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621.
E. Farhi A.K. Tagantsev R. Currat B. Hehlen E. Courtens L.A. Boatner 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,15(4):615-623
High resolution data on low energy phonon branches (acoustic and soft optic) along the three principal symmetry axes in pure
KTaO3 were obtained by cold neutron inelastic scattering between 10 and 80 K. Additional off-principal axis measurements were performed
to characterize the dispersion anisotropy (away from the and axes). The parameters of the phenomenological model proposed by Vaks [28] are refined in order to successfully describe the
experimental low temperature (10 <
T
< 100 K) dispersion curves, over an appreciable reciprocal space volume around the zone center ( rlu). The refined model, which involves only 4 temperature-independent adjustable parameters, is intended to serve as a basis
for quantitative computations of multiphonon processes.
Received: 29 September 1999 and Received in final form 6 January 2000 相似文献
622.
623.
A technique based on the repetition of the interference fringe pattern for the automated marking of the PZT phase shifting interference system is described. A closed-loop control is used to circumvent the inherent hysteresis and nonlinear characteristics of PZT. The whole interference system integrated under LabVIEW graphic programming environment provides users a friendly and ease-of-maintenance interface. An application of the algorithm is used to demonstrate the promotion of the Zygo GPI-LC model interferometer to upgrade its phase resolution ability. 相似文献
624.
A review of development and implementation of an active nonlinear vibration absorber 总被引:1,自引:0,他引:1
S. S. Oueini A. H. Nayfeh J. R. Pratt 《Archive of Applied Mechanics (Ingenieur Archiv)》1999,69(8):585-620
Summary We present an account of an implementation of an active nonlinear vibration absorber that we have developed. The control
technique exploits the saturation phenomenon that is known to occur in quadratically-coupled multi-degree-of-freedom systems
subjected to primary excitation and possessing a two-to-one internal resonance. The technique is based on introducing an absorber
and coupling it with the structure through a sensor and an actuator, where the feedback and control signals are quadratic.
First, we consider the case of controlling the vibrations of a single-degree-of-freedom system. We develop the equations governing
the response of the closed-loop system and use the method of multiple scales to obtain an approximate solution. We investigate
the performance of the control strategy by studying its steady-state and transient characteristics. Additionally, we compare
the performance of the quadratic absorber with that of a linear absorber. Then, we present theoretical and experimental results
that demonstrate the versatility of the technique. We design an electronic circuit to emulate the absorber and use a variety
of sensors and actuators to implement the active control strategy. First, we use a motor and a potentiometer to control the
vibration of a rigid beam. We develop a plant model that includes Coulomb friction and demonstrate that the closed-loop system
exhibits the saturation phenomenon. Second, we extend the strategy to multi-degree-of-freedom systems. We use PZT ceramics
and strain gages to suppress vibrations of flexible steel beams when subjected to single- and simultaneous two-mode excitations.
Third, we employ Terfenol-D, a nonlinear actuator, and accelerometers to control the vibrations of flexible beams. In all
instances, the technique is successful in reducing the response amplitude of the structures.
Received 3 May 1999; accepted for publication 3 June 1999 相似文献
625.
在Guyomar非线性模型基础上,通过机电等效法将晶堆前向负载作为等效质量和阻尼加入振动方程的质量项和阻尼项,推导了换能器振速、辐射声压级和谐振频率偏移率等表达式,计算分析了压电陶瓷非线性参数和结构参数对换能器声辐射性能的影响,研究了压电陶瓷的非线性对换能器结构参数匹配的影响。结果表明,换能器节面靠前,前盖板厚度越小,前盖板大径越小,都可以减少压电陶瓷非线性引起的换能器频率偏移。当设计频率确定时,压电陶瓷处于非线性工作域的换能器的结构参数有所减小。换能器加入辐射端匹配后,可以改善压电晶堆前向负载匹配,降低换能器的谐振频率偏移率。换能器激励电流也会出现频率偏移现象。在提高换能器激励电压时,换能器的结构参数应适当减小。得到的结论可为换能器设计提供理论依据和帮助。 相似文献
626.
627.
文章综述了几种典型结构水声换能器近些年的新发展,包括:弯张换能器、圆柱面辐射型换能器、纵向换能器等等,主要介绍这些结构类型水声换能器的设计新思想和多方面优化改进的新成果。 相似文献
628.
《Particuology》2023
Acoustic agglomeration technology use high-intensity acoustic field to make aerosol particles collide and condense rapidly. Existing studies have shown that 70%–90% of fine particles can be eliminated within minutes using compression drives and air-jet generators. Currently, there are limitations to the sound sources used. In this paper, an airborne ultrasonic transducer with a resonant frequency of 15 kHz is designed, followed by the corresponding numerical simulation and experiments for the evaluation of the vibration modal and sound pressure field. The sound pressure levels (SPL) of the open space and the agglomeration chamber can reach 150 dB and 156 dB, respectively. The agglomeration effect of water droplets, liquid phase smoke, solid phase smoke and mixed smoke is experimentally investigated, and the light transmittance rapidly increases from 8% to 60% within 4 s, 8 s, 5 s and 6 s, respectively. Agglomeration is also effective in the high-frequency range, and we infer that the acoustic wake effect is the predominant mechanism. The elimination effect is promoted with the increasing of SPL until the corresponding secondary acoustic effect is enhanced. Moreover, the agglomeration rate of higher concentration aerosol is significantly better than that of diluted aerosols in ultrasonic agglomeration process. 相似文献
629.
Finding damages and their prevalence in structures is a very challenging problem. In order to identify potential structural damage, non-destructive methods are not very helpful. One of the most popular piezoelectric ceramic materials used worldwide is macromolecular lead zirconate titanate (PZT), also known as Pb[Zr(x)Ti(1-x)]O3. PZT transducers are proving to be a successful alternative for assessing the structure's health. The Macro-molecular PZT's self-actuating and sensing properties are utilized by the electromechanical impedance (EMI) method. In this capacity, the macro-molecular PZT patches serve as co-located actuators and sensors and make use of ultrasonic vibrations to produce a distinctive admittance “signature” of the structure. PZT patches perform exceptionally well in terms of damage sensitivity. The higher modes of vibration are locally activated by the local application of an AC source on the PZT transducers attached to the host structure. The alteration of the admittance response is a sign of injury to the transducer's vicinity. In the current study, the damage percentage and its location in a 150 × 150 × 150 mm concrete cube are being examined. Regression analysis is also used to determine the concrete cube's strength. This method also can identify hair-like cracks at an early stage, which explains how it can shield the building from serious failures. 相似文献
630.