全文获取类型
收费全文 | 129979篇 |
免费 | 13385篇 |
国内免费 | 8179篇 |
专业分类
电工技术 | 9176篇 |
技术理论 | 7篇 |
综合类 | 11534篇 |
化学工业 | 19559篇 |
金属工艺 | 8121篇 |
机械仪表 | 8714篇 |
建筑科学 | 9692篇 |
矿业工程 | 4110篇 |
能源动力 | 3759篇 |
轻工业 | 11295篇 |
水利工程 | 3171篇 |
石油天然气 | 5465篇 |
武器工业 | 1338篇 |
无线电 | 15294篇 |
一般工业技术 | 14762篇 |
冶金工业 | 5449篇 |
原子能技术 | 1927篇 |
自动化技术 | 18170篇 |
出版年
2024年 | 348篇 |
2023年 | 1924篇 |
2022年 | 3894篇 |
2021年 | 5591篇 |
2020年 | 4113篇 |
2019年 | 3368篇 |
2018年 | 3635篇 |
2017年 | 3949篇 |
2016年 | 3839篇 |
2015年 | 5570篇 |
2014年 | 6763篇 |
2013年 | 8341篇 |
2012年 | 9361篇 |
2011年 | 9940篇 |
2010年 | 9186篇 |
2009年 | 8519篇 |
2008年 | 8671篇 |
2007年 | 8028篇 |
2006年 | 7456篇 |
2005年 | 6341篇 |
2004年 | 4713篇 |
2003年 | 4345篇 |
2002年 | 4968篇 |
2001年 | 4260篇 |
2000年 | 3140篇 |
1999年 | 2381篇 |
1998年 | 1650篇 |
1997年 | 1363篇 |
1996年 | 1165篇 |
1995年 | 1043篇 |
1994年 | 866篇 |
1993年 | 625篇 |
1992年 | 498篇 |
1991年 | 405篇 |
1990年 | 288篇 |
1989年 | 244篇 |
1988年 | 188篇 |
1987年 | 113篇 |
1986年 | 90篇 |
1985年 | 61篇 |
1984年 | 39篇 |
1983年 | 25篇 |
1982年 | 35篇 |
1981年 | 34篇 |
1980年 | 50篇 |
1979年 | 24篇 |
1976年 | 12篇 |
1975年 | 9篇 |
1959年 | 32篇 |
1951年 | 12篇 |
排序方式: 共有10000条查询结果,搜索用时 375 毫秒
61.
田继业 《中国水能及电气化》2021,(5):4-8
随着我国经济的快速发展,基础设施建设中建筑工程日益增多,许多工程建设周期比较长,跨越了春夏秋冬,更有一部分地区,长期处于严寒强风地带,为了缩短施工工期,保证施工的正常进行,需要进行冬期施工.文章针对冬期施工在低温强风条件下的技术措施进行了总结,可为同类工程提供参考. 相似文献
62.
63.
Xi Chen Zhengkun Yu Chen Yang Yao Chen Chao Jin Yuejiao Ding Wenbin Li Zhongmin Wan 《International Journal of Hydrogen Energy》2021,46(19):11127-11139
Flow field structure can largely determine the output performance of Polymer electrolyte membrane fuel cell. Excellent channel configuration accelerates electrochemical reactions in the catalytic layer, effectively avoiding flooding on the cathode side. In present study, a three-dimensional, multi-phase model of PEMFC with a 3D wave flow channel is established. CFD method is applied to optimize the geometry constructions of three-dimensional wave flow channels. The results reveal that 3D wave flow channel is overall better than straight channel in promoting reactant gases transport, removing liquid water accumulated in microporous layer and avoiding thermal stress concentration in the membrane. Moreover, results show the optimal flow channel minimum depth and wave length of the 3D wave flow channel are 0.45 mm and 2 mm, respectively. Due to the periodic geometric characteristics of the wave channel, the convective mass transfer is introduced, improving gas flow rate in through-plane direction. Furthermore, when the cell output voltage is 0.4 V, the current density in the novel channel is 23.8% higher than that of conventional channel. 相似文献
64.
65.
Muhammad Sheeraz Mamoon Ur Rashid Asad Ali Fazli Akram Ho Jeong Lee Jin San Choi Jong-Seong Bae Yong Soo Kim Young-Han Shin Chang Won Ahn Tae Heon Kim 《Journal of the European Ceramic Society》2021,41(10):5155-5162
We demonstrate the structural evolution of polymorphic phases in Al2O3-inserted SrMnO3 ceramics synthesized by solid state reaction. While the 4H-hexagonal phase is predominant in pure SrMnO3 ceramics, a small amount of 6H-hexagonal polymorph is identified in addition to the primary 4H-hexagonal SrMnO3 and the secondary hexagonal SrAl2O4 phases in the as-sintered ceramics, evidenced by x-ray diffraction and subsequent Rietveld refinement analyses. The existence of the 6H-hexagonal SrMnO3 phase is corroborated using Raman spectroscopy. The chemical compositions and electronic structures of the Al2O3-inserted SrMnO3 compounds are also examined using energy dispersive spectroscopy and x-ray photoelectron spectroscopy, respectively. The first-principles calculations reveal that there is no clear difference between the total energies of 4H- and 6H-hexagonal polymorphs regardless of the presence/absence of Sr and oxygen vacancies. Possible origins are discussed with the estimation of actual strain based on the refined lattice parameter of 6H SrMnO3. 相似文献
66.
Wei-Li Xie Xiao-Dong Zhang Wen-Hui Liu Qi Xie Guang-Wu Wen Xiao-Xiao Huang Jian-Dong Zhu Fei-Xiang Ma 《稀有金属(英文版)》2019,(3)
SiC nano wires were fabricated on the silicon substrate dipped with a layer of Ni catalyst at 900 ℃ by gas pressure annealing processing. The morphologies and crystal structures were determined by scanning electron microscopy(SEM), transmission electron microscopy(TEM)and X-ray diffraction(XRD). The results show that the assynthesized nanowires are β-SiC single crystalline with diameter range of 50-100 nm, and length of tens of micron by directly annealing at 900 ℃. The SiC nano wires grow along the [111] direction with highly uniform morphology. And the possible growth mechanism of SiC nano wires is proposed.The present work provides an efficient strategy for the production of high-quality SiC nano wires. 相似文献
67.
68.
69.
Cheng-Jun Tan Chuan-Xiang Tang Wen-Hui Huang Qing-Xiu Jin Ying-Chao Du Qun Luo Pei-Dong Wu Dong-Hai Liu Lu-Ming Zhang Cong Xu 《核技术(英文版)》2019,30(3)
Distributed X-ray sources comprise a single vacuum chamber containing multiple X-ray sources that are triggered and emit X-rays at a specific time and location. This process facilitates an application for innovative system concepts in X-ray and computer tomography. This paper proposes a novel electron beam focusing, shaping,and deflection electron gun for distributed X-ray sources.The electron gun uses a dispenser cathode as an electron emitter, a mesh grid to control emission current, and two electrostatic lenses for beam shaping, focusing, and deflection. Novel focusing and deflecting electrodes were designed to increase the number of focal spots in the distributed source. Two identical half-rectangle opening electrodes are controlled by adjusting the potential of the two electrodes to control the electron beam trajectory, and then, multifocal spots are obtained on the anode target. The electron gun can increase the spatial density of the distributed X-ray sources, thereby improving the image quality. The beam experimental results show that the focal spot sizes of the deflected(deflected amplitude 10.5 mm)and non-deflected electron beams at full width at half maximum are 0.80 mm 90.50 mm and 0.55 mm 90.40 mm, respectively(anode voltage 160 kV; beam current 30 mA). The imaging experimental results demonstrate the excellent spatial resolution and time resolution of an imaging system built with the sources, which has an excellent imaging effect on a field-programmable gate array chip and a rotating metal disk. 相似文献
70.
Liyan Wen Gang Tao Bin Jiang 《International Journal of Adaptive Control and Signal Processing》2021,35(3):373-400
In this article, adaptive compensation designs are developed for nonlinear systems with uncertainties from the system functions and persistent actuator failures of characterizations that (i) some unknown system inputs are stuck at some unknown fixed or varying values at unknown time instants and (ii) the failure pattern always switches from one to another and the switching does not stop. Such a controlled plant is described by an uncertain time-varying nonlinear system, and some robust adaptive feedback linearization based failure compensation results are studied for closed-loop system stabilization and bounded output tracking for some specific conditions. To improve the tracking performance in the presence of persistent actuator failures, a new adaptive control scheme is developed, using the failure indicator function which contains the failure pattern and failure time in the formulation. Detailed stability and tracking performance are shown. Simulation results are shown to verify the effectiveness of the proposed adaptive actuator failure compensation method. 相似文献