全文获取类型
收费全文 | 15215篇 |
免费 | 1353篇 |
国内免费 | 646篇 |
专业分类
电工技术 | 2613篇 |
技术理论 | 2篇 |
综合类 | 1445篇 |
化学工业 | 697篇 |
金属工艺 | 369篇 |
机械仪表 | 1457篇 |
建筑科学 | 1785篇 |
矿业工程 | 390篇 |
能源动力 | 324篇 |
轻工业 | 224篇 |
水利工程 | 219篇 |
石油天然气 | 303篇 |
武器工业 | 306篇 |
无线电 | 2295篇 |
一般工业技术 | 559篇 |
冶金工业 | 296篇 |
原子能技术 | 181篇 |
自动化技术 | 3749篇 |
出版年
2024年 | 49篇 |
2023年 | 123篇 |
2022年 | 194篇 |
2021年 | 246篇 |
2020年 | 325篇 |
2019年 | 203篇 |
2018年 | 206篇 |
2017年 | 332篇 |
2016年 | 410篇 |
2015年 | 508篇 |
2014年 | 1033篇 |
2013年 | 800篇 |
2012年 | 1291篇 |
2011年 | 1310篇 |
2010年 | 1067篇 |
2009年 | 985篇 |
2008年 | 1082篇 |
2007年 | 1340篇 |
2006年 | 1184篇 |
2005年 | 1078篇 |
2004年 | 785篇 |
2003年 | 697篇 |
2002年 | 532篇 |
2001年 | 361篇 |
2000年 | 285篇 |
1999年 | 186篇 |
1998年 | 119篇 |
1997年 | 103篇 |
1996年 | 102篇 |
1995年 | 63篇 |
1994年 | 50篇 |
1993年 | 28篇 |
1992年 | 36篇 |
1991年 | 25篇 |
1990年 | 12篇 |
1989年 | 21篇 |
1988年 | 9篇 |
1987年 | 6篇 |
1986年 | 2篇 |
1985年 | 6篇 |
1984年 | 2篇 |
1983年 | 1篇 |
1982年 | 11篇 |
1981年 | 1篇 |
1979年 | 2篇 |
1978年 | 1篇 |
1965年 | 1篇 |
1958年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
Narrow linewidth light source is a prerequisite for high-performance coherent optical communication and sensing.Waveguide-based external cavity narrow linewidth semiconductor lasers(WEC-NLSLs)have become a competitive and attractive candidate for many coherent applications due to their small size,volume,low energy consumption,low cost and the ability to integrate with other optical components.In this paper,we present an overview of WEC-NLSLs from their required technologies to the state-of-the-art progress.Moreover,we highlight the common problems occurring to current WEC-NLSLs and show the possible approaches to resolving the issues.Finally,we present the possible development directions for the next phase and hope this review will be beneficial to the advancements of WEC-NLSLs. 相似文献
2.
为解决定距螺旋桨与船用主机在船舶运行工况的机桨匹配问题,结合船舶系泊和航行试验的相关标准,分析和归纳船舶运行数据,将实船测试与船机桨匹配理论计算相结合,得出运输船和拖轮在常用工况及特殊工况下定距螺旋桨对主机外特性的定量要求,为配套不同细分市场时船用主机的优化和开发提供参考依据。 相似文献
3.
4.
Mostafa Dellahi Hattab Maker Guillermo Botella Enrique Alameda-Hernandez Azeddine Mouhsen 《International Journal of Circuit Theory and Applications》2020,48(6):887-905
The three-phase four-wire shunt active power filter (SAPF) was developed to suppress the harmonic currents generated by nonlinear loads, and for the compensation of unbalanced nonlinear load currents, reactive power, and the harmonic neutral current. In this work, we consider instantaneous reactive power theory (PQ theory) for reference current identification based on the following two algorithms: the classic low-pass filter (LPF) and the second-order generalized integrator (SOGI) filter. Furthermore, since an important process in SAPF control is the regulation of the DC bus voltage at the capacitor, a new controller based on the Lyapunov function is also proposed. A complete simulation of the resultant active filtering system confirms its validity, which uses the SOGI filter to extract the reference currents from the distorted line currents, compared with the traditional PQ theory based on LPF. In addition, the simulation performed also demonstrates the superiority of the proposed approach, for DC bus voltage control based on the Lyapunov function, compared with the traditional proportional-integral (PI) controller. Both novel approaches contribute towards an improvement in the overall performance of the system, which consists of a small rise and settling time, a very low or nonexistent overshoot, and the minimization of the total harmonic distortion (THD). 相似文献
5.
Mohamed Becherif 《Asian journal of control》2019,21(4):2137-2154
Induction machines (IM) constitute a theoretically interesting and practically important class of nonlinear systems. They are frequently used as wind generators for their power/cost ratio. They are described by a fifth‐order nonlinear differential equation with two inputs and only three state variables available for measurement. The control task is further complicated by the fact that IM are subject to unknown (load) disturbances and the parameters can be of great uncertainty. One is then faced with the challenging problem of controlling a highly nonlinear system, with unknown time‐varying parameters, where the regulated output, besides being unmeasurable, is perturbed by an unknown additive signal. Passivity‐based control (PBC) is a well‐established structure‐preserving design methodology which has shown to be very powerful to design robust controllers for physical systems described by Euler‐Lagrange equations of motion. PBCs provide a natural procedure to "shape" the potential energy yielding controllers with a clear physical interpretation in terms of interconnection of the system with its environment and are robust vis á vis to unmodeled dissipative effects. One recent approach of PBC is the Interconnection and Damping Assignment Passivity‐Based Control (IDA‐PBC) which is a very useful technique to control nonlinear systems assigning a desired (Port‐Controlled Hamiltonian) structure to the closed‐loop. The aim of this paper is to give a survey on different PBC of IM. The originality of this work is that the author proves that the well known field oriented control of IM is a particular case of the IDA‐PBC with disturbance. 相似文献
6.
通过对大直径平底负压容器平底板的设计计算,平底板计算厚度很厚。通过分析,提出了对平底板采取加强措施,从而减薄平底板计算厚度的方法。该容器在实际生产过程中性能可靠、稳定,对类似设备设计具有借鉴意义。 相似文献
7.
移动通信系统中功率控制研究 总被引:2,自引:0,他引:2
在阐述功率控制在移动通信系统中的发展过程的基础上,着重研究了WCDMA系统的功率控制,最后对功率控制未来的研究方向做了简要的分析。 相似文献
8.
国产风机盘管空调系统常见问题分析 总被引:2,自引:1,他引:1
分析了国产风机盘管使用中常见的问题,指出机组因风量不足、冷量风量匹配不合理以及风机盘管某些设备故障,导致了风机盘管精度低、舒适性差、能耗高等一系列问题。指出应引起空调设计和运行维护人员的注意。 相似文献
9.
10.