been optimal for collection of particulate samples for toxicological and chemical analyses. Differences were observed in the mass size distributions, total PM and PM(1) emissions, and GMMDs, probably due to the different sampling and dilution methods as well as different sampling substrates which affected the behavior of semi-volatile and volatile organic compounds. However, no significant differences were detected in the in vitro measurements of cytotoxicity between the samples collected with the PSTC and the HVCI systems. In measurements of genotoxicity, significant differences between the two sampling systems were seen only with the particles emitted from the sauna stove. In conclusion, due to compact size, PSTC is an applicable method for use in particle sampling as part of the toxicological and chemical characterization of particulate emissions from different combustion sources. It offers some advantages compared to the previously used high-volume sampling methods including compactness for field measurements, simple preparation of sample substrates and high extraction efficiency. 相似文献
99.
Raija Oilunkaniemi Risto S. Laitinen Jouni Pursiainen Markku Ahlgren 《Phosphorus, sulfur, and silicon and the related elements》2013,188(1):577-582
The preparation of [M(C4H3SECH3)2Cl2] (M = Pd, Pt; E = Se, Te) and [Pd6Te6(C4H3S)2(PPh3)6Cl2] from methyl(2-thienyl)chalcogenides and bis(2-thienyl) ditelluride is reported. The products are identified and characterized by X-ray crystallography and by 77Se and 125Te NMR spectroscopy. 相似文献
100.
Characteristic Spectral Patterns in the Carbon‐13 Nuclear Magnetic Resonance Spectra of Hexagonal and Crenellated Graphene Fragments
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Nergiz Özcan Jarkko Vähäkangas Dr. Perttu Lantto Prof. Dr. Juha Vaara 《Chemphyschem》2014,15(9):1799-1808
Nuclear magnetic resonance (NMR) spectroscopy is an important molecular characterisation method that may aid the synthesis and production of graphenes, especially the molecular‐scale graphene nanoislands that have gathered significant attention due to their potential electronic and optical applications. Herein, carbon‐13 NMR chemical shifts were calculated using density functional theory methods for finite, increasing‐size fragments of graphene, hydrogenated graphene (graphane) and fluorinated graphene (fluorographene). Both concentric hexagon‐shaped (zigzag boundary) and crenellated (armchair) fragments were investigated to gain information on the effect of different types of flake boundaries. Convergence trends of the 13C chemical shift with respect to increasing fragment size and the boundary effects were found and rationalised in terms of low‐lying electronically excited states. The results predict characteristic behaviour in the 13C NMR spectra. Particular attention was paid to the features of the signals arising from the central carbon atoms of the fragments, for graphene and crenellated graphene on the one hand and graphane and fluorographene on the other hand, to aid the interpretation of the overall spectral characteristics. In graphene, the central nuclei become more shielded as the system size increases whereas the opposite behaviour is observed for graphane and fluorographene. The 13C signals from some of the perimeter nuclei of the crenellated fragments obtain smaller and larger chemical shift values than central nuclei for graphene and graphane/fluorographene, respectively. The diameter of the graphenic quantum dots with zigzag boundary correlates well with the predicted carbon‐13 chemical shift range, thus enabling estimation of the size of the system by NMR spectroscopy. The results provide data of predictive quality for future NMR analysis of the graphene nanoflake materials. 相似文献