全文获取类型
收费全文 | 232164篇 |
免费 | 23499篇 |
国内免费 | 17208篇 |
专业分类
电工技术 | 34805篇 |
技术理论 | 9篇 |
综合类 | 24717篇 |
化学工业 | 14131篇 |
金属工艺 | 10154篇 |
机械仪表 | 21557篇 |
建筑科学 | 20609篇 |
矿业工程 | 8868篇 |
能源动力 | 6129篇 |
轻工业 | 6060篇 |
水利工程 | 7188篇 |
石油天然气 | 7182篇 |
武器工业 | 3789篇 |
无线电 | 18989篇 |
一般工业技术 | 16590篇 |
冶金工业 | 8841篇 |
原子能技术 | 1534篇 |
自动化技术 | 61719篇 |
出版年
2024年 | 683篇 |
2023年 | 2775篇 |
2022年 | 4659篇 |
2021年 | 5812篇 |
2020年 | 6660篇 |
2019年 | 5450篇 |
2018年 | 5036篇 |
2017年 | 7091篇 |
2016年 | 7943篇 |
2015年 | 8828篇 |
2014年 | 15332篇 |
2013年 | 13866篇 |
2012年 | 17379篇 |
2011年 | 18231篇 |
2010年 | 13999篇 |
2009年 | 14393篇 |
2008年 | 14165篇 |
2007年 | 17323篇 |
2006年 | 15360篇 |
2005年 | 13298篇 |
2004年 | 10986篇 |
2003年 | 9584篇 |
2002年 | 7705篇 |
2001年 | 6553篇 |
2000年 | 5719篇 |
1999年 | 4572篇 |
1998年 | 3548篇 |
1997年 | 3141篇 |
1996年 | 2529篇 |
1995年 | 2125篇 |
1994年 | 1793篇 |
1993年 | 1333篇 |
1992年 | 1051篇 |
1991年 | 803篇 |
1990年 | 640篇 |
1989年 | 564篇 |
1988年 | 395篇 |
1987年 | 225篇 |
1986年 | 153篇 |
1985年 | 153篇 |
1984年 | 202篇 |
1983年 | 155篇 |
1982年 | 145篇 |
1981年 | 96篇 |
1980年 | 74篇 |
1979年 | 86篇 |
1978年 | 55篇 |
1977年 | 57篇 |
1975年 | 15篇 |
1959年 | 18篇 |
排序方式: 共有10000条查询结果,搜索用时 139 毫秒
31.
针对自动飞行控制系统结构复杂、关联部件众多,发生故障时诊断时间长,从而影响飞机运行效率的问题,提出一种基于飞机通信寻址报告系统(ACARS)的远程实时故障诊断方案。首先,分析自动飞行控制系统的故障特点,设计搭建检测滤波器;然后,利用ACARS数据链实时发送的自动飞行控制系统的关键信息进行相关部件的残差计算,并根据残差决策算法进行故障诊断及定位;最后,针对不同故障部件残差间的差异大、决策门限无法统一的缺点,提出基于二次差值的残差决策改进算法,减缓了检测对象的整体变化趋势,降低了随机噪声和干扰的影响,避免了将瞬态故障诊断为系统故障的情况。实验仿真结果表明,基于二次差值的改进残差决策算法避免了多决策门限的复杂性,在采样时间为0.1 s的情况下,故障检测所需时间大约为2 s,故障检测时间大幅降低,有效故障检测率大于90%。 相似文献
32.
33.
This paper presents the Kriging model approach for stochastic free vibration analysis of composite shallow doubly curved shells. The finite element formulation is carried out considering rotary inertia and transverse shear deformation based on Mindlin’s theory. The stochastic natural frequencies are expressed in terms of Kriging surrogate models. The influence of random variation of different input parameters on the output natural frequencies is addressed. The sampling size and computational cost is reduced by employing the present method compared to direct Monte Carlo simulation. The convergence studies and error analysis are carried out to ensure the accuracy of present approach. The stochastic mode shapes and frequency response function are also depicted for a typical laminate configuration. Statistical analysis is presented to illustrate the results using Kriging model and its performance. 相似文献
34.
Microwave irradiation has been proven to be an effective heating source in synthetic chemistry, and can accelerate the reaction rate, provide more uniform heating and help in developing better synthetic routes for the fabrication of bone-grafting implant materials. In this study, a new technique, which comprises microwave heating and powder metallurgy for in situ synthesis of Ti/CaP composites by using Ti powders, calcium carbonate (CaCO3) powders and dicalcium phosphate dihydrate (CaHPO4·2H2O) powders, has been developed. Three different compositions of Ti:CaCO3:CaHPO4·2H2O powdered mixture were employed to investigate the effect of the starting atomic ratio of the CaCO3 to CaHPO4·2H2O on the phase, microstructural formation and compressive properties of the microwave synthesized composites. When the starting atomic ratio reaches 1.67, composites containing mainly alpha-titanium (α-Ti), hydroxyapatite (HA), beta-tricalcium phosphate (β-TCP) and calcium titanate (CaTiO3) with porosity of 26%, pore size up to 152 μm, compressive strength of 212 MPa and compressive modulus of 12 GPa were formed. The in vitro apatite-forming capability of the composite was evaluated by immersing the composite into a simulated body fluid (SBF) for up to 14 days. The results showed that biodissolution occurred, followed by apatite precipitation after immersion in the SBF, suggesting that the composites are suitable for bone implant applications as apatite is an essential intermediate layer for bone cells attachment. The quantity and size of the apatite globules increased over the immersion time. After 14 days of immersion, the composite surface was fully covered by an apatite layer with a Ca/P atomic ratio approximately of 1.68, which is similar to the bone-like apatite appearing in human hard tissue. The results suggested that the microwave assisted-in situ synthesis technique can be used as an alternative to traditional powder metallurgy for the fabrication of Ti/CaP biocomposites. 相似文献
35.
D. Yadav 《Materials Science & Technology》2015,31(4):494-500
Copper particles were incorporated and retained in elemental state in an aluminium matrix by friction stir processing thereby producing a non-equilibrium particulate composite. The processed Al–Cup composite exhibited improved strength with significantly high ductility. The composite was stable up to a temperature of more than 300°C. Thermal exposure at 350°C for more than 10 min led to diffusion of Cu atoms into the Al matrix forming a core-shell type structure in the Cu particles and thus producing an Al–Cu core-shell composite. The shell consists of multiple layers, the thickness of which was controllable. 相似文献
36.
37.
本文以喷淋液滴在空气环境下运动特性为工程背景,建立单个液滴在常温、常压空气环境中的动量方程,分析液滴沉降特性、追赶特性及运动轨迹行为。计算结果表明,不同喷淋液滴初始条件下,短时间内存在重力大于曳力和重力小于曳力两种情况,但最终减速液滴均会达到受力平衡状态;液滴离开喷淋头后,垂向位移均迅速增大,液滴粒径越大、初始速度越大,垂向位移增长的速率也越大,达到相同位移的用时越短;液滴尺寸、初始速度相差越大,液滴追赶所用的时间越短,追赶位移越小,液滴尺寸、初始速度越接近,液滴追赶所用的时间越长,追赶位移越大;液滴初始速度越大、初始直径越大、喷射角度越大,横向速度消失越慢,达到的横向位移越大,喷射液滴覆盖的面积也越大。计算结果有助于优化工程实际中喷淋系统的设计与布置。 相似文献
38.
ABSTRACTThis paper deals with asymptotic stabilisation of a class of nonlinear input-delayed systems via dynamic output feedback in the presence of disturbances. The proposed strategy has the structure of an observer-based control law, in which the observer estimates and predicts both the plant state and the external disturbance. A nominal delay value is assumed to be known and stability conditions in terms of linear matrix inequalities are derived for fast-varying delay uncertainties. Asymptotic stability is achieved if the disturbance or the time delay is constant. The controller design problem is also addressed and a numerical example with an unstable system is provided to illustrate the usefulness of the proposed strategy. 相似文献
39.
某出口型号交流电力机车牵引控制系统要求变流器控制逻辑具备接触器控制、牵引系统数据交互、变流器故障保护、变流器启动自检等功能。针对以上功能,基于MATLAB中的Simulink/Stateflow可视化编程工具进行牵引控制模型的搭建,遵循模块化编程理念,采用较少的程序代码编写实现复杂的逻辑控制模型,生成逻辑清晰的控制功能流程图,进行半实物仿真测试,增强控制模型的可靠性。通过该变流器产品型式试验检验,验证变流器控制逻辑的功能可以满足控制系统的需求。 相似文献
40.