全文获取类型
收费全文 | 6171篇 |
免费 | 792篇 |
国内免费 | 401篇 |
专业分类
电工技术 | 457篇 |
技术理论 | 1篇 |
综合类 | 655篇 |
化学工业 | 317篇 |
金属工艺 | 154篇 |
机械仪表 | 398篇 |
建筑科学 | 338篇 |
矿业工程 | 203篇 |
能源动力 | 127篇 |
轻工业 | 115篇 |
水利工程 | 134篇 |
石油天然气 | 159篇 |
武器工业 | 305篇 |
无线电 | 2025篇 |
一般工业技术 | 485篇 |
冶金工业 | 113篇 |
原子能技术 | 215篇 |
自动化技术 | 1163篇 |
出版年
2024年 | 29篇 |
2023年 | 79篇 |
2022年 | 153篇 |
2021年 | 194篇 |
2020年 | 199篇 |
2019年 | 184篇 |
2018年 | 154篇 |
2017年 | 214篇 |
2016年 | 265篇 |
2015年 | 307篇 |
2014年 | 405篇 |
2013年 | 472篇 |
2012年 | 452篇 |
2011年 | 451篇 |
2010年 | 384篇 |
2009年 | 385篇 |
2008年 | 327篇 |
2007年 | 447篇 |
2006年 | 369篇 |
2005年 | 284篇 |
2004年 | 231篇 |
2003年 | 196篇 |
2002年 | 174篇 |
2001年 | 174篇 |
2000年 | 135篇 |
1999年 | 126篇 |
1998年 | 90篇 |
1997年 | 83篇 |
1996年 | 72篇 |
1995年 | 72篇 |
1994年 | 42篇 |
1993年 | 39篇 |
1992年 | 36篇 |
1991年 | 26篇 |
1990年 | 28篇 |
1989年 | 12篇 |
1988年 | 12篇 |
1987年 | 15篇 |
1986年 | 10篇 |
1985年 | 5篇 |
1984年 | 4篇 |
1983年 | 4篇 |
1982年 | 6篇 |
1981年 | 3篇 |
1979年 | 3篇 |
1974年 | 2篇 |
1963年 | 1篇 |
1962年 | 1篇 |
1957年 | 2篇 |
1951年 | 1篇 |
排序方式: 共有7364条查询结果,搜索用时 0 毫秒
991.
雷达高分辨一维像反映了目标的精细结构信息在雷达视线上的投影,正确提取目标一维像尺寸是计算宽带RCS,反演目标真实长度,实现目标分类识别的基础。文中针对在目标一维像尺寸提取时存在的目标分裂、多目标情况等情况,提出一种基于多约束条件计数的目标一维像尺寸提取算法,可以实现宽带距离窗内多个目标一维像尺寸的同时提取,经过实测数据验证,文中提出的一维像尺寸提取算法平均提取误差小于2个距离门,具有优良的性能和提取稳定性,可有效避免海杂波,目标分裂多目标等情况的影响。 相似文献
992.
This study proposes a robust range‐only beacon mapping method for registering the locations of range‐only beacons automatically. The proposed method deals with the multipath propagation of signals from range‐only beacons using the range‐only measurement association (RoMA) and an unscented Kalman filter (UKF). The RoMA initially predicts the candidate positions of a range‐only beacon. The location of the range‐only beacon is then updated using the UKF. With the proposed method, the locations of range‐only beacons are accurately estimated in a multipath environment. The proposed method also provides the location uncertainty of each range‐only beacon. Simulation results using the model for multipath propagation and experimental results in a real indoor environment verify the performance of the proposed method. 相似文献
993.
Katrin Ortstein Sebastian Hutsch Alexander Hinderhofer Jrn Vahland Martin Schwarze Sebastian Schellhammer Martin Hodas Thomas Geiger Hans Kleemann Holger F. Bettinger Frank Schreiber Frank Ortmann Karl Leo 《Advanced functional materials》2020,30(32)
In modern electronics, it is essential to adapt band structures by adjusting energy levels and band gaps. At first sight, this “band structure engineering” seems impossible in organic semiconductors, which usually exhibit localized electronic states instead of Bloch bands. However, the strong Coulomb interaction in organic semiconductors allows for a continuous shift of the ionization energy (IE) over a wide range by mixing molecules with halogenated derivatives that exhibit different quadrupole moments. Here, this effect of energy level engineering on blends of pentacene and two fluorinated derivatives, in which the position but not the number of fluorine atoms differ, is studied. Structural investigations confirm that pentacene forms intermixed phases in blends with the fluorinated species. The investigation of electronic properties and simulations reveals a much larger shift of the ionization energy (1.5 eV) than in previous studies, allowing to test this model in a range not investigated so far, and emphasizing the role of the position of the halogen atoms. The tuning effect is preserved in electronic devices such as field‐effect transistors and significantly influences device characteristics. 相似文献
994.
为定量分析压力传感器的测量量程及其过载能力,提出一种微型光纤光栅土压力传感器并构建其气压标定系统。对微型光纤光栅土压力传感器进行理论分析得其灵敏度为7.5 nm/MPa,测量量程可达1.06 MPa。而分析光纤光栅土压力传感器性能测试数据得:该传感器压力灵敏度为5.9 nm/MP,线性度为99.93%,可测量实际量程为225 kPa,过载能力上限值为300 kPa。研究结果可用于指导设计规定量程的光纤光栅土压力传感器,具备一定应用价值。 相似文献
995.
The paper investigates the observer‐based H∞ synchronization for coronary artery time‐delay system under the state immeasurement and external uncertainty. A Luenberger‐like state observer, the observation system, is designed to realize the state reconstruction of the master system. Based on the Lyapunov stability theory and Lyapunov‐Krasovskii functional (LKF), the observer‐based synchronization control condition is derived for a coronary artery system subjected to the external uncertainty bounded by L2 norm. By introducing the delay‐interval bounds and delay‐derivative limits in LKF, the time‐delays are handled by the delay‐range‐dependent strategy. The tighter upper bound of inequality can be obtained to reduce the conservation by employing further improved result of Jensen inequality and reciprocally convex approach. Furthermore, a decoupling technique is utilized to render the separate and simple controller and observer synthesis condition, which can be further solved by applying the cone complementary linearization approach respectively. Numerical simulations are listed to exhibit the effectiveness of the presented methodology. 相似文献
996.
997.
The traditional Range Doppler (RD) algorithm is unable to meet practical
needs owing to the limit of resolution. The order of fractional Fourier Transform (FrFT)
and the length of sampling signals affect SAR imaging performance when FrFT is
applied to RD algorithm. To overcome the above shortcomings, the purpose of this paper
is to propose a high-resolution SAR image algorithm by using the optimal order of FrFT
and the sample length constraints for the range direction. The expression of the optimal
order of SAR range signals via FrFT is deduced in detail. The initial sample length and
its constraints are proposed to obtain the best sample length of SAR range signals.
Experimental results demonstrate that, when the range sampling-length changes in a
certain interval, the best sampling-length will be obtained, which the best values of the
range resolution, PSLR and ISLR, will be derived respectively. Compared with
traditional RD algorithm, the main-lobe width of the peak-point target of the proposed
algorithm is narrow in the range direction. While the peak amplitude of the first side-lobe
is reduced significantly, those of other side-lobes also drop in various degrees. 相似文献
998.
To address the low-resolution imaging problem in relation to traditional Range
Doppler (RD) algorithm, this paper intends to propose a new algorithm based on
Fractional Fourier Transform (FrFT), which proves highly advantageous in the
acquisition of high-resolution Synthetic Aperture Radar (SAR) images. The expression of
the optimal order of SAR range signals using FrFT is deduced in detail, and the
corresponding expression of the azimuth signal is also given. Theoretical analysis shows
that, the optimal order in range (azimuth) direction, which turns out to be very unique,
depends on the known imaging parameters of SAR, therefore the engineering
practicability of FrFT-RD algorithm can be greatly improved without the need of order
iteration. The FrFT-RD algorithm is established after an analysis of the optimal timefrequency transform. Experimental results demonstrate that, compared with traditional
RD algorithm, the main-lobe width of the peak-point target of FrFT-RD algorithm is
narrow in both range and azimuth directions. While the peak amplitude of the first sidelobe is reduced significantly, those of other side-lobes also drop in various degrees. In
this way, the imaging resolution of range and azimuth can be increased considerably. 相似文献
999.
Y. F. Liu Y. S. Zhao C. G. Liu Y. Y. Guo J. Zhang Y. S. Luo 《Materials Science & Technology》2018,34(10):1188-1196
Tensile tests within a temperature range from room temperature (RT) to 1100°C were performed on a novel second-generation single-crystal superalloy DD11. The experimental results indicated that the yield strength (YS) remained constant up to 760°C, while a maximum was reached at 850°C. The elongation and area reduction decreased gradually from RT to 760°C and then they increased rapidly at temperatures above 760°C. As for the deformation mechanism, when the temperature was below 850°C, the γ′ precipitates were sheared by isolated faults, faulted loops and dislocation pairs. The formation of dislocation networks and dislocation climb mechanism were confirmed at temperatures above 980°C. Finally, the relationship between the YS of the DD11 alloy and the operative deformation mechanism was discussed. 相似文献