全文获取类型
收费全文 | 37241篇 |
免费 | 4394篇 |
国内免费 | 1895篇 |
专业分类
电工技术 | 17062篇 |
综合类 | 3533篇 |
化学工业 | 947篇 |
金属工艺 | 934篇 |
机械仪表 | 2117篇 |
建筑科学 | 1543篇 |
矿业工程 | 891篇 |
能源动力 | 1024篇 |
轻工业 | 344篇 |
水利工程 | 637篇 |
石油天然气 | 528篇 |
武器工业 | 303篇 |
无线电 | 7708篇 |
一般工业技术 | 1470篇 |
冶金工业 | 676篇 |
原子能技术 | 431篇 |
自动化技术 | 3382篇 |
出版年
2024年 | 100篇 |
2023年 | 393篇 |
2022年 | 670篇 |
2021年 | 872篇 |
2020年 | 985篇 |
2019年 | 729篇 |
2018年 | 659篇 |
2017年 | 1162篇 |
2016年 | 1356篇 |
2015年 | 1470篇 |
2014年 | 2379篇 |
2013年 | 1902篇 |
2012年 | 2957篇 |
2011年 | 3116篇 |
2010年 | 2350篇 |
2009年 | 2446篇 |
2008年 | 2366篇 |
2007年 | 2819篇 |
2006年 | 2541篇 |
2005年 | 2101篇 |
2004年 | 1801篇 |
2003年 | 1576篇 |
2002年 | 1223篇 |
2001年 | 1127篇 |
2000年 | 912篇 |
1999年 | 727篇 |
1998年 | 490篇 |
1997年 | 441篇 |
1996年 | 385篇 |
1995年 | 313篇 |
1994年 | 284篇 |
1993年 | 184篇 |
1992年 | 173篇 |
1991年 | 127篇 |
1990年 | 93篇 |
1989年 | 91篇 |
1988年 | 81篇 |
1987年 | 36篇 |
1986年 | 17篇 |
1985年 | 22篇 |
1984年 | 17篇 |
1983年 | 9篇 |
1982年 | 8篇 |
1981年 | 2篇 |
1980年 | 2篇 |
1979年 | 7篇 |
1977年 | 2篇 |
1959年 | 1篇 |
1956年 | 1篇 |
1951年 | 3篇 |
排序方式: 共有10000条查询结果,搜索用时 937 毫秒
1.
2.
基于传统易碎薄板机械手位置伺服控制系统稳定性低、自动化分拣效率低等不足,设计了一种基于笛卡尔坐标式的气动码垛机器手和位置伺服稳定性控制系统。首先,设计并介绍笛卡尔坐标式码垛机械手的基本组成结构,对机械手末端吸盘气动回路控制系统进行设计和分析;然后分别对机械手X、Y、Z三个方向的伺服电机控制原理进行分析并设计了一种位置伺服系统的前馈自适应控制算法;最后,将传统位置闭环PID算法和前馈自适应控制算法进行位置跟踪稳定性对比试验。实验结果表明该笛卡尔坐标式的气动码垛机器手和位置伺服稳定性控制系统设计合理,满足实际生产要求。 相似文献
3.
针对传统低压回路电阻测试仪只能在被测设备停电时使用的一大限制,本文提出并设计了一种新型低压回路电阻测试仪。该仪器可在低压设备运行状态下对其回路电阻进行测量,在保证测量精度的前提下减少了设备停电率,大大提高了工作效率。 相似文献
4.
This study proposes that a novel integrated circuit (IC) and system design for renewable energy inverters can harvest renewable energy to power direct current (DC) and alternating current (AC) loads. In addition, an intelligent synthesis and management tool is developed to design the proposed system and to judge the system’s operational maintenance decisions. Finally, a renewable energy inverter’s information is posted to an online system. Users can obtain the proposed system’s information at any time and place. The accurate and superior performance of the proposed IC and system is confirmed by computer simulations and experimental results. 相似文献
5.
6.
本文结合HTH电路的复杂性等特征分析与实际应用现状,研究了HTH电路的具体检测技术方法并对当前热点技术进行对比分析,探讨了HTH电路检测方法的技术发展趋势。 相似文献
7.
An alternative Equivalent Electrical Circuit for Proton Exchange Membrane Fuel Cells is modelled in this study. Both I–V characteristics and H2 consumptions corresponding to generated power under load and no-load conditions are investigated. For this purpose, H2 consumptions and I–V characteristics of three different sized PEMFCs are tested. There is a very good harmony between the model results and measured values (relative error %0.7, %6.4 and %2.5 for FC-A, FC-B and FC-C respectively). In the proposed model current passes only on parallel resistance and not on serial resistance at no-load condition. Thus, a FC with higher parallel resistance should be preferred. Another key output of this study is that based on the proposed model, performance comparison of FCs can be performed with the parameters defined in this work. Proposals made in this study can easily be used for performance analysis of FCs under for both steady state and transient analysis. 相似文献
8.
The 3D structure electromagnetic computation presents several difficulties related to the volume mesh. In fact, the entire volume space must be taken into account even the smallest details. In this article, we propose a formulation based on the reciprocity theorem combined with the generalized equivalent circuit method to model a planar 3D structure with both coaxial and planar excitation. The major advantage of this formulation is the fact to reduce the computational volume into 2D ones in the discontinuity plane. In addition, we focused on the calculation of the discontinuity between the excitation source and the planar structure to determine the exact behavior of the electric coaxial excitation model. The obtained current density, electric field distributions, and the input impedance are presented and discussed in the following sections. An approximately good agreement of input impedance with those obtained by the simulator and measurement is shown. 相似文献
9.
Mohammadmahdi Davoudi 《工程优选》2019,51(5):775-795
Although topology optimization is established for linear static problems, more effort is required for solving nonlinear plastic problems. A new topology optimization approach with equivalent static loads (ESLs) is suggested to find the optimum topologies and locations of plastic hinges of thin-walled crash boxes by considering crash-induced deformation, the main crash energy-absorbing mechanism. Together with finite element method crashworthiness analyses, considering all nonlinearities with rate-dependent plasticity, the method was developed using an appropriate time-incremental scheme of ESLs without removing any high values of loads. Analyses show that the crash boxes with optimum topologies have energy-absorbing capabilities equivalent to the original structure. The proposed method is evaluated for two crashes: a crash box at low speed and a double cell subjected to high-speed collision. The results indicate that this method captures nonlinear crushing behaviours and accurate locations of plastic hinges where, if proper reinforcements are made, energy absorption can be enhanced. 相似文献
10.
Longbang Qing Yuehua Cheng Ru Mu 《Fatigue & Fracture of Engineering Materials & Structures》2019,42(11):2533-2543
Based on theoretical analysis and numerical simulation, the impact of steel fibres on the stress intensity factor (SIF) at the crack tip for cementitious composite was studied. The enhanced toughness of steel fibre reinforced cementitious composite (SFRC) in resisting cracks was explained by the decrement of SIF caused by steel fibre inclusions at the crack tip of the composite. The equivalent initial fracture toughness was used to characterize the crack initiation of SFRC. A simplified method for determining the of SFRC was proposed based on a linear regression method. Fracture tests were conducted on three‐point bending notched beams with different steel fibre volume fractions and specimen sizes to study the crack initiation behaviour of aligned steel fibre reinforced cementitious composite (ASFRC). of ASFRC was calculated, and the size effect of was analysed. The results showed that slightly increased with the steel fibre volume fraction and gradually became stable. For the tested specimens, whose heights varied between 40 and 100 mm, the specimen size had little impact on the . 相似文献