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951.
Hutchison C Ganeev RA Witting T Frank F Okell WA Tisch JW Marangos JP 《Optics letters》2012,37(11):2064-2066
We present a method for the creation of stable weakly ionized plasmas from laser ablation of solid targets using a 1 kHz pulse repetition rate laser, which can be used for stable high-order harmonic generation from plasma plumes. The plasma plumes were generated from cylindrical rotating targets. Without target rotation the intensity of harmonics in the 40-80 nm range drops by more than one order of magnitude during less than 10(3) shots, while, with rotation of the target at typically 30 revolutions per minute, stable emission of high-order harmonics from aluminum plasma plumes with variation of less than 10% was maintained for >10(6) laser shots. 相似文献
952.
Griesmaier A Stuhler J Koch T Fattori M Pfau T Giovanazzi S 《Physical review letters》2006,97(25):250402
We have measured the relative strength epsilon dd of the magnetic dipole-dipole interaction compared with the contact interaction in a dipolar chromium Bose-Einstein condensate. We analyze the asymptotic velocities of expansion of the condensate with different orientations of the atomic magnetic moments. By comparing the experimental results with numerical solutions of the hydrodynamic equations for dipolar condensates, we obtain epsilon dd = 0.159+/-0.034. We use this result to determine the s-wave scattering length a = (5.08+/-1.06 x 10(-9)) m = (96+/-20) a0 of 52Cr. This is fully consistent with our previous measurements on the basis of Feshbach resonances and therefore confirms the validity of the theoretical approach used to describe the dipolar Bose-Einstein condensate. 相似文献
953.
We establish a general scaling law for the entanglement of a large class of ground states and dynamically evolving states of quantum spin chains: we show that the geometric entropy of a distinguished block saturates, and hence follows an entanglement-boundary law. These results apply to any ground state of a gapped model resulting from dynamics generated by a local Hamiltonian, as well as, dually, to states that are generated via a sudden quench of an interaction as recently studied in the case of dynamics of quantum phase transitions. We achieve these results by exploiting ideas from quantum information theory and tools provided by Lieb-Robinson bounds. We also show that there exist noncritical fermionic systems and equivalent spin chains with rapidly decaying interactions violating this entanglement-boundary law. Implications for the classical simulatability are outlined. 相似文献
954.
Combinatorial auctions are formulated as frustrated lattice gases on sparse random graphs, allowing the determination of the optimal revenue by methods of statistical physics. Transitions between computationally easy and hard regimes are found and interpreted in terms of the geometric structure of the space of solutions. We introduce an iterative algorithm to solve intermediate and large instances, and discuss competing states of optimal revenue and maximal number of satisfied bidders. The algorithm can be generalized to the hard phase and to more sophisticated auction protocols. 相似文献
955.
Stefan Kedenburg Andy Steinmann Robin Hegenbarth Tobias Steinle Harald Giessen 《Applied physics. B, Lasers and optics》2014,117(3):803-816
We use liquid-filled capillary fibers with different core diameters to precisely characterize the nonlinear refractive index of the highly nonlinear liquids carbon disulfide, nitrobenzene, and toluene. We present measurements with two different femtosecond pump sources at wavelengths of 1032 and 1560 nm. The large nonlinearity of the liquids results from the retarded nonlinear optical response of the liquid molecules which includes a strong non-instantaneous contribution due to molecular reorientation. The nonlinear refractive index of the liquids is determined by fitting numerical simulations based on solving the generalized nonlinear Schrödinger equation including retarded response to the measured broadened output spectra. Our work is important for the novel field of near- and mid-IR supercontinuum generation in liquid-core optical fibers. 相似文献
956.
Frank?Hubenthal Nils?Borg Tobias?Weidner Ulrich?Siemeling Frank?Tr?ger 《Applied Physics A: Materials Science & Processing》2009,94(1):11-17
In this contribution we demonstrate that densely packed gold nanoparticles can be grown by Volmer–Weber mode on ferrocenyl
functionalized terpyridine (FcTerp) on graphite. FcTerp forms highly ordered and dense self-assembled monolayers (SAMs) on
graphite which significantly reduces the diffusion length of gold atoms and increases the sticking coefficient compared to
bare graphite. Both effects lead to an increased nucleation and thus, to the growth of densely packed gold nanoparticles with
diameters in the nanometer range. The optical properties of the nanoparticles as well as their morphology and the structure
of the SAMs were characterized by optical extinction spectroscopy and scanning tunneling microscopy. 相似文献
957.
Bernhard Lamprecht Elke Kraker Martin Sagmeister Stefan Köstler Nicole Galler Harald Ditlbacher Birgit Ungerböck Tobias Abel Torsten Mayr 《固体物理学:研究快报》2011,5(9):344-346
We present a novel optical sensor platform, combining monolithically integrated ring‐like sensor waveguides together with ring‐shaped thin‐film organic photodiodes (OPDs) on one substrate. The OPDs serve as integrated light detectors, simplifying the detection system by minimizing the number of required optical components. The waveguide structures, including a means of coupling light in and out of the waveguides, serve as sensing elements. The functionality of the concept is demonstrated by an integrated carbon dioxide sensor, utilizing absorbance as sensing principle. The integrated optical sensor platform is suitable for the parallel detection of multiple parameters in a single sensor chip using sensor arrays. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
958.
D. Filges F. Goldenbaum M. Enke J. Galin C.-M. Herbach D. Hilscher U. Jahnke A. Letourneau B. Lott R.-D. Neef K. Nünighoff N. Paul A. Péghaire L. Pienkowski H. Schaal U. Schröder G. Sterzenbach A. Tietze V. Tishchenko J. Toke M. Wohlmuther 《The European Physical Journal A - Hadrons and Nuclei》2001,11(4):467-490
A recent renascent interest in energetic proton-induced production of neutrons originates largely from the inception of projects
for target stations of intense spallation neutron sources, like the planned European Spallation Source (ESS), accelerator-driven
nuclear reactors, nuclear waste transmutation, and also from the application for radioactive beams. In the framework of such
a neutron production, of major importance is the search for ways for the most efficient conversion of the primary beam energy
into neutron production. Although the issue has been quite successfully addressed experimentally by varying the incident proton
energy for various target materials and by covering a huge collection of different target geometries --providing an exhaustive
matrix of benchmark data-- the ultimate challenge is to increase the predictive power of transport codes currently on the
market. To scrutinize these codes, calculations of reaction cross-sections, hadronic interaction lengths, average neutron
multiplicities, neutron multiplicity and energy distributions, and the development of hadronic showers are confronted with
recent experimental data of the NESSI collaboration. Program packages like HERMES, LCS or MCNPX master the prevision of reaction
cross-sections, hadronic interaction lengths, averaged neutron multiplicities and neutron multiplicity distributions in thick
and thin targets for a wide spectrum of incident proton energies, geometrical shapes and materials of the target generally
within less than 10% deviation, while production cross-section measurements for light charged particles on thin targets point
out that appreciable distinctions exist within these models.
Received: 22 May 2001 / Accepted: 3 September 2001 相似文献
959.
Thomas Gottschall Tobias Meyer Martin Baumgartl Cesar Jauregui Michael Schmitt Jürgen Popp Jens Limpert Andreas Tünnermann 《Laser \u0026amp; Photonics Reviews》2015,9(5):435-451
During the past decade coherent anti‐Stokes Raman scattering (CARS) microscopy has evolved to one of the most powerful imaging techniques in the biomedical sciences, enabling the label‐free visualization of the chemical composition of tissue in vivo in real time. While the acquisition of high‐contrast images of single cells up to large tissue sections enables a wide range of medical applications from routine diagnostics to surgical guidance, to date CARS imaging is employed in fundamental research only, essentially because the synchronized multiple wavelength pulsed laser sources required for CARS microscopy are large, expensive and require regular maintenance. Laser sources based on optical fibers can overcome these limitations combining highest efficiency and peak powers with an excellent spatial beam profile and thermal stability. In this review we summarize the different fiber‐based approaches for laser sources dedicated to coherent Raman imaging, in particular active fiber technology and passive fiber‐based frequency conversion processes, i.e. supercontinuum generation, soliton self‐frequency shift and four‐wave mixing. We re‐evaluate the ideal laser parameters for CARS imaging and discuss the suitability of different laser concepts for turn‐key operation required for routine application in clinics.
960.
Sann H Jahnke T Havermeier T Kreidi K Stuck C Meckel M Schöffler MS Neumann N Wallauer R Voss S Czasch A Jagutzki O Weber T Schmidt-Böcking H Miyabe S Haxton DJ Orel AE Rescigno TN Dörner R 《Physical review letters》2011,106(13):133001
We doubly ionize H(2)O by single photon absorption at 43 eV leading to H(+) + OH(+). A direct double ionization and a sequential process in which single ionization is followed by rapid dissociation into a proton and an autoionizing OH(*) are identified. The angular distribution of this delayed autoionization electron shows a preferred emission in the direction of the emitted proton. From this diffraction feature we obtain internuclear distances of 700 to 1100 a.u. at which the autoionization of the OH(*) occurs. The experimental findings are in line with calculations of the excited potential energy surfaces and their lifetimes. 相似文献