全文获取类型
收费全文 | 11485篇 |
免费 | 223篇 |
国内免费 | 46篇 |
专业分类
化学 | 5802篇 |
晶体学 | 87篇 |
力学 | 357篇 |
数学 | 1633篇 |
物理学 | 2472篇 |
无线电 | 1403篇 |
出版年
2022年 | 99篇 |
2021年 | 120篇 |
2020年 | 133篇 |
2019年 | 142篇 |
2018年 | 144篇 |
2017年 | 113篇 |
2016年 | 222篇 |
2015年 | 175篇 |
2014年 | 190篇 |
2013年 | 586篇 |
2012年 | 390篇 |
2011年 | 478篇 |
2010年 | 357篇 |
2009年 | 319篇 |
2008年 | 459篇 |
2007年 | 452篇 |
2006年 | 406篇 |
2005年 | 373篇 |
2004年 | 390篇 |
2003年 | 322篇 |
2002年 | 327篇 |
2001年 | 241篇 |
2000年 | 240篇 |
1999年 | 192篇 |
1998年 | 151篇 |
1997年 | 169篇 |
1996年 | 212篇 |
1995年 | 164篇 |
1994年 | 155篇 |
1993年 | 177篇 |
1992年 | 177篇 |
1991年 | 189篇 |
1990年 | 144篇 |
1989年 | 141篇 |
1988年 | 160篇 |
1987年 | 190篇 |
1986年 | 162篇 |
1985年 | 210篇 |
1984年 | 195篇 |
1983年 | 162篇 |
1982年 | 176篇 |
1981年 | 187篇 |
1980年 | 181篇 |
1979年 | 181篇 |
1978年 | 171篇 |
1977年 | 172篇 |
1976年 | 146篇 |
1975年 | 164篇 |
1974年 | 131篇 |
1973年 | 130篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
2.
3.
4.
5.
6.
7.
Per-tone equalization has recently been proposed as an alternative receiver structure for discrete multitone-based systems improving upon the well-known structure based on time-domain equalization. Fast initialization of all the equalizer coefficients has been identified as an open problem. In this letter, a recursive initialization scheme based on recursive least squares with inverse updating is presented for the per-tone equalizers. Simulation results show convergence with an acceptably small number of training symbols. Complexity calculations are made for per-tone equalization and for the case where tones are grouped. It is demonstrated with an example that in the latter case, initialization complexity becomes sufficiently low and comparable to complexity during data transmission. 相似文献
8.
A finite element method (FEM) is implemented to compute the radar cross section of a two-dimensional (2D) cavity embedded in an infinite ground plane. The method is based on the variational formulation which uses the Fourier transform to couple the fields outside the cavity and those inside the cavity; hence, the scattering problem can be reduced to a bounded domain. The convergence of the discrete finite element problem is analyzed. Numerical results are presented and compared with those obtained by the standard finite element-Green function method and by the 2D integral equation method. 相似文献
9.
Ho Van Khuong Hyung-Yun Kong 《Communications Letters, IEEE》2006,10(3):159-161
In order to evaluate exactly the performance of some diversity schemes, the probability density function (pdf) of a sum of independent exponential random variables (r.v.'s) must be known. This paper proposes a simple method to find it by using characteristic function., The resultant pdf is successfully applied to formulate the closed-form BER expression of 2 Tx-J Rx transmit diversity as well as the outage probability of repetition coding. 相似文献
10.
Montanari D. Van Houdt J. Groeseneken G. Maes H.E. 《Solid-State Circuits, IEEE Journal of》1998,33(7):1090-1095
This paper presents a high-speed, small-area circuit specifically designed to identify the levels in the read out operation of a flash multilevel memory. The circuit is based on the analog computation of the Euclidean distance between the current read out from a memory cell and the reference currents that represent the different logic levels. An experimental version of the circuit has been integrated in a standard double-metal 0.7-μm CMOS process with a die area of only 140×100 μm2. Operating under a 5-V power supply, this circuit identifies the read-out current of a memory cell, and associates it with the appropriate logic level in 9 ns 相似文献