全文获取类型
收费全文 | 195315篇 |
免费 | 27714篇 |
国内免费 | 7526篇 |
专业分类
电工技术 | 10494篇 |
技术理论 | 7篇 |
综合类 | 10892篇 |
化学工业 | 42659篇 |
金属工艺 | 9575篇 |
机械仪表 | 10965篇 |
建筑科学 | 14600篇 |
矿业工程 | 4672篇 |
能源动力 | 5915篇 |
轻工业 | 17237篇 |
水利工程 | 3161篇 |
石油天然气 | 9116篇 |
武器工业 | 1184篇 |
无线电 | 24951篇 |
一般工业技术 | 30009篇 |
冶金工业 | 8089篇 |
原子能技术 | 1878篇 |
自动化技术 | 25151篇 |
出版年
2024年 | 752篇 |
2023年 | 2744篇 |
2022年 | 4807篇 |
2021年 | 6884篇 |
2020年 | 6351篇 |
2019年 | 7107篇 |
2018年 | 7442篇 |
2017年 | 8298篇 |
2016年 | 8070篇 |
2015年 | 9961篇 |
2014年 | 11334篇 |
2013年 | 13891篇 |
2012年 | 12656篇 |
2011年 | 13050篇 |
2010年 | 12176篇 |
2009年 | 11548篇 |
2008年 | 10740篇 |
2007年 | 10034篇 |
2006年 | 9895篇 |
2005年 | 8490篇 |
2004年 | 6700篇 |
2003年 | 6641篇 |
2002年 | 6896篇 |
2001年 | 6103篇 |
2000年 | 5219篇 |
1999年 | 4490篇 |
1998年 | 3335篇 |
1997年 | 2789篇 |
1996年 | 2564篇 |
1995年 | 2187篇 |
1994年 | 1748篇 |
1993年 | 1246篇 |
1992年 | 1032篇 |
1991年 | 792篇 |
1990年 | 600篇 |
1989年 | 517篇 |
1988年 | 416篇 |
1987年 | 291篇 |
1986年 | 211篇 |
1985年 | 131篇 |
1984年 | 89篇 |
1983年 | 65篇 |
1982年 | 78篇 |
1981年 | 57篇 |
1980年 | 52篇 |
1979年 | 19篇 |
1978年 | 10篇 |
1977年 | 7篇 |
1976年 | 10篇 |
1959年 | 13篇 |
排序方式: 共有10000条查询结果,搜索用时 27 毫秒
991.
线性规划模型的自动生成与求解 总被引:1,自引:0,他引:1
本文描述了《有色企业经济活动分析决策支持系统》模型库中线性规划模型的自动生成与求解系统的设计思想、方法及实现 相似文献
992.
采用同调约束快速识别的有功校正控制计算 总被引:1,自引:0,他引:1
本文发展了文(5)提出的同调约束概念,将同调约束进一步分为正同调约束和反同调约束两组。文中提出了一种新的同调约束识别方法,不必增加任何计算便可快速识别出正反同调约束,显著地降低了解题规模。IEEE30节点样本网络的计算实例证实了本文方法的有效性。 相似文献
993.
Sang‐Heung Lee Seung‐Yun Lee Hyun‐Cheol Bae Ja‐Yol Lee Sang‐Hoon Kim Bo Woo Kim Jin‐Yeong Kang 《ETRI Journal》2005,27(5):569-578
The purpose of this paper is to describe the implementation of monolithically matching circuits, interface circuits, and RF core circuits to the same substrate. We designed and fabricated on‐chip 1 to 6 GHz up‐conversion and 1 to 8 GHz down‐conversion mixers using a 0.8 µm SiGe hetero‐junction bipolar transistor (HBT) process technology. To fabricate a SiGe HBT, we used a reduced pressure chemical vapor deposition (RPCVD) system to grow a base epitaxial layer, and we adopted local oxidation of silicon (LOCOS) isolation to separate the device terminals. An up‐conversion mixer was implemented on‐chip using an intermediate frequency (IF) matching circuit, local oscillator (LO)/radio frequency (RF) wideband matching circuits, LO/IF input balun circuits, and an RF output balun circuit. The measured results of the fabricated up‐conversion mixer show a positive power conversion gain from 1 to 6 GHz and a bandwidth of about 4.5 GHz. Also, the down‐conversion mixer was implemented on‐chip using LO/RF wideband matching circuits, LO/RF input balun circuits, and an IF output balun circuit. The measured results of the fabricated down‐conversion mixer show a positive power conversion gain from 1 to 8 GHz and a bandwidth of about 4.5 GHz. 相似文献
994.
Localization via ultra-wideband radios: a look at positioning aspects for future sensor networks 总被引:3,自引:0,他引:3
Gezici S. Zhi Tian Giannakis G.B. Kobayashi H. Molisch A.F. Poor H.V. Sahinoglu Z. 《Signal Processing Magazine, IEEE》2005,22(4):70-84
UWB technology provides an excellent means for wireless positioning due to its high resolution capability in the time domain. Its ability to resolve multipath components makes it possible to obtain accurate location estimates without the need for complex estimation algorithms. In this article, theoretical limits for TOA estimation and TOA-based location estimation for UWB systems have been considered. Due to the complexity of the optimal schemes, suboptimal but practical alternatives have been emphasized. Performance limits for hybrid TOA/SS and TDOA/SS schemes have also been considered. Although the fundamental mechanisms for localization, including AOA-, TOA-, TDOA-, and SS-based methods, apply to all radio air interface, some positioning techniques are favored by UWB-based systems using ultrawide bandwidths. 相似文献
995.
Y1.94-xMgxO2S:0.06Ti (0≤x≤0.10) phosphors with long afterglow were synthesized by solid state reaction route. The photoluminescence spectra, decay curves, thermoluminescent spectra and chromaticity coordinate curves were investigated. The results show that the luminescence intensity of Y1.94-xMgxO2S:0.06Ti (0≤x≤0.10) phosphors decrease gradually with increasing Mg2 ion content, and the shape of luminescence spectra and chromaticity coordinate change as well. Furthermore, two thermoluminescent peaks in single Ti-doped Y2O2S sample are found at 91.8 and 221.5 ℃, respectively. Nevertheless, significant different spectra were found for the Mg, Ti co-doped Y2O2S samples that three thermoluminescence peaks appear at 52.3, 141.7 and 226.8 ℃, respectively. These results indicate that the co-doped Mg ion changes the inherent trap depth of single Ti-doped Y2O2S:Ti phosphor, and induces simultaneously a new trap level in the Y1.94-xMgxO2S:0.06Ti phosphor. Based on the analysis of thermoluminescent spectra, photoluminescent spectra, decay curve and crystal structure defect, it was proposed that the varied structure defect and introduced new trap level by the doped Mg2 ions should be responsible for reducing luminescence intensity and varying color in the Y1.94-xMgxO2S:0.06Ti phosphor. 相似文献
996.
Lijun Xu Naichang Yuan 《Microwave and Wireless Components Letters, IEEE》2005,15(12):892-894
The JE convolution finite-difference-time-domain (JEC-FDTD) method is extended to the anisotropic magnetized plasma which incorporates both anisotropy and frequency dispersion at the same time, enabling the transient solution of the electromagnetic wave propagation in anisotropic magnetized plasmas. Two-dimensional JEC-FDTD formulations for magnetized plasma are derived. The back scattering radar cross section (RCS) of a perfectly conducting cylinder coated by a layer of magnetized plasmas is calculated. 相似文献
997.
Ning Yang Zhi Ning Chen 《Microwave and Wireless Components Letters, IEEE》2005,15(12):835-837
In this letter, a coplanar stripline (CPS) series resonator composed of serially-connected series-stubs is proposed. This kind of resonator provides two transmission zeros close to the resonant frequency. With the proposed structure, the reactance slope parameters of the resonators are significantly increased and adjustable by changing the length ratio of the two series stubs. This is useful for designing narrowband filters which is difficult to realize with conventional series CPS resonators. The structures of the resonators are optimized for a lower radiation loss and used to design a narrowband Chebyshev bandpass filter. The simulation and experimental results show that the proposed filter provides multiple transmission zeros and high selectivity. 相似文献
998.
999.
We propose an asymmetric integral imaging method to adjust the resolution and depth of a three‐dimensional image. Our method is obtained by use of two lenticular sheets with different pitches fabricated under the same F/#. The asymmetric integral imaging is the generalized version of integral imaging, including both conventional integral imaging and one‐dimensional integral imaging. We present experimental results to test and verify the performance of our method computationally. 相似文献
1000.
本文研究了在以电子加速器的电子射线为辐射源时,剂量率对PTFE辐射裂解的影响。在剂量相同的条件下,剂量率从1.44×10~4 rad/s增至5.75×10~4 rad/s,裂解效率提高3.3倍。剂量率和各断裂参数(单位剂量裂解度a_0,G(s)值等)均成线性关系。当裂解度一定时,剂量率与剂量成反变关系。 相似文献