首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   4314篇
  免费   402篇
  国内免费   263篇
电工技术   402篇
技术理论   1篇
综合类   674篇
化学工业   284篇
金属工艺   127篇
机械仪表   248篇
建筑科学   468篇
矿业工程   66篇
能源动力   53篇
轻工业   101篇
水利工程   58篇
石油天然气   78篇
武器工业   23篇
无线电   276篇
一般工业技术   362篇
冶金工业   263篇
原子能技术   13篇
自动化技术   1482篇
  2024年   7篇
  2023年   41篇
  2022年   63篇
  2021年   79篇
  2020年   89篇
  2019年   71篇
  2018年   67篇
  2017年   102篇
  2016年   126篇
  2015年   131篇
  2014年   238篇
  2013年   219篇
  2012年   289篇
  2011年   260篇
  2010年   213篇
  2009年   278篇
  2008年   251篇
  2007年   258篇
  2006年   288篇
  2005年   261篇
  2004年   214篇
  2003年   199篇
  2002年   267篇
  2001年   211篇
  2000年   202篇
  1999年   153篇
  1998年   104篇
  1997年   91篇
  1996年   53篇
  1995年   27篇
  1994年   27篇
  1993年   13篇
  1992年   12篇
  1991年   7篇
  1990年   6篇
  1989年   5篇
  1988年   5篇
  1987年   6篇
  1986年   2篇
  1985年   3篇
  1984年   7篇
  1983年   3篇
  1982年   7篇
  1981年   3篇
  1976年   3篇
  1964年   2篇
  1961年   2篇
  1957年   3篇
  1956年   3篇
  1955年   3篇
排序方式: 共有4979条查询结果,搜索用时 15 毫秒
1.
为了研究激光刻痕工艺参数对取向电工钢表面的磁畴形貌、刻痕线宽度和铁损的影响规律,开展了激光刻痕工艺试验。结果表明,激光刻痕后取向电工钢表面的磁畴宽度明显细化,且随着输入电流的增加,磁畴宽度先减小后增大;刻痕线宽度随着输入电流的增加而增大。对于本次试验样品,通过对比分析,确定最佳激光刻痕工艺参数为电流为 12 A,激光频率为 5 kHz,刻痕速度为 800 mm/s,该参数下铁损改善率可达 11.81%。  相似文献   
2.
设计了一种开关磁阻直线电机,使用JMAG软件对其进行了仿真和优化。进行了推力公式的推导,研究了导通顺序和初始位置对电机推力的影响,并分析了三种典型情况的磁力线分布。对电机的定子和动子的齿部和轭部高度、宽度及铁耗进行仿真优化,得出了最优参数。将有取向硅钢应用于该电机,研究了推力与轧制角的关系,并与使用普通硅钢的开关磁阻直线电机进行了对比,推力有一定提升。提出在动子齿部开切向槽的方案,结果表明,开切向槽对推力的影响较小,并能显著减小推力波动。  相似文献   
3.
对2250 mm热轧生产线生产的取向硅钢热轧钢带的合金体系进行了设计,制定了合理的加热制度和热轧轧制工艺。对添加稀土元素Ce的取向硅钢铸坯和热轧钢带进行了分析,探究了稀土元素Ce对取向硅钢低倍组织、热轧织构及成品磁性能的影响。结果表明,稀土元素Ce能够细化取向硅钢连铸坯低倍组织和热轧显微组织,提高取向硅钢成品磁性能。  相似文献   
4.
Regarded as one solution to the problem of how to enable older people to retain their independence, extra-care housing, where each resident has their own self-contained dwelling and access to communal facilities and to care, has received extensive funding in recent years. Implicit in the concept of specialist housing is the notion of ‘special’ occupants, imagined older people. Adopting a socio-technical approach, this paper considers how ideas about ageing inform those aspects of extra-care-housing-design that relate to thermal comfort. The paper draws on semi-structured interviews with 13 people involved in the design, development and management of UK-based extra-care housing. Participants characterised imagined occupants as vulnerable to cold, at risk from fuel poverty and liable to be burned by hot surfaces or fall from high windows. These user representations were reportedly inscribed into the design of extra-care housing schemes through the inclusion of building features such as communal heating, under-floor heating, restricted window opening and heated corridors. The utilisation of stereotypical user representations of older people raises questions, given that older people's thermal comfort needs can be highly diverse. The paper explores the implications for energy demand.  相似文献   
5.
Induction machines (IM) constitute a theoretically interesting and practically important class of nonlinear systems. They are frequently used as wind generators for their power/cost ratio. They are described by a fifth‐order nonlinear differential equation with two inputs and only three state variables available for measurement. The control task is further complicated by the fact that IM are subject to unknown (load) disturbances and the parameters can be of great uncertainty. One is then faced with the challenging problem of controlling a highly nonlinear system, with unknown time‐varying parameters, where the regulated output, besides being unmeasurable, is perturbed by an unknown additive signal. Passivity‐based control (PBC) is a well‐established structure‐preserving design methodology which has shown to be very powerful to design robust controllers for physical systems described by Euler‐Lagrange equations of motion. PBCs provide a natural procedure to "shape" the potential energy yielding controllers with a clear physical interpretation in terms of interconnection of the system with its environment and are robust vis á vis to unmodeled dissipative effects. One recent approach of PBC is the Interconnection and Damping Assignment Passivity‐Based Control (IDA‐PBC) which is a very useful technique to control nonlinear systems assigning a desired (Port‐Controlled Hamiltonian) structure to the closed‐loop. The aim of this paper is to give a survey on different PBC of IM. The originality of this work is that the author proves that the well known field oriented control of IM is a particular case of the IDA‐PBC with disturbance.  相似文献   
6.
在内外层算法的基础上,采用联立方程思想将主塔、侧线汽提塔视为一个整体进行建模,并针对复杂炼油塔的特点对算法提出了改进。首先,由于传统内外层法简化的K值模型对组成的变化不敏感,在处理带有石油的体系时,容易出现迭代次数较多,甚至部分塔板温度更新异常的问题,因此采用了汽相分数加和式推导了简化的K值模型加权因子。其次,借鉴流量加和法思想,规定侧线汽提塔的塔底产品流量作为设计变量,增强了算法收敛的稳定性。为验证改进后算法的有效性,采用不同的算法对实际的常压塔进行了模拟,结果显示改进后的算法适合应用于复杂炼油塔的模拟计算。  相似文献   
7.
卢喜东  段哲民  钱叶魁  周巍 《软件学报》2020,31(5):1454-1464
针对当前恶意代码静态分析方法精度不足的问题,将恶意代码映射为无压缩的灰度图像,然后根据图像变换方法将图像变换为恒定大小的图像,使用方向梯度直方图提取图像的特征,最后提出一种基于深度森林的恶意代码分类方法.实验中选择不同家族的多个恶意代码样本进行分类,验证了该方法的有效性,并且实验结果优于近期提出的SPAM-GIST方法.  相似文献   
8.
This paper critically discusses the concept of intergenerational family support in housing for young people. Recognizing increased difficulties faced by the younger generation in the housing market, this paper highlights that support from older family members is increasingly important. Nonetheless, it is critiqued that the role of the family home has been largely ignored in the current ‘generation rent’ discourse. By drawing on recent youth studies debates, this paper argues living in the family home could be an important form of support in housing, especially for marginalized youth. This paper presents insights from qualitative studies in Hong Kong and Scotland and analyses interview accounts of socially disengaged young people. It reflects how remaining at the family home could be interpreted as intergenerational support, and further elicits complexities in expectations, negotiations and emotions involved. This analysis offers new evidence and a more nuanced perspective of intergenerational family support in housing research.  相似文献   
9.
Online social media networks are gaining attention worldwide, with an increasing number of people relying on them to connect, communicate and share their daily pertinent event-related information. Event detection is now increasingly leveraging online social networks for highlighting events happening around the world via the Internet of People. In this paper, a novel Event Detection model based on Scoring and Word Embedding (ED-SWE) is proposed for discovering key events from a large volume of data streams of tweets and for generating an event summary using keywords and top-k tweets. The proposed ED-SWE model can distill high-quality tweets, reduce the negative impact of the advent of spam, and identify latent events in the data streams automatically. Moreover, a word embedding algorithm is used to learn a real-valued vector representation for a predefined fixed-sized vocabulary from a corpus of Twitter data. In order to further improve the performance of the Expectation-Maximization (EM) iteration algorithm, a novel initialization method based on the authority values of the tweets is also proposed in this paper to detect live events efficiently and precisely. Finally, a novel automatic identification method based on the cosine measure is used to automatically evaluate whether a given topic can form a live event. Experiments conducted on a real-world dataset demonstrate that the ED-SWE model exhibits better efficiency and accuracy than several state-of-art event detection models.  相似文献   
10.
随着变压器新能效标准GB 20052-2020的正式实施,变压器各能效等级普遍提升,也推动取向硅钢产品等级的提高。本文结合新能效标准,针对宝钢低铁损取向硅钢产品应用实绩,给出选材建议,并针对产品使用过程中存在的问题进行剖析,以期对变压器制造厂家选材和使用起到参考作用。  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号