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   2248篇
  免费   255篇
  国内免费   515篇
电工技术   4篇
综合类   97篇
化学工业   42篇
金属工艺   1570篇
机械仪表   175篇
矿业工程   16篇
能源动力   24篇
石油天然气   6篇
武器工业   22篇
无线电   29篇
一般工业技术   731篇
冶金工业   282篇
原子能技术   14篇
自动化技术   6篇
  2024年   13篇
  2023年   86篇
  2022年   124篇
  2021年   147篇
  2020年   99篇
  2019年   113篇
  2018年   107篇
  2017年   121篇
  2016年   87篇
  2015年   100篇
  2014年   114篇
  2013年   162篇
  2012年   168篇
  2011年   174篇
  2010年   101篇
  2009年   118篇
  2008年   85篇
  2007年   113篇
  2006年   138篇
  2005年   93篇
  2004年   80篇
  2003年   86篇
  2002年   94篇
  2001年   71篇
  2000年   42篇
  1999年   53篇
  1998年   54篇
  1997年   38篇
  1996年   48篇
  1995年   27篇
  1994年   28篇
  1993年   40篇
  1992年   22篇
  1991年   12篇
  1990年   21篇
  1989年   19篇
  1988年   10篇
  1987年   3篇
  1986年   1篇
  1984年   2篇
  1982年   1篇
  1981年   3篇
排序方式: 共有3018条查询结果,搜索用时 15 毫秒
1.
基于弹塑性有限元理论,采用三维塑性体/塑性体摩擦副模型,考虑实际焊接过程中两侧工件散热条件的差异,建立了FGH96高温合金管惯性摩擦焊过程有限元模型,计算了焊接过程中瞬态温度场和轴向应力场的分布,研究了初始转速、顶锻力和转动惯量对接头温度场和飞边形貌的影响。模拟的飞边形貌与试验所得焊件误差仅为5%,验证模型的可靠性。模拟结果表明,惯性摩擦焊过程中,摩擦界面升温迅速,峰值温度可达1 335 ℃,塑性变形主要发生在距界面4 mm的区域内,该区域轴向温度梯度较大。摩擦界面附近压应力值从中心到边缘逐渐降低,界面边缘应力状态由压应力转变为拉应力,飞边根部由于挤压变形,存在压应力集中。提高初始转速和转动惯量均能增加焊接热输入,延长摩擦时间,提升峰值温度,增加飞边挤出量;加大顶锻力可提高机械能转化成热能的效率,缩短摩擦时间,增加轴向缩短量和飞边卷曲度。 创新点: 塑性体/塑性体有限元模型能够综合考虑接触面力的相互作用,采用更符合实际的三维双塑性体模型,对FGH96高温合金环形工件惯性摩擦焊过程进行了数值模拟。  相似文献   
2.
杨延华 《焊接》2022,(1):48-54
X60/625双金属复合管环缝焊接时,由于2种材料化学成分和物理性能差异太大,易引起镍基合金层氧化、稀释等问题,从而影响覆层耐腐蚀性和管道完整性。针对该问题,文中通过对X60/625双金属复合管焊接性的分析和焊接工艺的研究,制定出适用于X60/625双金属复合管环缝焊接工艺。经过焊缝无损检验、理化性能检验、耐腐蚀性能检验及稀释率检验,结果符合相关标准与规范。焊接工艺成功应用于沙特哈拉德项目管线及站场焊接施工一期管道项目中,焊接612道焊口的焊接一次合格率达99.7%。  相似文献   
3.
梁钪  郑松波  高颂  张涛  张艳 《冶金分析》2022,42(10):16-23
准确测定粉末高温合金中微量及痕量元素,对粉末高温合金的生产、应用具有重要意义。将样品在放电电流40~45 mA,放电电压1 100~1 200 V,氩气流速400~450 mL/min下进行辉光放电激发,选择合适的同位素和分辨率以消除质谱干扰,使用基体匹配的内控标准样品和标准物质校准各待测元素的相对灵敏度因子(RSF),实现了高流速高分辨辉光放电质谱法(GDMS)对粉末高温合金中硼、钠、镁等26种微量及痕量元素的测定。采用实验方法对粉末高温合金内控样品中26种微量及痕量元素进行测定,各待测元素的测定值与参考值基本一致,测定结果的RSD(n=6)在0.9%~15.4%之间。采用实验方法对粉末高温合金样品进行测定,测定结果分别与电感耦合等离子体原子发射光谱法(ICP-AES)测定硼、铁和锆,高频感应燃烧红外吸收法测定硫,原子荧光光谱法测定硒,高分辨电感耦合等离子体质谱法(HR-ICP-MS)测定其余元素(钠、镁、硅、磷、钙、钒、锰、铜、镓、砷、银、锡、锑、碲、镧、铈、铪、钽、铊、铅和铋)的结果保持一致,测定结果的RSD(n=6)在0.2%~26.6%之间。  相似文献   
4.
In this study, a kind of Ni-based superalloy specially designed for additive manufacturing (AM) was investigated. Thermo-Calc simulation and differential scanning calorimetry (DSC) analysis were used to determine phases and their transformation temperature. Experimental specimens were prepared by laser metal deposition (LMD) and traditional casting method. Microstructure, phase constitution and mechanical properties of the alloy were characterized by scanning electron microscopy (SEM), transmission scanning electron microscopy (TEM), X-ray diffraction (XRD) and tensile tests. The results show that this alloy contains two basic phases, γ/γ', in addition to these phases, at least two secondary phases may be present, such as MC carbides and Laves phases. Furthermore, the as-deposited alloy has finer dendrite, its mean primary dendrite arm space (PDAS) is about 30-45 μm, and the average size of γ' particles is 100-150 nm. However, the dendrite size of the as-cast alloy is much larger and its PDAS is 300-500 μm with secondary and even third dendrite arms. Correspondingly, the alloy displays different tensile behavior with different processing methods, and the as-deposited specimen shows better ultimate tensile stress (1,085.7±51.7 MPa), yield stress (697±19.5 MPa) and elongation (25.8%±2.2%) than that of the as-cast specimen. The differences in mechanical properties of the alloy are due to the different morphology and size of dendrites, γ', and Laves phase, and the segregation of elements, etc. Such important information would be helpful for alloy application as well as new alloy development.  相似文献   
5.
The uniform refinement mechanisms and methods of deformed mixed and coarse grains inside a solution-treatment Ni-based superalloy during two-stage annealing treatment have been investigated.The two-stage heat treatment experiments include an aging annealing treatment(AT)and a subsequent recrystallization annealing treatment(RT).The object of AT is to precipitate some δ phases and consume part of storage energy to inhibit the grain growth during RT,while the RT is to refine mixed and coarse grains by recrystallization.It can be found that the recrystallization grains will quickly grow up to a large size when the AT time is too low or the RT temperature is too high,while the deformed coarse grains cannot be eliminated when the AT time is too long or the RT temperature is too low.In addition,the mixed microstructure composed of some abnormal coarse recrystallization grains(ACRGs)and a large number of fine grains can be observed in the annealed specimen when the AT time is 3 h and RT tem-perature is 980℃.The phenomenon attributes to the uneven distribution of δ phase resulted from the heterogeneous deformation energy when the AT time is too short.In the regions with a large number of δ phases,the recrystallization nucleation rate is promoted and the growth of grains is limited,which results in fine grains.However,in the regions with few δ phases,the recrystallization grains around grain boundaries can easily grow up,and the new recrystallization nucleus is difficult to form inside grain,which leads to ACRGs.Thus,in order to obtain uniform and fine annealed microstructure,it is a prereq-uisite to precipitate even-distributed δ phase by choosing a suitable AT time,such as 12 h.Moreover,a relative high RT temperature is also needed to promote the recrystallization nucleation around δ phase.The optimal annealing parameters range for uniformly refining mixed crystal can be summarized as:900℃×12 h+990℃×(40-60 min)and 900℃×12 h+1000℃×(10-15 min).  相似文献   
6.
研究了镍基高温合金GH202在800~1100 ℃高温氧化后晶粒、碳化物和强化相的演变过程。采用透射电子显微镜、扫描电子显微镜和电子背散射衍射对其微观结构进行了表征。结果表明:镍基高温合金的硬度随氧化温度的升高而降低,1100 ℃氧化100 h后,硬度降低了43.5%。800和900 ℃氧化后晶粒生长速度较慢,而经900 ℃氧化后晶界碳化物析出显著增加。在1000和1100 ℃氧化后,晶粒尺寸明显增大。氧化过程中晶界迁移是由晶界两侧自由能差决定,温度越高,晶界向曲率中心迁移越快,大量细小晶粒被吞并形成了大晶粒。大块状碳化物(MC)分解成大量的碳原子,与Cr原子结合形成少量的富Cr颗粒状M23C6。在900 ℃氧化150 h后,M23C6演化为富Ti的M6C。随着氧化温度的升高,碳化物在γ相中回熔。在800、900和1000 ℃氧化后,γ′相逐渐长大,在1100 ℃氧化100 h后,完全溶解于γ相。  相似文献   
7.
通过不同扫描速度和扫描方式的选区激光熔化(SLM)技术制备了Inconel 718合金,研究了工艺参数对熔池的形态、凝固组织、晶粒大小和晶粒取向的影响。结果表明,随着扫描速度增加,熔池的深度与宽度的比值增大,曲率增大;而扫描速度为1 450mm/s时,采用单向扫描比十字交叉扫描时深宽比值更大。在熔池内,凝固组织由熔池底部的胞晶向熔池侧面的胞枝晶转变。晶粒以<001>方向择优生长,其晶粒间的取向差角以小角度(<15°)为主。当十字交叉扫描时,随着扫描速度增加,小角度取向差角的分布分数增加。当速度一定、采用十字交叉扫描时,小角度的取向差角占比为62.57%,而采用单向扫描时为47.69%。  相似文献   
8.
《Ceramics International》2022,48(6):8025-8030
In order to meet the high demand for joining ceramic/superalloy composite structure in extreme environments, a novel high-temperature resistant adhesion technique was developed for joining ZrO2 and Inconel 625 by applying an aluminum phosphate emulsion/zirconium sol based adhesive. With increasing temperature, a series of reactions occurred in adhesive, and its high-temperature bonding was attributed to the formation of a composite structure containing various ceramics and intermetallics. The adhesive after RT curing could find direct applications in extreme environments, and provide bonding strength no less than 2.5 MPa in the temperature range of RT-1100 °C. The bonding strength was higher than 4 MPa in the temperature range of 800–1000 °C, which was further attributed to the formation of an effective CTE-gradient relationship among ZrO2, adhesive and Inconel 625, as well as the interfacial reactions between the two substrates. The work broadened the application of adhesion technique and brought new ideas for joining dissimilar engineering materials.  相似文献   
9.
The combined effect of resistance spot welding and precipitation hardening on the localised corrosion of A286 superalloy is studied. The specimens tested by double loop electrochemical potentiokinetic reactivation were welded in the solution treated condition, and then subjected to different precipitation hardening treatments. For both base metal and weld nugget, the maximum localised corrosion is reached when η phase is clearly observable. The fact that the localised corrosion resistance of weld nugget is different from that shown by base metal may be explained by the segregation of Ni and Ti towards the interdendritic region of weld nugget (studied by using scanning electron microscope/energy dispersive X-ray analysis).  相似文献   
10.
不同气氛对激光熔覆IN718涂层形貌、组织与性能的影响   总被引:2,自引:2,他引:0  
目的研究不同气氛条件下激光熔覆IN718高温合金涂层的微观偏析。方法利用激光熔覆技术,在不同送粉气和不同保护气条件下制备了IN718高温合金涂层,并对制备的涂层进行双时效热处理。采用光学显微镜观察显微组织结构和特征,采用扫描电镜和能谱仪对涂层组织和相成分进行分析,采用维氏硬度计对涂层热处理前后的硬度进行测定。结果送粉气种类对熔覆层的形貌和组织有一定影响,而保护气种类对熔覆层的形貌和组织影响不明显。与氩气作为送粉气制备的涂层相比,氦气作为送粉气制备的涂层组织更加细密,Laves相的尺寸更小且分布更均匀,Laves相的体积分数由氩气送粉的9.35%减少到氦气送粉的5.25%,并且Laves相中Nb的质量分数由20%下降到16%,涂层硬度由287HV0.2提高到306HV0.2。双时效热处理后,涂层的显微硬度明显提高,氦气作为送粉气制备的涂层硬度为468HV0.2,高于氩气作为送粉气制备的涂层硬度447HV0.2。结论氦气作为送粉气能有效降低激光熔覆IN718涂层的Nb元素偏析,同时细化涂层组织,提高涂层显微硬度。氦气作为保护气对涂层形貌和组织的影响不明显。  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