全文获取类型
收费全文 | 4467篇 |
免费 | 1306篇 |
国内免费 | 2588篇 |
专业分类
化学 | 4880篇 |
晶体学 | 187篇 |
力学 | 406篇 |
综合类 | 154篇 |
数学 | 183篇 |
物理学 | 2551篇 |
出版年
2024年 | 38篇 |
2023年 | 137篇 |
2022年 | 178篇 |
2021年 | 170篇 |
2020年 | 155篇 |
2019年 | 178篇 |
2018年 | 118篇 |
2017年 | 158篇 |
2016年 | 187篇 |
2015年 | 231篇 |
2014年 | 393篇 |
2013年 | 353篇 |
2012年 | 306篇 |
2011年 | 353篇 |
2010年 | 377篇 |
2009年 | 463篇 |
2008年 | 413篇 |
2007年 | 400篇 |
2006年 | 422篇 |
2005年 | 361篇 |
2004年 | 364篇 |
2003年 | 344篇 |
2002年 | 291篇 |
2001年 | 265篇 |
2000年 | 197篇 |
1999年 | 191篇 |
1998年 | 180篇 |
1997年 | 176篇 |
1996年 | 174篇 |
1995年 | 160篇 |
1994年 | 126篇 |
1993年 | 92篇 |
1992年 | 87篇 |
1991年 | 65篇 |
1990年 | 88篇 |
1989年 | 80篇 |
1988年 | 29篇 |
1987年 | 16篇 |
1986年 | 13篇 |
1985年 | 14篇 |
1984年 | 9篇 |
1983年 | 9篇 |
排序方式: 共有8361条查询结果,搜索用时 359 毫秒
931.
932.
933.
光纤布拉格光栅自致啁啾效应的研究 总被引:3,自引:0,他引:3
根据耦合模理论,采用传输矩阵法分析了相位掩模法制作的光纤布拉格光栅的反射谱特性.设计了一种新的写制光纤光栅的光路,利用高斯激光光束写制出具有短波自致啁啾效应的切趾光栅(栅长0.015 m).对具有短波自致啁啾效应的光纤光栅进行了物理切割(剩余光栅的长度分别取0.007 m和0.0055 m),得到了一种新型的具有长波自致啁啾效应的光纤光栅.原本的自致啁啾光栅反射谱中旁瓣分布在短波长方向,而得到的新型自致啁啾光栅的反射谱中长波长方向的旁瓣更为明显.基于对光纤布拉格光栅自致啁啾效应的分析,提出一种新型类高斯切趾函数,以此函数对自致啁啾效应进行数值模拟,得到了与实验结果相一致的光谱图. 相似文献
934.
An All-Thin-Film Electrochromic Device Composed of MoO3--LiBSO--NiOx Multilayer Structure 总被引:1,自引:0,他引:1 下载免费PDF全文
An all-thin-tilm (ATF) electrochromic device for modulating the optical transmittance is manufactured using magnetron sputtering. The devices consists of MoO3 as the main electrochromic layer, LiBO2 +Li2SO4 (LiBSO) as the ion conductor layer, and NiOx as the complementary electrochromic layer. Glass covered with indium tin oxide (ITO) is used as the substrate and the ITO film is used as the bottom electrode. The ITO film deposited on the top of the devices is used as the other electrode. The structure and morphology of the films are characterized by x-ray diffraction (XRD) and scanning electron microscopy (SEM). The devices exhibit good optical properties with low transmittance values in the coloured state, and the optical modulation is measured by spectrophotometer in the wavelength range from 400 to 800nm. The average visible light transmittance reaches 50.2% and 3.7% in bleached and coloured state, respectively. The results indicate that such a monolithic system has great potential to be applied in smart windows. 相似文献
935.
We investigate the effect of dipole-dipole interaction on the intrinsic decoherence of a system which consists of two two-level atoms and an optical cavity. The entanglement of the system is calculated by making use of concurrence. Our results show that the appropriate choice for the coupling constant Ω of dipole-dipole interaction can restrain the intrinsic deeoherenee of the system. We also find a special phenomenon. No matter what the value of γ is, the concurrence of system slowly increases and cannot exceed 0.71 when Ω= 1. 相似文献
936.
We measure zero-field resistivity and magnetoresistance of multiwalled carbon nanotube yarns (CNTYs). The CNTYs are drawn from superaligned multiwalled carbon nanotube arrays synthesized by the low-pressure chemical vapour deposition method. The zero-field resistivity shows a logarithmic decrease from 2 K to 300K. In the presence of a magnetic field applied perpendicular to the yarn axis, a pronounced negative magnetoresistance is observed. A magnetoresistance ratio of 22% is obtained. These behaviours can be explained by the weak localization effect. 相似文献
937.
Cylinder-shaped CusoNi20 alloy melt is undercooled and solidified by the combination of the electromagnetic levitation technique and the flux treatment method. Nearly constant temperature gradient of 8-10 K/cm is realized for the cylindrical melts with differen~ undercooling levels at the bottom ends. The experimental results reveal that with the increase of the undercoo]ing of the melts from 35 to 220 K, the microstructures undergo transition from coarse dendrites to granular grains, unidirectional dendrites, and finally to equiaxed grains. 相似文献
938.
We propose and theoretically analyse a double magnetic tunnel device that takes advantages of the spin filter effect. Two magnetic tunnel barriers are formed by different spin filters which have different barrier heights. The magnetoresistance of the device is low (high) when the magnetic moments of the two spin filters are parallel (antiparallel). We present a theoretical calculation of the magnetoresistance based on electric tunnel effect. In addition, the effect of the difference barrier heights and exchange splitting energies between the two spin filters are also analysed in detail. The numerical results show that the spin filter in this configuration gives a magnetoresistance larger than that with standard magnetic tunnel junctions. 相似文献
939.
940.
用固相反应和高能球磨合成后续热处理两种方法分别得到钙钛矿结构Nd0.7Sr0.3MnO3氧化物.两种不同方法得到的多晶样品,虽然晶体结构相同,化学成分和晶粒大小相近,但它们电输运性质却表现出很大差异.用固相反应法制得的样品的电阻几乎不随负载电流的变化而变化,即不表现电致电阻行为;而通过高能球磨合成后续热处理方法得到的样品电阻随外加电流增大而急剧减小,出现显著电致电阻效应.产生这种截然不同电输运特性的原因可能与样品的显微结构和界面性质有关.
关键词:
电致电阻效应
显微结构
钙钛矿结构锰氧化物
界面电阻 相似文献