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   1814篇
  免费   156篇
  国内免费   108篇
电工技术   65篇
综合类   186篇
化学工业   118篇
金属工艺   143篇
机械仪表   209篇
建筑科学   83篇
矿业工程   27篇
能源动力   17篇
轻工业   49篇
水利工程   13篇
石油天然气   37篇
武器工业   28篇
无线电   362篇
一般工业技术   171篇
冶金工业   216篇
原子能技术   50篇
自动化技术   304篇
  2024年   3篇
  2023年   21篇
  2022年   41篇
  2021年   51篇
  2020年   41篇
  2019年   36篇
  2018年   34篇
  2017年   50篇
  2016年   55篇
  2015年   55篇
  2014年   87篇
  2013年   102篇
  2012年   94篇
  2011年   145篇
  2010年   101篇
  2009年   116篇
  2008年   117篇
  2007年   139篇
  2006年   119篇
  2005年   108篇
  2004年   95篇
  2003年   88篇
  2002年   75篇
  2001年   66篇
  2000年   40篇
  1999年   43篇
  1998年   34篇
  1997年   20篇
  1996年   26篇
  1995年   11篇
  1994年   13篇
  1993年   8篇
  1992年   7篇
  1991年   3篇
  1989年   2篇
  1988年   3篇
  1987年   3篇
  1986年   1篇
  1983年   1篇
  1980年   1篇
  1975年   1篇
  1966年   1篇
  1964年   5篇
  1963年   3篇
  1962年   1篇
  1961年   4篇
  1960年   1篇
  1959年   2篇
  1958年   3篇
  1954年   1篇
排序方式: 共有2078条查询结果,搜索用时 15 毫秒
1.
为解决贵重物品与其内包装“契合度”不高的问题,提出基于纸浆纤维的贵重物品内包装塑造系统。系统通过三维扫描获取待包装物品的点云信息,经主控计算机进行数据处理,以下位机为执行中枢,辅之其他外部设备,利用纸浆纤维为贵重物品塑造“量身定制”的内包装,提升内包装契合度,增强保护效果,绿色环保,安全稳定。  相似文献   
2.
Laser additive manufactured zirconia-alumina ceramic (ZrO2-Al2O3) parts demonstrate severe problems resulting from cracking and inhomogeneous material dispersion. To reduce these problems, we propose a novel ultrasonic vibration-assisted laser engineered net shaping (LENS) process for fabrication of bulk ZrO2-Al2O3 parts. Results showed that the initiation of cracks and the crack propagation were suppressed in the parts fabricated by LENS process with ultrasonic vibration. For the parts fabricated without ultrasonic vibration, the sizes of cracks decreased with the increase of laser power. Scanning electron microscope analyses proved that the introduction of ultrasonic vibration was beneficial for grain refinement and uniform material dispersion. Due to the suppressed cracking, refined grains, and homogenized material dispersion, the parts fabricated with ultrasonic vibration demonstrated better mechanical properties (including higher microhardness, higher wear resistance, and better compressive properties), compared with the parts fabricated without ultrasonic vibration.  相似文献   
3.
The gas permeability of Y0.03Zr0.97O2 (3Y-TZP) porous supports from thermoplastic feedstocks has been improved by adding MgO as a non-pyrolyzable pore former. Common pyrolyzable pore formers such as graphite often produce tortuous and narrow pore channels with low gas permeability, limiting the performance of oxygen transport membranes or other membranes relying on gas transport to the active membrane surface. Thermoplastic feedstocks for extrusion of tubular 3Y-TZP supports were prepared with four different amounts of pyrolyzable pore formers and/or MgO as non-pyrolyzable pore former. The MgO was removed after sintering by leaching in acetic acid. With this technique we obtained porosities above 70 vol% and gas permeabilities above 3?10?14?m2. Compared to samples with only pyrolyzable pore formers, the non-pyrolyzable pore former increases the gas permeability and reduces the tortuosity.  相似文献   
4.
Methamphetamine (MA) use disorder is a chronic neuropsychiatric disease characterized by recurrent binge episodes, intervals of abstinence, and relapses to MA use. Therefore, identification of the key genes and pathways involved is important for improving the diagnosis and treatment of this disorder. In this study, high-throughput RNA sequencing was performed to find the key genes and examine the comparability of gene expression between whisker follicles and the striatum of rats following MA self-administration. A total of 253 and 87 differentially expressed genes (DEGs) were identified in whisker follicles and the striatum, respectively. Multivariate and network analyses were performed on these DEGs to find hub genes and key pathways within the constructed network. A total of 129 and 49 genes were finally selected from the DEG sets of whisker follicles and of the striatum. Statistically significant DEGs were found to belong to the classes of genes involved in nicotine addiction, cocaine addiction, and amphetamine addiction in the striatum as well as in Parkinson’s, Huntington’s, and Alzheimer’s diseases in whisker follicles. Of note, several genes and pathways including retrograde endocannabinoid signaling and the synaptic vesicle cycle pathway were common between the two tissues. Therefore, this study provides the first data on gene expression levels in whisker follicles and in the striatum in relation to MA reward and thereby may accelerate the research on the whisker follicle as an alternative source of biomarkers for the diagnosis of MA use disorder.  相似文献   
5.
Aiming at human-robot collaboration in manufacturing, the operator's safety is the primary issue during the manufacturing operations. This paper presents a deep reinforcement learning approach to realize the real-time collision-free motion planning of an industrial robot for human-robot collaboration. Firstly, the safe human-robot collaboration manufacturing problem is formulated into a Markov decision process, and the mathematical expression of the reward function design problem is given. The goal is that the robot can autonomously learn a policy to reduce the accumulated risk and assure the task completion time during human-robot collaboration. To transform our optimization object into a reward function to guide the robot to learn the expected behaviour, a reward function optimizing approach based on the deterministic policy gradient is proposed to learn a parameterized intrinsic reward function. The reward function for the agent to learn the policy is the sum of the intrinsic reward function and the extrinsic reward function. Then, a deep reinforcement learning algorithm intrinsic reward-deep deterministic policy gradient (IRDDPG), which is the combination of the DDPG algorithm and the reward function optimizing approach, is proposed to learn the expected collision avoidance policy. Finally, the proposed algorithm is tested in a simulation environment, and the results show that the industrial robot can learn the expected policy to achieve the safety assurance for industrial human-robot collaboration without missing the original target. Moreover, the reward function optimizing approach can help make up for the designed reward function and improve policy performance.  相似文献   
6.
Even using simple techniques like taking the stairs, many individuals struggle to maintain the motivation to be physically active. Health gamification systems can aid this goal by providing points earned through exercise that are redeemable for tangible extrinsic rewards. Using self-determination theory, we conduct research on one such system and investigate rewards’ effectiveness to promote exercise considering reward value, redemption frequency patterns, and fitness levels. We find that rewards do significantly increase activity levels, and this effect is larger for advanced users who redeem multiple times for higher value rewards. We close by offering future research avenues and advice to optimize reward portfolios.  相似文献   
7.
8.
项目进度管理实施中的奖惩机制研究   总被引:1,自引:0,他引:1  
对项目进度管理中的奖惩机制建立了数学模型,从承包商和业主两方面分析研究奖惩机制的决定因素,并对其进行了优化分析,提出了资源制约强度,浮动资金使用强度两个新概念。在此基础上从承包商和业主双方分别对以往的项目进度模型进行了优化,并建立了两个新的优化模型并对模型进行了说明。  相似文献   
9.
翟思安 《山西建筑》2006,32(15):323-325
简述了水泥稳定碎石基层的作用,介绍了基层施工中的原材料质量控制措施,详细阐述了基层施工的各项工艺技术,总结了施工中的有关注意事项,以保证工程施工质量。  相似文献   
10.
汤思琦  彭浪  毛华松 《中国园林》2022,38(10):139-144
作为“琴棋书画”之首,古琴与其相关的抚琴、听琴等活动,是中国古代山水与园林中的重要活动,塑造了以古琴为主题的园林空间与园林意境。基于古琴活动的图文史料和园林实存,通过图文互证的方法,归纳了古琴活动文化意象从神性到诗性的变迁历程,以及此历程推动下的活动方式雅化和活动场所范式化。最后从古琴声音审美的“和”“静”“清”“远”4个方面,总结了园林古琴声景空间组织的典型方式。探索了古琴活动文化内涵和空间场所的耦合关系,对理解中国园林的内在形成机制具有积极意义。  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