全文获取类型
收费全文 | 1329篇 |
免费 | 138篇 |
国内免费 | 16篇 |
专业分类
化学 | 4篇 |
力学 | 4篇 |
综合类 | 5篇 |
数学 | 9篇 |
物理学 | 79篇 |
无线电 | 1382篇 |
出版年
2024年 | 2篇 |
2023年 | 11篇 |
2022年 | 21篇 |
2021年 | 26篇 |
2020年 | 18篇 |
2019年 | 24篇 |
2018年 | 41篇 |
2017年 | 35篇 |
2016年 | 56篇 |
2015年 | 67篇 |
2014年 | 102篇 |
2013年 | 78篇 |
2012年 | 144篇 |
2011年 | 125篇 |
2010年 | 111篇 |
2009年 | 87篇 |
2008年 | 95篇 |
2007年 | 123篇 |
2006年 | 94篇 |
2005年 | 70篇 |
2004年 | 51篇 |
2003年 | 24篇 |
2002年 | 26篇 |
2001年 | 10篇 |
2000年 | 13篇 |
1999年 | 8篇 |
1998年 | 3篇 |
1997年 | 4篇 |
1996年 | 2篇 |
1995年 | 1篇 |
1994年 | 6篇 |
1992年 | 3篇 |
1989年 | 1篇 |
1986年 | 1篇 |
排序方式: 共有1483条查询结果,搜索用时 9 毫秒
101.
分析了箔条雷达散射截面,讨论了箔条干扰在平面位置显示器(PPI)上的显示,建立了箔条干扰显示模型,最后实现了箔条干扰PPI动态显示,并对显示的有效性进行了验证。 相似文献
102.
103.
研究毫米波成像导引头的干扰途径和方法,分析了毫米波导引头制导的特点和主要抗干扰措施,重点分析不同的干扰措施对毫米波导引头的干扰效果,仿真结果证明了分析的正确性。 相似文献
104.
���� 《Frontiers of Physics》2011,6(1):109-123
Amorphous systems undergo the jamming transition when the density increases, temperature drops, or external shear stress decreases, as described by the jamming phase diagram which was proposed to unify different processes such as the glass transition, random close packing, and yielding under shear stress. At zero temperature and shear stress, the jamming transition occurs at a critical density at Point J. In this paper, we review recent studies of the material properties of marginally jammed solids and the glassy dynamics in the vicinity of Point J. As the only singular point in the jamming phase diagram, Point J exhibits special criticality in both mechanical and vibrational quantities. Dynamics approaching the glass transition in the vicinity of Point J show critical scalings, suggesting that the molecular glass transition and the colloidal glass transition are equivalent in the hard sphere limit. All these studies shed light on the long-standing puzzles of the glass transition and unusual properties of amorphous solids. 相似文献
105.
Mechanical properties of jammed packings of frictionless spheres under an applied shear stress 下载免费PDF全文
By minimizing a thermodynamic-like potential, we unbiasedly sample the potential energy landscape of soft and frictionless spheres under a constant shear stress. We obtain zero-temperature jammed states under desired shear stresses and investigate their mechanical properties as a function of the shear stress. As a comparison, we also obtain the jammed states from the quasistatic-shear sampling in which the shear stress is not well-controlled. Although the yield stresses determined by both samplings show the same power-law scaling with the compression from the jamming transition point J at zero temperature and shear stress, for finite size systems the quasistatic-shear sampling leads to a lower yield stress and a higher critical volume fraction at point J. The shear modulus of the jammed solids decreases with increasing shear stress. However, the shear modulus does not decay to zero at yielding. This discontinuous change of the shear modulus implies the discontinuous nature of the unjamming transition under nonzero shear stress, which is further verified by the observation of a discontinuous jump in the pressure from the jammed solids to the shear flows. The pressure jump decreases upon decompression and approaches zero at the critical-like point J, in analogy with the well-known phase transitions under an external field. The analysis of the force networks in the jammed solids reveals that the force distribution is more sensitive to the increase of the shear stress near point J. The force network anisotropy increases with increasing shear stress. The weak particle contacts near the average force and under large shear stresses it exhibit an asymmetric angle distribution. 相似文献
106.
107.
单脉冲导引头对多干扰源的角分辨 总被引:8,自引:0,他引:8
当多个噪声调频干扰同时进入单脉信号引头主波束内时,导引头对干扰源的角度分辨是非常困难的。本文主要研究了导引头单脉冲接收机对宽带噪声调频干扰源的响应,分析了当单脉冲主波束内存在多个噪声调频干扰源时,导引头指向角的跟踪规律,并重点讨论了一种用聚类来提取角信息的方法,最后仿真证实了该方法的正确性和有效性。 相似文献
108.
激光直接制造金属零件过程的闭环控制研究 总被引:13,自引:1,他引:13
对激光直接制造金属零件过程中熔池温度和熔覆层厚度的变化进行了研究,指出对确定的材料,当激光功率增大到一定值时,熔池内的金属溶液大多已达到了热饱和,温度累积效应并不显著,熔池温度基本保持平稳,而在制造过程中若零件由于工艺不稳定而产生凹凸点,在多次层叠制造后,凹处越凹、凸处越凸,严重影响零件的制造精度。所以通过传感器来直接监测金属零件的熔覆高度,进而通过控制送粉量来保证制造过程中熔覆高度的稳定性比起温度控制来更具有实际意义。提出了熔覆高度的检测方案,并对送粉量的闭环控制系统进行了研究,对送粉量的时间延迟提出了相应的对策。结果表明对熔覆层高度的检测和对送粉量的调节能够提高激光直接制造过程的稳定性和制造精度。 相似文献
109.
110.