全文获取类型
收费全文 | 29824篇 |
免费 | 2267篇 |
国内免费 | 894篇 |
专业分类
化学 | 14679篇 |
晶体学 | 211篇 |
力学 | 783篇 |
综合类 | 51篇 |
数学 | 2302篇 |
物理学 | 5872篇 |
无线电 | 9087篇 |
出版年
2023年 | 402篇 |
2022年 | 418篇 |
2021年 | 703篇 |
2020年 | 648篇 |
2019年 | 704篇 |
2018年 | 572篇 |
2017年 | 590篇 |
2016年 | 942篇 |
2015年 | 921篇 |
2014年 | 1123篇 |
2013年 | 1718篇 |
2012年 | 1987篇 |
2011年 | 2205篇 |
2010年 | 1446篇 |
2009年 | 1518篇 |
2008年 | 1830篇 |
2007年 | 1780篇 |
2006年 | 1613篇 |
2005年 | 1449篇 |
2004年 | 1309篇 |
2003年 | 1162篇 |
2002年 | 1095篇 |
2001年 | 853篇 |
2000年 | 735篇 |
1999年 | 522篇 |
1998年 | 414篇 |
1997年 | 388篇 |
1996年 | 422篇 |
1995年 | 338篇 |
1994年 | 339篇 |
1993年 | 293篇 |
1992年 | 284篇 |
1991年 | 229篇 |
1990年 | 240篇 |
1989年 | 183篇 |
1988年 | 180篇 |
1987年 | 108篇 |
1986年 | 100篇 |
1985年 | 147篇 |
1984年 | 112篇 |
1983年 | 102篇 |
1982年 | 87篇 |
1981年 | 75篇 |
1980年 | 78篇 |
1979年 | 62篇 |
1978年 | 56篇 |
1977年 | 58篇 |
1976年 | 60篇 |
1974年 | 56篇 |
1973年 | 66篇 |
排序方式: 共有10000条查询结果,搜索用时 853 毫秒
91.
Jinwook Kim Jeongsik Yang Sangjin Byun Hyunduk Jun Jeongkyu Park Conroy C.S.G. Beomsup Kim 《Solid-State Circuits, IEEE Journal of》2005,40(2):462-471
This work presents a quad-channel serial-link transceiver providing a maximum full duplex raw data rate of 12.5Gb/s for a single 10-Gbit eXtended Attachment Unit Interface (XAUI) in a standard 0.18-/spl mu/m CMOS technology. To achieve low bit-error rate (BER) and high-speed operation, a mixed-mode least-mean-square (LMS) adaptive equalizer and a low-jitter delay-immune clock data recovery (CDR) circuit are used. The transceiver achieves BER lower than <4.5/spl times/10/sup -15/ while its transmitted data and recovered clock have a low jitter of 46 and 64 ps in peak-to-peak, respectively. The chip consumes 178 mW per each channel at 3.125-Gb/s/ch full duplex (TX/RX simultaneous) data rate from 1.8-V power supply. 相似文献
92.
Jui-Chieh Chiu Chieh-Pin Chang Mau-Phon Houng Yeong-Her Wang 《Microwave and Wireless Components Letters, IEEE》2006,16(1):19-21
A novel configuration of balanced frequency InGaAs pseudomorphic high electron mobility transistor (PHEMT) monolithic microwave integrated circuit (MMIC) tripler is proposed. A resonant LC filter is used to eliminate the fundamental frequency and a phase delay line is employed to suppress the second harmonic. The separation of the independent phase shifters makes the tripler more compact and flexible. The conversion loss of the tripler operating from 12 to 36GHz is less than 9.4dB at 9-dBm input power. As compared to the third-harmonic frequency, the fundamental frequency is suppressed more than 21.4dB while for the second harmonic is more than 22.3dB at 36GHz. 相似文献
93.
Trajectory design considering derivative of jerk for head-positioning of disk drive system with mechanical vibration 总被引:1,自引:0,他引:1
In this paper, we propose a novel design method of target trajectory for high-speed and high-precision head positioning of a hard disk drive (HDD) system. To realize smooth acceleration and deceleration, the derivative of jerk is considered not to activate any mechanical vibrations. We applied the well-known optimal control theory to fix the initial and terminal conditions. Moreover, we show that various performances can be improved by introducing time-varying weighting coefficients. Some experimental results using a 2.5-in HDD are shown to verify the effectiveness of the proposed method. 相似文献
94.
Da Yeon Park 《Tetrahedron letters》2007,48(9):1633-1636
Poly-substituted nitrobenzenes were synthesized from Baylis-Hillman adducts via the [3+3] annulation strategy as the key step. 1,3-Dinitroalkanes served as the 1,3-dinucleophilic component and the Baylis-Hillman acetates as a 1,3-dielectrophilic part. 相似文献
95.
The new phenylpropanoid diglycoside ligusinenoside A ( 1 ), and the two new 8,4′‐oxyneolignan(‘8‐O‐4′‐neolignan’) diglycosides ligusinenosides B ( 2 ) and C ( 3 ), together with nine known compounds, were isolated from the rhizomes of Ligusticum sinensis Oliv. The structures of 1 – 3 were elucidated on the basis of spectroscopic analyses. 相似文献
96.
97.
Ju Yeon Woo Eun Hee Kim Tae Hoon Yoon Jae Chang Kim Byung Kyu Kim 《Liquid crystals》2007,34(9):1115-1120
Chiral dopants were added to the formulation of holographic polymer-dispersed liquid crystals and the effects studied in terms of grating formation dynamics, morphology, diffraction efficiency, contrast ratio and electro-optical properties of the films. A gradual increase of real-time diffraction efficiency, decrease of droplet size and increase of diffraction efficiency of the composite film were obtained with the addition and increasing content of chiral dopant, due to the increased viscosity of the liquid crystal (LC) doped with the chiral dopant leading to decreased droplet coalescence. The contrast ratio decreased with increasing content of chiral dopant due to the difficult orientation of LC molecules caused by the formation of a helical structure. Addition of a small amount of the chiral dopant increased the driving voltage slightly, whereas the decay time is decreased significantly as a result of the high twisting of the helical structure. 相似文献
98.
Jin-Woo Park Jae Yeong Park Yeun-Ho Joung Allen M.G. 《Components and Packaging Technologies, IEEE Transactions on》2002,25(1):106-111
A new process for the fabrication of high current and very low profile micromachined inductors has been developed. This process involves the combination of mechanical lamination and electrodeposition of copper windings by means of LIGA-like lithography through thick epoxy photoresists. The dimension of the fabricated inductor is 16 mm×19 mm×1 mm. The fabricated inductor has an inductance value of 1.2 μH with DC saturation current of 3 A and an electrical resistance of less than 30 mΩ at 10 kHz 相似文献
99.
Young-Taek Lee Jong-Sik Lim Jun-Seok Park Ahn D. Sangwook Nam 《Microwave and Wireless Components Letters, IEEE》2002,12(2):39-41
A new technique to reduce the phase noise in microwave oscillators is developed using the resonant characteristic of the defected ground structure (DGS). Two kinds of oscillators have been designed and measured for the examination of the reduction of phase noise by the DGS. The first adopts the DGS section under the microstrip line at the gate circuit, while the second has only the conventional microstrip line. Measurement shows reduced phase noise by 10-15 dB in the oscillator with the DGS compared to the conventional one 相似文献
100.