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71.
Small amounts of crystallinity may be present in “amorphous” alloy specimens in the form of “cast-in” crystallites or partially crystallized surfaces. in this paper the possible effects of such low-level crystallinity upon the measured electrical transport properties are considered. It is found that the observed ageing effects in the transport properties of a number of amorphous alloys may be explained as due to surface crystallization driven by selective oxidation. It is further argued that for the ferromagnetic Metglasses cast-in crystallites could have a significant effect particularly upon the thermopower, and that this is probably part of the explanation of the observed discrepancies between the different measured values. It is shown that even very small levels of crystallinity can have significant effects upon the measured transport properties and the many disagreements to be found in the published values are discussed in the light of this. 相似文献
72.
Edmonds KW van der Laan G Freeman AA Farley NR Johal TK Campion RP Foxon CT Gallagher BL Arenholz E 《Physical review letters》2006,96(11):117207
Remarkably anisotropic Mn L2,3 x-ray magnetic circular dichroism spectra from the ferromagnetic semiconductor (Ga,Mn)As are reported. States with cubic and uniaxial symmetry are distinguished by careful analysis of the angle dependence of the spectra. The multiplet structures with cubic symmetry are qualitatively reproduced by calculations for an atomiclike d5 configuration in tetrahedral environment, and show zero anisotropy in the orbital and spin moments within the experimental uncertainty. However, hybridization with the host valence bands is reflected by the presence of a preedge feature with a uniaxial anisotropy and a marked dependence on the hole density. 相似文献
73.
Mašek J Máca F Kudrnovský J Makarovsky O Eaves L Campion RP Edmonds KW Rushforth AW Foxon CT Gallagher BL Novák V Sinova J Jungwirth T 《Physical review letters》2010,105(22):227202
We analyze microscopically the valence and impurity band models of ferromagnetic (Ga,Mn)As. We find that the tight-binding Anderson approach with conventional parametrization and the full potential local-density approximation+U calculations give a very similar band structure whose microscopic spectral character is consistent with the physical premise of the k·p kinetic-exchange model. On the other hand, the various models with a band structure comprising an impurity band detached from the valence band assume mutually incompatible microscopic spectral character. By adapting the tight-binding Anderson calculations individually to each of the impurity band pictures in the single Mn impurity limit and then by exploring the entire doping range, we find that a detached impurity band does not persist in any of these models in ferromagnetic (Ga,Mn)As. 相似文献
74.
In this paper we continue to develop an alternative viewpoint on recent studies of Navier–Stokes regularity in critical spaces, a program which was started in the recent work by Kenig and Koch (Ann Inst H Poincaré Anal Non Linéaire 28(2):159–187, 2011). Specifically, we prove that strong solutions which remain bounded in the space ${L^3(\mathbb R ^3)}$ do not become singular in finite time, a known result established by Escauriaza et al. (Uspekhi Mat Nauk 58(2(350)):3–44, 2003) in the context of suitable weak solutions. Here, we use the method of “critical elements” which was recently developed by Kenig and Merle to treat critical dispersive equations. Our main tool is a “profile decomposition” for the Navier–Stokes equations in critical Besov spaces which we develop here. As a byproduct of this tool, assuming a singularity-producing initial datum for Navier–Stokes exists in a critical Lebesgue or Besov space, we show there is one with minimal norm, generalizing a result of Rusin and Sverak (J Funct Anal 260(3):879–891, 2011). 相似文献
75.
Adamson P Andreopoulos C Arms KE Armstrong R Auty DJ Ayres DS Baller B Barr G Barrett WL Becker BR Belias A Bernstein RH Bhattacharya D Bishai M Blake A Bock GJ Boehm J Boehnlein DJ Bogert D Bower C Buckley-Geer E Cavanaugh S Chapman JD Cherdack D Childress S Choudhary BC Coleman SJ Culling AJ de Jong JK Diwan MV Dorman M Dytman SA Escobar CO Evans JJ Falk Harris E Feldman GJ Frohne MV Gallagher HR Goodman MC Gouffon P Gran R Grashorn EW Grossman N Grzelak K Habig A Harris D Harris PG 《Physical review letters》2008,101(15):151601
A search for a sidereal modulation in the MINOS near detector neutrino data was performed. If present, this signature could be a consequence of Lorentz and CPT violation as predicted by the effective field theory called the standard-model extension. No evidence for a sidereal signal in the data set was found, implying that there is no significant change in neutrino propagation that depends on the direction of the neutrino beam in a sun-centered inertial frame. Upper limits on the magnitudes of the Lorentz and CPT violating terms in the standard-model extension lie between 10(-4) and 10(-2) of the maximum expected, assuming a suppression of these signatures by a factor of 10(-17). 相似文献
76.
Novák V Olejník K Wunderlich J Cukr M Výborný K Rushforth AW Edmonds KW Campion RP Gallagher BL Sinova J Jungwirth T 《Physical review letters》2008,101(7):077201
We observe a singularity in the temperature derivative drho/dT of resistivity at the Curie point of high-quality (Ga,Mn)As ferromagnetic semiconductors with Tc's ranging from approximately 80 to 185 K. The character of the anomaly is sharply distinct from the critical contribution to transport in conventional dense-moment magnetic semiconductors and is reminiscent of the drho/dT singularity in transition metal ferromagnets. Within the critical region accessible in our experiments, the temperature dependence on the ferromagnetic side can be explained by dominant scattering from uncorrelated spin fluctuations. The singular behavior of drho/dT on the paramagnetic side points to the important role of short-range correlated spin fluctuations. 相似文献
77.
H. Jamie Kim O. Tara Liyanage Marina R. Mulenos Elyssia S. Gallagher 《Journal of the American Society for Mass Spectrometry》2018,29(10):2030-2040
Characterizing glycans is analytically challenging since glycans are heterogeneous, branched polymers with different three-dimensional conformations. Hydrogen/deuterium exchange-mass spectrometry (HDX-MS) has been used to analyze native conformations and dynamics of biomolecules by measuring the mass increase of analytes as labile protons are replaced with deuterium following exposure to deuterated solvents. The rate of exchange is dependent on the chemical functional group, the presence of hydrogen bonds, pH, temperature, charge, and solvent accessibility. HDX-MS of carbohydrates is challenging due to the rapid exchange rate of hydroxyls. Here, we describe an observed HDX reaction associated with residual solvent vapors saturating electrospray sources. When undeuterated melezitose was infused after infusing D2O, samples with up to 73% deuterium exchange were detected. This residual solvent HDX was observed for both carbohydrates and peptides in multiple instruments and dependent on sample infusion rate, infusion time, and deuterium content of the solvent. This residual solvent HDX was observed over several minutes of sample analysis and persisted long enough to alter the measured deuterium labeling and possibly change the interpretation of the results. This work illustrates that residual solvent HDX competes with in-solution HDX for rapidly exchanging functional groups. Thus, we propose conditions to minimize this effect, specifically for top-down, in-electrospray ionization, and quench-flow HDX experiments. 相似文献
78.
M. Henini P. A. Crump P. J. Rodgers B. L. Gallagher A. J. Vickers G. Hill 《Journal of Crystal Growth》1995,150(1-4):446-450
We report on a series of Be-doped GaAs/AlGaAs two-dimensional hole gas (2DHG) structures grown on (110), (111)B, (211)B and (311)B oriented substrates and compare their properties with high-mobility samples grown on (311)A using Si doping. The samples were prepared and grown under the same conditions so as to render them comparable. They are found to have mobilities which are strongly anisotropic within the plane. The highest mobility is found on the (110) surface with 100,000 cm2 V−1 s−1, while the (211) surface gave the lowest values 10,000 cm2 V−1 s−1. However, the later samples are found to have quantum Hall effect critical currents of >70 μA: an exceptionally high value for a hole gas which makes them suitable for metrology. All the samples show strong low-field positive magnetoresistance with resistance increases of up to 30% at magnetic fields of only 0.1 T. The presence of this feature on all the different planes shows that it does not depend upon the details of the band structure. It is identified with the lifting of the degeneracy of the spin sub-bands by the asymmetrical potential giving rise to a classical two-band magnetoreresistance. 相似文献
79.
Giordano Paniconi Ronald I. Smith Bryan L. Gallagher 《Journal of solid state chemistry》2008,181(1):158-165
Zn3N2 powders were prepared by ammonolysis reactions at 600 °C and examined by thermogravimetric analysis, powder X-ray and neutron diffraction. The powders obtained in this way are unstable in an oxygen atmosphere above 450 °C. In an argon atmosphere, the powders are stable up to their decomposition point at around 700 °C. Structural models obtained from Rietveld refinements against the powder neutron diffraction data indicate that the Zn3N2 powders so-prepared have the anti-bixbyite structure and are almost certainly stoichiometric with no compelling evidence of nitrogen vacancies. Further, no evidence was found for aliovalent oxygen substitution at the nitrogen sites. The calculated bond valence sums imply that Zn3N2 cannot be described as a 100% ionic compound. The structural findings are supported by photoluminescence measurements that reveal a band gap of approximately 0.9 eV. 相似文献
80.
Variable temperature 1H NMR studies were conducted to investigate whether steric congestion is influencing the structural rigidity of (IMesH2)(PCy3)(Cl)2RuCHPh (IMesH2 = 1,3-dimesityl-4,5-dihydroimidazol-2-ylidene) in solution. It was shown that both mesityl ligands rotate at about the same rate around the N-Mesityl bonds in the IMesH2 ligand and that changing the solvent does not significantly alter this rotation. It was found that the increased steric congestion in (IMesH2)(PCy3)(Cl)2RuCHPh compared to (PCy3)2(Cl)2RuCHPh does affect the rates of rotation around the Calkylidene-Ph bonds. Unusual chemical shift positions were also observed in the low temperature 1H NMR spectrum for the aromatic proton signals for (IMesH2)(PCy3)(Cl)2RuCHPh and (PCy3)2(Cl)2RuCHPh. 相似文献