全文获取类型
收费全文 | 232篇 |
免费 | 84篇 |
国内免费 | 14篇 |
专业分类
化学 | 143篇 |
晶体学 | 2篇 |
力学 | 18篇 |
综合类 | 29篇 |
数学 | 18篇 |
物理学 | 120篇 |
出版年
2024年 | 4篇 |
2023年 | 6篇 |
2022年 | 2篇 |
2021年 | 4篇 |
2020年 | 3篇 |
2019年 | 7篇 |
2018年 | 5篇 |
2017年 | 3篇 |
2016年 | 4篇 |
2015年 | 6篇 |
2014年 | 4篇 |
2013年 | 7篇 |
2012年 | 7篇 |
2011年 | 11篇 |
2010年 | 8篇 |
2009年 | 7篇 |
2008年 | 3篇 |
2007年 | 3篇 |
2006年 | 2篇 |
2005年 | 2篇 |
2004年 | 6篇 |
2003年 | 44篇 |
2002年 | 63篇 |
2001年 | 57篇 |
2000年 | 24篇 |
1999年 | 26篇 |
1998年 | 2篇 |
1997年 | 2篇 |
1996年 | 1篇 |
1995年 | 3篇 |
1994年 | 1篇 |
1993年 | 1篇 |
1985年 | 2篇 |
排序方式: 共有330条查询结果,搜索用时 523 毫秒
141.
142.
给出了一种处理宽带天线双端匹配的改进实频法。该方法将匹配网络输入阻抗的实部近似用对数坐标中的若干直线段表示,简化了相位函数的计算,降低了功率增益传输函数的非线性。结合实际天线进行了宽带匹配网络的设计和计算,结果表明文中所述方法的正确性。 相似文献
143.
高频地波雷达接收机研制 总被引:16,自引:2,他引:14
论述了调频中断连续波(FMICW)信号解调原理,分析了用于海洋环境监测、采用FMICW体制接收机的特点,给出了相控阵高频地波雷达多通道接收机的技术要求及设计要点,对工作在干扰和噪声特别大环境中的短波低频段接收机提出了应采取的抗干扰措施。现场实验表明,该多通道接收机在选择性、灵敏度和抗干扰性能方面达到了设计技术指标要求。 相似文献
144.
用甲基紫催化褪色的新指示反应测定痕量钯 总被引:8,自引:2,他引:6
研究了痕量 Pd( )对次磷酸钠还原甲基紫的催化作用的最优化条件和动力学参数 ,建立了催化动力学光度法测定痕量钯的方法。在最大吸收波长 590 nm处分别测定催化体系和非催化体系的吸光度 A和 A0 ,以 ΔA=A0 - A定量 ,线性范围 4.0~ 2 8ng·ml-1,检出限 9.63× 1 0 -2 ng·ml-1,用于合金试样的测定 ,结果满意。 相似文献
145.
应用于聚合物中的正电子湮没寿命谱技术 总被引:3,自引:0,他引:3
正电子湮没寿命谱技术是一种新型聚合物结构探测与表征技术,针对此技术在聚合物自由体积研究中的应用,首先介绍了该技术的基本原理和应用理论,接着针对寿命谱数据的处理手段和计算方法,对国内外的研究进展进行了概述和总结,最后展示了该技术在聚合物材料研究中用于基本理论,实际运用和结构理论等三个方面的情况。 相似文献
146.
147.
148.
Dongxian Zhuo Aijuan Gu Yuanzhen Wang Guozheng Liang Jiang‐tao Hu Li Yuan Wei Yao 《先进技术聚合物》2012,23(7):1121-1128
The correlation between microstructure and dielectric properties of cyanate ester (CE)/hollow silicate tube (HST) hybrids was investigated by positron annihilation lifetime spectroscopy, coincidence Doppler‐broadening spectroscopy, Fourier transform infrared spectra, and dynamic mechanical analyses. The addition of HST to CE resin brings a multi‐aspect influence (cross‐linked structure and density, free volume, and interfacial action) on the structure of the cross‐linked network and thus results in significantly varied dielectric properties. There is an optimum content of HST in hybrids to get the lowest dielectric constant and loss. When the content of HST is smaller than the percolation threshold, the hybrid has decreased dielectric constant and loss; this mainly results in the reduced size of free volume and orthopositronium intensity (I3), although when the content of HST is larger than the threshold, the increased I3 and the size of free volume as well as the interfacial polarization are responsible for the significantly enlarged dielectric constant and loss. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
149.
Li rong Yang Cai yun Shao Zi liang Wang Jiang tao Liu Lin fang Zhou 《Journal of chemical crystallography》2010,40(1):58-63
Abstract
The complex [Mn(PMBP)2(CH3OH)2] of manganese(II) with 1-phenyl-3-methyl- 4-benzoyl-5-pyrazolone (PMBP) was prepared and characterized by elemental analysis, thermal analysis, IR. The crystal structure of the complex determined by single crystal X-ray analysis, indicates that PMBP is a bidentate ligand in the complex and Mn(II) atom is six-coordinated and is in a meridional octahedral environment. The compound crystallizes in the monoclinic system, space group P 2(1)/c, with a = 11.038(10) ?, b = 16.254(15) ?, c = 9.540(9) ?, α = 90.00°, β = 105.112(10)°, γ = 90.00°, V = 1,652(3) ?3, D x = 1.354 g cm−3 and Z = 2. The thermal decomposition kinetics of the complex was investigated under nonisothermal conditions using the Achar differential method and the Coats–Redfern integral method. 相似文献150.
Jiang‐tao Hu Aijuan Gu Zhijun Jiang Guozheng Liang Dongxian Zhuo Li Yuan Beijing Zhang Xiangxiu Chen 《先进技术聚合物》2012,23(8):1219-1228
An improved method is developed to synthesize octavinylsilsesquioxanes (VPOSS) with shorter time and higher yield, and then VPOSS is used to prepare new hybrids based on bismaleimide‐triazine (BD/CE) resin, coded as VPOSS/BD/CE. The effect of the content of VPOSS on the key properties including curing behavior, thermal, mechanical, and dielectric properties as well as water resistance of VPOSS/BD/CE hybrids were systematically discussed. Compared with BD/CE resin, hybrids show similar curing behavior but different chemical structures and thus macro‐performance. These key properties of hybrids are dependent on the content of VPOSS, all hybrids show significantly improved dielectric properties, water resistance, and dimensional stability; moreover, the hybrids with suitable content of VPOSS have bigger impact strengths. Specifically, with the addition of 7 wt% VPOSS to BD/CE resin, the dielectric constant decreases from 3.7 to 3.2, the dielectric loss decreases 55%, and the coefficient of thermal expansion reduces 23%; moreover, the glass transition temperature and initial decomposition temperature increase about 15°C. The attractive integrated properties suggest that VPOSS/BD/CE hybrids have great potential to be used as structural and functional materials for many cutting‐edge fields. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献