全文获取类型
收费全文 | 119267篇 |
免费 | 15513篇 |
国内免费 | 6473篇 |
专业分类
电工技术 | 49781篇 |
技术理论 | 3篇 |
综合类 | 8842篇 |
化学工业 | 4052篇 |
金属工艺 | 6029篇 |
机械仪表 | 6443篇 |
建筑科学 | 3165篇 |
矿业工程 | 2271篇 |
能源动力 | 8269篇 |
轻工业 | 1400篇 |
水利工程 | 2629篇 |
石油天然气 | 896篇 |
武器工业 | 1041篇 |
无线电 | 26455篇 |
一般工业技术 | 6739篇 |
冶金工业 | 2231篇 |
原子能技术 | 2484篇 |
自动化技术 | 8523篇 |
出版年
2024年 | 634篇 |
2023年 | 1759篇 |
2022年 | 2991篇 |
2021年 | 3574篇 |
2020年 | 3995篇 |
2019年 | 3263篇 |
2018年 | 2982篇 |
2017年 | 4230篇 |
2016年 | 4442篇 |
2015年 | 5027篇 |
2014年 | 8164篇 |
2013年 | 6840篇 |
2012年 | 9386篇 |
2011年 | 9866篇 |
2010年 | 7250篇 |
2009年 | 7286篇 |
2008年 | 7489篇 |
2007年 | 8843篇 |
2006年 | 7877篇 |
2005年 | 6415篇 |
2004年 | 5385篇 |
2003年 | 4401篇 |
2002年 | 3478篇 |
2001年 | 3110篇 |
2000年 | 2565篇 |
1999年 | 1956篇 |
1998年 | 1398篇 |
1997年 | 1194篇 |
1996年 | 1134篇 |
1995年 | 896篇 |
1994年 | 855篇 |
1993年 | 628篇 |
1992年 | 514篇 |
1991年 | 378篇 |
1990年 | 279篇 |
1989年 | 172篇 |
1988年 | 127篇 |
1987年 | 68篇 |
1986年 | 46篇 |
1985年 | 43篇 |
1984年 | 72篇 |
1983年 | 50篇 |
1982年 | 55篇 |
1981年 | 27篇 |
1980年 | 17篇 |
1979年 | 14篇 |
1978年 | 15篇 |
1977年 | 8篇 |
1975年 | 5篇 |
1959年 | 16篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
41.
研制了用于远程激光脉冲测距机的板条激光器。使用半导体泵浦的MOPA激光结构实现了大于250 mJ的脉冲激光输出,输出脉冲宽度为12.83 ns,最终输出激光光束束散角为0.18 mrad。该激光测照器可应用于远程激光测距。对激光测距机的测距与照射能力进行了理论计算与分析。理论分析表明,应用于机载平台时,该激光测照器能够实现50 km距离的激光测距。该型激光测距机具有测距距离远,重量轻,结构紧凑等特点,具有广泛的应用前景。 相似文献
42.
43.
Artificial bee colony (ABC) algorithm has several characteristics that make it more attractive than other bio-inspired methods. Particularly, it is simple, it uses fewer control parameters and its convergence is independent of the initial conditions. In this paper, a novel artificial bee colony based maximum power point tracking algorithm (MPPT) is proposed. The developed algorithm, does not allow only overcoming the common drawback of the conventional MPPT methods, but it gives a simple and a robust MPPT scheme. A co-simulation methodology, combining Matlab/Simulink™ and Cadence/Pspice™, is used to verify the effectiveness of the proposed method and compare its performance, under dynamic weather conditions, with that of the Particle Swarm Optimization (PSO) based MPPT algorithm. Moreover, a laboratory setup has been realized and used to experimentally validate the proposed ABC-based MPPT algorithm. Simulation and experimental results have shown the satisfactory performance of the proposed approach. 相似文献
44.
Traditional maximum power point tracking (MPPT) methods can hardly find global maximum power point (MPP) because output characteristics curve of photovoltaic (PV) array may have multi local maximum power points in irregular shadow, and thus easily fall into the local maximum power point. To address this drawback, Considering that sliding mode variable structure (SMVS) control strategy have such advantages as simple structure, fast response and strong robustness, and P&O method have the advantages of simple principle and convenient implementation, so a new algorithm combining SMVS control method and P&O method is proposed, besides, PI controller is applied to reduce system chattering caused by switching sliding surface. It is applied to MPPT control of PV array in irregular shadow to solve the problem of multi-peak optimization in partial shadow. In order to verity the rationality of the proposed algorithm, the experimental circuit is built, which achieves MPPT control by means of the proposed algorithm and P&O method. The experimental results show that compared with the traditional P&O algorithm, the proposed algorithm can fast track the global MPP, tracking speed increases by 60% and the relative error decreased by 20%. Moreover, the system becomes more stable near the MPP, the fluctuations of output power is greatly reduced, and thus make full use of solar energy. 相似文献
45.
Zhen Wu Jing Yao Pengfei Zhu Fusheng Yang Xiangyu Meng Sandra Kurko Zaoxiao Zhang 《International Journal of Hydrogen Energy》2021,46(19):11183-11198
Advanced biogas power generation technology has been attracting attentions, which contributes to the waste disposal and the mitigation of greenhouse gas emissions. This work proposes and models a novel biogas-fed hybrid power generation system consisting of solid oxide fuel cell, water gas shift reaction, thermal swing adsorption and proton exchange membrane fuel cell (SOFC-WGS-TSA-PEMFC). The thermodynamic, exergetic, and thermo-economic analyses of this hybrid system for power generation were conducted to comprehensively evaluate its performance. It was found that the novel biogas-fed hybrid system has a gross energy conversion efficiency of 68.63% and exergy efficiency of 65.36%, indicating high efficiency for this kind of hybrid power technology. The market sensitivity analysis showed that the hybrid system also has a low sensitivity to market price fluctuation. Under the current subsidy level for the distributed biogas power plant, the levelized cost of energy can be lowered to 0.02942 $/kWh for a 1 MW scale system. Accordingly, the payback period and annual return on investment can reach 1.4 year and about 20%, respectively. These results reveal that the proposed hybrid system is promising and economically feasible as a distributed power plant, especially for the small power scale (no more than 2 MW). 相似文献
46.
47.
针对传统的小区内开环功率控制算法通常以提升本小区的吞吐量性能为目标,忽略了当前小区用户对邻小区用户同频干扰的问题,为提升边缘用户性能的同时兼顾系统整体性能,提出了一种LTE系统小区间上行联合功率控制(UJPC)算法。该算法采用单基站三扇区为系统模型,以最优化系统吞吐量比例公平函数为目标,首先根据最小信干噪比(SINR)约束值和用户最大发射功率这两个约束条件得到相应的数学优化模型,然后采用连续凸近似的方法求解优化问题得出各个基站所管辖的小区内所有用户的最优发射功率。仿真结果表明,与基准的开环功控方案相比,联合功控方案在保证系统平均频谱利用率的情况下能够较大幅度地提高小区边缘频谱利用率,其最佳性能增益能达到50%。 相似文献
48.
49.
ABSTRACTSocial licence to operate (SLO) is a term that is finding increasing acceptance in a number of industries. Like all new terms, its precise meaning and implications are still being investigated. Using data from previous studies, this paper offers an analysis of the SLO of two case studies with each study being viewed separately through the grid of a distinct theoretical framework. Case study 1 looks at the development of differential social licence negotiated in the Hamlet of Cambridge Bay, Nunavut, as a result of an impact and benefit agreement negotiated between Tahera Diamond Corp. and the Kitikmeot Inuit Organisation in 2004. The study demonstrates that general acceptance of resource development can be uneven and reflect an unequal distribution of decision-making power. In case study 2, stakeholders of a failed mineral development project were queried across time about the specifics of the proposed mine development and were queried about resource development across different levels of consciousness. Perhaps, SLO is variable across different levels of consciousness. The paper concludes with observations about the variable nature of SLO acceptance across populations and across levels of consciousness within individuals. Perhaps, the concept of SLO is, in fact, complex, difficult to define and measure and, at this point, of limited utility as a measure of resource development acceptance. 相似文献
50.
《Microelectronics Journal》2015,46(11):1012-1019
This paper presents a voltage reference generator architecture and two different realizations of it that have been fabricated within a standard 0.18 μm CMOS technology. The architecture takes the advantage of utilizing a sampled-data amplifier (SDA) to optimize the power consumption. The circuits achieve output voltages on the order of 190 mV with temperature coefficients of 43 ppm/°C and 52.5 ppm/°C over the temperature range of 0 to 120°C without any trimming with a 0.8 V single supply. The power consumptions of the circuits are less then 500 nW while occupying an area of 0.2 mm2 and 0.08 mm2, respectively. 相似文献