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31.
G. Van der Snickt W. De Nolf B. Vekemans K. Janssens 《Applied Physics A: Materials Science & Processing》2008,92(1):59-68
For the non-destructive identification of pigments and colorants in works of art, in archaeological and in forensic materials,
a wide range of analytical techniques can be used. Bearing in mind that every method holds particular limitations, two complementary
spectroscopic techniques, namely confocal μ-Raman spectroscopy (μ-RS) and μ-X-ray fluorescence spectroscopy (μ-XRF), were
joined in one instrument. The combined μ-XRF and μ-RS device, called PRAXIS unites both complementary techniques in one mobile
setup, which allows μ- and in situ analysis. μ-XRF allows one to collect elemental and spatially-resolved information in a
non-destructive way on major and minor constituents of a variety of materials. However, the main disadvantages of μ-XRF are
the penetration depth of the X-rays and the fact that only elements and not specific molecular combinations of elements can
be detected. As a result μ-XRF is often not specific enough to identify the pigments within complex mixtures. Confocal Raman
microscopy (μ-RS) can offer a surplus as molecular information can be obtained from single pigment grains. However, in some
cases the presence of a strong fluorescence background limits the applicability. In this paper, the concrete analytical possibilities
of the combined PRAXIS device are evaluated by comparing the results on an illuminated sheet of parchment with the analytical
information supplied by synchrotron radiation μ-X-ray diffraction (SR μ-XRD), a highly specific technique.
PACS 33.20.Fb; 61.05.cp; 33.20.Rm; 07.85.Qe; 91.65.An 相似文献
32.
K.A. Schmidt M. Bergström G.B. Hagemann B. Herskind G. Sletten P.G. Varmette J. Domscheit H. Hübel S.W. Ødegård S. Frattini A. Bracco B. Million M.P. Carpenter R.V.F. Janssens T.L. Khoo T. Lauritsen C.J. Lister S. Siem I. Wiedenhöver D.J. Hartley L.L. Riedinger A. Maj W.C. Ma R. Terry 《The European Physical Journal A - Hadrons and Nuclei》2001,12(1):15-28
High-spin properties of the nucleus 169Hf have been studied through the fusion evaporation reaction 96Zr(76Ge,3n)169Hf at a beam energy of 310 MeV. The known rotational bands have been extended considerably and 6 new bands have been established,
four of which form coupled bands with pronounced M1 connections. Quasiparticle assignments are suggested for the new band structures, and it appears that coupling to vibrational
degrees of freedom plays a role. Both coupled bands involve the excitation of quasiprotons. In the region of highest spin,
a large alignment gain is interpreted in terms of a mixed crossing where an h
9/2 and an h
11/2 quasiproton provide the two signatures of the aligning configuration.
Received: 23 March 2001 / Accepted: 20 September 2001 相似文献
33.
LaSrMnNbO6 has been synthesized by high temperature solid state reaction under 1% H2/Ar dynamic flow. The structure is determined by Rietveld refinement of the powder X-ray diffraction data. It crystallizes in the monoclinic space group P21/n with the unit cell parameters: a=5.69187(12), b=5.74732(10), c=8.07018(15) Å and β=90.0504(29)°, which were also confirmed by electron diffraction. The Mn2+ and Nb5+ ions, whose valence states are confirmed by X-ray absorption near-edge spectroscopy, are almost completely ordered over the B-site (<1% inversion) of the perovskite structure due to the large differences of both cationic size (0.19 Å) and charge. The octahedral framework displays significant tilting distortion according to Glazer’s tilt system a−b−c+. Upon heating, LaSrMnNbO6 decomposes at 690 °C under O2 flow or at 775 °C in air. The magnetic susceptibility data indicate the presence of long-range antiferromagnetic ordering at TN=8 K; the experimentally observed effective paramagnetic moment, μeff=5.76 μB for high spin Mn2+ (3d5, S=5/2) is in good agreement with the calculated value (μcalcd=5.92 μB). 相似文献
34.
Wee LH Bajpe SR Janssens N Hermans I Houthoofd K Kirschhock CE Martens JA 《Chemical communications (Cambridge, England)》2010,46(43):8186-8188
Nanomaterial of Cu(3)(BTC)(2) (BTC = benzene tricarboxylic acid) incorporating Keggin heteropolyacid conveniently prepared at room temperature and recovered by freeze drying outperforms ultrastable Y zeolite in acid catalysed esterification reaction. 相似文献
35.
Frederik Detobel Ken Broeckhoven Joke Wellens Bert Wouters Remco Swart Mario Ursem Gert Desmet Sebastiaan Eeltink 《Journal of chromatography. A》2010,1217(18):3085-3090
An experimental study was performed to investigate the effects of column parameters and gradient conditions on the separation of intact proteins using styrene-based monolithic columns. The effect of flow rate on peak width was investigated at constant gradient steepness by normalizing the gradient time for the column hold-up time. When operating the column at a temperature of 60 °C a small C-term effect was observed in a flow rate range of 1–4 μL/min. However, the C-term effect on peak width is not as strong as the decrease in peak width due to increasing flow rate. The peak capacity increased according to the square root of the column length. Decreasing the macropore size of the polymer monolith while maintaining the column length constant, resulted in an increase in peak capacity. A trade-off between peak capacity and total analysis time was made for 50, 100, and 250 mm long monolithic columns and a microparticulate column packed with 5 μm porous silica particles while operating at a flow rate of 2 μL/min. The peak capacity per unit time of the 50 mm long monolithic column with small pore size was superior when the total analysis time is below 120 min, yielding a maximum peak capacity of 380. For more demanding separations the 250 mm long monolith provided the highest peak capacity in the shortest possible time frame. 相似文献
36.
R. Broda P. J. Daly Z. W. Grabowski H. Helppi M. Kortelahti J. McNeill R. V. F. Janssens R. D. Lawson D. C. Radford J. Blomqvist 《Zeitschrift für Physik A Hadrons and Nuclei》1985,321(2):287-295
The level structure of theN=81 nucleus147Dy has been studied byγ-ray spectroscopy following reactions of 230–250 MeV58,60Ni beams on89Y and90,92Zr targets. Yrast and near-yrast levels in147Dy above the known 59-s 11/2? state are established up to ~3.7 MeV; they include isomeric levels at 2,681, 3,407 and 3,650 keV. Guided by the results of shell model calculations, we interpret most of the observed level as senioritythree states arising from the coupling ofs 1/2,d 3/2, andh 11/2 neutron holes withπh 11/2 2. 相似文献
37.
Gerrit K. Janssens Kenneth Sörensen Wout Dullaert 《Mathematical and Computer Modelling》2009,49(3-4):563-572
Stochastic marked graphs, a special class of stochastic timed Petri nets, are used for modelling and analyzing decision-free dynamic systems with uncertainties in timing. The model allows evaluating the performance of such systems under a cyclic process. Given the probabilistic characteristics of the transition times, the cycle time of the system can be determined from the initial marking. In this contribution, we compute an upper bound on the cycle time of a stochastic marked graph in case the probabilistic characteristics of the transition times are not fully specified. 相似文献
38.
Prof. Ewald Janssens Hai Thuy Le Prof. Peter Lievens 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(43):15256-15262
The adsorption of propene on neutral gold clusters is investigated in a collision cell under a few collision conditions. The adsorption reaction is studied by pressure‐dependent kinetic measurements and delayed unimolecular dissociation of the excited Aun?propene complexes. The cluster size (n=9–25) and temperature (T=90–300 K) dependence of the propene adsorption is analyzed. Strong size dependences of the absorption reaction are observed; a larger propene adsorption probability was found for gold clusters composed of an even number of atoms. Propene binding energies are estimated by comparison of the temperature‐dependent unimolecular dissociation rates with rates obtained by using statistical RRKM modeling. The Aun–propene binding energies decrease non‐monotonously with cluster size and are in the range of 1.2–0.85 eV for n=9–25. Finally, the bonding of C3H6 on Aun is qualitatively described and similarities with the absorption of CO molecules on gold clusters are discussed. 相似文献
39.
Let S be a semigroup. We study the structure of graded-simple S-graded algebras A and the exponential rate PIexp S-gr(A):= limn→∞ \(\sqrt[n]{{c_n^{S - gr}\left( A \right)}}\) of growth of codimensions c n S-gr (A) of their graded polynomial identities. This is of great interest since such algebras can have non-integer PIexp S-gr(A) despite being finite dimensional and associative. In addition, such algebras can have a non-trivial Jacobson radical J(A). All this is in strong contrast with the case when S is a group since in the group case J(A) is trivial, PIexp S-gr(A) is always integer and, if the base field is algebraically closed, then PIexp S-gr(A) equals dimA. Without any restrictions on the base field F, we classify graded-simple S-graded algebras A for a class of semigroups S which is complementary to the class of groups. We explicitly describe the structure of J(A) showing that J(A) is built up of pieces of a maximal S-graded semisimple subalgebra of A which turns out to be simple. When F is algebraically closed, we get an upper bound for \({\overline {\lim } _{n \to \infty }}\sqrt[n]{{c_n^{S - gr}\left( A \right)}}\). If A/J(A) ≈ M 2(F) and S is a right zero band, we show that this upper bound is sharp and PIexp S-gr(A) indeed exists. In particular, we present an infinite family of graded-simple algebras A with arbitrarily large non-integer PIexp S-gr(A). 相似文献
40.