全文获取类型
收费全文 | 35880篇 |
免费 | 4592篇 |
国内免费 | 2082篇 |
专业分类
电工技术 | 8239篇 |
技术理论 | 1篇 |
综合类 | 3677篇 |
化学工业 | 1113篇 |
金属工艺 | 1020篇 |
机械仪表 | 3143篇 |
建筑科学 | 1338篇 |
矿业工程 | 1146篇 |
能源动力 | 1055篇 |
轻工业 | 672篇 |
水利工程 | 775篇 |
石油天然气 | 1208篇 |
武器工业 | 481篇 |
无线电 | 9615篇 |
一般工业技术 | 3030篇 |
冶金工业 | 1210篇 |
原子能技术 | 309篇 |
自动化技术 | 4522篇 |
出版年
2024年 | 196篇 |
2023年 | 459篇 |
2022年 | 808篇 |
2021年 | 930篇 |
2020年 | 1104篇 |
2019年 | 898篇 |
2018年 | 909篇 |
2017年 | 1192篇 |
2016年 | 1426篇 |
2015年 | 1603篇 |
2014年 | 2322篇 |
2013年 | 2188篇 |
2012年 | 2903篇 |
2011年 | 3020篇 |
2010年 | 2384篇 |
2009年 | 2254篇 |
2008年 | 2272篇 |
2007年 | 2785篇 |
2006年 | 2390篇 |
2005年 | 1897篇 |
2004年 | 1513篇 |
2003年 | 1340篇 |
2002年 | 1089篇 |
2001年 | 929篇 |
2000年 | 754篇 |
1999年 | 630篇 |
1998年 | 459篇 |
1997年 | 361篇 |
1996年 | 314篇 |
1995年 | 274篇 |
1994年 | 233篇 |
1993年 | 164篇 |
1992年 | 111篇 |
1991年 | 110篇 |
1990年 | 71篇 |
1989年 | 57篇 |
1988年 | 39篇 |
1987年 | 35篇 |
1986年 | 21篇 |
1985年 | 14篇 |
1984年 | 17篇 |
1983年 | 4篇 |
1982年 | 10篇 |
1981年 | 7篇 |
1980年 | 9篇 |
1979年 | 8篇 |
1975年 | 5篇 |
1963年 | 4篇 |
1959年 | 4篇 |
1954年 | 3篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
101.
102.
In this paper, we present some new results on frequency‐weighted balanced truncation which is a significant improvement on Lin and Chiu's frequency‐weighted balanced truncation technique. The reduced‐order models, which are guaranteed to be stable in the case of double‐sided weighting, are obtained by direct truncation. Two sets of simple, elegant and easily calculatable a priori error bounds are also derived. Numerical examples and comparison with other well‐known techniques show the effectiveness of the proposed technique. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
103.
104.
105.
106.
电感电容损耗电阻的讨论 总被引:3,自引:0,他引:3
通过对电容电感阻抗的测量,发现实验值偏离理论值。定性地分析了误差的来源,得出的结论是电感电容内部的损耗电阻随着频率的变化而变化,变化方向相反而并非相同。 相似文献
107.
引汉济渭工程黄金峡水利枢纽是陕西省境内一项重要的大型跨流域调水工程,泵站装机容量和设计流量均为目前国内甚至亚洲在建和已建泵站之最,且调水过程复杂、调水流量分布范围宽广。在分析黄金峡泵站调度原则及运行方式的基础上,综合比较目前国内外大型泵站机组设计制造水平、枢纽建筑物及机电设备投资等因素,详细论证了大型单级单吸离心式水泵机组台数和性能参数的确定方法及其影响因素,并给出了黄金峡泵站机组选型设计的最优方案,同时论证了采用变频调节的必要性及其效果。研究结果可为大型调水泵站机组的选型设计提供参考。 相似文献
108.
Zhen Zhou 《Ergonomics》2014,57(5):693-713
The dependence of biodynamic responses of the seated human body on the frequency, magnitude and waveform of vertical vibration has been studied in 20 males and 20 females. With sinusoidal vibration (13 frequencies from 1 to 16 Hz) at five magnitudes (0.1–1.6 ms? 2 r.m.s.) and with random vibration (1–16 Hz) at the same magnitudes, the apparent mass of the body was similar with random and sinusoidal vibration of the same overall magnitude. With increasing magnitude of vibration, the stiffness and damping of a model fitted to the apparent mass reduced and the resonance frequency decreased (from 6.5 to 4.5 Hz). Male and female subjects had similar apparent mass (after adjusting for subject weight) and a similar principal resonance frequency with both random and sinusoidal vibration. The change in biodynamic response with increasing vibration magnitude depends on the frequency of the vibration excitation, but is similar with sinusoidal and random excitation. 相似文献
109.
Zhen Zhou 《Ergonomics》2014,57(5):714-732
Frequency weightings for predicting vibration discomfort assume the same frequency-dependence at all magnitudes of vibration, whereas biodynamic studies show that the frequency-dependence of the human body depends on the magnitude of vibration. This study investigated how the frequency-dependence of vibration discomfort depends on the acceleration and the force at the subject–seat interface. Using magnitude estimation, 20 males and 20 females judged their discomfort caused by sinusoidal vertical acceleration at 13 frequencies (1–16 Hz) at magnitudes from 0.1 to 4.0 ms? 2 r.m.s. The frequency-dependence of their equivalent comfort contours depended on the magnitude of vibration, but was less dependent on the magnitude of dynamic force than the magnitude of acceleration, consistent with the biodynamic non-linearity of the body causing some of the magnitude-dependence of equivalent comfort contours. There were significant associations between the biodynamic responses and subjective responses at all frequencies in the range 1–16 Hz.Practitioner Summary: Vertical seat vibration causes discomfort in many forms of transport. This study provides the frequency-dependence of vibration discomfort over a range of vibration magnitudes and shows how the frequency weightings in the current standards can be improved. 相似文献
110.
《Expert systems with applications》2014,41(2):622-634
This paper presents a low power and low phase noise CMOS integer-N frequency synthesizer based on the charge-pump Phase Locked Loop (PLL) topology. The frequency synthesizer can be used for IEEE 802.16 unlicensed band of WiMAX (World Interoperability for Microwave Access). The operation frequency of the proposed design is ranged from 5.13 to 5.22 GHz. The proposed Voltage-Controlled Oscillator (VCO) achieves low power consumption and low phase noise. The high speed divider is implemented by an optimal extended true single phase clock (E-TSPC) prescaler. It can achieve higher operating frequency and lower power consumption. A new frequency divider is also proposed to eliminate the hardware overhead of the S counter in the conventional programmable divider. The proposed frequency synthesizer consists of a phase-frequency detector (PFD), a charge pump, a low-pass loop filter, a VCO, and a frequency divider. The simulated phase noise of the proposed VCO is −121.6 dBc/Hz at 1 MHz offset from the carrier frequency. The proposed frequency synthesizer consumes 13.1 mW. The chip with an area of 1.048 × 1.076 mm2 is fabricated in a TSMC 0.18 μm CMOS 1P6M technology process. 相似文献