全文获取类型
收费全文 | 44644篇 |
免费 | 5871篇 |
国内免费 | 4773篇 |
专业分类
化学 | 24099篇 |
晶体学 | 342篇 |
力学 | 2220篇 |
综合类 | 347篇 |
数学 | 3794篇 |
物理学 | 11724篇 |
无线电 | 12762篇 |
出版年
2024年 | 112篇 |
2023年 | 1028篇 |
2022年 | 1020篇 |
2021年 | 1480篇 |
2020年 | 1581篇 |
2019年 | 1510篇 |
2018年 | 1260篇 |
2017年 | 1241篇 |
2016年 | 1740篇 |
2015年 | 1811篇 |
2014年 | 2226篇 |
2013年 | 2979篇 |
2012年 | 3562篇 |
2011年 | 3695篇 |
2010年 | 2588篇 |
2009年 | 2607篇 |
2008年 | 2748篇 |
2007年 | 2564篇 |
2006年 | 2391篇 |
2005年 | 2079篇 |
2004年 | 1496篇 |
2003年 | 1374篇 |
2002年 | 1302篇 |
2001年 | 1081篇 |
2000年 | 1052篇 |
1999年 | 1105篇 |
1998年 | 970篇 |
1997年 | 864篇 |
1996年 | 923篇 |
1995年 | 755篇 |
1994年 | 693篇 |
1993年 | 584篇 |
1992年 | 564篇 |
1991年 | 467篇 |
1990年 | 349篇 |
1989年 | 260篇 |
1988年 | 204篇 |
1987年 | 170篇 |
1986年 | 165篇 |
1985年 | 143篇 |
1984年 | 108篇 |
1983年 | 77篇 |
1982年 | 52篇 |
1981年 | 42篇 |
1980年 | 23篇 |
1978年 | 23篇 |
1977年 | 25篇 |
1976年 | 21篇 |
1975年 | 34篇 |
1974年 | 28篇 |
排序方式: 共有10000条查询结果,搜索用时 328 毫秒
101.
Jihua Zhang Xi WangWeidong Yu Tao FengFumin Zhang Zhihong ZhengQiong Li Xianghuai Liu 《Solid State Communications》2003,127(4):289-293
Effects of ion impinging on the microstructure and field electron emission properties of screen-printed carbon nanotube films were investigated. We observed that the plasma treatment modified the microstructure of CNTs along with the remarkable increase of emission site density. With the prolongation of ion impinging time, the emission current falls down first, and then rises up to higher than that of the untreated films. It is proposed that the change of emission characteristics is due to the different emission mechanisms. After the treatment, electrons are emitted predominantly from the nano-nodes on the tube wall instead from the nanotube tips. 相似文献
102.
A fluorous osmium catalyst was firstly developed. It had been effectively used as recoverable and reusable catalyst in the dihydroxylation of olefins. 相似文献
103.
变频器在暖通空调行业中的应用 总被引:1,自引:0,他引:1
本文提出中央空调系统的一种变频调速改造方案,介绍了该系统的结构组成及运行原理,对系统各部分的作用进行了讨论。 相似文献
104.
Li Yingle Huang Jiying Gong Shuohong 《International Journal of Infrared and Millimeter Waves》2003,24(6):953-961
The dielectric constant for rain medium is investigated by utilizing the system identification method. The rain rate model and frequency model of permittivity in millimeter waves band for rain medium are presented. The results obtained with models are in very good agreement with references in calculating the attenuation of electromagnetic waves induced by rain, which Shows that the obtained models are valid and practicable. The cross-polar discrimination gotten with rain rate model is in agreement with references. 相似文献
105.
106.
A Low-Power CMOS Linear-in-Decibel Variable Gain Amplifier With Programmable Bandwidth and Stable Group Delay 总被引:1,自引:0,他引:1
Tsou S.-C. Li C.-F. Huang P.-C. 《Circuits and Systems II: Express Briefs, IEEE Transactions on》2006,53(12):1436-1440
This brief presents a new circuit architecture for linear-in-decibel, constant-bandwidth variable gain amplifier (VGA). To obtain high linearity under low-voltage operation, this VGA is a closed-loop structure. In loop amplifier design, two techniques are applied: first, the loop amplifier is given finite input impedance. This arrangement keeps the VGA bandwidth constant under different gain setting. Second, a current-buffered compensation is applied for loop stability. Compared to the Miller compensation, this method achieves wider bandwidth. The prototype chip using 0.18-mum CMOS technology demonstrates that -10- to 20-dB gain and 0.5- to 30-MHz bandwidth can be programmed independently. The group delay difference within 30-dB gain control range is smaller than 1%. The total circuit dissipates 1.35 mA from a 1.8-V supply 相似文献
107.
Zhang Xinliang Huang Dexiu Sun Junqiang Liu Deming 《Optical and Quantum Electronics》2004,36(7):627-634
A simple scheme for single to multi-channel wavelength conversion based on cross-gain modulation of amplified spontaneous emission (ASE) spectrum in semiconductor optical amplifier (SOA) is described. Single to 16-channel wavelength conversion at 10 Gb/s is first demonstrated without any additional probe lights, the modulation information carried by input signal could be converted into arbitrary many channels if only the demultiplexer with enough channels is exploited. Output performance and pattern effects are investigated experimentally. 相似文献
108.
Wei Li Zhang Wei Pan Bin Luo Xi Hua Zou Meng Yao Wang 《Photonics Technology Letters, IEEE》2008,20(9):712-714
A theoretical construction of one-to-many (OTM) and many-to-one (MTO) chaos synchronization communications using semiconductor lasers is presented. One center laser provides strong injections (strong link) to other side lasers, and the side lasers also provide weak injections (weak link) to the center one. Simulation results show that the side lasers synchronize with the center laser through injection-locking. In addition, messages transmitted via the strong links or the weak links experience strong chaos pass filtering, enabling us to realize OTM and MTO communications. 相似文献
110.
J. Song H. Jiang Z.J. Liu D.Y. Khang Y. Huang J.A. Rogers C. Lu C.G. Koh 《International Journal of Solids and Structures》2008,45(10):3107-3121
A finite-deformation theory is developed to study the mechanics of thin buckled films on compliant substrates. Perturbation analysis is performed for this highly nonlinear system to obtain the analytical solution. The results agree well with experiments and finite element analysis in wavelength and amplitude. In particular, it is found that the wavelength depends on the strain. Based on the accurate wavelength and amplitude, the membrane and peak strains in thin films, and stretchability and compressibility of the system are also obtained analytically. 相似文献