全文获取类型
收费全文 | 157篇 |
免费 | 78篇 |
国内免费 | 109篇 |
专业分类
化学 | 171篇 |
晶体学 | 1篇 |
数学 | 7篇 |
物理学 | 165篇 |
出版年
2022年 | 2篇 |
2021年 | 8篇 |
2020年 | 3篇 |
2019年 | 7篇 |
2018年 | 4篇 |
2017年 | 8篇 |
2016年 | 5篇 |
2015年 | 12篇 |
2014年 | 14篇 |
2013年 | 22篇 |
2012年 | 31篇 |
2011年 | 19篇 |
2010年 | 29篇 |
2009年 | 29篇 |
2008年 | 28篇 |
2007年 | 21篇 |
2006年 | 20篇 |
2005年 | 14篇 |
2004年 | 13篇 |
2003年 | 11篇 |
2002年 | 12篇 |
2001年 | 5篇 |
2000年 | 3篇 |
1999年 | 7篇 |
1998年 | 3篇 |
1997年 | 3篇 |
1996年 | 5篇 |
1995年 | 2篇 |
1994年 | 1篇 |
1992年 | 1篇 |
1990年 | 1篇 |
1981年 | 1篇 |
排序方式: 共有344条查询结果,搜索用时 15 毫秒
111.
Design of Infrared Inverted Telephoto-Optical System with Double-Layer Harmonic Diffractive Element 总被引:1,自引:0,他引:1 下载免费PDF全文
A double-layer harmonic diffractive element (HDE) structure is investigated and the optimization procedure is given based on the equation of diffraction efficiency of the double-layer diffractive optical element. A new infrared double-layer inverted telephoto-optical system with an HDE is designed, which can work in the mid- and farinfrared wavebands. The diffraction efficiency of the system at each wavelength in the designed two wavebands is larger than 90%, which improves the image contrast and the imaging quality significantly. 相似文献
112.
113.
We report on the formation of one- and two-dimensional (1D and 2D) nanohole arrays on the surface of a silicon wafer by scanning with a femtosecond laser with appropriate power and speed. The underlying physical mechanism is revealed by numerical simulation based on the finite-difference time-domain technique. It is found that the length and depth of the initially formed gratings (or ripples) plays a crucial role in the generation of 1D or 2D nanohole arrays. The silicon surface decorated with such nanohole arrays can exhibit vivid structural colors through efficiently diffracting white light. 相似文献
114.
115.
Qi Pan Hui Chen Zhenguo Wu Yuan Wang Benhe Zhong Li Xia Prof. Hai-Ying Wang Prof. Guanwei Cui Prof. Xiaodong Guo Prof. Xuping Sun 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(4):971-975
The design and development of electrode materials with high specific capacity and long cycling life for sodium-ion batteries (SIBs) is still a critical challenge. In this communication, we report the development of tungsten phosphide (WP) nanowire on carbon cloth (WP/CC) as an anode for SIBs. The WP/CC exhibits superior sodium storage capability with 502 mA h g−1 at 0.1 A g−1. Moreover, this anode is capable of delivering a long lifespan at 2 A g−1 with an excellent capacity retention of 99 % after 1000 cycles. 相似文献
116.
Luo Na Wang Xue Huang Li-Jia Mi Qi-Li Zeng Wan-Li Xiang Hai-Ying Li Jing Liu Xin Hu Qiu-Fen Guo Ya-Dong Yang Guang-Yu Deng Liang Gao Qian 《Chemistry of Natural Compounds》2021,57(5):840-843
Chemistry of Natural Compounds - Eight phenolic compounds (1–8), including two new compounds (1 and 2), were isolated from the twigs of Gardenia jasminoides. Their structures were determined... 相似文献
117.
This paper describes the sensing properties of a potentiometric sensor based on a palladium oxide (PdO) electrode. Our investigation of the sensing mechanism is also discussed. We studied carbon monoxide (CO) sensing performance of a PdO electrode doped with Mg, Ni, and La, printed on zirconia. The results indicated that defects on the surface of PdO, which allow adsorption of CO, can effectively enhance the sensitivity of the sensors. To explore the source of the signal, a PdO-based electrode was printed on an alumina disc and a zeolite pellet for CO detection at 450℃. Notably the zeolite coupled with the PdO-based electrode to generate potentiometric responses to changes in CO concentration. According to the resistance and impedance measurements, the response to CO was ascribed to the changing interfacial potential between the PdO electrode and electrolyte. A model based on an electrochemical double layer between the PdO and electrolyte was determined to explain the behavior of the potentiometric sensor. It may be possible to harness these effects at PdO electrodes for the development of electrochemical sensors. 相似文献
118.
A monolithic distributed phase shifter based on right-handed nonlinear transmission lines at 30 GHz 下载免费PDF全文
The epitaxial material, device structure, and corresponding equivalent large signal circuit model of GaAs planar Schottky varactor diode are successfully developed to design and fabricate a monolithic phase shifter, which is based on right-handed nonlinear transmission lines and consists of a coplanar waveguide transmission line and periodically distributed GaAs planar Schottky varactor diode. The distributed-Schottky transmission-line-type phase shifter at a bias voltage greater than 1.5 V presents a continuous 0°–360° differential phase shift over a frequency range from 0 to 33 GHz. It is demonstrated that the minimum insertion loss is about 0.5 dB and that the return loss is less than-10 dB over the frequency band of 0–33 GHz at a reverse bias voltage less than 4.5 V. These excellent characteristics, such as broad differential phase shift, low insertion loss, and return loss, indicate that the proposed phase shifter can entirely be integrated into a phased array radar circuit. 相似文献
119.
The immunoactivity was evaluated of Dendrobium officinale Kimura & Migo, a Chinese herbal plant, and its crude polysaccharides. Different dosages of D. officinale and its polysaccharides were orally administered to healthy BALB/c mice. The control group was given distilled water. After 4 weeks, immune parameters, including cellular immunity (delayed-type hypersensitivity and natural killer cell activity), humoral immunity (serum hemolytic complement activity), nonspecific immunity (peritoneal macrophage phagocytosis) and interferon-gamma production by splenocytes were measured. The results showed that D. officinale and its polysaccharides can significantly enhance cellular immunity and nonspecific immunity in mice. Humoral immunity was also enhanced after oral administration of D. officinale, but the polysaccharides had no influence. Both D. officinale and its polysaccharides markedly increased IFN-gamma production by murine splenocytes. Six fractions were isolated from the polysaccharides; the molecular weight of the major fraction was 533,700 Da, and composed of mannose, glucose and rhamnose in a molar ratio of 7.3:1.3:1.0. 相似文献
120.