全文获取类型
收费全文 | 621篇 |
免费 | 56篇 |
国内免费 | 52篇 |
专业分类
电工技术 | 31篇 |
综合类 | 39篇 |
化学工业 | 65篇 |
金属工艺 | 13篇 |
机械仪表 | 18篇 |
建筑科学 | 3篇 |
矿业工程 | 3篇 |
轻工业 | 8篇 |
水利工程 | 2篇 |
石油天然气 | 15篇 |
武器工业 | 1篇 |
无线电 | 385篇 |
一般工业技术 | 91篇 |
冶金工业 | 5篇 |
原子能技术 | 35篇 |
自动化技术 | 15篇 |
出版年
2024年 | 3篇 |
2023年 | 3篇 |
2022年 | 11篇 |
2021年 | 25篇 |
2020年 | 15篇 |
2019年 | 6篇 |
2018年 | 14篇 |
2017年 | 20篇 |
2016年 | 14篇 |
2015年 | 18篇 |
2014年 | 22篇 |
2013年 | 35篇 |
2012年 | 47篇 |
2011年 | 36篇 |
2010年 | 28篇 |
2009年 | 24篇 |
2008年 | 35篇 |
2007年 | 33篇 |
2006年 | 31篇 |
2005年 | 34篇 |
2004年 | 36篇 |
2003年 | 27篇 |
2002年 | 25篇 |
2001年 | 39篇 |
2000年 | 24篇 |
1999年 | 15篇 |
1998年 | 18篇 |
1997年 | 13篇 |
1996年 | 13篇 |
1995年 | 9篇 |
1994年 | 9篇 |
1993年 | 11篇 |
1992年 | 13篇 |
1991年 | 9篇 |
1990年 | 3篇 |
1989年 | 2篇 |
1987年 | 1篇 |
1985年 | 3篇 |
1983年 | 1篇 |
1982年 | 1篇 |
1978年 | 1篇 |
1977年 | 1篇 |
1958年 | 1篇 |
排序方式: 共有729条查询结果,搜索用时 140 毫秒
41.
42.
Ioannis?M.?KalogerasEmail author Aglaia?Vassilikou-Dova 《Materials Research Innovations》2003,7(5):263-268
The dielectric response of poly(methyl methacrylate) (PMMA) in solid solutions of perylene derivative laser dyes in PMMA and
PMMA + SiO2 has been studied by means of the thermally stimulated depolarization currents (TSDC) technique, with the aim to isolate molecular
and phase interactions in the dye blends. The changes in characteristics of the β-relaxation mode of PMMA are interpreted
with respect to the dissimilar local environments of the polar carboxy-methyl pendant groups of PMMA. An important "chemical"
effect on the β relaxation mechanism recorded in the organic-inorganic composites, is the formation of hydrogen bonds between
the acidic pore surfaces of SiO2 and the acetate side-groups. Several "physical" effects produced by the chromophores and the geometrical confinement, like
the modification of the monomer-to-polymer conversion rates, the polymer's free volume and the extent of the PMMA-SiO2 interaction, are discussed. 相似文献
43.
从理论上分析了高功率双包层光纤激光器的受激布里渊散射效应,建立了考虑受激布里渊散射的光纤激光器速率方程,并采用打靶法对其求解,对数值求解算法进行了详尽的描述。通过比较不同的纤芯直径、光纤长度以及掺杂浓度的情况下输出激光功率极限值的不同,发现增大纤芯直径、减小光纤长度以及降低掺杂浓度可以有效地减少受激布里渊散射的影响。 相似文献
44.
A recurrent stochastic binary network 总被引:1,自引:0,他引:1
赵杰煜 《中国科学F辑(英文版)》2001,44(5):376-388
Stochastic neural networks are usually built by introducing random fluctuations into the network. A natural method is to use stochastic connections rather than stochastic activation functions. We propose a new model in which each neuron has very simple functionality but all the connections are stochastic. It is shown that the stationary distribution of the network uniquely exists and it is approxi-mately a Boltzmann-Gibbs distribution. The relationship between the model and the Markov random field is discussed. New techniques to implement simulated annealing and Boltzmann learning are pro-posed. Simulation results on the graph bisection problem and image recognition show that the network is powerful enough to solve real world problems. 相似文献
45.
K. Somaiah K. Ravi Kanth V. Dayakar K. Radhakrishna Rao P. Veeresham 《Materials Chemistry and Physics》2001,70(3):259-262
Thermally stimulated luminescence (TSL) of Na2ZnCl4 single crystals showed three glow peaks having their peak maxima at 343, 425 and 475 K. Optical absorption (OA) data of unirradiated samples revealed an absorption band at 272 nm while X-irradiation caused additional bands at 462 and 723 nm. Growth and room temperature annealing studies of TSL and OA supported the idea of attribution of 425 K glow peak and 462 nm absorption band to F-centres. The 272 nm OA band is due to Zn2+ centres whereas the 723 nm absorption band and 475 K glow peak have been assigned to Zn+ centres. 相似文献
46.
The dipolar relaxation in poly(vinyl alcohol) (PVA), sodium carboxy methyl cellulose (NaCMCs), and their blends were studied using a thermally stimulated depolarization current (TSDC) technique. The mutual effects of polarization conditions such as heating rate, poling temperature, time, and field on the properties of TSDC were investigated. Quantitative analysis of the experimental data is given in terms of dipolar and space charge polarization. A thermal sampling (TS) technique was applied to decompose the complex relaxations in individual polymers and their blend of 0.5/0.5 wt/wt into its normal distribution components. The activation energy of TS‐formed electrets was determined by fitting the experimental curve to Bucci and Fieschi equations. Peak parameters such as activation energy and preexponential factor τ0 were obtained. A linear relationship between the activation energy and logarithm of the preexponential factor was found, thus confirming operation of the compensation law. In addition, by using the Eyring equation of the rate theory, the activation enthalpy ΔH≠ and the activation entropy ΔS≠ were calculated. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 95: 1342–1353, 2005 相似文献
47.
为了研究用于高功率激光器的掺Yb3+激光玻璃的制备和光谱特性,采用高温熔融工艺制备了两块碱金属元素含量不同的掺Yb3+硅酸盐激光玻璃,利用相应的光谱仪器测试了两块玻璃样品的吸收光谱和荧光光谱;分析了不同碱金属离子对吸收系数和荧光强度的影响;比较了倒易法和Fuchtbauer-Ladenburg(F-L)法两种不同方法得到的受激发射截面图,得到了Yb3+掺杂玻璃的各个光谱参量和激光参量。结果表明,随着碱金属离子半径的增大,吸收系数和荧光强度减小;样品的吸收截面图与倒易法计算所得的受激发射截面图相似,而与F-L法计算所得的受激发射截面图差别较大,并且倒易法发射截面图中主峰波长较F-L法发射截面图的主峰波长蓝移;最终样品1的增益性能比较好。 相似文献
48.
相干光时域反射仪中受激布里渊散射的抑制 总被引:1,自引:1,他引:0
采用对分布反馈半导体激光器(DFB-LD)直接进行小信号电流调制的方法抑制相干光时域反射仪(COT-DR)中的受激布里渊散射(SBS),分析了DFB-LD受到小信号电流调制时的频谱特性以及SBS阈值和频谱宽度的关系,设计了实验电路和光路抑制光纤中SBS。理论分析和实验结果表明,在低频调制电流处,光源频谱宽度随调制频率增加而减小,随调制幅度增加而增加,而SBS随频谱宽度增加而减弱,直接用电流调制激光器可抑制COTDR中的SBS。 相似文献
49.
Luc THVENAZ 《中国光电子学前沿》2010,3(1)
Optical fiber sensors based on stimulated Brillouin scattering have now clearly demonstrated their excellent capability for long-range distributed strain and temperature measurements. The fiber is used as sensing element, and a value for temperature and/or strain can be obtained from any point along the fiber. After explaining the principle and presenting the standard implementation, the latest developments in this class of sensors will be introduced, such as the possibility to measure with a spatial resolution of 10 cm and below while preserving the full accuracy on the determination of temperature and strain. 相似文献
50.
Practical silicon photonic interconnects become possible nowadays after the realization of the practical silicon light sources,where the hybrid integrations of Ⅲ-Ⅴ semiconductors and silicon by bonding... 相似文献