全文获取类型
收费全文 | 24957篇 |
免费 | 2950篇 |
国内免费 | 1989篇 |
专业分类
电工技术 | 3706篇 |
技术理论 | 1篇 |
综合类 | 2536篇 |
化学工业 | 1216篇 |
金属工艺 | 1848篇 |
机械仪表 | 3303篇 |
建筑科学 | 924篇 |
矿业工程 | 1163篇 |
能源动力 | 1319篇 |
轻工业 | 830篇 |
水利工程 | 515篇 |
石油天然气 | 604篇 |
武器工业 | 388篇 |
无线电 | 2274篇 |
一般工业技术 | 1603篇 |
冶金工业 | 1686篇 |
原子能技术 | 106篇 |
自动化技术 | 5874篇 |
出版年
2024年 | 55篇 |
2023年 | 271篇 |
2022年 | 607篇 |
2021年 | 696篇 |
2020年 | 833篇 |
2019年 | 643篇 |
2018年 | 672篇 |
2017年 | 874篇 |
2016年 | 1000篇 |
2015年 | 1035篇 |
2014年 | 1692篇 |
2013年 | 1346篇 |
2012年 | 2022篇 |
2011年 | 2094篇 |
2010年 | 1606篇 |
2009年 | 1550篇 |
2008年 | 1429篇 |
2007年 | 1808篇 |
2006年 | 1549篇 |
2005年 | 1375篇 |
2004年 | 994篇 |
2003年 | 1027篇 |
2002年 | 846篇 |
2001年 | 787篇 |
2000年 | 662篇 |
1999年 | 520篇 |
1998年 | 361篇 |
1997年 | 334篇 |
1996年 | 269篇 |
1995年 | 216篇 |
1994年 | 183篇 |
1993年 | 106篇 |
1992年 | 93篇 |
1991年 | 62篇 |
1990年 | 56篇 |
1989年 | 57篇 |
1988年 | 35篇 |
1987年 | 30篇 |
1986年 | 10篇 |
1985年 | 10篇 |
1984年 | 8篇 |
1983年 | 4篇 |
1981年 | 5篇 |
1980年 | 5篇 |
1964年 | 5篇 |
1963年 | 5篇 |
1962年 | 7篇 |
1960年 | 6篇 |
1959年 | 6篇 |
1954年 | 3篇 |
排序方式: 共有10000条查询结果,搜索用时 18 毫秒
11.
Pythagorean fuzzy sets (PFSs) were proposed by Yager in 2013 to treat imprecise and vague information in daily life more rigorously and efficiently with higher precision than intuitionistic fuzzy sets. In this paper, we construct new distance and similarity measures of PFSs based on the Hausdorff metric. We first develop a method to calculate a distance between PFSs based on the Hasudorff metric, along with proving several properties and theorems. We then consider a generalization of other distance measures, such as the Hamming distance, the Euclidean distance, and their normalized versions. On the basis of the proposed distances for PFSs, we give new similarity measures to compute the similarity degree of PFSs. Some examples related to pattern recognition and linguistic variables are used to validate the proposed distance and similarity measures. Finally, we apply the proposed methods to multicriteria decision-making by constructing a Pythagorean fuzzy Technique for Order Preference by Similarity to an Ideal Solution and then present a practical example to address an important issue related to social sector. Numerical results indicate that the proposed methods are reasonable and applicable and also that they are well suited in pattern recognition, linguistic variables, and multicriteria decision-making with PFSs. 相似文献
12.
针对金融领域中智能客服的句子相似度计算方法进行了研究。利用基于词性的分词纠正模型减少中文歧义词、金融相关词汇的分词错误;通过词向量方法和循环神经网络分别提取词语级和句子级的语义特征,并且得到句子向量;用融合层计算出句子向量间的差异特征;对差异特征进行降维和归一化得到句子相似度计算结果。实验结果表明,该方法具有较高的准确率和[F1]值。 相似文献
13.
An Improved Torque Sensorless Speed Control Method for Electric Assisted Bicycle With Consideration of Coordinate Conversion 下载免费PDF全文
Tinghua Li Qinghua Yang Xiaowei Tu Bin Ren 《IEEE/CAA Journal of Automatica Sinica》2020,7(6):1575-1584
In this paper, we propose an improved torque sensorless speed control method for electric assisted bicycle, this method considers the coordinate conversion. A low-pass filter is designed in disturbance observer to estimate and compensate the variable disturbance during cycling. A DC motor provides assisted power driving, the assistance method is based on the real-time wheel angular velocity and coordinate system transformation. The effect of observer is proved, and the proposed method guarantees stability under disturbances. It is also compared to the existing methods and their performances are illustrated through simulations. The proposed method improves the performance both in rapidity and stability. 相似文献
14.
为了解决定子分段式永磁直线同步电机(PMLSM)存在的因磁阻效应、负载阻力、摩擦力、参数摄动以及动子进出定子时耦合面积变化所造成的控制性能下降的难题,根据动子和定子的耦合状态,提出一种在完全耦合阶段和动子退出定子阶段的分段式控制方法。首先,在动子与定子完全耦合阶段采用改进滑模控制器减小推力波动导致的速度波动,再通过加入扰动观测器降低滑模切换项所带来的抖振现象;在动子退出定子阶段,建立相关电磁参数与动子位置的函数关系,实时补偿由耦合面积变化引起的动子失速,使动子速度在退出时接近给定值。仿真及实验结果表明动定子完全耦合过程中的速度稳态误差为0.005 m/s,收敛时间为0.3 s,动子退出定子阶段的速度波动不超过0.04 m/s,满足定子分段式PMLSM用于长行程自动运输系统对平稳性及快速性的需求。 相似文献
15.
In dense traffic railway networks, trains may often slow down or stop between stations owing to previous train delays. If preceding train trajectory can be predicted, energy‐efficient driving can be achieved by suppressing unnecessary speed changes. In this paper, we propose an algorithm to find energy‐efficient driving considering fixed‐block signaling (FBS) system by using dynamic programming (DP). DP is suitable for use because it can optimize the control inputs with discrete and state constraints. In this paper, we discuss energy‐efficient driving by considering a FBS system using some case studies of simulation. In the simulation, we examine a technique to drive an express train in an energy‐efficient way when the preceding local train is running toward the station with passing loops. The results show that the proposed method can derive complex speed profiles for energy‐efficient driving and the train can be operated with a maximum reduced energy consumption of 8.3%. 相似文献
16.
混沌识别是对非线性时间序列进行混沌预测的前提。针对时间序列风速确定性与随机性相结合的复杂非线性特征,研究了不同的混沌识别方法,并对风速时间序列进行混沌特征识别。应用随机噪声、周期运动及经典混沌系统的时间序列对所选方法进行可靠性验证。对美国国家风能研究中心M2测风塔实测时间序列风速数据进行非线性混沌特征识别。结果表明:风速时间序列具有明显的混沌特征;各风速时间序列表现出不同程度的混沌特征;各混沌识别方法对风速时间序列混沌特征的表达形式不同,互为补充,相互验证。 相似文献
17.
An up to date review of continuously variable speed wind turbines with mechatronic variable transmissions 下载免费PDF全文
Xiuxing Yin 《国际能源研究杂志》2018,42(4):1442-1454
As a promising and potential alternative to conventional fixed or variable speed wind turbines, continuously variable speed wind turbines (CVSWTs) with variable transmissions offer improved power efficiency and enhanced power control capabilities. The CVSWTs can be generally achieved by adapting mechatronic variable transmissions in the turbine drive train for continuously variable speed operations for wind turbines. Therefore, this paper serves to provide an up to date and exhaustive review of the CVSWTs with mechatronic variable transmissions such as mechanical variable transmission, electrical variable transmission, and power splitting transmission. In this paper, the analysis of CVSWTs with different mechatronic transmission topologies is performed regarding basic configurations, dynamic characteristics, control principles, and experimental or simulation results. Review results indicate the feasibility of applying CVSWTs with such mechatronic transmissions and highlight superiorities of the CVSWTs with power splitting transmission. The CVSWT with power splitting transmission will be particularly suitable for megawatt‐scale turbine systems and will hence increase the economic competitiveness of these turbines due to its large power capacity and high reliability. The directions or challenges for future investigations of CVSWTs with such mechatronic transmissions are also presented to foster in‐depth understanding of such CVSWTs and their control strategies. 相似文献
18.
为研究夹紧力可调的机电控制无级变速器(EMCVT)电控电动执行机构的可靠性,及其速比和从动带轮夹紧力动态响应的影响因素,采用MATLAB/Simulink构建了EMCVT执行机构的动力学模型,设计了针对EMCVT电控电动执行机构的速比和夹紧力闭环控制器。对EMCVT输入转矩突变和目标速比突变两种工况进行了仿真分析,仿真结果表明:速比和从动带轮夹紧力动态响应的超调量和调节时间满足CVT的使用要求,从动带轮夹紧力响应时间小于1s,速比变化率可以达到2;EMCVT速比和从动带轮夹紧力动态响应的主要影响因素是执行电动机的负载和转动方向。 相似文献
19.
由于汽车造型有着各种突出的棱线,在拉伸模的冲压过程中,板料和上、下模的各个棱线接触,在型腔内部形成形状各异的密闭空间。如果在上下模闭合时,模具排气不通畅,密闭空间内的空气会对产品造成不可恢复的鼓包或凹坑,此缺陷严重影响了整车的外观品质。通过成形性分析,查看各个气腔的形成过程,并通过推理、计算空气在排气孔处的排气速度,从而得出在不产生面品缺陷时的排气孔所应有的数量及大小,使整车SE阶段及模具设计阶段有效预防,避免后期无法增加排气孔的尴尬情况。 相似文献
20.
由于双馈风机风电场故障特性与传统同步机存在较大差别,因此传统方向元件应用于双馈风机风电场时存在适应性问题。针对双馈风机风电场存在的频率偏移、等值内阻抗不稳定和弱馈等特点,提出一种基于时域波形相似度的故障方向元件。根据推算的联络线对侧电压与保护安装处记忆电压波形的余弦相似度判断故障方向,能够有效解决双馈风机风电场出口故障方向判别存在的问题。在PSCAD/EMTDC中搭建典型的双馈风机接入系统,仿真结果表明,所提故障方向元件针对不同的故障类型均能有效判断故障方向。 相似文献