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661.
662.
隧道中高速列车空气阻力的数值计算 总被引:2,自引:0,他引:2
对高速列车在隧道中行驶时所引起的湍流场进行了数值模拟,计算了列车所受到的空气阻力。数值计算采用变密度、轴对称的k~ε模型和PISO算法,并将粗糙面速度分布公式和尼古拉兹公式引入壁函数法中,以反映壁面粗糙度的影响,提出了对不规则边界的速度修正法。针对不同的车速、阻塞比和车头细长比,分别进行了模拟,获得了全场的压力分布,以及空气阻力与基本参数的关系,并与传统的经典方法阻力计算结果进行了对比分析。 相似文献
663.
浅埋隧道围岩应力场的解析解 总被引:5,自引:0,他引:5
隧道围岩应力和变形分析是隧道设计的重要内容。对深埋隧道的研究已取得了很多结果。但对于受地表边界和地面荷载的影响,浅埋隧道围岩分析在数学处理上仍存在一定的困难。一般采用边界元或有限元等数值方法,未见有解析解的报导。本文采用复变函数解法研究地面荷载作用下浅埋圆形隧道围岩的平面弹性问题,该解法利用复变函数保角变换将物理平面上的研究域映射到像平面上的圆环域内。将复势函数进行罗伦级数展开,通过边界条件得到罗伦级数展开式系数的递推公式,并由复势函数确定应力分量和位移分量。最后通过算例给出了围岩应力分布和沉降曲线。所得结果适用于任意分布荷载的情况,具有通用性。 相似文献
664.
665.
The sensitivity of the flow along the nozzle and in the test section of high enthalpy wind tunnels to the thermochemical response
of the nozzle expansion process, as well as effects on the pressure and heat transfer distributions over the Electre blunt
cone standard test model, are examined in the framework of properly characterizing the test section flow field in such facilities.
Particularly sensitive to the thermochemical behaviour of the nozzle flow, in the facilities under consideration, are the
static pressure, static temperature and Mach number, whereas stagnation point (pitot) pressure and heat transfer data or freestream
velocity are inadequate for the characterization of the thermochemical state of the flow. The Electre and nozzle wall pressure
data in the F4 arc jet wind tunnel suggest, in contrast to nonequilibrium computations, that the flow in the F4 nozzle is
close to equilibrium. In the HEG and, to some extent, the T5 piston-driven shock tunnels, there are indications that significant
heat losses occur in the reservoir. Lastly, simple semi-empirical formulations for stagnation point heating are shown to perform
reasonably well in high enthalpy flow conditions. 相似文献
666.
667.
In this paper, the design requirements of an experimental apparatus for the measurement of the direct derivatives on an oscillating aircraft model in a wind tunnel are discussed. The elaboration of the signal output of the force transducer is analysed, according to the direct forced oscillation technique. The distorsions of the primary oscillatory motion were previously evaluated and corrected, adopting an open loop control technique. This algorithm is presented and its reliability is verified. Finally, the behaviour of the experimental stability parameters, adopting different oscillation amplitudes and frequencies, is discussed.
Sommario Nel presente lavoro vengono analizzate le principali caratteristiche di un sistema per l'esecuzione delle prove di oscillazione forzata in galleria del vento, al fine di valutare le derivate aerodinamiche dirette, secondo i gradi di libertá alla rotazione di un velivolo. Inizialmente l'attenzione viene concentrata sul principio di funzionamento e sull'algoritmo di elaborazione dei segnali estensimetrici. L'analisi procede quindi con lo studio delle caratteristiche cinematiche del sistema di movimentazione e supporto, ed in particolare si discutono lc problematiche connesse con il controllo del moto oscillatorio del modello. Infine, viene discusso l'utilizzo dell'apparecchiatura in oggetto con lo acopo di evidenziare come i parametri di stabilitá rilevati sperimentalmente dipendano daile caratteristiche del moto armonico di forzamento.相似文献
668.
The cable shovel excavator is used for primary production in many surface mining operations. A major problem in excavation is the variability of material diggability, resulting in varying mechanical energy input and stress loading of shovel dipper-and-tooth assembly across the working bench. This variability impacts the shovel dipper and tooth assembly in hard formations. In addition, the geometrical constraints within the working environment impose production limitations resulting in low production efficiency and high operating costs. A potential solution to the above problems is the deployment of an intelligent shovel excavation (ISE) technology, with real-time formation identification, recording and knowledge transmission capabilities. This paper advances the ISE technology by developing dynamic models of the cable shovel using the Newton-Euler techniques. The models include the main factors that influence shovel performance including the effect of both linear and angular motions of dipper handle and dipper. A path trajectory is modeled to demonstrate the dynamic velocity and acceleration profiles. Numerical examples show that the critical performance variables include geometrical and physical properties of the dipper and dipper handle, digging strategies and formation properties. The kinematic results show that the critical phase occurs between 1.5 and 2.0 s of a 3-s excavation cycle with occurrence of maximum kinematic effects. The dynamic results also show a similar trend with maximum dynamic effects between 1.5 and 2.0 s. The results also show that the maximum resistive force occurs at 1.625 s within the excavation cycle. At this point the maximum breakout force of the equipment is reached and any increase in the resistive load will require further fragmentation. The results provide appropriate information for excavation planning and execution. These models form the basis for developing dynamic shovel simulators for the ISE technology. 相似文献
669.
Extended-source broken gate tunnel FET for improving direct current and analog/radio-frequency performance
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《中国物理 B》2021,30(7):78503-078503
The various advantages of extended-source(ES), broken gate(BG), and hetero-gate-dielectric(HGD) technology are blended together for the proposed tunnel field-effect transistor(ESBG TFET) in order to enhance the direct-current and analog/radio-frequency performance. The source of the ESBG TFET is extended into channel for the purpose of increasing the point and line tunneling in the device at the tunneling junction, and then, the on-state current for the ESBG TFET increases. The influence of the source region length on the direct-current and radio-frequency performance parameters of the ESBG TFET is analyzed in detail. The results show that the proposed TFET exhibits a high on-state current to off-state current ratio of 1013, large transconductance of 1200 μS/μm, high cut-off frequency of 72.8 GHz, and high gain bandwidth product of 14.3 GHz. Apart from these parameters, the ESBG TFET also demonstrates high linearity distortion parameters in terms of the second-and third-order voltage intercept points, the third-order input interception point, and the third-order intermodulation distortion. Therefore, the ESBG TFET greatly promotes the application potential of conventional TFETs. 相似文献
670.
超前大管棚支护是隧道施工中穿越软弱破碎围岩的一种有效的加固施工方法。通过介绍超前大管棚在不良地质隧道施工中的受力原理、大管棚设计与施工要点及适用范围等内容,并结合重庆玉峰山隧道出口洞口段超前大管棚施工实例,对超前管棚在施工中的应用价值做一论证,有助于该方法的应用推广。 相似文献