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81.
A. L. Lapolli A. W. Carbonari J. Mestnik-Filho D. M. T. Leite R. N. Saxena 《Hyperfine Interactions》2007,176(1-3):75-79
Perturbed gamma-gamma angular correlation (PAC) technique was used to measure the hyperfine interactions in the intermetallic compound GdPdIn using 111In→ 111Cd and 140La→ 140Ce probe nuclei at the In and Gd sites, respectively. The PAC results for 111Cd show two well-defined electric quadrupole frequencies above T C assigned to probes occupying Gd and In sites, with ~50% of site occupation each. The fraction corresponding to In sites increases with temperature reaching 95% around 500 K. Below T C the measurements for 111Cd probe showed combined electric quadrupole plus magnetic dipole interaction with sharp increase in the magnetic field below around 80 K. A pure magnetic interaction with lower hyperfine field values was observed at the Gd sites occupied by 140Ce below 100 K. 相似文献
82.
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84.
The cosmological constant problem is examined within the context of the covariant brane-world gravity, based on Nash’s embedding
theorem for Riemannian geometries. We show that the vacuum structure of the brane-world is more complex than General Relativity’s
because it involves extrinsic elements, in specific, the extrinsic curvature. In other words, the shape (or local curvature)
of an object becomes a relative concept, instead of the “absolute shape” of General Relativity. We point out that the immediate
consequence is that the cosmological constant and the energy density of the vacuum quantum fluctuations have different physical
meanings: while the vacuum energy density remains confined to the four-dimensional brane-world, the cosmological constant
is a property of the bulk’s gravitational field that leads to the conclusion that these quantities cannot be compared, as
it is usually done in General Relativity. Instead, the vacuum energy density contributes to the extrinsic curvature, which
in turn generates Nash’s perturbation of the gravitational field. On the other hand, the cosmological constant problem ceases
to be in the brane-world geometry, reappearing only in the limit where the extrinsic curvature vanishes. 相似文献
85.
D. Wardecki R. Przeniosło A. N. Fitch M. Bukowski R. Hempelmann 《Journal of nanoparticle research》2011,13(3):1151-1161
The microstructure of electrodeposited nanocrystalline chromium (n-Cr) was studied by using synchrotron radiation (SR) diffraction,
SEM, TEM, and EDX techniques. The as-prepared n-Cr samples show the standard bcc crystal structure of Cr with volume-averaged
column lengths varying from 25 to 30 nm. The grain growth kinetics and the oxidation kinetics were studied by time resolved
SR diffraction measurements with n-Cr samples annealed at 400, 600, and 800 °C. The grain growth process is relatively fast
and it occurs within the first 10 min of annealing. The final crystallite size depends only on the annealing temperature and
not on the initial grain size or on the oxygen content. The final volume-averaged column lengths observed after 50 min annealing
are 40(4), 80(1), and 120(2) nm for temperatures 400, 600, and 800 °C, respectively. It is shown that annealing ex situ of
n-Cr at 800 °C both under vacuum and in air gives a grain growth process with the same final crystallite sizes. The formation
of the Cr2O3 and CrH phases is observed during annealing. 相似文献
86.
Eduardo de Almeida Paulo Rogério Massoni Amauri Antonio Menegário Laudi Cunha Leite Dante Pazzanese Duarte Lanna Virgílio Franco do Nascimento Filho 《X射线光谱测定》2011,40(6):424-426
This article describes a comparison of conventional energy‐dispersive X‐ray fluorescence (EDXRF) and synchrotron radiation total‐reflection X‐ray fluorescence (SRTXRF) for Co determination in ruminal fluid from Holstein cow. This element is used as marker for animal nutrition studies. For EDXRF, 200 µl of the sample were dried on 6.35 µm Mylar film at 60 °C. The excitation was carried out using an X‐ray tube with Mo target and Zr filter operated at 30 kV/20 mA. For SRTXRF, 10 µl of the sample were pipetted on a Lucite carrier and dried at 60 °C. In both the techniques, Ga was used as internal standard and the acquisition time was 200 s. The trueness of both techniques was evaluated through the standard addition method, the recoveries obtained by SRTXRF and EDXRF were 76 and 99%, and the limits of detection, 13 and 240 µg l?1, respectively. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
87.
Miniussi E Pozzo M Baraldi A Vesselli E Zhan RR Comelli G Menteş TO Niño MA Locatelli A Lizzit S Alfè D 《Physical review letters》2011,106(21):216101
We report on a novel approach to determine the relationship between the corrugation and the thermal stability of epitaxial graphene grown on a strongly interacting substrate. According to our density functional theory calculations, the C single layer grown on Re(0001) is strongly corrugated, with a buckling of 1.6 ?, yielding a simulated C 1s core level spectrum which is in excellent agreement with the experimental one. We found that corrugation is closely knit with the thermal stability of the C network: C-C bond breaking is favored in the strongly buckled regions of the moiré cell, though it requires the presence of diffusing graphene layer vacancies. 相似文献
88.
Tatiane M. Arantes Giovanni P. Mambrini Daniel G. Stroppa Edson R. Leite Elson Longo Antonio J. Ramirez Emerson R. Camargo 《Journal of nanoparticle research》2010,12(8):3105-3110
Nanocrystalline zirconium oxide was synthesized by hydrothermal treatment of ZrO(NO3)2 and ZrOCl2 aqueous solutions at different temperatures and time in presence of hydrogen peroxide. Hydrothermal treatment of zirconium salts (0.25 and 0.50 mol L?1) produced nanocrystalline monoclinic ZrO2 powders with narrow size distribution, which were formed by the attachment of the smaller particles with crystallites size of 3.5 nm, estimated by means of the Scherrer’s equation and confirmed by transmission electronic microscopy. Typical monoclinic zirconium oxide X-ray powder diffraction patterns and Raman spectra were obtained for all the crystalline powders. It was observed that the crystallization depends strongly on the temperature, resulting in amorphous material when the synthesis was realized at 100 °C, and crystalline with monoclinic phase when synthesized at 110 °C, independently of the salt used. Zirconium oxide colloidal nanoparticles were formed only at hydrothermal treatments longer than 24 h. The stability of the colloids was successfully characterized of zeta potential, showing an initial value of + 59.2 mV in acid media and isoelectric point at pH = 5.2, in good agreement with previous studies. 相似文献
89.
P. M. Ferreira Jo?o P. Silva 《The European Physical Journal C - Particles and Fields》2010,69(1-2):45-52
We analyze generalized CP symmetries of two-Higgs doublet models, extending them from the scalar to the fermion sector of the theory. We show that, other than the usual CP transformation, there is only one of those symmetries which does not imply massless charged fermions. That single model which accommodates a fermionic mass spectrum compatible with experimental data possesses a remarkable feature. Through a soft breaking of the symmetry it displays a new type of spontaneous CP violation, which does not occur in the scalar sector responsible for the symmetry breaking mechanism but, rather, in the fermion sector. 相似文献
90.
Leitão JM Esteves da Silva JC Girón AJ Muñoz de la Peña A 《Journal of fluorescence》2008,18(6):1065-1076
Excitation emission fluorescence matrices (EEMs) of Verapamil drug were obtained by direct and by derivatization fluorescence
spectroscopy. The fluorescence excitation and emission wavelengths were displaced to longer wavelengths and the fluorescence
intensity was enhanced upon derivation with respect to the native fluorescence of the drug. The complete EEM of the native
fluorescence of the drug and of the derivatization product were rapidly acquired by using a charged-coupled device detector
(CCD), which is advantageous in terms of speed in the analysis, with respect to the use of a conventional photomultiplier
detector. The EEMs were analyzed by several second-order multivariate calibration methods exploiting the second order advantage.
The three-dimensional decomposition methods used, based in different assumptions about the trilinearity of the three way data
structure under analysis, were parallel factor analysis (PARAFAC), bilinear least squares (BLLS), parallel factor analysis
2 (PARAFAC2) and multivariate curve resolution—alternating least squares (MCR-ALS). The determination was performed by using
the standard addition approach. The figures of merit of the PARAFAC and BLLS methods were calculated, obtaining a lower limit
of detection with the derivatization procedure, when compared with the direct measurement of the fluorescence of the drug.
In Verapamil drug the best estimations were found with the BLLS and the MCR-ALS models. In the quantification of Verapamil
in a pharmaceutical formulation the best estimation, when compared with the result obtained by the US Pharmacopeia high performance
liquid chromatography approach, was obtained by direct fluorescence spectroscopy with MCR-ALS and by derivatization fluorescence
spectroscopy with the PARAFAC2 model. 相似文献