全文获取类型
收费全文 | 226640篇 |
免费 | 19948篇 |
国内免费 | 13353篇 |
专业分类
电工技术 | 34814篇 |
技术理论 | 25篇 |
综合类 | 26385篇 |
化学工业 | 10343篇 |
金属工艺 | 7539篇 |
机械仪表 | 19033篇 |
建筑科学 | 19012篇 |
矿业工程 | 8993篇 |
能源动力 | 8276篇 |
轻工业 | 4820篇 |
水利工程 | 6937篇 |
石油天然气 | 6705篇 |
武器工业 | 4256篇 |
无线电 | 24104篇 |
一般工业技术 | 11975篇 |
冶金工业 | 6803篇 |
原子能技术 | 2336篇 |
自动化技术 | 57585篇 |
出版年
2024年 | 318篇 |
2023年 | 2035篇 |
2022年 | 3889篇 |
2021年 | 5136篇 |
2020年 | 5537篇 |
2019年 | 4133篇 |
2018年 | 3815篇 |
2017年 | 5403篇 |
2016年 | 6428篇 |
2015年 | 7584篇 |
2014年 | 14325篇 |
2013年 | 12296篇 |
2012年 | 16952篇 |
2011年 | 18008篇 |
2010年 | 13640篇 |
2009年 | 13644篇 |
2008年 | 14020篇 |
2007年 | 17867篇 |
2006年 | 16038篇 |
2005年 | 14304篇 |
2004年 | 11734篇 |
2003年 | 10582篇 |
2002年 | 8024篇 |
2001年 | 6750篇 |
2000年 | 5506篇 |
1999年 | 4431篇 |
1998年 | 3332篇 |
1997年 | 2691篇 |
1996年 | 2421篇 |
1995年 | 2093篇 |
1994年 | 1724篇 |
1993年 | 1151篇 |
1992年 | 967篇 |
1991年 | 705篇 |
1990年 | 560篇 |
1989年 | 477篇 |
1988年 | 328篇 |
1987年 | 187篇 |
1986年 | 123篇 |
1985年 | 123篇 |
1984年 | 110篇 |
1983年 | 98篇 |
1982年 | 73篇 |
1981年 | 65篇 |
1980年 | 54篇 |
1979年 | 45篇 |
1978年 | 39篇 |
1977年 | 28篇 |
1976年 | 24篇 |
1959年 | 21篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
51.
Michael Lommel Vera Froese Moritz Sieber Marvin Jentzsch Tim Bierewirtz Ümit Hasirci Tim Rese Josef Seefeldt Sebastian Schimek Ulrich Kertzscher Christian Oliver Paschereit 《Indoor air》2021,31(6):1860-1873
The SARS-CoV-2 pandemic has created a great demand for a better understanding of the spread of viruses in indoor environments. A novel measurement system consisting of one portable aerosol-emitting mannequin (emitter) and a number of portable aerosol-absorbing mannequins (recipients) was developed that can measure the spread of aerosols and droplets that potentially contain infectious viruses. The emission of the virus from a human is simulated by using tracer particles solved in water. The recipients inhale the aerosols and droplets and quantify the level of solved tracer particles in their artificial lungs simultaneously over time. The mobile system can be arranged in a large variety of spreading scenarios in indoor environments and allows for quantification of the infection probability due to airborne virus spreading. This study shows the accuracy of the new measurement system and its ability to compare aerosol reduction measures such as regular ventilation or the use of a room air purifier. 相似文献
52.
To solve the special requirements of the high orbit optical remote sensing-satellite for the thermal deformation of the platform, the thermal deformation test and measurement scheme of the satellite platform is designed. Through the comparative analysis of test results, the rationality of the thermal deformation design of the platform structure is verified. The results of thermal deformation measurement show that the maximum deformation of A camera mounting surface is 57.5~〃, and the maximum deformation of B camera mounting surface points to 79.3~〃, which can be used as the basis for thermal deformation prediction of satellite during the orbit operation. 相似文献
53.
为了解决长行程定子不连续永磁直线同步电机存在的因无法全程安装位置传感器和不同动子和定子之间的电磁参数不固定所造成的控制性能下降的难题,提出一种在每一段定子内先进行参数标定,再进行速度控制的控制系统设计。首先,在动子进入过程中,对电机进行电磁参数标定,根据标定参数对控制器参数进行调整,以达到更好的控制效果。然后,使用无位置传感器控制系统使动子快速达到设定速度值并稳定运行。实验结果表明:动子进入过程参数标定精度分别为0.002Wb和0.000 4H;无位置传感器控制中位置估计精度为0.63mm,速度收敛时间为0.45s,稳态误差为0.02m/s。基本满足永磁直线同步电机用于长行程运输的控制快速性、稳定性等要求。 相似文献
54.
55.
匡红云 《上海第二工业大学学报》2019,(4):298-303
澳大利亚职业教育在全球享有较高的声誉,这与其坚持严格的"基于能力本位的评估"(competency based assessment, CBA)密不可分。介绍了澳大利亚CBA的内涵特征,并详细描述"准备评估、开发评估工具、开展评估、对评估结果进行评估"的CBA运作过程,关注评估工具的开发和后续常规系统性检查及完善,以期对我国的高等职业教育质量评估起到启示和借鉴作用。 相似文献
56.
Xin-Yu Zhang Li Tang Yan-Jun Liu 《International Journal of Adaptive Control and Signal Processing》2021,35(7):1404-1416
In this article, based on partial differential equations (PDEs), the flexible manipulator system with both dead-zone input and state constraints is studied. The dynamic model of the flexible manipulator system is described by PDEs. The parameters of the dead-zone input are unknown, and the state constraint problem is also considered. An adaptive approach is proposed to offset the effects caused by dead-zone input. Thus, to guarantee that all states remain within their respective constraint regions, the boundary control law based on the barrier Lyapunov function is given, and an adaptive controller is designed. According to the Lyapunov analysis method, the control method is given to ensure that all signals of the closed-loop system are bounded and all states satisfy the constraint conditions. Finally, simulation results show the effectiveness of the proposed control method in this article. 相似文献
57.
58.
Hao Yuan Haifeng Dai Wei Wu Jiaping Xie Jun Shen Xuezhe Wei 《International Journal of Hydrogen Energy》2021,46(7):5714-5728
In a vehicular fuel cell system, alternative load and frequent purge action can lead to anode pressure varies with the hydrogen mass flow fluctuation. It's crucial to control the pressure difference between anode and cathode within a reasonable range to avoid adverse phenomena such as membrane failure, reactant starvation, or even water management fault. In this paper, an improved proportional integrative (PI) controller by the fuzzy logic technique that considers the engineer experience and knowledge on the hydrogen supply system behavior is proposed for hydrogen pressure control, in which the PI parameters are tuned by a fuzzy decision process. Furthermore, load current and purge action regarded as input disturbances are applied for feedforward compensation to reduce the pressure response hysteresis. A hydrogen supply subsystem based on the proportional valve is modeled, and corresponding parameters are determined by analyzing the response time and steady pressure fluctuation. The performance of the conventional PI controller, the fuzzy logic PI (FLPI) controller and fuzzy logic PI with feedforward (FLPIF) controller is validated. The presented results indicated that the FLPI controller significantly improves the dynamic response of hydrogen pressure compared to the PI controller, and the FLPIF controller can further reduce overshoot caused by disturbance. Finally, the proposed FLPIF controller is implemented on a rapid prototype platform of the hydrogen supply subsystem and an actual fuel cell system, exhibiting satisfactory performance. 相似文献
59.
《International Journal of Hydrogen Energy》2021,46(59):30267-30287
This work aims to improve the existing monitoring systems MS for two grid-connected PV stations GCPVS of URERMS ADRAR, to eliminate its limitations. This improvement consists of developing an MS which is used for two PV stations with different configurations. This MS contains new LabVIEW-based monitoring software for visualizing real-time measured data and evaluating GCPVS performance. In addition, it illustrates the 2D and 3D real-time relationships of PV system parameters, which allow us to understand the dynamic behavior of PV system components. This developed monitoring software synchronizes also the various data acquisition units DAU of GCPVS, allowing simultaneous data access.To perform a reliable performance analysis and a comparative study of different GCPVS based on accurate measurements, the sensor's calibration is performed with its DAU. The MS autonomy is ensured by integrating developed PV-UPS. A graphical user interface is provided for the evaluation of PV-UPS performance. 相似文献
60.
《International Journal of Hydrogen Energy》2021,46(64):32665-32675
The thermal management of a proton exchange membrane fuel cell (PEMFC) is crucial for fuel cell vehicles. This paper presents a new simulation model for the water-cooled PEMFC stacks for automotive vehicles and cooling systems. The cooling system model considers both the cooling of the stack and cooling of the compressed air through the intercooler. Theoretical analysis was carried out to calculate the heat dissipation requirements for the cooling system. The case study results show that more than 99.0% of heat dissipation requirement is for thermal management of the PEMFC stack; more than 98.5% of cooling water will be distributed to the stack cooling loop. It is also demonstrated that controlling cooling water flow rate and stack inlet cooling water temperature could effectively satisfy thermal management constraints. These thermal management constraints are differences in stack inlet and outlet cooling water temperature, stack temperature, fan power consumption, and pump power consumption. 相似文献