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941.
Frank?Pf?ffle Christoph?A.?StephanEmail author 《Communications in Mathematical Physics》2011,307(1):261-273
We investigate the Holst action for closed Riemannian 4-manifolds with orthogonal connections. For connections whose torsion
has zero Cartan type component we show that the Holst action can be recovered from the heat asymptotics for the natural Dirac
operator acting on left-handed spinor fields. 相似文献
942.
Frank?Calegari Scott?Morrison Noah?SnyderEmail author 《Communications in Mathematical Physics》2011,303(3):845-896
Dimensions of objects in fusion categories are cyclotomic integers, hence number theoretic results have implications in the
study of fusion categories and finite depth subfactors. We give two such applications. The first application is determining
a complete list of numbers in the interval (2, 76/33) which can occur as the Frobenius-Perron dimension of an object in a
fusion category. The smallest number on this list is realized in a new fusion category which is constructed in the Appendix
written by V. Ostrik, while the others are all realized by known examples. The second application proves that in any family
of graphs obtained by adding a 2-valent tree to a fixed graph, either only finitely many graphs are principal graphs of subfactors
or the family consists of the A
n
or D
n
Dynkin diagrams. This result is effective, and we apply it to several families arising in the classification of subfactors
of index less than 5. 相似文献
943.
Entanglement entropy appears as a central property of quantum systems in broad areas of physics. However, its precise value is often sensitive to unknown microphysics, rendering it incalculable. By considering parametric dependence on correlation length, we extract finite, calculable contributions to the entanglement entropy for a scalar field between the interior and exterior of a spatial domain of arbitrary shape. The leading term is proportional to the area of the dividing boundary; we also extract finite subleading contributions for a field defined in the bulk interior of a waveguide in 3+1 dimensions, including terms proportional to the waveguide's cross-sectional geometry: its area, perimeter length, and integrated curvature. We also consider related quantities at criticality and suggest a class of systems for which these contributions might be measurable. 相似文献
944.
The change in energy of an ideal Fermi gas when a local one-body potential is inserted into the system, or when the density is changed locally, are important quantities in condensed matter physics. We show that they can be rigorously bounded from below by a universal constant times the value given by the semiclassical approximation. 相似文献
945.
A generic bubble structure in a 230 kHz ultrasonic field is observed in a partly developed standing wave field in water. It is characterized by high-speed imaging, sonoluminescence recordings, and surface cleaning tests. The structure has two distinct bubble populations. Bigger bubbles (much larger than linear resonance size) group on rings in planes parallel to the transducer surface, apparently in locations of driving pressure minima. They slowly rise in a jittering, but synchronous way, and they can have smaller satellite bubbles, thus resembling the arrays of bubbles observed by Miller [D. Miller, Stable arrays of resonant bubbles in a 1-MHz standing-wave acoustic field, J. Acoust. Soc. Am. 62 (1977) 12]. Smaller bubbles (below and near linear resonance size) show a fast "streamer" motion perpendicular to and away from the transducer surface. While the bigger bubbles do not emit light, the smaller bubbles in the streamers show sonoluminescence when they pass the planes of high driving pressure. Both bubble populations exhibit cleaning potential with respect to micro-particles attached to a glass substrate. The respective mechanisms of particle removal, though, might be different. 相似文献
946.
Juraj Racko Miroslav Mikolá?ek Ralf Granzner Juraj Breza Daniel Donoval Alena Grmanová Ladislav Harmatha Frank Schwierz Karol Fr?hlich 《Central European Journal of Physics》2011,9(1):230-241
A new model is presented of current transport in Metal Insulator Metal (MIM) structures by quantum mechanical tunnelling.
In addition to direct tunnelling through an insulating layer, tunnelling via defects present in the insulating layer plays
an important role. Examples of the influence of the material and thickness of the insulating layer, energy distribution of
traps, and metal work functions are also provided. 相似文献
947.
Stefan Buschhorn Frank Brüssing Radu Abrudan Hartmut Zabel 《Journal of synchrotron radiation》2011,18(2):212-216
A new set‐up is presented to measure element‐selective magnetization dynamics using the ALICE chamber [Grabis et al. (2003), Rev. Sci. Instrum. 74 , 4048–4051] at the BESSY II synchrotron at the Helmholtz‐Zentrum Berlin. A magnetic‐field pulse serves as excitation, and the magnetization precession is probed by element‐selective X‐ray resonant magnetic scattering. With the use of single‐bunch‐generated X‐rays a temporal resolution well below 100 ps is reached. The ALICE diffractometer environment enables investigations of thin films, described here, multilayers and laterally structured samples in reflection or diffuse scattering geometry. The combination of the time‐resolved set‐up with a cryostat in the ALICE chamber will allow temperature‐dependent studies of precessional magnetization dynamics and of damping constants to be conducted over a large temperature range and for a large variety of systems in reflection geometry. 相似文献
948.
Ye Sun Stela Canulescu Peijie Sun Frank Steglich Nini Pryds Jørgen Schou Bo Brummerstedt Iversen 《Applied Physics A: Materials Science & Processing》2011,104(3):883-887
Thermoelectric FeSb2 films were produced by pulsed laser deposition on silica substrates in a low-pressure Ar environment. The growth conditions
for near phase-pure FeSb2 films were confirmed to be optimized at a substrate temperature of 425°C, an Ar pressure of 2 Pa, and deposition time of
3 h by ablating specifically prepared compound targets made of Fe and Sb powders in atomic ratio of 1:4. The thermoelectric
transport properties of FeSb2 films were investigated. Pulsed laser deposition was demonstrated as a method for production of good-quality FeSb2 films. 相似文献
949.
At the LHC and Tevatron strong initial-state radiation (ISR) plays an important role. It can significantly affect the partonic luminosity available to the hard interaction or contaminate a signal with additional jets and soft radiation. An ideal process to study ISR is isolated Drell-Yan production, pp → X?+ ?- without central jets, where the jet veto is provided by the hadronic event shape beam thrust τB. Most hadron collider event shapes are designed to study central jets. In contrast, requiring τ B < 1 provides an inclusive veto of central jets and measures the spectrum of ISR. For τ B < 1 we carry out a resummation of α s(n)ln(m)τ B corrections at next-to-next-to-leading-logarithmic order. This is the first resummation at this order for a hadron-hadron collider event shape. Measurements of τ B at the Tevatron and LHC can provide crucial tests of our understanding of ISR and of τ B's utility as a central jet veto. 相似文献
950.
William J. Durand Andrew A. Peterson Felix Studt Frank Abild-Pedersen Jens K. Nørskov 《Surface science》2011,605(15-16):1354-1359
Polycrystalline copper electrocatalysts have been experimentally shown to be capable of reducing CO2 into CH4 and C2H4 with relatively high selectivity, and a mechanism has recently been proposed for this reduction on the fcc(211) surface of copper, which was assumed to be the most active facet. In the current work, we use computational methods to explore the effects of the nanostructure of the copper surface and compare the effects of the fcc(111), fcc(100) and fcc(211) facets of copper on the energetics of the electroreduction of CO2. The calculations performed in this study generally show that the intermediates in CO2 reduction are most stabilized by the (211) facet, followed by the (100) facet, with the (111) surface binding the adsorbates most weakly. This leads to the prediction that the (211) facet is the most active surface among the three in producing CH4 from CO2, as well as the by-products H2 and CO. HCOOH production may be mildly enhanced on the more close-packed surfaces ((111) and (100)) as compared to the (211) facet, due to a change in mechanism from a carboxyl intermediate to a formate intermediate. The results are compared to published experimental data on these same surfaces; the predicted trends in voltage requirements are consistent between the experimental and computational data. 相似文献