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921.
A novel compact supercontinuum (SC) source using the single mode photonic crystal fibers (PCF) pumped with an all fiber MOPA
fiber laser is demonstrated experimentally. A bandwidth of 700 nm is achieved by operating the pumping fiber laser at a wavelength
of 1064 nm, pulse duration of 10 ns, repetition rate of 50 kHz and peak power of 1 kW. The SC generation is initiated through
modulation instability (MI) which breakups the nanosecond pump pulses into picosecond or femtosecond pulses, and further broadened
through nonlinear effects of PCF. 相似文献
922.
L.Q. EnglishS.G. Wheeler Y. ShenG.P. Veldes N. WhitakerP.G. Kevrekidis D.J. Frantzeskakis 《Physics letters. A》2011,375(9):1242-1248
We study experimentally, analytically and numerically the backward-wave propagation, and formation of discrete bright and dark solitons in a nonlinear electrical lattice. We observe experimentally that a focusing (defocusing) effect occurs above (below) a certain carrier frequency threshold, and backward-propagating bright (dark) discrete solitons are formed. We develop a discrete model emulating the relevant circuit and benchmark its linear properties against the experimental dispersion relation. Using a perturbation method, we derive a nonlinear Schrödinger equation, that predicts accurately the carrier frequency threshold. Finally, we use numerical simulations to corroborate our findings and monitor the space-time evolution of the discrete solitons. 相似文献
923.
In this paper, we describe a new computer simulation technique of generating Fresnel diffraction images from rectangular apertures of arbitrary dimensions by using Fresnel integrals instead of the more common fast Fourier transform methods. The simulation can be performed in almost any PC using the software MATLAB. Diffraction images can be generated for any wavelength of light and for any aperture–screen and aperture-source distances. Images for rectangular obstacles can also be simulated. Details of the algorithm and program are presented, as well as the interesting insights than can be gained from using the program. Finally, it is shown that the simulated images reduce to the simple Fraunhofer diffraction patterns for certain limiting situations. 相似文献
924.
P. Servati A. Colli S. Hofmann Y.Q. Fu P. Beecher Z.A.K. Durrani A.C. Ferrari A.J. Flewitt J. Robertson W.I. Milne 《Physica E: Low-dimensional Systems and Nanostructures》2007,38(1-2):64
This paper presents photodetectors having vertically stacked electrodes with sub-micron (300 nm) separation based on silicon nanowire (SiNW) nanocomposites. The thin-film-like devices are made using standard photolithography instead of electron beam lithography and thus are amenable to scalable low-cost manufacturing. The processing technique is not limited to SiNWs and can be extended to different nanowires (NWs) (e.g., ZnO, CdSe) and substrates. The current–voltage characteristics show Schottky behaviour that is dependent on the properties of the contact metal and that of the pristine SiNWs. This makes these devices suitable for examination of electronic transport in SiNWs. Preliminary results for light sensitivity show promising photoresponse that is a function of effective NW density. 相似文献
925.
We grew SrTiO(3) on SrTiO(3)(001) by pulsed laser deposition, while observing x-ray diffraction at the (00(1/2)) position. The drop DeltaI in the x-ray intensity following a laser pulse contains information about plume-surface interactions. Kinematic theory predicts DeltaI/I = -4sigma(1 - sigma), so that DeltaI /I depends only on the amount of deposited material sigma. In contrast, we observed experimentally that |DeltaI /I| < 4sigma(1 - sigma) and that DeltaI /I depends on the phase of x-ray growth oscillations. The combined results suggest a fast smoothing mechanism that depends on surface step-edge density. 相似文献
926.
Y. B. Kale A. Ray N. Singh Q. V. Lawande B. N. Jagatap 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2011,61(1):221-229
We investigate modulation transfer through pump induced atomic coherence in pump-probe spectroscopy of Doppler broadened medium
of cesium atoms. The mechanism of modulation transfer is discussed for a three level Λ configuration under slow frequency modulation. Modulation transfer is demonstrated by performing frequency modulation spectroscopy
(FMS) on a sub-natural linewidth (<2 MHz) electromagnetically induced transparency (EIT) signal. Here the pump laser is modulated by acousto-optic frequency
modulation and the modulation is transferred to the probe laser through atomic coherence. Finally the probe laser is locked
on the first derivative spectrum of EIT signal. Such atomic frequency offset locking system totally removes the necessity
of direct modulation of laser frequency, so that the spectral resolution is limited only by the practical linewidth of the
laser systems. Moreover it provides a novel way to eliminate the additional
frequency and intensity noise associated with direct frequency dithering, which may limit the experimental resolution. 相似文献
927.
B.Y. Man S.C. XuC. Yang M. LiuS.Z. Jiang Y.Y. MaC.S. Chen A.H. LiuX.G. Gao C.C. WangB. Hu 《Applied Surface Science》2011,257(15):6321-6325
Single-phase β-FeSi2 films on silicon (1 0 0) were fabricated by pulse laser deposition. The structure and crystal quality of the samples were characterized by X-ray diffraction and Fourier transform infrared spectroscopy. The field scanning electron microscopy showed that the film thickness increases with the increasing of the laser fluence. Moreover, atomic force microscopy observations revealed the changes of surface properties with different laser fluence. Based upon all experimental results, it is found that 7 J/cm2 is the most favorable for the formation of β-FeSi2 thin films. 相似文献
928.
A series of measurements on the high pressure (up to 18 bar) coaxial e-beam pumped Ar/Xe laser has been made at high power loading (up to 25 MW/cm~2) for various Xe mole fraction in Ar. We found that the optimum laser gas composition in our system was 0.4% Xe in Ar which was independent of the total gas pressure. At the optimum gas composition the output energy increased with increasing total gas pressure up to 16 bar, but the intrinsic efficiency reached a maximum at the total gas pressure of 8 bar. It was also found that at the optimum power deposition for both the 2.63μm and 2.65μm transitions the ratio of the integrated optical energy to that of the 1.73μm transition had a minimum in most cases at the optimum gas mixture for various gas pressures. This ratio increased with increasing gas pressure. The experimental results suggested that besides the 2-body Xe quenching at high Xe fraction and electron collision mixing at high power depositions the heavy particle quenching from Ar at high gas press 相似文献
929.
We prove a theorem about idempotents in compact semigroups. This theorem gives a new proof of van der Waerden’s theorem on
arithmetic progressions as well as the Hales-Jewett theorem. It also gives an infinitary version of the Hales-Jewett theorem
which includes results of T. J. Carlson and S. G. Simpson.
Research supported by the National Science Foundation under Grant No. DMS86-05098. 相似文献
930.
This paper describes an optical system for high temperature creep strain measurement using quartz optical fiber, super long working distance microscope and digital image processing techniques. In this system one end of the quartz optical fibers is arrayed in a small area on the specimen surface and the other end is illuminated by a laser beam. The fiber ends on the specimen surface form the spot array. The small optical spots on the specimen are tracked by a CCD camera and the images are processed by digital image processing software. The diameter of each quartz fiber is 100 μm and the fibers can be arrayed in a small area. The local strains are determined by measuring the variety of relative distance between two spots. Experimental results of local creep strain on the welding joints of 15CrMo and HK40 at 850°C are obtained. 相似文献