全文获取类型
收费全文 | 61618篇 |
免费 | 7024篇 |
国内免费 | 3651篇 |
专业分类
电工技术 | 14686篇 |
技术理论 | 7篇 |
综合类 | 7368篇 |
化学工业 | 3760篇 |
金属工艺 | 1526篇 |
机械仪表 | 5829篇 |
建筑科学 | 4543篇 |
矿业工程 | 2149篇 |
能源动力 | 1760篇 |
轻工业 | 1275篇 |
水利工程 | 1065篇 |
石油天然气 | 1378篇 |
武器工业 | 1914篇 |
无线电 | 6189篇 |
一般工业技术 | 3266篇 |
冶金工业 | 2608篇 |
原子能技术 | 261篇 |
自动化技术 | 12709篇 |
出版年
2024年 | 135篇 |
2023年 | 726篇 |
2022年 | 1348篇 |
2021年 | 1798篇 |
2020年 | 1978篇 |
2019年 | 1538篇 |
2018年 | 1423篇 |
2017年 | 2093篇 |
2016年 | 2189篇 |
2015年 | 2509篇 |
2014年 | 4109篇 |
2013年 | 3392篇 |
2012年 | 4772篇 |
2011年 | 5194篇 |
2010年 | 3757篇 |
2009年 | 3841篇 |
2008年 | 3752篇 |
2007年 | 4656篇 |
2006年 | 4002篇 |
2005年 | 3434篇 |
2004年 | 2598篇 |
2003年 | 2376篇 |
2002年 | 1897篇 |
2001年 | 1676篇 |
2000年 | 1278篇 |
1999年 | 951篇 |
1998年 | 648篇 |
1997年 | 586篇 |
1996年 | 457篇 |
1995年 | 401篇 |
1994年 | 353篇 |
1993年 | 200篇 |
1992年 | 165篇 |
1991年 | 134篇 |
1990年 | 127篇 |
1989年 | 73篇 |
1988年 | 72篇 |
1987年 | 58篇 |
1986年 | 45篇 |
1985年 | 145篇 |
1984年 | 245篇 |
1983年 | 290篇 |
1982年 | 205篇 |
1981年 | 314篇 |
1980年 | 116篇 |
1979年 | 39篇 |
1978年 | 40篇 |
1977年 | 15篇 |
1975年 | 21篇 |
1974年 | 23篇 |
排序方式: 共有10000条查询结果,搜索用时 78 毫秒
61.
A mechanistic analysis of the influence of iron‐oxidizing bacteria on antimony (V) removal from water by microscale zero‐valent iron 下载免费PDF全文
62.
We study a dynamic version of the assembly routing problem. The assembly lot sizing section deals with decisions concerning the production phase, whereas the routing section organises the collection of raw materials necessary for the production. Traditionally, these two problems are treated separately, and more specifically, in a hierarchical way. We propose three linear programming models: a non-vehicle index model, a two-commodity flow formulation and a logic-based benders decomposition. We develop aggregated rounded capacity constraints for non-vehicle index model and separated them dynamically during the Branch & Cut procedure. Logic-based benders decomposition algorithm solves the Dynamic Assembly Routing Problem iteratively and obtains a feasible solution at each iteration. The numerical tests show that, the two first models are particularly effective at finding the optimal solutions in a reasonable amount of time on instances with up to 50 components and 3 periods. 相似文献
63.
64.
开关磁阻电机结构性转矩脉动抑制方法 总被引:5,自引:0,他引:5
开关磁阻电机具有结构简单、成本低和调速范围广等优势,但其双凸极结构和控制器的开关特性,导致存在转矩脉动现象,使得抑制转矩脉动成为焦点问题。首先从开关磁阻电机的结构和运行机理出发,针对线性解析方法难以分析转矩特征的问题,建立电机有限元模型求解出转矩特征并进行样机验证试验。分析样机结构参数对转矩脉动的影响,针对结构参数耦合问题,选择NSGA-Ⅱ算法在参数优化平台上对样机结构参数进行多目标寻优,在保证优化后样机的转矩脉动系数和平均转矩均优于初始电机的条件下,最终获得样机最优化结果。结果表明,不同结构参数对电机转矩的影响有较大的差异,对结构参数的优化能有效地抑制转矩脉动,该参数优化方法可以为开关磁阻电机结构性转矩脉动抑制提供参考。 相似文献
65.
为了有效降低因驾驶员紧急换道行为而诱发的交通事故,提高道路交通事故链阻断效率,提出一种基于高斯混合隐马尔科夫模型(GMM-HMM)和人工神经网络(ANN)的紧急换道行为预测方法。首先利用GMM-HMM对车辆行驶状态以及驾驶行为连续观察序列进行换道意图辨识,采用ANN预测下一时段的驾驶行为,再预测换道过程中的横向加速度变化率,从而判断紧急换道的危险程度。驾驶员在环仿真实验及实车实验结果表明,该方法预测避险成功率达92.83%,实验避险成功率达90.32%。该方法能有效地对紧急换道行为进行提前警告与干预。 相似文献
66.
67.
Multifunctional or structural electrolytes are characterized by ionic conductivity high enough to be used in the electrochemical devices and mechanical performance suitable for the structural applications. Preliminary insights are provided into the combustion behavior of structural bi-continuous electrolytes based on bisphenol A diglycidyl ether (DGEBA), synthesized using the techniques of reaction induced phase separation and emulsion templating. The effect of the composition of the structural electrolytes and external heat flux on the behavior of the formulations were studied using a cone calorimeter with gases formed during testing analyzed using FTIR. The composition of the formulations investigated was changed by varying the type and amount of the ion conductive part of the bi-continuous electrolyte. Two ionic liquids, 1-ethyl-3-methylimidazolium bis(fluorosulfonyl)imide (EMIM-TFSI) and 1-butyl-3-methylimidazolium tetrafluoroborate (BMIM-BF4), as well as a deep eutectic solvent (DES) based on ethylene glycol and choline chloride, were used. The results obtained confirm that time to ignition, heat release rate (HRR), total mass loss, as well as the composition of the gases released during tests depend on the composition of the formulations. Addition of liquid electrolyte is found to reduce the time to ignition by up to 10% and the burning time by between 28% and 60% with the added benefit of reducing the HRR by at least 34%. Gaseous products such as CO2, CO, H2O, CH4, C2H2, N2O, NO, and HCN were detected for all formulations with the gases SO2, NH3, HCl, C2H4, and NH3 found to be for certain formulations only. 相似文献
68.
《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
69.
This paper contributes to the water privatization and governance literatures by examining the case of Pittsburgh where renewed efforts of water privatization have emerged after a failed private management arrangement between the local water authority and Veolia ended abruptly in 2015. We argue that, as the water authority aims to rebuild trust in the community, resident mobilization has played a key role in hindering further privatizing arrangements and has exerted influence in defining what constitutes the “new public” water in Pittsburgh, by advocating for increased transparency and accountability in governance, infrastructure improvements and protections for low-income residents. 相似文献
70.
V. Boscaino A. Odetti G. Marsala D. Di Cara N. Panzavecchia M. Caccia G. Tinè 《International Journal of Hydrogen Energy》2021,46(39):20732-20749
Autonomous surface vehicles are becoming consolidated robotic tools for marine, coastal and inland surveys. Autonomous surface vehicles are usually equipped with electronic instruments to perform remotely controlled or autonomous geo-morphological, biological, chemical, physical analyses and data collection. Actually, well-established solutions provide battery power but the research focuses on introducing a fuel cell to decrease the environmental impact meanwhile increasing the cruising range. In this paper, the design of the Eco-SWAMP, a fuel cell powered autonomous surface vehicle, is presented starting from its battery-powered version, the SWAMP prototype. The experimental power consumption profile of the SWAMP during four missions is analysed to define the primary energy sources ratings of the Eco-SWAMP. After a commercial choice of primary sources, power management algorithms are designed and compared in MATLAB/Simulink environment by simulation results. The proposed procedure can be easily applied to any autonomous marine vehicle. 相似文献