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   5866篇
  免费   487篇
  国内免费   242篇
电工技术   225篇
综合类   665篇
化学工业   448篇
金属工艺   855篇
机械仪表   1170篇
建筑科学   519篇
矿业工程   234篇
能源动力   123篇
轻工业   154篇
水利工程   108篇
石油天然气   227篇
武器工业   97篇
无线电   264篇
一般工业技术   751篇
冶金工业   186篇
原子能技术   53篇
自动化技术   516篇
  2024年   16篇
  2023年   51篇
  2022年   92篇
  2021年   116篇
  2020年   135篇
  2019年   101篇
  2018年   113篇
  2017年   141篇
  2016年   173篇
  2015年   206篇
  2014年   308篇
  2013年   326篇
  2012年   408篇
  2011年   404篇
  2010年   311篇
  2009年   361篇
  2008年   288篇
  2007年   425篇
  2006年   416篇
  2005年   331篇
  2004年   310篇
  2003年   268篇
  2002年   254篇
  2001年   180篇
  2000年   167篇
  1999年   113篇
  1998年   103篇
  1997年   89篇
  1996年   65篇
  1995年   62篇
  1994年   60篇
  1993年   45篇
  1992年   42篇
  1991年   21篇
  1990年   22篇
  1989年   22篇
  1988年   11篇
  1987年   7篇
  1986年   5篇
  1985年   3篇
  1984年   4篇
  1982年   4篇
  1981年   4篇
  1980年   3篇
  1979年   3篇
  1978年   1篇
  1975年   1篇
  1965年   1篇
  1959年   1篇
  1957年   1篇
排序方式: 共有6595条查询结果,搜索用时 62 毫秒
81.
面向装配的通用三维零件库管理系统   总被引:1,自引:1,他引:1  
在面向装配环境下 ,采用OLEAutomation技术、参数化建模技术及数据管理技术等 ,开发建立了一个通用的三维零件库管理系统———Super3D -Lib ,该系统同样也适用于模具设计 ,是一个实用性强的三维设计辅助工具。  相似文献   
82.
斜齿圆柱齿轮无差动滚切技术研究   总被引:1,自引:1,他引:1  
对无差动滚切技术进行了系统的研究,提出了一种用无差动法滚切斜齿圆柱齿轮及其挂轮选择的新方法。用本方法可以快速地选择高精度挂轮,达到较高的加工精度.在生产中有实际意义。  相似文献   
83.
宋克非 《铸造技术》2007,28(4):465-467
介绍了使用石墨预处理方法生产风电机球墨铸铁件的生产实例,试验表明,使用预处理可以在一定程度上细化石墨,单位面积上的石墨球数量提高了2%,较为圆整的石墨球数量提高了8%,球化率提高了1%。采用预处理工艺获得的试样与采用传统工艺获得的试样相比,其平均屈服强度提高5%,抗拉强度提高3%,伸长率提高9%,低温抗冲击强度的平均值和3点最小值都有小幅上升,硬度则有小幅下降。采用预处理工艺后,生产的稳定性和可靠性亦有所提高。  相似文献   
84.
分析了气膜片零件胀形质量差的原因,对原模具结构进行了改进,解决了原模具成形后贴模不理想、型面不准确的问题,提高了零件质量。  相似文献   
85.
Direct laser fabrication of thin-walled metal parts under open-loop control   总被引:2,自引:0,他引:2  
Direct laser fabrication (DLF) is an advanced manufacturing technology, which can build full density metal parts directly from CAD files without using any modules or tools. The investigation on the fabrication of thin-walled parts of nickel alloy using open-loop DLF process is introduced in this paper. The experimental setup consisted of a CO2 laser, a 3-axis CNC table, a coaxial powder nozzle and a powder recycler. The 3D-CAD file of a thin-walled metal part was converted into the STL file format and imported into software HUST-RP to generate ‘pseudo-random’ scanning paths of laser beam. The influence of process parameters on the build height of thin-walled metal parts was studied by 1–10 layered single-bead stacks of nickel alloy. The result shows that the interference factors which affect the build height of thin-walled metal parts occur randomly during the process. For open-loop DLF process, thin-walled metal parts can achieve much better shape quality if the process parameters are suitable. Multilayer single-bead walls were built up with different scanning velocity to obtain the optimal process parameters of thin-walled parts of nickel alloy. It shows that thin walls of nickel alloy with uniform height can be built up layer by layer in a certain range of specific energy. However, it is difficult to control the build height of complex thin-walled metal parts in an accurate manner just using optimal parameters. A special coaxial powder nozzle was designed in this paper. In a certain range, the deposition thickness of the nozzle is nearly linearly increased with increase in the standoff distance between the powder focusing point of the nozzle and the deposition substrate. By means of the nozzle, a novel method to control the build height of thin-walled metal parts using open-loop DLF process was introduced. The difference in build height of a thin-walled part can be compensated automatically in one or several layers during the process. It is proved that the build height of a thin-walled metal part can be accurately controlled in theory using the nozzle. A complex single-bead part of nickel alloy whose geometry was designed to be the well-known Chinese ‘FU’ was fabricated and explained in this paper. The result shows that the shape quality of the sample is quite good, and actual build height of the sample is 53.54 mm while the designed value is 54 mm.  相似文献   
86.
介绍了接地板多工位级进模的结构特点和设计要点,分析了模具设计中的技术问题,得出了排样设计和解决内凹弯曲件的卸料问题的方法,对同类零件的模具设计有一定的借鉴作用.  相似文献   
87.
In this communication, triple band hybrid multi‐input–multi‐output (MIMO) cylindrical dielectric resonator antenna (CDRA) with high isolation is examined. The proposed MIMO antenna includes two symmetric folded microstrip line feeding structures along with CDRA at two different ends of substrate. Two inverted L‐shaped strips on the ground plane are used to enhance the isolation (S12 < ?15 dB) as well as to generates 2.7 GHz frequency band. Metallic strip on the ground plane act as an electromagnetic reflector and also enhance the isolation between two antennas (S12 < ?20 dB). Archetype of proposed MIMO antenna design has been fabricated and tested to validate the simulated results. The proposed antenna operates at three different frequency bands 2.24–2.38 GHz, 2.5–3.26 GHz, and 4.88–7.0 GHz (S11 < ?6 dB) with the fractional bandwidth 6.06%, 26.4%, and 35.7%, respectively. Folded microstrip lines generate path delay between the electric field lines and originate circular polarization characteristics in the frequency range 5.55–5.75 GHz with the fractional bandwidth of 3.55%. In order to satisfy the different performance requirement of MIMO antenna such as envelop correlation coefficient, mean effective gain, effective diversity gain, peak gain are also examined. The proposed antenna is found suitable for LTE2500, WLAN, and WiMAX applications. © 2016 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2016.  相似文献   
88.
为了满足X频段机载雷达天线的指标要求,使得矩形平面天线与柱面共形,通过并联侧馈方式进行馈电。在微带共形阵天线的相关理论基础上,阵元采用介电常数2.2,厚度为0.5mm的介质基板。通过HFSS12对微带共形阵天线进行仿真设计并优化。实验结果表明,在X波段内实现了方位面的全向扫描,实测阻抗带宽为9.80-10.20GHz,最大增益可达10dB,全向辐射性能稳定,满足了指标要求。  相似文献   
89.
吉林省西部水环境改善探讨   总被引:1,自引:0,他引:1  
邹景臣 《中国水利》2011,(15):34-35
吉林省西部水环境恶化,干旱日趋严重,土地荒漠化、盐渍化进程加快,牧草退化,湿地萎缩,生物物种减少,使得农业生产的不稳定性加剧。通过对该地区水环境现状的研究,提出了相应的改善措施,即利用流经吉林省西部地区境内的嫩江、洮儿河和霍林河的天然过境水和洪水,以及三大灌区的回归水,充盈星罗棋布的泡塘,扩大水面面积和湿地面积,从根本上解决吉林省西部地区水环境恶化的问题。  相似文献   
90.
Abstract: Pedestrian detection techniques are important and challenging especially for complex real world scenes. They can be used for ensuring pedestrian safety, ADASs (advance driver assistance systems) and safety surveillance systems. In this paper, we propose a novel approach for multi-person tracking-by-detection using deformable part models in Kalman filtering framework. The Kalman filter is used to keep track of each person and a unique label is assigned to each tracked individual. Based on this approach, people can enter and leave the scene randomly. We test and demonstrate our results on Caltech Pedestrian benchmark, which is two orders of magnitude larger than any other existing datasets and consists of pedestrians varying widely in appearance, pose and scale. Complex situations such as people occluded by each other are handled gracefully and individual persons can be tracked correctly after a group of people split. Experiments confirm the real-time performance and robustness of our system, working in complex scenes. Our tracking model gives a tracking accuracy of 72.8% and a tracking precision of 82.3%. We can further reduce false positives by 2.8%, using Kalman filtering.  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