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Clement Levard F. Marc Michel Yingge Wang Yongseong Choi Peter Eng Gordon E. Brown Jr 《Journal of synchrotron radiation》2011,18(6):871-878
Characterizing interfacial reactions is a crucial part of understanding the behavior of nanoparticles in nature and for unlocking their functional potential. Here, an advanced nanostructure characterization approach to study the corrosion processes of silver nanoparticles (Ag‐Nps), currently the most highly produced nanoparticle for nanotechnology, is presented. Corrosion of Ag‐Nps under aqueous conditions, in particular in the presence of organic matter and halide species common to many natural environments, is of particular importance because the release of toxic Ag+ from oxidation/dissolution of Ag‐Nps may strongly impact ecosystems. In this context, Ag‐Nps capped with polyvinolpyrrolidone (PVP) in contact with a simple proxy of organic matter in natural waters [polyacrylic acid (PAA) and Cl? in solution] has been investigated. A combination of synchrotron‐based X‐ray standing‐wave fluorescence yield‐ and X‐ray diffraction‐based experiments on a sample consisting of an approximately single‐particle layer of Ag‐Nps deposited on a silicon substrate and coated by a thin film of PAA containing Cl revealed the formation of a stable AgCl corrosion product despite the presence of potential surface stabilizers (PVP and PAA). Diffusion and precipitation processes at the Ag‐Nps–PAA interface were characterized with a high spatial resolution using this new approach. 相似文献
64.
Anfosso-Lédée F Dangla P Bérengier M 《The Journal of the Acoustical Society of America》2007,122(2):731-736
Acoustic impedance of an absorbing interface is easily introduced in boundary element codes provided that a local reaction is assumed. But this assumption is not valid in the case of porous road surface. A two-domain approach was developed for the prediction of sound propagation above a porous layer that takes into account the sound propagation inside the porous material. The porous material is modeled by a homogeneous dissipative fluid medium. An alternative to this time consuming two-domain approach is proposed by using the grazing incidence approximate impedance in the traditional single-domain boundary element method (BEM). It can be checked that this value is numerically consistent with the surface impedance calculated at the interface from the pressure and surface velocity solutions of the two-domain approach. The single-domain BEM introducing this grazing incidence impedance is compared in terms of sound attenuation with analytical solutions and two-domain BEM. The comparison is also performed with the single-domain BEM using the normal incidence impedance, and reveals a much better accuracy for the prediction of sound propagation above a porous interface. 相似文献
65.
V. Doya O. Legrand C. Michel F. Mortessagne 《The European physical journal. Special topics》2007,145(1):49-61
We propose to use a multimode optical fiber with a D-shaped cross section as a privileged system to image wavefunctions of
a chaotic system. Scar modes are in particular the subject of our investigations. We study their imprints on the statistics
of intensity and we show how the introduction of a localized gain region in the fiber is used to perform a selective amplification
of scar modes. 相似文献
66.
Pump−probe experiments at the TEMPO beamline using the low‐α operation mode of Synchrotron SOLEIL 下载免费PDF全文
Mathieu G. Silly Tom Ferté Marie Agnes Tordeux Debora Pierucci Nathan Beaulieu Christian Chauvet Federico Pressacco Fausto Sirotti Horia Popescu Victor Lopez-Flores Marina Tortarolo Maurizio Sacchi Nicolas Jaouen Philippe Hollander Jean Paul Ricaud Nicolas Bergeard Christine Boeglin Bharati Tudu Renaud Delaunay Jan Luning Gregory Malinowski Michel Hehn Cédric Baumier Franck Fortuna Damjan Krizmancic Luigi Stebel Rudi Sergo Giuseppe Cautero 《Journal of synchrotron radiation》2017,24(4):886-897
The SOLEIL synchrotron radiation source is regularly operated in special filling modes dedicated to pump–probe experiments. Among others, the low‐α mode operation is characterized by shorter pulse duration and represents the natural bridge between 50 ps synchrotron pulses and femtosecond experiments. Here, the capabilities in low‐α mode of the experimental set‐ups developed at the TEMPO beamline to perform pump–probe experiments with soft X‐rays based on photoelectron or photon detection are presented. A 282 kHz repetition‐rate femtosecond laser is synchronized with the synchrotron radiation time structure to induce fast electronic and/or magnetic excitations. Detection is performed using a two‐dimensional space resolution plus time resolution detector based on microchannel plates equipped with a delay line. Results of time‐resolved photoelectron spectroscopy, circular dichroism and magnetic scattering experiments are reported, and their respective advantages and limitations in the framework of high‐time‐resolution pump–probe experiments compared and discussed. 相似文献
67.
A high-power linearly polarized Yb-doped silica fiber master oscillator power amplifier at 1150 nm is reported. It produced 3.35 W cw and 2.33 W of average power in 1 micros pulses at a 100 kHz repetition rate, both with 8 pm linewidth. This is the first report, to the best of our knowledge, of a high-power Yb-doped fiber amplifier at a wavelength longer than 1135 nm. The pulsed output was frequency doubled in a bulk periodically poled near-stoichiometric LiTaO(3) chip to generate 976 mW of average power at 575 nm with an overall system optical-to-optical efficiency of 9.8% with respect to launched pump power. 相似文献
68.
Parthey CG Matveev A Alnis J Bernhardt B Beyer A Holzwarth R Maistrou A Pohl R Predehl K Udem T Wilken T Kolachevsky N Abgrall M Rovera D Salomon C Laurent P Hänsch TW 《Physical review letters》2011,107(20):203001
We have measured the 1S-2S transition frequency in atomic hydrogen via two-photon spectroscopy on a 5.8 K atomic beam. We obtain f(1S-2S) = 2,466,061,413,187,035 (10) Hz for the hyperfine centroid, in agreement with, but 3.3 times better than the previous result [M. Fischer et al., Phys. Rev. Lett. 92, 230802 (2004)]. The improvement to a fractional frequency uncertainty of 4.2 × 10(-15) arises mainly from an improved stability of the spectroscopy laser, and a better determination of the main systematic uncertainties, namely, the second order Doppler and ac and dc Stark shifts. The probe laser frequency was phase coherently linked to the mobile cesium fountain clock FOM via a frequency comb. 相似文献
69.
Michel Perrottet 《Annals of Physics》1978,115(1):107-135
The front-back asymmetry of outgoing muons in the inclusive reaction anything is calculated in the framework of the Drell-Yan model. We get very general expressions for the front-back asymmetry and the differential cross section in terms of the weak coupling constants and the parton distributions. Results for W± production and proton-proton collisions are also given. Numerical estimates are made using various parton distributions and the Weinberg-Salam model for definiteness. We comment on the predictions of gauge theories that accommodate the absence of parity violating effects in atomic physics. We also give a new estimate of the inclusive cross sections or pp → Z(→ μ+μ?) or W±(→ μ±νμ) + anything. The effects of asymptotic freedom in the frontback asymmetries and the total cross sectons are investigated. We reanalyze results for the purely leptonic reaction e+e? → γ, Z → μ+μ?. 相似文献
70.
Emmanuelle Canet Didier Revel Rmy Forrat Claire Baldy-Porcher Michel de Lorgeril Laurent Sebbag Jean-Paul Vallee Dominique Didier Michel Amiel 《Magnetic resonance imaging》1993,11(8):1139-1145
Superparamagnetic iron oxide particles (SPIOs) are usually referred to as T2 MR contrast agents, reducing signal intensity (SI) on T2-weighted MR images (negative enhancement). This study reports the original use of SPIOs as T1-enhancing contrast agents, primarily assessed in vitro, and then applied to an in vivo investigation of a myocardial perfusion defect. Using a strongly T1-weighted subsecond MR sequence with SPIOs intravenous (IV) bolus injection, MR imaging of myocardial vascularization after reperfusion was performed, on a dog model of coronary occlusion followed by reperfusion. Immediately after the intravenous bolus injection of 20 μmol/kg of SPIOs, a positive signal intensity enhancement was observed respectively, in the right and left ventricular cavity and in the nonischemic left myocardium. Moreover, compared to normal myocardium, the remaining ischemic myocardial region (anterior wall of the left ventricle) appeared as a lower and delayed SI enhancing area (cold spot). Mean peak SIE in the nonischemic myocardium (posterior wall) was significantly higher than in the ischemic myocardium (anterior wall) (110 ± 23% vs. 74 ± 22%, Mann-Whitney test < 1%, n1 = 6, n2 − n1 = 0, U > 2). In conclusion, the T1 effect of SPIOs at low dose, during their first intravascular distribution, suggests their potential use as positive markers to investigate the regional myocardial blood flow and some perfusion defects such as the “no-reflow phenomenon”. 相似文献