全文获取类型
收费全文 | 16192篇 |
免费 | 2522篇 |
国内免费 | 1645篇 |
专业分类
电工技术 | 3376篇 |
技术理论 | 2篇 |
综合类 | 1744篇 |
化学工业 | 440篇 |
金属工艺 | 527篇 |
机械仪表 | 1236篇 |
建筑科学 | 715篇 |
矿业工程 | 291篇 |
能源动力 | 282篇 |
轻工业 | 174篇 |
水利工程 | 197篇 |
石油天然气 | 189篇 |
武器工业 | 191篇 |
无线电 | 3507篇 |
一般工业技术 | 1285篇 |
冶金工业 | 358篇 |
原子能技术 | 63篇 |
自动化技术 | 5782篇 |
出版年
2024年 | 103篇 |
2023年 | 357篇 |
2022年 | 556篇 |
2021年 | 580篇 |
2020年 | 710篇 |
2019年 | 553篇 |
2018年 | 499篇 |
2017年 | 704篇 |
2016年 | 732篇 |
2015年 | 767篇 |
2014年 | 1092篇 |
2013年 | 1111篇 |
2012年 | 1317篇 |
2011年 | 1295篇 |
2010年 | 1009篇 |
2009年 | 1034篇 |
2008年 | 1038篇 |
2007年 | 1154篇 |
2006年 | 1021篇 |
2005年 | 897篇 |
2004年 | 636篇 |
2003年 | 594篇 |
2002年 | 484篇 |
2001年 | 410篇 |
2000年 | 343篇 |
1999年 | 242篇 |
1998年 | 173篇 |
1997年 | 166篇 |
1996年 | 171篇 |
1995年 | 144篇 |
1994年 | 104篇 |
1993年 | 84篇 |
1992年 | 48篇 |
1991年 | 49篇 |
1990年 | 35篇 |
1989年 | 45篇 |
1988年 | 13篇 |
1987年 | 9篇 |
1986年 | 12篇 |
1985年 | 11篇 |
1984年 | 14篇 |
1983年 | 11篇 |
1982年 | 10篇 |
1980年 | 2篇 |
1979年 | 4篇 |
1978年 | 3篇 |
1977年 | 4篇 |
1975年 | 4篇 |
1957年 | 1篇 |
1951年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
When five axis CNC machine tools follow series linear toolpath segments, the drives experience velocity, acceleration and jerk discontinuities at the block transition points. The discontinuities result in fluctuations on machine tool motions which lead to poor surface quality. This paper proposes to insert quintic and septic micro-splines for the tool tip and tool-orientation, respectively, at the adjacent linear toolpath segments. Optimal control points are calculated for position and orientation splines to achieve C3 continuity at the junctions while respecting user-defined tolerance limits. The geometrically smoothed corners are traveled at a smoothly varying feed with cubic acceleration trajectory profile. The proposed method is experimentally demonstrated to show improvements in motion smoothness and tracking accuracy in five-axis machining of free-form surfaces found in dies, molds and aerospace parts. 相似文献
2.
We propose all printed and highly stable organic resistive switching device (ORSD) based on graphene quantum dots (G-QDs) and polyvinylpyrrolidone (PVP) composite for non-volatile memory applications. It is fabricated by sandwiching G-QDs/PVP composite between top and bottom silver (Ag) electrodes on a flexible substrate polyethylene terephthalate (PET) at ambient conditions through a cost effective and eco-friendly electro-hydrodynamic (EHD) technique. Thickness of the active layer is measured around 97 nm. The proposed ORSD is fabricated in a 3 × 3 crossbar array. It operates switching between high resistance state (HRS) and low resistance state (LRS) with OFF/ON ratio ∼14 for more than 500 endurance cycles, and retention time for more than 30 days. The switching voltage for set/reset of the devices is ±1.8 V and the bendability down to 8 mm diameter for 1000 cycles are tested. The elemental composition and surface morphology are characterized by XPS, FE-SEM, and microscope. 相似文献
3.
为了减小传统的最差情况设计方法引入的电压裕量,提出了一种变化可知的自适应电压缩减(AVS)技术,通过调整电源电压来降低电路功耗.自适应电压缩减技术基于检测关键路径的延时变化,基于此设计了一款预错误原位延时检测电路,可以检测关键路径延时并输出预错误信号,进而控制单元可根据反馈回的预错误信号的个数调整系统电压.本芯片采用SMIC180 nm工艺设计验证,仿真分析表明,采用自适应电压缩减技术后,4个目标验证电路分别节省功耗12.4%,11.3%,10.4%和11.6%. 相似文献
4.
Optimization of tool path planning using metaheuristic algorithms such as ant colony systems (ACS) and particle swarm optimization (PSO) provides a feasible approach to reduce geometrical machining errors in 5-axis flank machining of ruled surfaces. The optimal solutions of these algorithms exhibit an unsatisfactory quality in a high-dimensional search space. In this study, various algorithms derived from the electromagnetism-like mechanism (EM) were applied. The test results of representative surfaces showed that all EM-based methods yield more effective optimal solutions than does PSO, despite a longer search time. A new EM-MSS (electromagnetism-like mechanism with move solution screening) algorithm produces the most favorable results by ensuring the continuous improvement of new searches. Incorporating an SPSA (simultaneous perturbation stochastic approximation) technique further improves the search results with effective initial solutions. This work enhances the practical values of tool path planning by providing a satisfactory machining quality. 相似文献
5.
移动机器人路径规划方法研究 总被引:3,自引:0,他引:3
移动机器人技术研究中的一个重要领域是路径规划技术,它分为基于模型的环境已知的全局路径规划和基于传感器的环境未知的局部路径规划。综述了移动机器人路径规划技术的发展现状指出了各种方法的优点与不足,最后对移动机器人路径规划技术的发展趋势进行了展望。 相似文献
6.
7.
中国工程勘察设计咨询业产业整合的路径选择 总被引:2,自引:0,他引:2
产业是由具有相互联系、相互制约的若干组成部分结合在一起并且有特定动能的有机体,产业分工越合理,资金、人力资源和各种自然资源与物质资料在产业内发挥的功能越大;中国工程勘察设计业的产业结构“中间大,两头小”,产业内部资源分布极不合理;结构调整的最佳选择是以工程项目总承包和分包为分工协作的垂直一体化:分化重组中间的工程咨询单位,组建顶端的EPC工程公司,发展低端的专业咨询公司、事务所。 相似文献
8.
The switchable optical properties of Pd-protected RCo2-type Ho0.6Mm0.4Co2 alloy thin films have been investigated in a KOH electrolyte. The reversible optical switching has been carried out simultaneously by measuring transmitted light through the thin film during electrochemical charging–discharging of hydrogen. The dependence of switching speed and cyclic durability of the film on the charging and discharging current density as well as concentration of KOH electrolyte has been studied. In addition, cyclic voltammetric measurements have been performed to examine the hydride formation and decomposition reactions. 相似文献
9.
Ahmadreza Momeni Amir G. Aghdam 《International Journal of Adaptive Control and Signal Processing》2007,21(10):885-910
Most of the existing switching control techniques are developed specifically for finite-dimensional linear time-invariant (LTI) systems. In many practical applications, however, it is essential to take time delay into consideration in the modelling as the control system can be highly sensitive to delay. In this paper, a multi-model switching control algorithm is proposed for retarded time-delay systems. It is assumed that the plant is represented by a family of known multi-input multi-output, observable, LTI models with multiple delays in the states, and that corresponding to each model in the known family, there exists a high-performance finite-dimensional LTI controller. In addition, it is supposed that a bound on the magnitude of the external inputs and disturbances is available. It is then shown that the proposed switching controller can stabilize the uncertain system, and that under some mild conditions, output tracking can be achieved in the given problem setting. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献
10.