全文获取类型
收费全文 | 81915篇 |
免费 | 6811篇 |
国内免费 | 4012篇 |
专业分类
电工技术 | 5060篇 |
技术理论 | 8篇 |
综合类 | 7025篇 |
化学工业 | 13055篇 |
金属工艺 | 4622篇 |
机械仪表 | 5326篇 |
建筑科学 | 6419篇 |
矿业工程 | 2092篇 |
能源动力 | 2141篇 |
轻工业 | 8109篇 |
水利工程 | 1811篇 |
石油天然气 | 3701篇 |
武器工业 | 831篇 |
无线电 | 8487篇 |
一般工业技术 | 8335篇 |
冶金工业 | 3263篇 |
原子能技术 | 984篇 |
自动化技术 | 11469篇 |
出版年
2024年 | 273篇 |
2023年 | 976篇 |
2022年 | 2059篇 |
2021年 | 2830篇 |
2020年 | 2167篇 |
2019年 | 1761篇 |
2018年 | 2029篇 |
2017年 | 2286篇 |
2016年 | 2171篇 |
2015年 | 3231篇 |
2014年 | 4119篇 |
2013年 | 5031篇 |
2012年 | 5883篇 |
2011年 | 6415篇 |
2010年 | 5913篇 |
2009年 | 5774篇 |
2008年 | 5751篇 |
2007年 | 5404篇 |
2006年 | 5194篇 |
2005年 | 4359篇 |
2004年 | 3125篇 |
2003年 | 2387篇 |
2002年 | 2361篇 |
2001年 | 2062篇 |
2000年 | 1650篇 |
1999年 | 1552篇 |
1998年 | 1143篇 |
1997年 | 963篇 |
1996年 | 835篇 |
1995年 | 684篇 |
1994年 | 534篇 |
1993年 | 403篇 |
1992年 | 328篇 |
1991年 | 260篇 |
1990年 | 174篇 |
1989年 | 166篇 |
1988年 | 132篇 |
1987年 | 70篇 |
1986年 | 77篇 |
1985年 | 41篇 |
1984年 | 34篇 |
1983年 | 24篇 |
1982年 | 16篇 |
1981年 | 21篇 |
1980年 | 27篇 |
1979年 | 11篇 |
1976年 | 9篇 |
1975年 | 4篇 |
1958年 | 2篇 |
1951年 | 3篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
22.
Zhimei Zheng Taixiu Liu Qibin Liu Jing Lei Juan Fang 《International Journal of Hydrogen Energy》2021,46(38):19846-19860
Solar thermochemical hydrogen production with energy level upgraded from solar thermal to chemical energy shows great potential. By integrating mid-and-low temperature solar thermochemistry and solid oxide fuel cells, in this paper, a new distributed energy system combining power, cooling, and heating is proposed and analyzed from thermodynamic, energy and exergy viewpoints. Different from the high temperature solar thermochemistry (above 1073.15 K), the mid-and-low temperature solar thermochemistry utilizes concentrated solar thermal (473.15–573.15 K) to drive methanol decomposition reaction, reducing irreversible heat collection loss. The produced hydrogen-rich fuel is converted into power through solid oxide fuel cells and micro gas turbines successively, realizing the cascaded utilization of fuel and solar energy. Numerical simulation is conducted to investigate the system thermodynamic performances under design and off-design conditions. Promising results reveal that solar-to-hydrogen and net solar-to-electricity efficiencies reach 66.26% and 40.93%, respectively. With the solar thermochemical conversion and hydrogen-rich fuel cascade utilization, the system exergy and overall energy efficiencies reach 59.76% and 80.74%, respectively. This research may provide a pathway for efficient hydrogen-rich fuel production and power generation. 相似文献
23.
In this paper we investigated the BER performance of DS-CDMA using various chip-waveforms, which include three time-limited chip-waveforms and two band-limited chip-waveforms. Closed-form formulae were derived for evaluating the achievable bit-error rate performance with the aid of the standard Gaussian approximation, when communicating over a Nakagami-m channel. The time-limited waveforms impose a low implementational complexity, since they maybe over sampled and read from a look-up table. However, they are outperformed by the frequency-domain raised-cosine waveform as well as the optimum waveform specifically designed by Cho and Lehnert for achieving the lowest possible bit error rate 相似文献
24.
Li D. You-Song Gu Xiang-Rong Chang Fu-Shen Li Li-Jie Qiao Zhong-Zhuo Tian Fang G.-D. Qing-Shan Song 《IEEE transactions on magnetics》2003,39(6):3554-3558
We deposited Fe-Ti-N magnetic films with a high sputtering power of 7 W/cm/sup 2/. When the composition of the films was in the range of Fe-Ti(3.9 at.%)-N(8.8 at.%) to Fe-Ti(3.3 at.%)-N(13.5 at.%), the films were composed of /spl alpha/' and Ti/sub 2/N precipitates. With the addition of nitrogen, 4/spl pi/M/sub s/ became higher than that of pure iron, reaching a maximum of 23.8 kG. At the same time, H/sub c/ was reduced to a minimum of 1.12 Oe. The best films can meet the needs of the recording head in dual-element giant magnetoresistive/inductive heads, yielding high storage density (10 Gb/in/sup 2/). The incorporation of N in /spl alpha/-Fe brought about the /spl alpha/' phase with its higher saturation magnetization. Ti additions inhibited the equilibrium decomposition /spl alpha/'/spl rarr//spl alpha/+/spl gamma/'. Because H/sub C//sup D//spl prop/D/sup 6/, where D is average grain diameter, grain size control is very important. The nitrogen induces severe distortion of the /spl alpha/' lattice, which can cause the grains to break into pieces and reduce the grain size. High sputtering power also led to the formation of fine grains, with diameter in the order of 14 nm. Probably Ti/sub 2/N is preferentially precipitated on the grain boundary, pinning the grain boundary and stabilizing the grain size during high-temperature heat treatment. The temperature limit for stability of the structure and its associated low coercivity was not less than 520/spl deg/C. 相似文献
25.
声波测井换能器的激发响应由换能器振动时所表现出来的动态阻抗和激发电路参数决定。而换能器的动态(阻抗)参数随压电晶体及其装配方式(力学边界条件)改变。为了测量换能器动态参数的影响,采用声波测井仪器常用的压电晶体和升压变压器,通过改变激发脉冲宽度和直流电压进行了实验,结果发现:在换能器两端的瞬态响应中,一共有三个二阶网络响应,分别对应于不同的频率。最低的一个影响声波测井波形的基线、与换能器主频接近的一个决定激发效率以及电路与压电晶体之间的匹配关系,是激发电路设计中比较关键的,其参数可以通过导纳圆测量仪器得到。 相似文献
26.
房家贵 《石油化工设备技术》2006,27(1):1-5
文章介绍了近年来在催化裂化装置上应用的新设备、新技术,如BY型旋风分离器、BSX型旋分式三级旋风分离器、上下拱型三级旋风分离器、下拱型三级旋风分离器、SHS“自蔓延”技术、SWY外取热器、BWJ型喷嘴、自流浇注料、Actehem高耐磨衬里、弓形钢丝纤维、侧拉环锚固钉、分体可拆人孔等的结构特点及实际应用情况。 相似文献
27.
28.
A decision support system for interactive decision making - Part II: analysis and output interpretation 总被引:2,自引:0,他引:2
Liping Fang K.W. Hipel D.M. Kilgour Xiaoyong Peng 《IEEE transactions on systems, man and cybernetics. Part C, Applications and reviews》2003,33(1):56-66
For pt.I see ibid., p.42-55 (2003). The development of a comprehensive decision support system, GMCR II, for the systematic study of real-world interactive decision problems is presented. The companion paper (Part I), discusses how GMCR II elicits, stores, and manages conflict models; here (Part II), the focus is on GMCR IIs analysis and output interpretation subsystems. Specifically, this paper describes the powerful and efficient analysis engine contained in GMCR II, its informative output presentation and interpretation facilities, and a number of follow-up analyses. Furthermore, an illustrative case study is used to demonstrate how GMCR II can be conveniently applied in practice. 相似文献
29.
Field Static Load Test on Kao-Ping-Hsi Cable-Stayed Bridge 总被引:1,自引:0,他引:1
Field load testing is an effective method for understanding the behavior and fundamental characteristics of a cable-stayed bridge. This paper presents the results of field static load tests on the Kao-Ping-Hsi cable-stayed bridge, the longest cable-stayed bridge in Taiwan, before it was open to traffic. A total of 40 loading cases, including the unit and distributed bending and torsion loading effects, were conducted to investigate the bridge behavior. The atmospheric temperature effect on the variations of the main girder deflections was also monitored. The results of static load testing include the main girder deflections, the flexural strains of the prestressed concrete girder, and the variations of the cable forces. A three-dimensional finite-element model was developed. The results show that the bridge under the planned load test conditions has linear superposition characteristics and the analytical model shows a very good agreement with the bridge responses. Further discussion of deflection and cable forces of the design specifications for a cable-stayed bridge is also presented. 相似文献
30.