全文获取类型
收费全文 | 318284篇 |
免费 | 26176篇 |
国内免费 | 18910篇 |
专业分类
电工技术 | 42133篇 |
技术理论 | 25篇 |
综合类 | 32111篇 |
化学工业 | 30210篇 |
金属工艺 | 13672篇 |
机械仪表 | 26276篇 |
建筑科学 | 23044篇 |
矿业工程 | 10746篇 |
能源动力 | 11586篇 |
轻工业 | 11519篇 |
水利工程 | 7397篇 |
石油天然气 | 10964篇 |
武器工业 | 4861篇 |
无线电 | 34338篇 |
一般工业技术 | 22231篇 |
冶金工业 | 9592篇 |
原子能技术 | 3463篇 |
自动化技术 | 69202篇 |
出版年
2024年 | 685篇 |
2023年 | 3118篇 |
2022年 | 5306篇 |
2021年 | 7667篇 |
2020年 | 7642篇 |
2019年 | 6252篇 |
2018年 | 5846篇 |
2017年 | 7970篇 |
2016年 | 9299篇 |
2015年 | 10443篇 |
2014年 | 18467篇 |
2013年 | 17188篇 |
2012年 | 22143篇 |
2011年 | 24304篇 |
2010年 | 19093篇 |
2009年 | 19993篇 |
2008年 | 19862篇 |
2007年 | 24161篇 |
2006年 | 22255篇 |
2005年 | 19317篇 |
2004年 | 16099篇 |
2003年 | 14802篇 |
2002年 | 11540篇 |
2001年 | 9498篇 |
2000年 | 8033篇 |
1999年 | 6439篇 |
1998年 | 4768篇 |
1997年 | 3834篇 |
1996年 | 3461篇 |
1995年 | 3058篇 |
1994年 | 2555篇 |
1993年 | 1882篇 |
1992年 | 1554篇 |
1991年 | 1055篇 |
1990年 | 790篇 |
1989年 | 699篇 |
1988年 | 488篇 |
1987年 | 301篇 |
1986年 | 221篇 |
1985年 | 202篇 |
1984年 | 175篇 |
1983年 | 135篇 |
1982年 | 143篇 |
1981年 | 134篇 |
1980年 | 79篇 |
1979年 | 66篇 |
1978年 | 56篇 |
1977年 | 48篇 |
1976年 | 47篇 |
1959年 | 25篇 |
排序方式: 共有10000条查询结果,搜索用时 187 毫秒
91.
Adaptive robust boundary control of shaft vibrations under perturbations with unknown upper bounds 下载免费PDF全文
This paper presents robust and adaptive boundary control designs to stabilize the two‐dimensional vibration of hybrid shaft model. The hybrid shaft is mathematically represented by a set of partial differential equations, governing the shaft vibrations, coupled to ordinary differential equations, describing rigid body spinning and dynamic boundary conditions. The control objective is to stabilize the transverse vibrations of the perturbed shaft while regulating the spinning rate. To achieve this, the paper first establishes robust boundary control laws that fulfil the control objective in the presence of modeling uncertainties and external disturbances operating over the shaft domain and boundary. Lyapunov‐based analyses show that the proposed robust control exponentially stabilizes the shaft with vanishing distributive perturbations, while assuring ultimately bounded vibrations in the case of nonvanishing perturbations. Then, adaptive control philosophy is utilized to achieve redesigned robust controllers that only use online adaptation of control gains without acquiring the knowledge of bounds on perturbations, as well as dynamic parameters. An advantage of this design is avoiding an overconservative robust control law, which may induce poor stability and chattering in tackling system perturbations with unknown upper bounds. Simulations through finite element method illustrate the results. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献
92.
通过制备不同晶相结构〔单斜相(m-ZrO_2)、四方相(t-ZrO_2)和无定型(a-ZrO_2)〕ZrO_2载体,再通过沉积沉淀法制得Cu/m-ZrO_2、Cu/t-ZrO_2和Cu/a-ZrO_2催化剂,分别用于催化二乙醇胺脱氢合成亚氨基二乙酸反应。采用XRD、氮气物理吸附脱附、XPS、H_2-TPR、CO_2-TPD对催化剂的结构进行了表征。结果表明,Cu/m-ZrO_2催化剂界面更加有利于Cu~+/Cu~0稳定存在,具有更多的碱性位点,且抗氧化性较好。在二乙醇胺脱氢反应中,Cu/m-ZrO_2催化剂性能最好,反应时间为2.5 h,亚氨基二乙酸收率为97.64%。 相似文献
93.
《International Journal of Hydrogen Energy》2020,45(38):19720-19732
The need to reduce PEMFC systems cost as well as to increase their durability is crucial for their integration in various applications and especially for transport applications. A new simplified architecture of the anode circuit called Alternating Fuel Feeding (AFF) offers to reduce the development costs. Requiring a new stack concept, it combines the simplicity of Dead-End Anode (DEA) with the operation advantages of the hydrogen recirculation. The three architectures (DEA, recirculation and AFF) are compared in terms of performance on a 5-kW test bench in automotive conditions, through a sensitivity analysis. A gain of 17% on the system efficiency is observed when switching from DEA to AFF. Moreover, similar performances are obtained both for AFF and for recirculation after an accurate optimization of the AFF tuning parameters. Based on DoE data, a gain of 25% on the weight of the anodic line has been identified compared to pulsed ejector architecture and 43% with the classic recirculation architecture with blower only (Miraï). 相似文献
94.
95.
As a symbol of sharing economy, ride-hailing services have spread to Asia, where various forms of services have been established according to the existing socio-technical regimes, including legal, policy, and environmental concerns. China, in particular, has accepted ride-hailing services by revising existing institutions. This study analyzes China’s acceptance of ride-hailing services in the socio-technical system context set up for legacy services. Simulation modeling, combined with transition theory and an agent-based model, is used to analyze the data. This study calculates consumer disutility based on mobility market share, reflecting consumer preference, and predicts the sustainability of ride-hailing services. The simulation results conclude that legalization and socio-technical context are of importance for sustainable mobility. 相似文献
96.
97.
Grzegorz Moskal 《Microscopy research and technique》2020,83(5):523-530
The presented article characterized microstructural aspects of thermal barrier coatings (TBCs) analysis using methods of electron microscopy such as electron backscatter diffraction (EBSD), transmission/scanning electron microscopy (S/TEM), and TEM. The analyzed TBC system is based on gadolinium zirconate deposited by air plasma spraying method, and additionally, it was subjected to an oxidation test for 500 hr at a temperature of 1,100°C. Moreover, the morphological characterization of feedstock powder was showed. EBSD analysis revealed the inhomogeneity of feedstock materials in the form of complex phase composition. In the case of deposited coating, this method was used to characterize the crystallite size of zirconate coating and phase composition of thermally grown oxide zone. S/TEM and TEM analysis showed morphological details of this zone but not revealed such phase as perovskite oxide of GdAlO3 type. 相似文献
98.
《Journal of the European Ceramic Society》2020,40(8):2731-2745
Thermal barrier coatings (TBCs) play a pivotal role in protecting the hot structures of modern turbine engines in aerospace as well as utility applications. To meet the increasing efficiency of gas turbine technology, worldwide research is focused on designing new architecture of TBCs. These TBCs are mainly fabricated by atmospheric plasma spraying (APS) as it is more economical over the electron beam physical vapor deposition (EB-PVD) technology. Notably, bi-layered, multi-layered and functionally graded TBC structures are recognized as favorable designs to obtain adequate coating performance and durability. In this regard, an attempt has been made in this article to highlight the structure, characteristics, limitations and future prospects of bi-layered, multi-layered and functionally graded TBC systems fabricated using plasma spraying and its allied techniques like suspension plasma spray (SPS), solution precursor plasma spray (SPPS) and plasma spray –physical vapor deposition (PS-PVD). 相似文献
99.
针对区域地面沉降监测点数量有限、分布不均的情况,一般采用空间插值的手段建立表面拟合模型来解决。基于分形插值,采用随机选择迭代函数的思想对传统的趋势面拟合法作出改进,改进后拟合优度系数提高0.03,达到0.995,且改进前后的拟合结果符合显著性检验的要求。实验结果表明:改进前后趋势面拟合法拟合结果满足地面沉降监测的精度要求,改进后方法的拟合优度更高,对现实地面沉降量变化的描绘更加真实,可为沉降灾害评价工作提供更准确的依据。 相似文献
100.
王学鹏 《电子制作.电脑维护与应用》2015,(6)
CAN-BUS系统自问世以来,已将近30年,当代各品牌车辆纷纷采用,但大部分技术人员对CAN总线系统既熟悉又陌生。经常能听到,但具体操作又显得有些力不从心。本文通过对奇瑞A3品牌轿车CAN总线的巧妙应用,引导大家进一步理解和应用CAN总线。 相似文献