全文获取类型
收费全文 | 151064篇 |
免费 | 22517篇 |
国内免费 | 17235篇 |
专业分类
化学 | 79953篇 |
晶体学 | 1278篇 |
力学 | 6667篇 |
综合类 | 781篇 |
数学 | 14017篇 |
物理学 | 43995篇 |
无线电 | 44125篇 |
出版年
2024年 | 629篇 |
2023年 | 3487篇 |
2022年 | 4689篇 |
2021年 | 5825篇 |
2020年 | 5773篇 |
2019年 | 5229篇 |
2018年 | 4905篇 |
2017年 | 4735篇 |
2016年 | 6524篇 |
2015年 | 7017篇 |
2014年 | 8611篇 |
2013年 | 10888篇 |
2012年 | 12618篇 |
2011年 | 12883篇 |
2010年 | 9547篇 |
2009年 | 9518篇 |
2008年 | 9916篇 |
2007年 | 8875篇 |
2006年 | 8416篇 |
2005年 | 7304篇 |
2004年 | 5380篇 |
2003年 | 4491篇 |
2002年 | 4129篇 |
2001年 | 3467篇 |
2000年 | 3181篇 |
1999年 | 3272篇 |
1998年 | 2784篇 |
1997年 | 2375篇 |
1996年 | 2350篇 |
1995年 | 2087篇 |
1994年 | 1755篇 |
1993年 | 1477篇 |
1992年 | 1304篇 |
1991年 | 1094篇 |
1990年 | 907篇 |
1989年 | 648篇 |
1988年 | 510篇 |
1987年 | 411篇 |
1986年 | 409篇 |
1985年 | 334篇 |
1984年 | 248篇 |
1983年 | 204篇 |
1982年 | 153篇 |
1981年 | 93篇 |
1980年 | 69篇 |
1979年 | 30篇 |
1978年 | 32篇 |
1976年 | 30篇 |
1975年 | 27篇 |
1957年 | 31篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
论文提出了一种混沌通信系统的噪音衰减算法,该算法利用混沌同步现象在接收端获得正确的噪音估计值,从而从接收信号中滤除噪音恢复出正确的信号。通过数值仿真试验表明该方法是可行的。 相似文献
82.
人工智能的原理及应用 总被引:7,自引:0,他引:7
介绍了人工智能的发展,并对改进的神经网络专家系统的优越性做了介绍,指出了神经网络专家系统广阔的应用前景及实现。 相似文献
83.
We consider the effect of multiple fibers on wavelength division multiplexing networks without wavelength conversion. We study networks with dynamic wavelength routing and develop accurate analytical models to compare various possible options using single- and multiple-fiber networks. We use results of an analytical model and simulation-based studies to evaluate the blocking performance and cost of multifiber networks. The number of fibers required providing high performance in multifiber networks and their costs are compared. A case is made for using multiple fibers in each link with fewer wavelengths instead of using a single fiber with many wavelengths. In particular, we show that a network with four fibers per link and with four wavelengths on each fiber without any wavelength conversion on any node yields similar same performance as the networks with one fiber per link and 16 wavelengths per fiber on each link and with full wavelength conversion capability on all nodes. In addition, the multifiber network may also offer the cost advantage depending on the relative cost of components. We develop a parametric cost model to show that multiple fibers in each link are an attractive option. Finally, such multifiber networks also has fault tolerance, with respect to a single fiber failure, already built into the system. 相似文献
84.
Shi-Jin Ding Hang Hu Lim H.F. Kim S.J. Yu X.F. Chunxiang Zhu Li M.F. Byung Jin Cho Chan D.S.H. Rustagi S.C. Yu M.B. Chin A. Dim-Lee Kwong 《Electron Device Letters, IEEE》2003,24(12):730-732
For the first time, we successfully fabricated and demonstrated high performance metal-insulator-metal (MIM) capacitors with HfO/sub 2/-Al/sub 2/O/sub 3/ laminate dielectric using atomic layer deposition (ALD) technique. Our data indicates that the laminate MIM capacitor can provide high capacitance density of 12.8 fF//spl mu/m/sup 2/ from 10 kHz up to 20 GHz, very low leakage current of 3.2 /spl times/ 10/sup -8/ A/cm/sup 2/ at 3.3 V, small linear voltage coefficient of capacitance of 240 ppm/V together with quadratic one of 1830 ppm/V/sup 2/, temperature coefficient of capacitance of 182 ppm//spl deg/C, and high breakdown field of /spl sim/6 MV/cm as well as promising reliability. As a result, the HfO/sub 2/-Al/sub 2/O/sub 3/ laminate is a very promising candidate for next generation MIM capacitor for radio frequency and mixed signal integrated circuit applications. 相似文献
85.
介绍数字正交上变频器AD9857的原理、功能和基本使用方法以及如何通过单片机8051实现对它的编程控制。 相似文献
86.
Yang C.W. Fang Y.K. Lin C.S. Tsair Y.S. Chen S.M. Wang W.D. Wang M.F. Cheng J.Y. Chen C.H. Yao L.G. Chen S.C. Liang M.S. 《Electronics letters》2003,39(21):1499-1501
A novel technique to form high-K dielectric of HfSiON by doping base oxide with Hf and nitridation with NH/sub 3/, sequentially, is proposed. The HfSiON gate dielectric demonstrates excellent device performances such as only 10% degradation of saturation drain current and almost 45 times of magnitude reduction in gate leakage compared with conventional SiO/sub 2/ gate at the approximately same equivalent oxide thickness. Additionally, negligible flatband voltage shift is achieved with this technique. Time-dependent dielectric breakdown tests indicate that the lifetime of HfSiON is longer than 10 years at V/sub dd/=2 V. 相似文献
87.
VCOs fully integrated in an SiGe preproduction technology are presented. By cutting interconnection lines a wide frequency range can be covered, up to 88.4 GHz. Special effort has been made to meet the demands for 77 GHz automotive radar. In the corresponding tuning range from 75.3 to 79.6 GHz, an output power of about 11 dBm (with -2.2 dBm potential measurement uncertainty) was achieved for each of the two complementary outputs, i.e. in total 14 dBm. The phase noise is about -94 dBc/Hz at 1 MHz offset frequency. 相似文献
88.
89.
90.
Jun-Fa Mao Zheng-Fan Li 《Microwave Theory and Techniques》1992,40(4):637-644
A new method for analysis of the time response of multiconductor transmission lines with frequency-dependent losses is presented. This method can solve the time response of various kinds of transmission lines with arbitrary terminal networks. Particularly, it can analyze nonuniform lines with frequency-dependent losses, for which no effective method for analyzing their time response exists. This method starts from the frequency-domain telegrapher's equations. After decoupling and inversely Fourier transforming, then a set of decoupled time-domain equations including convolutions are given. These equations can be solved with the characteristic method. The results obtained with this method are stable and accurate. Two examples are given to illustrate the application of this method to various multiconductor transmission lines 相似文献