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11.
G. Bollen F. Ames G. Audi D. Beck J. Dilling O. Engels S. Henry F. Herfurth A. Kellerbauer H.-J. Kluge A. Kohl E. Lamour D. Lunney R. B. Moore M. Oinonen C. Scheidenberger S. Schwarz G. Sikler J. Szerypo C. Weber 《Hyperfine Interactions》2001,132(1-4):213-220
Penning trap mass spectrometry has reached a state that allows its application to very short-lived nuclides available from
various sources of radioactive beams. Mass values with outstanding accuracy are achieved even far from stability. This paper
illustrates the state of the art by summarizing the status of the ISOLTRAP experiment at ISOLDE/CERN. Furthermore, results
of mass measurements on unstable rare earth isotopes will be given.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
12.
F. Ames T. Brumm K. Jäger H. -J. Kluge B. M. Suri H. Rimke N. Trautmann R. Kirchner 《Applied physics. B, Lasers and optics》1990,51(3):200-206
We report here on the development of a high-temperature laser ion source useful for trace analysis and other applications. It consists of a high temperature ionization chamber, three tunable dye lasers pumped by copper vapor lasers for stepwise resonant ionization and a Mattauch-Herzog mass spectrometer for the analysis of photo-ions. The principle of the laser ion source and its theoretical efficiency are discussed, where the efficiency of a laser ion source is the ratio of photo-ions extracted out to the number of atoms introduced into the cavity. Experimentally, an efficiency of 2×10–3 has been achieved for technetium. The scheme of gated detection is described which is used for suppressing isobaric background of molybdenum. The possible improvements are briefly mentioned for achieving isotopic analysis of 108 atoms of 97,98Tc in the presence of 1015 atoms of molybdenum, as separated chemically from molybdenum ore. Such an analysis of technetium isotopes produced in molybdenite ore by a (v,e
–) reaction, is expected to yield information about the solar neutrino flux.Permanent address: Bhabha Atomic Research Centre, Bombay 400085, India 相似文献
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We prove Holder-continuous dependence results for the difference between solutions of certain ill-posed and approximate
well-posed problems in both Hilbert and Banach spaces. We use operator-theoretic methods, including C-semigroups, to treat the abstract Cauchy problem $\frac{du}{dt} = Au, u(0) = \chi, 0 \leq t < T,$ where the operator $-A$ is the infinitesimal generator
of a holomorphic semigroup. 相似文献
16.
One of the systems of equations approximating the large deflection of plates consists of two coupled non-linear fourth order partial differential equations, known as the von Karman equations. The full symmetry group for the steady equations is a finitely generated Lie group with ten parameters. For the time-dependent system the full symmetry group is an infinite parameter Lie group. Several subgroups of the full group are used to generate exact solutions of the time-independent and the time-dependent systems. These include the dilatation group (similar solutions), rotation group, screw group and others. Physical implications and applications are discussed. 相似文献
17.
Ames W Pantazis DA Krewald V Cox N Messinger J Lubitz W Neese F 《Journal of the American Chemical Society》2011,133(49):19743-19757
Protonation states of water ligands and oxo bridges are intimately involved in tuning the electronic structures and oxidation potentials of the oxygen evolving complex (OEC) in Photosystem II, steering the mechanistic pathway, which involves at least five redox state intermediates S(n) (n = 0-4) resulting in the oxidation of water to molecular oxygen. Although protons are practically invisible in protein crystallography, their effects on the electronic structure and magnetic properties of metal active sites can be probed using spectroscopy. With the twin purpose of aiding the interpretation of the complex electron paramagnetic resonance (EPR) spectroscopic data of the OEC and of improving the view of the cluster at the atomic level, a complete set of protonation configurations for the S(2) state of the OEC were investigated, and their distinctive effects on magnetic properties of the cluster were evaluated. The most recent X-ray structure of Photosystem II at 1.9 ? resolution was used and refined to obtain the optimum structure for the Mn(4)O(5)Ca core within the protein pocket. Employing this model, a set of 26 structures was constructed that tested various protonation scenarios of the water ligands and oxo bridges. Our results suggest that one of the two water molecules that are proposed to coordinate the outer Mn ion (Mn(A)) of the cluster is deprotonated in the S(2) state, as this leads to optimal experimental agreement, reproducing the correct ground state spin multiplicity (S = 1/2), spin expectation values, and EXAFS-derived metal-metal distances. Deprotonation of Ca(2+)-bound water molecules is strongly disfavored in the S(2) state, but dissociation of one of the two water ligands appears to be facile. The computed isotropic hyperfine couplings presented here allow distinctions between models to be made and call into question the assumption that the largest coupling is always attributable to Mn(III). The present results impose limits for the total charge and the proton configuration of the OEC in the S(2) state, with implications for the cascade of events in the Kok cycle and for the water splitting mechanism. 相似文献
18.
D. Beck F. Ames G. Audi G. Bollen H.-J. Kluge A. Kohl M. König I. Martel D. Lunney R.B. Moore H. Raimbault-Hartmann M. de Saint Simon E. Schark S. Schwarz J. Szerypo the ISOLDE Collaboration 《Hyperfine Interactions》1997,108(1-3):219-225
First direct mass measurements on rare earth isotopes around 146Gd have been performed with the Penning trap mass spectrometer ISOLTRAP at ISOLDE/CERN. More than 40 isotopes of the elements
Pr, Nd, Pm, Sm, Eu, Dy and Ho have been measured with an accuracy of typically 1 × 10-7. In the case of 141Sm isomeric and ground state (ΔE = 175 keV) were resolved. Since isobaric contaminations are present in the ISOLDE beam, these
measurements on rare earth isotopes became only possible after the installation of a new cooler trap which acts an isobar
separator.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
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The preparation of a new aluminum reagent, dmiethylaluminum methaneselenolate (Me2AlSeMe) is described. The reactivity of this aluminum reagent toward a variety of organic substrates has been studied. Me2AlSeMe will convert O-alkyl esters to selenoesters in high yield. These selenoesters function as extremely reactive acyl transfer agents and are converted to acids, esters, and amides on reaction with water, alcohols or amines in the presence of a selenophilic metal cation. The selenoesters will, moreover, acylate reactive arenes and heterocyclic compounds when cuprous triflate is employed as the selenophilic metal cation. This latter transformation constitutes a new transition metal promoted variant of the Friedel-Crafts acylation reaction. 相似文献