全文获取类型
收费全文 | 88408篇 |
免费 | 345篇 |
国内免费 | 382篇 |
专业分类
化学 | 24809篇 |
晶体学 | 800篇 |
力学 | 6747篇 |
数学 | 32099篇 |
物理学 | 15283篇 |
无线电 | 9397篇 |
出版年
2018年 | 11826篇 |
2017年 | 11449篇 |
2016年 | 6951篇 |
2015年 | 906篇 |
2014年 | 360篇 |
2013年 | 365篇 |
2012年 | 4180篇 |
2011年 | 11695篇 |
2010年 | 6859篇 |
2009年 | 6812篇 |
2008年 | 7213篇 |
2007年 | 9675篇 |
2006年 | 258篇 |
2005年 | 1620篇 |
2004年 | 1803篇 |
2003年 | 2217篇 |
2002年 | 1114篇 |
2001年 | 264篇 |
2000年 | 314篇 |
1999年 | 168篇 |
1998年 | 211篇 |
1997年 | 165篇 |
1996年 | 218篇 |
1995年 | 142篇 |
1994年 | 103篇 |
1993年 | 111篇 |
1992年 | 70篇 |
1991年 | 83篇 |
1990年 | 66篇 |
1989年 | 80篇 |
1988年 | 69篇 |
1987年 | 68篇 |
1986年 | 69篇 |
1985年 | 67篇 |
1984年 | 61篇 |
1983年 | 53篇 |
1982年 | 68篇 |
1981年 | 71篇 |
1980年 | 72篇 |
1979年 | 65篇 |
1978年 | 61篇 |
1977年 | 43篇 |
1976年 | 33篇 |
1973年 | 43篇 |
1914年 | 47篇 |
1913年 | 40篇 |
1912年 | 40篇 |
1909年 | 41篇 |
1908年 | 41篇 |
1907年 | 33篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
81.
Inspired by an intuitive analogy that exists between the gray level textures and the miscibility in the multiphase fluids, the aura concept was developed from set theory tools in order to modeling the texture image. The gray level aura matrix (GLAM) has been then proposed to generalize the gray level cooccurrence matrix (GLCM) which remains very popular in the texture analysis. The GLAM indicates how much each gray level is present in the neighborhood of each other gray level. The neighborhood is defined by a structuring element as one used in mathematical morphology. The GLAM is mainly used and studied in synthesis and classification of textures framework but very few works are devoted to the segmentation. The aim of this paper is to exploit the GLAM for the segmentation of textured images. Experiments results over synthetic and real images show the efficiency of the GLAM. The influence of the shape and the size of the structuring element on the segmentation results are also studied. 相似文献
82.
Multi-electrode cuffs have been proposed as a means for the parallel recording of naturally-occurring neural signals. Compared to a conventional tripole cuff providing a single channel signal, additional information about the velocity and direction of nerve signals can be extracted from the multi-electrode recordings. Moreover, interference suppression is improved and overall power consumption reduced, as the analysis shows. In this paper a new recording system is proposed, each channel of which consists of a low-noise preamplifier employing lateral bipolar transistors to provide an impedance match to the tissue and a path to ground for the switching currents of a single high-gain amplifier, which is multiplexed between the channels. The proposed system provides low-noise, low-power operation and practically identical channel gains and is suitable for integration in a larger CMOS-based system. 相似文献
83.
84.
85.
86.
Raphael C.-W. Phan Jiang Wu Khaled Ouafi Douglas R. Stinson 《Wireless Personal Communications》2011,61(1):69-81
In this paper, we analyze the first known provably secure Radio Frequency Identification (RFID) authentication schemes that are designed to provide forward untraceability and backward untraceability: the L-K and S-M schemes. We show how to trace tags in the L-K scheme without needing to corrupt tags. We also show that if a standard cryptographic pseudorandom bit generator (PRBG) is used in the S-M scheme, then the scheme may fail to provide forward untraceability and backward untraceability. To achieve the desired untraceability features, we show that the S-M scheme can use a robust PRBG which provides forward security and backward security. We also note that the backward security is stronger than necessary for the backward untraceability of the S-M scheme. 相似文献
87.
M-ary phase-silence-shift-keying (PSSK), one of power-efficient modulation schemes, has enhanced symbol error rate (SER) performance by 6 dB compared with that of the conventional phase-shift-keying (PSK). Phase tracking problem of the PSSK with phase-locked-loop (PLL) is discussed in this paper. Capacity of the PSSK for the additive white Gaussian noise (AWGN) channel and Rayleigh fading channel is analyzed. Capacity loss of the PSSK due to the PLL is small, which tells us that the PSSK demodulator can be practically implemented. 相似文献
88.
89.
90.