全文获取类型
收费全文 | 2299篇 |
免费 | 560篇 |
国内免费 | 239篇 |
专业分类
化学 | 560篇 |
晶体学 | 94篇 |
力学 | 95篇 |
综合类 | 12篇 |
数学 | 341篇 |
物理学 | 1325篇 |
无线电 | 671篇 |
出版年
2024年 | 4篇 |
2023年 | 40篇 |
2022年 | 55篇 |
2021年 | 56篇 |
2020年 | 72篇 |
2019年 | 71篇 |
2018年 | 93篇 |
2017年 | 118篇 |
2016年 | 125篇 |
2015年 | 112篇 |
2014年 | 179篇 |
2013年 | 227篇 |
2012年 | 183篇 |
2011年 | 206篇 |
2010年 | 157篇 |
2009年 | 186篇 |
2008年 | 171篇 |
2007年 | 150篇 |
2006年 | 132篇 |
2005年 | 112篇 |
2004年 | 118篇 |
2003年 | 101篇 |
2002年 | 74篇 |
2001年 | 65篇 |
2000年 | 56篇 |
1999年 | 29篇 |
1998年 | 33篇 |
1997年 | 33篇 |
1996年 | 21篇 |
1995年 | 16篇 |
1994年 | 14篇 |
1993年 | 12篇 |
1992年 | 7篇 |
1991年 | 9篇 |
1990年 | 9篇 |
1989年 | 12篇 |
1988年 | 6篇 |
1987年 | 6篇 |
1986年 | 5篇 |
1985年 | 4篇 |
1984年 | 3篇 |
1983年 | 2篇 |
1982年 | 5篇 |
1981年 | 3篇 |
1980年 | 1篇 |
1979年 | 2篇 |
1978年 | 1篇 |
1977年 | 1篇 |
1976年 | 1篇 |
排序方式: 共有3098条查询结果,搜索用时 781 毫秒
991.
利用复折射率的方法和膜系设计软件TFcalc分别研究了入射角和杂质吸收对一维光子晶体反射镜反射谱和透射谱的影响.结果表明:随着入射角的增大,一维光子晶体反射镜的禁带中心位置蓝移,禁带宽度减小.入射角小于60°时,带隙势阱深度几乎不变,大于60°后带隙势阱深度变化较大.当入射角无限接近90°时,P偏振光的带隙几乎消失,S偏振光的带隙几乎保留.杂质吸收对于一维光子晶体的反射谱和透射谱显著影响时的临界消光系数值分别是0.001和0.0003.高折射率介质层的杂质吸收对光谱的影响较小. 相似文献
992.
Shuji Watanabe 《Journal of Mathematical Analysis and Applications》2011,383(2):353-364
The existence and the uniqueness of the solution to the BCS gap equation of superconductivity are established in previous papers, but the temperature dependence of the solution is not discussed. In this paper, in order to show how the solution varies with the temperature, we first give another proof of the existence and the uniqueness of the solution and point out that the unique solution belongs to a certain set. Here this set depends on the temperature T. We define another certain subset of a Banach space consisting of continuous functions of both T and x. Here, x stands for the kinetic energy of an electron minus the chemical potential. Let the solution be approximated by an element of the subset of the Banach space above. Second, we show, under this approximation, that the transition to a superconducting state is a second-order phase transition. 相似文献
993.
We address the integrality gap of the integer linear program introduced by Grigoriev et al. (2006) [3] for the periodic maintenance problem. We prove that the integrality gap of this program is bounded by a constant. 相似文献
994.
Gökhan Çınar Hülya Öztürk Özge Yanaz Çınar 《Mathematical Methods in the Applied Sciences》2011,34(2):220-230
The diffraction of acoustic waves by an infinitely long annular duct having a finite gap on the inner wall is investigated rigorously. The related boundary‐value problem is formulated into a modified Wiener–Hopf equation, which is then reduced to a pair of simultaneous Fredholm integral equations of the second kind. At the end of the analysis, numerical results illustrating the effects of the width of the coaxial cylindrical waveguide and the gap length on the diffraction phenomenon are presented. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
995.
996.
997.
以拼接光栅作为色散元件的激光脉冲压缩器中,要求脉冲压缩光栅表面光强分布均匀、能量输出效率高。利用菲涅耳-基尔霍夫衍射原理对脉冲压缩光栅表面光强和远场光强分布进行了研究。计算了拼接光栅缝隙宽度对光栅表面光强变化量和远场光强极大值的影响。在利特罗角附近入射时发现激光脉冲光强分布与拼接光栅缝隙宽度相关,得出了光栅拼接缝隙宽度应控制在0.5 mm以内。适当提高缝隙衍射效率能够改善光强分布均匀性和提高光能量输出,提出了对拼接缝隙采用两次重复曝光以提高其衍射效率的方法。 相似文献
998.
999.
Low-frequency band gaps in one-dimensional thin phononic crystal plate with periodic stubbed surface
Using supercell plane wave expansion method, the Lamb wave band structure of one-dimensional thin plate with periodic stubs is investigated. The numerical results show that flat bands will appear and band gap can exist in a low-frequency domain. The position of the flat bands and width of the low-frequency Lamb wave band gap can be tuned by the stub height, plate thickness and filling fraction. The band gap is obtained by opening the folding points of the same plate modes not the crossing point of different plate mode when the stub height is small. 相似文献
1000.
Nanostructured bismuth ferrite (BiFeO3) thin films were deposited on glass substrate by the sol-gel process. The as-fired film at 250 °C was found to be amorphous crystallizing to pure rhombohedral phase after annealing at 450 °C for 2 h in air. The XRD pattern shows that the sample is polycrystalline in nature. The average grain size of the film calculated from the XRD data was found to be 16 nm. The as-fired film show high transmittance that decreases after crystallization. The absorption edge of the films was found to be sharper and shifting towards the lower energy as the annealing temperature increases. The optical energy band gaps of the amorphous and crystalline films were found to be 2.63 and 2.31 eV, respectively. The refractive indices of the amorphous and crystalline films were 2.05 and 2.26, respectively. 相似文献