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921.
922.
A finite element method for highly viscous fluid is used to calculate the velocity and stress fields in the surrounding soft
rock of a tunnel. In order to fit the calculated values with the measured displacement of tunnel wall, we inverted the boundary
forces and the mechanical parameters of the surrounding rocks. 相似文献
923.
Mechanism of circular tunnel rockburst is that, when the carrying capacity of the centralized zone of plastic deformation in limiting state reduces, the comparatively intact part in rock mass unloads by way of elasticity; rockburst occurs immediately when the elastic energy released by the comparatively intact part exceeds the energy dissipated by plastic deformation. The equivalent strain was taken as a state variable to establish a catastrophe model of tunnel rockburst, and the computation expression of the earthquake energy released by tunnel rockburst was given. The analysis shows that, the conditions of rockburst occurrence are relative to rock's ratio of elastic modulus to descendent modulus and crack growth degree of rocks; to rock mass with specific rockburst tendency, there exists a corresponding critical depth of softened zone, and rockburst occurs when the depth of softened zone reaches. 相似文献
924.
On the influence of elevated surface temperatures on hypersonic shock wave/boundary layer interaction at a heated ramp model 总被引:2,自引:0,他引:2
Although important flow parameters as Mach number, Reynolds number and total enthalpy can be reproduced in most hypersonic experiments quite well, due to different surface temperature effects in wind tunnel and flight, scaling as well as specific flow properties of shock wave/boundary layer interactions are different. This especially holds for short-duration facilities like, e.g. shock tunnels where due to short running times the models remain more or less at ambient temperature. To overcome this shortcoming, an experimental study has been conducted using a preheatable ramp model with 15° ramp angle. This allowed us to adjust the surfaces to an arbitrary temperature just before the experiment started. Pressure and heat flux measurements clearly showed the effect of varying surface and free stream temperatures. These results are supported by schlieren pictures and infrared measurements. The comparison of the measurements with theoretical and numerical results shows a good agreement. Separation bubble scaling laws proposed by Katzer and Davis have been applied and partially confirmed using the local conditions of the boundary layer at separation. 相似文献
925.
复杂地质条件下地下工程围岩稳定性问题,一直是地质工程界备受关注的热门议题。文中针对云南思茅-小勐养高速公路曼歇4号连拱隧道的特殊复杂地质结构,通过数值模拟对穿越古滑坡的浅埋偏压连拱隧道施工过程围岩应力场、位移场和塑性区变化规律进行了数值分析,从而有效揭示出施工各阶段围岩应力集中位置和潜在塑性破坏区,不仅为隧道的安全顺利施工提供了预警信息和直接指导,同时为连拱隧道的优化设计提供可靠的理论依据。在穿越古滑坡的浅埋偏压连拱隧道施工中,应高度重视古滑坡的彻底治理和中隔墙的支护加固,从而确保整座连拱隧道的围岩稳定和安全运营。 相似文献
926.
Tang Guiming 《Acta Mechanica Sinica》1994,10(3):220-226
This paper describes flow visualization techniques employing surface oil flow and liquid crystal thermography suitable for
use in impulse wind tunnels. High spatial resolution photographs of oil flow patterns and liquid crystal thermograms have
been obtained within test times ranging from 7 to 500 ms and have been shown to be very useful for revealing the detailed
features of 3-D separated flow. The results from oil flow patterns, liquid crystal thermograms, schlieren photographs and
heat flux measurements are shown to be in good agreement. 相似文献
927.
SWT-120风洞稳定段的性能测量 总被引:1,自引:0,他引:1
在普通超音速风洞中,由于受到噪声干扰,很难进行有效的边界层转捩特性试验研究,针对超声速流动特点发展较低噪声风洞十分必要,而稳定段设计的好坏直接影响到下游试验段噪声水平。本文介绍一座低噪声风洞稳定段的结构和性能测量结果。先对稳定段的结构设计做了简单介绍,然后对实验结果进行分析,实验结果表明在大角度扩散段内装置孔锥,稳定段安装消音夹层和阻尼网组等部件后,气流的速度脉动和压力脉动明显降低,其中压力脉动降低一个量级,速度脉动为1%。进一步优化设计和改进工艺,速度脉动还可进一步降低。测量结果表明SWT-120稳定段的设计是成功的,对我们以后发展更高性能的静风洞有借鉴和参考价值。 相似文献
928.
Nguyen Tuan Anh Nguyen Anh Tuan Nguyen Tuyet Nga Nguyen Anh Tue Giap Van Cuong 《Current Applied Physics》2014,14(10):1389-1395
Double-barrier magnetic tunnel junctions (DBMTJs) were prepared from Co(75 nm)/Al2O3(2.3 nm)/Co(5 nm)/Al2O3(2.3 nm)/Co(50 nm) sputtering pentalayer films. The ac electrical properties of as-deposited DBMTJs and those annealed in a vacuum at 100–350 °C for 30 min were then investigated using a complex impedance spectroscopic technique. The ac impedance responses as a function of annealing temperature were further analyzed based on Maxwell's layered dielectric barrier and Maxwell–Wagner capacitor models after considering the DBMTJs as having double-capacitor-type structures. The effect of thermal annealing on the ac transport behavior of the DBMTJs was interpreted by examining the equivalent electric circuits fitted to Nyquist plots of each different sample. The effects were found to be due to changes in the structural characteristics in both bulk and interface morphologies of Co and Al2O3 layers. The structural morphology determined the different ac transport modes that occurred in the DBMTJs. 相似文献
929.
《Current Applied Physics》2014,14(3):528-532
Magnetic tunnel junctions have not been easily accessible for research because of not only their complicated fabrication processes but also side effects induced during the fabrication. The method utilizing arrays composed of in-line four-point probes with various spacings is promising as an alternative to the fabrication method. We found in the current-in-plane tunneling measurement that the determination of the probe spacing is the most important to evaluate the characteristics of magnetic tunnel junctions. Our simulation indicates that if one would choose at least more than three sets of an array with probe spacings centered at the spacing at which the maximum current-in-plane tunneling magnetoresistance is observed, the statistics should become improved resulting in the accurate evaluation of the properties of tunnel junctions. We also found that the suitable probe spacings with a change in the resistance of electrodes are not as sensitive as those with a change in the RA of the tunnel junction. Our results alert that the failure of selecting suitable probe spacings observes no tunneling signals because tunneling is very sensitive to the resistances of the tunnel junction and electrodes, which makes the current-in-plane tunneling method useless. 相似文献
930.
纳米钛氧化物忆阻器的导电过程因自身参数的改变及不同机理的共存而呈现复杂特性,但现有研究缺乏针对横截面积参数的改变对忆阻器导电特性影响的讨论.基于杂质漂移及隧道势垒机理,本文分析了忆阻器导电过程,研究了横截面积参数与导电过程中各关键物理要素间的关联,并基于此,分别研究了钛氧化物横截面积及隧道势垒横截面积的改变对忆阻器导电特性的影响,分析了两者的区别与联系.验证了两种机理共存情况下,相对于钛氧化物横截面积的改变,隧道势垒横截面积的改变是引发忆阻器导电特性变化的主要因素,且是导致忆阻器非理想导电特性的可能因素.研究成果有助于进一步解释忆阻器导电过程的复杂性,并为优化忆阻器模型的构建提供依据. 相似文献