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   210053篇
  免费   12694篇
  国内免费   7202篇
电工技术   9481篇
技术理论   14篇
综合类   11051篇
化学工业   30764篇
金属工艺   12117篇
机械仪表   11670篇
建筑科学   12726篇
矿业工程   4463篇
能源动力   4883篇
轻工业   12321篇
水利工程   4136篇
石油天然气   7577篇
武器工业   1353篇
无线电   24420篇
一般工业技术   30194篇
冶金工业   8400篇
原子能技术   1887篇
自动化技术   42492篇
  2024年   554篇
  2023年   2058篇
  2022年   3810篇
  2021年   5200篇
  2020年   4017篇
  2019年   3294篇
  2018年   17706篇
  2017年   17227篇
  2016年   13526篇
  2015年   6036篇
  2014年   6946篇
  2013年   8122篇
  2012年   12087篇
  2011年   18864篇
  2010年   16657篇
  2009年   13446篇
  2008年   14813篇
  2007年   15593篇
  2006年   7662篇
  2005年   7469篇
  2004年   5451篇
  2003年   4594篇
  2002年   3779篇
  2001年   2974篇
  2000年   2857篇
  1999年   2752篇
  1998年   2249篇
  1997年   1809篇
  1996年   1726篇
  1995年   1323篇
  1994年   1218篇
  1993年   835篇
  1992年   653篇
  1991年   519篇
  1990年   374篇
  1989年   294篇
  1988年   272篇
  1987年   167篇
  1986年   117篇
  1985年   87篇
  1984年   41篇
  1983年   39篇
  1982年   44篇
  1968年   43篇
  1966年   42篇
  1965年   44篇
  1959年   44篇
  1958年   37篇
  1955年   63篇
  1954年   68篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
利用正交设计实验的方法安排了一组Zr-Nb二元合金,考查了两个水平的Nb含量,淬火温度,时效温度,时间以及合金组织状态对耐蚀性能的影响,500℃蒸汽腐蚀结果表明,Nb含量控制在固溶极限范围内Zr-Nb二元含金具有较佳的耐蚀性,而当Nb含量较高时,采用双相区淬火,较高温度长时间时效处理是获得较好耐蚀性的工艺方向。  相似文献   
992.
含稀土硅化铁热电材料的电学性能初探   总被引:1,自引:0,他引:1  
采用悬浮真空熔炼和800℃,168h真空退火方法制备了含稀土Sm的FeSi2基金属硅化物,并对其晶体结构、See-beck系数、电阻率进行了初步研究。实验发现,名义组成为Fe0.6Sm0.4Si2的试样的热电功率因子从室温时的0.26×10-4W·m-1K-2随温度上升到500℃时的1.6×10-4W·m-1K-2,比不含Sm或含Sm量很少的对比试样高一个数量级左右。其原因被认为是由于Sm的外层4f电子的贡献。  相似文献   
993.
针对钛制容器产品试板弯曲角度按现行标准执行中出现的问题,从力学角度进行探讨,导了了试板压弯对所采用的压头直径与试板厚度和延伸率的关系,即D〉(1/δ-1)t,并提出了设定试板弯曲压头直径的新思路。  相似文献   
994.
利用喷射成形技术制备了7A60合金。借助扫描电镜(SEM),透射电镜(TEM),X射线衍射(XRD)等手段研究了喷射成形与铸造7A60合金微观组织的特点。结果表明,铸造7A60合金的组织粗大,偏析严重。喷射成形7A60合金主要由细化的等轴晶组成,无明显偏析。与传统铸锭冶金工艺相比,喷射成形工艺大大提高了冷却速率,显著细化了7A60合金的微观组织。  相似文献   
995.
何经  朱诚 《上海金属》1997,19(3):51-56
阐述了我国不锈钢品种、质量、产量和工业装备等方面的基本情况,并分析了与先进工业国家间的差距,对加快我国不锈钢发展提出了建议。  相似文献   
996.
Fabrication of cost-effective, nano-grained net-shaped components has brought considerable interest to Department of Defense, National Aeronautics and Space Administration, and Department of Energy. The objective of this paper is to demonstrate the versatility of electron beam-physical vapor deposition (EB-PVD) technology in engineering new nanostructured materials with controlled microstructure and microchemistry in the form of coatings and net-shaped components for many applications including the space, turbine, optical, biomedical, and auto industries. Coatings are often applied on components to extent their performance and life under severe environmental conditions including thermal, corrosion, wear, and oxidation. Performance and properties of the coatings depend upon their composition, microstructure, and deposition condition. Simultaneous co-evaporation of multiple ingots of different compositions in the high energy EB-PVD chamber has brought considerable interest in the architecture of functional graded coatings, nano-laminated coatings, and design of new structural materials that could not be produced economically by conventional methods. In addition, high evaporation and condensate rates allowed fabricating precision net-shaped components with nanograined microstructure for various applications. Using EB-PVD, nano-grained rhenium (Re) coatings and net-shaped components with tailored microstructure and properties were fabricated in the form of tubes, plates, and Re-coated spherical graphite cores. This paper will also present the results of various metallic and ceramic coatings including chromium, titanium carbide (TiC), titanium diboride (TiB2), hafnium nitride (HfN), titanium-boron-carbonitride (TiBCN), and partially yttria stabilized zirconia (YSZ) TBC coatings deposited by EB-PVD for various applications. This paper was presented at the International Symposium on Manufacturing, Properties, and Applications of Nanocrystalline Materials sponsored by the ASM International Nanotechnology Task Force and TMS Powder Materials Committee, October 18–20, 2004, Columbus, OH.  相似文献   
997.
The conversion coating can be obtained by using a solution containing titanium tetrachloride, fluorosilicate acid and nitric acid. The results of X-ray photoelectron spectroscopy (XPS) showed that the titanium conversion coating consisted of ZnO, TiO2 and Zn4Si2O7(OH)2. The formation process of the titanium conversion coating was studied. Effects of the immersion time, pH value and solution temperature on the corrosion resistance and the chemical composition of the titanium conversion coating were investigated by the salt spray test (SST) and XPS, respectively. The results of XPS and SST showed that the titanium conversion coating displayed better corrosion resistance with higher contents of Si and Ti. Results of corrosion tests (the salt spray and electrochemical test) indicate that the corrosion resistance of the conversion coating by titanium solution is better than that of the conversion coating using the traditional chromate solution.  相似文献   
998.
采用DTG ,DDTA等热分析手段 ,研究了高温固化、炭化过程中 ,铝电解用TiB2 阴极涂层糊料的质量和能量的变化速率 ,制定了涂层的变速固化、炭化升温制度 ;在此基础上 ,研究了升温制度对TiB2 阴极涂层性能的影响。结果表明 :变速升温制度优于匀速升温制度 ,采用变速固化、炭化升温制度所制备的涂层形变小、无裂纹 ,其抗拉强度达 3.13MPa,电阻率为 2 3.2 μΩ·m ;而采用升温速度为 10 .3℃ /h的匀速固化、炭化升温制度制备的涂层形变大、裂纹多 ,抗拉强度小 (2 .6 9MPa) ,电阻率大 (2 8.6 μΩ·m)。  相似文献   
999.
During the last ten years, techniques have been developed to measure the distribution of grain boundaries in polycrystals as a function of both lattice misorientation and grain boundary plane orientation. This paper presents a brief overview of the techniques used for these measurements and the principle findings of studies implementing these techniques. The most significant findings are that grain boundary plane distributions are anisotropic, that they are scale invariant during normal grain growth, that the most common grain boundary planes are those with low surface energies, that the grain boundary populations are inversely correlated with the grain boundary energy, and that the coincident site lattice number is a poor predictor of the grain boundary energy and population.  相似文献   
1000.
This paper introduces a new titanium alloys surface strengthening treatment by using the arc-added glow discharge plasmas non-hydrogen carburization technique. High purity and high strength graphite is selected as cooling cathode arc source for supplying carbon atoms and particle, which migrate to the titanium alloy(Ti6Al4V) surface and form modified layer. Thus, the hydrogen embrittlement is avoided while the tfibological behavior of the titanium alloy surface is improved in the respects of anti-friction and anti-wear ability.The tribological behavior of the modified layer under dry sliding against SAE52100 steel was evaluated on a ball-on-disc test rig. The results showed that the modified layer obtained a thickness of 30μm at 980℃, 30minutes. The microhardness of the Ti6Al4V alloy surface attained 936 HV, which was much larger than that of the Ti6AI4V alloy. The Ti6AI4V alloy was characterized by adhesion wear and scuffing under dry sliding against the steel, while the surface modified layer experienced much abated adhesion wear and scuffing under the same testing condition. This could be attributed to the carbon dement with different modalities exists in the modified layer.The modified layer showed good friction-reducing and fair anti-wear ability in dry sliding against the steel. Using the SEM,XRD and XPS, the phase structure and morphology of the carburization modified layer was analyzed.  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