全文获取类型
收费全文 | 27181篇 |
免费 | 4229篇 |
国内免费 | 3020篇 |
专业分类
化学 | 14476篇 |
晶体学 | 208篇 |
力学 | 1526篇 |
综合类 | 196篇 |
数学 | 2328篇 |
物理学 | 8003篇 |
无线电 | 7693篇 |
出版年
2024年 | 114篇 |
2023年 | 666篇 |
2022年 | 812篇 |
2021年 | 1064篇 |
2020年 | 1048篇 |
2019年 | 981篇 |
2018年 | 831篇 |
2017年 | 733篇 |
2016年 | 1159篇 |
2015年 | 1273篇 |
2014年 | 1481篇 |
2013年 | 1906篇 |
2012年 | 2196篇 |
2011年 | 2387篇 |
2010年 | 1569篇 |
2009年 | 1564篇 |
2008年 | 1586篇 |
2007年 | 1495篇 |
2006年 | 1536篇 |
2005年 | 1255篇 |
2004年 | 1060篇 |
2003年 | 825篇 |
2002年 | 748篇 |
2001年 | 675篇 |
2000年 | 648篇 |
1999年 | 609篇 |
1998年 | 568篇 |
1997年 | 470篇 |
1996年 | 459篇 |
1995年 | 431篇 |
1994年 | 397篇 |
1993年 | 305篇 |
1992年 | 313篇 |
1991年 | 251篇 |
1990年 | 211篇 |
1989年 | 179篇 |
1988年 | 112篇 |
1987年 | 103篇 |
1986年 | 87篇 |
1985年 | 85篇 |
1984年 | 48篇 |
1983年 | 46篇 |
1982年 | 40篇 |
1981年 | 24篇 |
1980年 | 15篇 |
1979年 | 9篇 |
1977年 | 7篇 |
1975年 | 7篇 |
1969年 | 4篇 |
1957年 | 8篇 |
排序方式: 共有10000条查询结果,搜索用时 8 毫秒
111.
Ma Z.J. Chen J.C. Liu Z.H. Krick J.T. Cheng Y.C. Hu C. Ko P.K. 《Electron Device Letters, IEEE》1994,15(3):109-111
It has been reported that high-temperature (~1100°C) N2 O-annealed oxide can block boron penetration from poly-Si gates to the silicon substrate. However, this high-temperature step may be inappropriate for the low thermal budgets required of deep-submicron ULSI MOSFETs. Low-temperature (900~950°C) N2O-annealed gate oxide is also a good barrier to boron penetration. For the first time, the change in channel doping profile due to compensation of arsenic and boron ionized impurities was resolved using MOS C-V measurement techniques. It was found that the higher the nitrogen concentration incorporated at Si/SiO2 interface, the more effective is the suppression of boron penetration. The experimental results also suggest that, for 60~110 Å gate oxides, a certain amount of nitrogen (~2.2%) incorporated near the Si/SiO2 interface is essential to effectively prevent boron diffusing into the underlying silicon substrate 相似文献
112.
中国宽带业务的发展面临诸多问题:内容建设严重滞后于网络建设、缺少盈利的“杀手”业务、服务水平尚未达到宽带需求、恶性竞争产生网络泡沫以及产业环境尚不完善等。要想改善现状,宽带接入建设应采取下列措施:借助政府力量、联合社会力量、准确定位市场、丰富接入手段以及加强技术培训等。 相似文献
113.
This paper presents a novel approach to computing tight upper bounds on the processor utilization for general real-time systems where tasks are composed of subtasks and precedence constraints may exist among subtasks of the same task. By careful analysis of preemption effects among tasks, the problem is formulated as a set of linear programming (LP) problems. Observations are made to reduce the number of LP problem instances required to be solved, which greatly improves the computation time of the utilization bounds. Furthermore, additional constraints are allowed to be included under certain circumstances to improve the quality of the bounds. 相似文献
114.
Design of a 3780-point IFFT processor for TDS-OFDM 总被引:2,自引:0,他引:2
Zhi-Xing Yang Yu-Peng Hu Chang-Yong Pan Lin Yang 《Broadcasting, IEEE Transactions on》2002,48(1):57-61
This correspondence presents a design of 3780-point IFFT processor for TDS-OFDM terrestrial DTV transmitter using FPGA. It demonstrates the algorithm design and error analysis of the processor, which can achieve a throughput of 7.56M complex IFFT operations per second. This design meets the signal-to-quantization noise ratio requirement of the TDS-OFDM system. It consists of two FPGA and one dual-port RAM. The data stream pipeline algorithm is implemented 相似文献
115.
116.
结构振动控制中压电阻尼技术研究—压电被动阻尼技术(一) 总被引:6,自引:3,他引:3
压电阻尼技术有两种类型:压电被动阻尼技术和压电主动阻尼技术。本文对其中的压电被动阻尼技术进行了研究,结果表明:通过给压电元件并联适当的外部电路,可使压电系统具有与粘弹阻尼材料及动力吸振器相似的物理特性。合理配置电路参数,可以实现最优阻尼比。 相似文献
117.
The study of bed-load transport is of great significance both in theory and in practice. This paper discusses the saltation
of bed-load solid grains in flowing water. Experiments and theoretic analysis have been made by means of high-speed photographing
and advanced data processing technique with a combined method based on mechanical and statistical theories. It indicates that
the saltation is the main form of the bed-load transport under ordinary flowing conditions. In the meantime, taking successive
saltation as the model of bed-load transport, systematic analysis has been made with regard to the kinematic properties and
mechanism of saltation. The statistical analysis shows that the probability density functions of the relative height and length
of saltation are in conformity with Γ-type distribution, while the probability density functions of the relative velocities
of saltation are in conformity with the Gaussian distribution.
The project supported by National Natural Science Foundation of China 相似文献
118.
An electromigration failure model which can be used to project the electromigration lifetime under pulsed DC and AC current stressing has been reported. The experimental results indicate that different metallization systems (Al-2%Si, Al4%Cu/TiW, and Cu) show similar failure behaviors, which can be explained and predicted by this model. The pulsed DC lifetime is found to be longer than DC lifetime, and the AC lifetime is found to be very much longer. This recognition can provide significant relief to circuit designs involving metals carrying pulsed DC and AC currents, and allow a more aggressive design to improve circuit density and speed 相似文献
119.
Hu Gang 《Zeitschrift für Physik B Condensed Matter》1986,64(2):247-252
The master equation and the Fokker-Planck equation are compared thoroughly in both of the stationary and the time-dependent cases for a one-dimensional system. The comparison includes the master equation without detailed balance. 相似文献
120.
Seoijin Park R. Leavitt R. Enck V. Luciani Y. Hu P.J.S. Heim D. Bowler M. Dagenais 《Photonics Technology Letters, IEEE》2005,17(5):980-982
A semiconductor optical amplifier was developed for coarse wavelength-division-multiplexing (CWDM) operating over 1540-1620 nm (C-L band). A unique quantum-well structure was designed to meet the requirements for the CWDM operation such as wide bandwidth, low polarization-dependent gain, and high-saturation power at the short wavelength end of the band (1540 nm). Over the band, 24-dB maximum chip gain was obtained with less than 4.3-dB gain flatness and more than 14.6-dBm saturation power. 相似文献