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   195篇
  免费   7篇
管理学   13篇
民族学   1篇
人口学   1篇
丛书文集   6篇
理论方法论   2篇
综合类   164篇
社会学   3篇
统计学   12篇
  2023年   1篇
  2021年   1篇
  2020年   1篇
  2019年   2篇
  2018年   2篇
  2016年   7篇
  2015年   5篇
  2014年   8篇
  2013年   5篇
  2012年   1篇
  2011年   6篇
  2010年   5篇
  2009年   12篇
  2008年   10篇
  2007年   9篇
  2006年   14篇
  2005年   10篇
  2004年   7篇
  2003年   4篇
  2002年   3篇
  2001年   6篇
  2000年   10篇
  1999年   4篇
  1998年   9篇
  1997年   9篇
  1996年   6篇
  1995年   5篇
  1994年   3篇
  1993年   5篇
  1992年   10篇
  1991年   2篇
  1990年   2篇
  1989年   6篇
  1988年   6篇
  1987年   4篇
  1985年   2篇
排序方式: 共有202条查询结果,搜索用时 15 毫秒
61.
在数字复合正交神经网络(NN)的基础上提出一种模拟复合正交神经网络,并用于轴向磁轴承的控制中.控制器采用模拟复合正交神经网络与PID的并行控制方法,对带有负载干扰的轴向磁轴承控制系统作了PID控制与NN PID控制的仿真实验.仿真结果表明,相对于常规PID控制器,该并行控制法具有非常好的抗干扰与自适应能力,获得了满意的控制效果.  相似文献   
62.
退火对软磁合金的最大磁导率影响的机理研究   总被引:6,自引:0,他引:6  
本文以Fe-Ni软磁合金为研究对象,从晶体缺陷及内应力两方面分析了退火参数对最大磁导率影响的机理,指出位错、晶界以及晶格畸变应力是影响最大磁导率的主要因素。  相似文献   
63.
文章采用超磁致伸缩材料Terfenol-D(Tb0.37Dy0.63Fe2)、金属玻璃Metglas 2605SA1和压电材料PZT(Pb(Zr, Ti)O3),设计了一种基于功能梯度磁电复合材料的新型自偏置磁传感器.利用Metglas和Terfenol-D之间的磁导率和矫顽力差异产生较强的磁化梯度,打破原有的平衡状态,导致内建磁场产生,进一步提高了零偏置磁场下磁致伸缩材料的压磁系数和磁电响应.实验结果表明:该传感器获得了较高的低频和高频零偏置磁电电压系数,分别达到9.14 mV/Oe和572 mV/Oe,并且谐振磁电电压输出和激励交变磁场之间呈线性变化关系.该自偏置磁传感器避免了传统磁电传感器对偏置磁场的依赖,具有制作简单、成本低、体积小,无需偏置磁场以及灵敏度高等优点.  相似文献   
64.
根据纯电动汽车整丰在运行条件下制动力矩的需求,设计了一种磁助力启动制动系统。利用电磁同性相斥、异性相吸的原理,根据车轮速度时时变化控制和改变磁极磁性,在汽车起步和制动过程起到磁助力作用。计算了电磁启动制动力矩,设计了电磁制动控制电路。基于ECE法规设计了制动力分配算法,计算表明:在高响应测速传感器的反馈控刺中,磁动力启动制动结构能够迅速有效地起到助力作用,为改善纯电动汽车的行车效能提供了新的思路。  相似文献   
65.
本文以最普遍的方式讨论了任意形状的平面载流圈在均匀磁场中的力学性质,从而在普遍的意义上定义了平面载流圈的磁矩.  相似文献   
66.
We consider the problem of statistical inference for functional and dynamic magnetic resonance imaging (MRI). A new approach is proposed which extends the adaptive weights smoothing procedure of Polzehl and Spokoiny that was originally designed for image denoising. We demonstrate how the adaptive weights smoothing method can be applied to time series of images, which typically occur in functional and dynamic MRI. It is shown how signal detection in functional MRI and the analysis of dynamic MRI can benefit from spatially adaptive smoothing. The performance of the procedure is illustrated by using real and simulated data.  相似文献   
67.
Extremely low frequency electric and magnetic fields (ELF EMFs) are a common exposure for modern populations. The prevailing public‐health protection paradigm is that quantitative exposure limits are based on the established acute effects, whereas the possible chronic effects are considered too uncertain for quantitative limits, but might justify precautionary measures. The choice of precautionary measures can be informed by a health‐economics analysis (HEA). We consider four such analyses of precautionary measures that have been conducted at a national or state level in California, the Netherlands, the United Kingdom, and Israel. We describe the context of each analysis, examine how they deal with some of the more significant issues that arise, and present a comparison of the input parameters and assumptions used. The four HEAs are methodologically similar. The most significant qualitative choices that have to be made are what dose‐response relationship to assume, what allowance if any to make for uncertainty, and, for a CBA only, what diseases to consider, and all four analyses made similar choices. These analyses suggest that, on the assumptions made, there are some low‐cost measures, such as rephasing, that can be applied to transmission in some circumstances and that can be justifiable in cost‐benefit terms, but that higher cost measures, such as undergrounding, become unjustifiable. Of the four HEAs, those in the United Kingdom and Israel were influential in determining the country's EMF policy. In California and Netherlands, the HEA may well have informed the debate, but the policy chosen did not stem directly from the HEA.  相似文献   
68.
为获得二同轴方形载流线圈间相互作用磁力,计算出了线圈间的互感系数。将虚功原理作为一种简捷方法加以运用,对该力极值位置进行了分析和图示。讨论平面内二同心方形线圈载流时一线圈不受磁张力的优良力学状态。  相似文献   
69.
Read  Daniel  Morgan  M. Granger 《Risk analysis》1998,18(5):603-610
The AC electric and magnetic fields associated with high voltage power lines have become a concern as a possible health risk. In most cases the strength of these fields decreases as the inverse square of the distance from the line. In earlier work, we found that laypeople do not understand how rapidly field strength decreases with distance. Most believe that any high voltage power line they can see is exposing them to strong fields. This paper confirms the earlier finding and explores a number of strategies which might be used in risk communications to correct this misperception. We found it relatively easy to provide subjects with a better understanding of the range-dependency of magnetic field strength. Moreover, the quality of this acquisition was apparently independent of the manner in which they were instructed. Such successful instruction is markedly different from the well-established difficulty of teaching people about many qualitative domains, such as physics or ideas in probability. Clearly, while some erroneous beliefs are highly resistant to change, others can be altered quite readily. We suspect that an important distinction between knowledge about the range-dependency of power-frequency magnetic fields and less tractable topics involves the presence or absence of prior folk-theories or "mental models" of the domain.  相似文献   
70.
提出一种新颖的窄线宽半导体激光器测试技术—延迟光纤干涉法。利用部分相干光理论推出延迟光纤干涉的计算公式,通过模拟计算,总结出采用这种技术的测试方法,建立了实验系统,对实验结果进行数据分析,证明了这种新的测试技术方案是正确可行的。  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