全文获取类型
收费全文 | 50815篇 |
免费 | 5155篇 |
国内免费 | 2604篇 |
专业分类
电工技术 | 1072篇 |
综合类 | 3368篇 |
化学工业 | 4713篇 |
金属工艺 | 5272篇 |
机械仪表 | 3956篇 |
建筑科学 | 1472篇 |
矿业工程 | 730篇 |
能源动力 | 1222篇 |
轻工业 | 1619篇 |
水利工程 | 243篇 |
石油天然气 | 869篇 |
武器工业 | 578篇 |
无线电 | 16695篇 |
一般工业技术 | 7809篇 |
冶金工业 | 1126篇 |
原子能技术 | 540篇 |
自动化技术 | 7290篇 |
出版年
2024年 | 210篇 |
2023年 | 833篇 |
2022年 | 1157篇 |
2021年 | 1246篇 |
2020年 | 1252篇 |
2019年 | 1290篇 |
2018年 | 1117篇 |
2017年 | 1558篇 |
2016年 | 1603篇 |
2015年 | 1642篇 |
2014年 | 2070篇 |
2013年 | 2198篇 |
2012年 | 2941篇 |
2011年 | 2907篇 |
2010年 | 1984篇 |
2009年 | 2287篇 |
2008年 | 2427篇 |
2007年 | 2648篇 |
2006年 | 2430篇 |
2005年 | 2112篇 |
2004年 | 2683篇 |
2003年 | 2133篇 |
2002年 | 2642篇 |
2001年 | 2298篇 |
2000年 | 2025篇 |
1999年 | 1725篇 |
1998年 | 1173篇 |
1997年 | 1212篇 |
1996年 | 2040篇 |
1995年 | 1275篇 |
1994年 | 1033篇 |
1993年 | 529篇 |
1992年 | 418篇 |
1991年 | 415篇 |
1990年 | 314篇 |
1989年 | 146篇 |
1988年 | 121篇 |
1987年 | 56篇 |
1986年 | 74篇 |
1985年 | 81篇 |
1984年 | 62篇 |
1983年 | 36篇 |
1982年 | 42篇 |
1981年 | 36篇 |
1980年 | 19篇 |
1979年 | 19篇 |
1978年 | 12篇 |
1977年 | 8篇 |
1976年 | 8篇 |
1975年 | 9篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
981.
C. -F. Li D. B. Johnson R. Kovacevic 《International Journal of Machine Tools and Manufacture》2003,43(9):325
Waterjet guided laser processing is an internationally patented technique based on guiding a laser inside a thin, high-speed waterjet. The process combines the advantages of laser processing with those of waterjet cutting and offers promise as a method for processing thin and heat sensitive materials with a high degree of precision. An improved understanding of the complex interaction between laser, waterjet, and workpiece is required to enable the process to achieve its potential. A model for waterjet guided laser grooving of silicon is presented that treats the energy input of the laser, the cooling effect of the waterjet, and the melting and removal of the silicon. The thermal process is represented in detail in the new method. The model is validated by comparisons of simulation and experimental results, and the simulation provides insight regarding the details of the interactions among laser, waterjet, and workpiece. 相似文献
982.
研究了等离子-激光(plasma spraying and laser remelting,PS&LR)复合制备NiCrAlY-Al2O3层的抗氧化性能.Al2O3的加入量为(质量分数,%)10~30,粒度分50~75μm和0.31μm两种.1000℃、1050℃下的等温氧化结果表明,PS&LR法制备的涂层氧化速率仅为等离子喷涂层的1/2,NiCrAlY-Al2O3层的氧化速率低于NiCrAlY层,且随Al2O3第二相含量的增加或粒径的减小,涂层氧化速率减小。通过氧化动力学曲线、氧化物的形貌和结构,分析了Al2O3第二相和激光重熔改善NiCrAlY等离子喷涂层抗氧化性的机理。 相似文献
983.
984.
Zhongmin Yang Shiqing Xu Lili Hu Zhonghong Jiang 《Journal of Alloys and Compounds》2004,370(1-2):94-98
Yb3+–Er3+ co-doped Na2O–GeO2–PbO glass suitable for developing optical fiber lasers and amplifiers has been fabricated. The energy transfer efficiency from Yb3+ to Er3+ was investigated in the glasses with different Yb3+–Er3+ concentration ratios and the maximum energy transfer efficiency was found to be 67% at the Yb3+–Er3+ concentration ratio of 5:1. Subsequently, the studies of upconversion emissions in the visible range were performed. An intense green together with a relatively weak red emission was observed under the excitation of 976 nm diode laser. The quadratic dependence of the green emission on excitation power indicates that a two-photon absorption process occurs under a 976 nm excitation. However, for the red emission the slope of log-log plot of integrated intensity versus pump power declines with increasing Yb3+ ions content, indicating it is not resulted from a biphotonic process. 相似文献
985.
986.
987.
激光焊接的裁焊板及其在汽车中的应用 总被引:5,自引:0,他引:5
介绍了激光焊接用于汽车裁焊板的新技术。使用裁焊板可以实现汽车部件尺寸和材质的优花配合。与滚压缝焊相比,激光焊接具有焊接质量高、适应性广、生产费用和维护费用低的优点,特别适合进行裁焊板的焊接加工。激光焊接裁焊板的技术问题主要有:采用激光切割坯板方案的可行性、接头的成形性、焊接质量的控制和大板拼接变形的控制。 相似文献
988.
M. Marchionni D. Goldschmidt M. Maldini 《Journal of Materials Engineering and Performance》1993,2(4):497-503
CMSX4 + Y, a highly strengthened rhenium-containing second-generation single-crystal nickel-base su-peralloy, has been studied
by creep, low-cycle, and thermomechanical fatigue in the temperature range 500 to 1100 °C. The alloy exhibits good high-temperature
mechanical properties that are superior or com-parable to other single-crystal superalloys. Thermomechanical fatigue resistance
is equivalent to low-cy-cle fatigue and is cycle-shape dependent. High-temperature mechanical properties have been studied
using life prediction relationships that are frequently used for creep and low-cycle fatigue data evalu-ation. Examination
of fracture surfaces revealed that fracture induced by creep damage is internal and starts from pore-initiated cracks; however,
fatigue damage starts on the external surface and propagates inward in stage II mode. 相似文献
989.
Li Peng Ji Shengqin Zeng Xiaoyan Hu Qianwu Xiong Weihao 《International Journal of Machine Tools and Manufacture》2007,47(6):996-1002
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
990.
建立了模拟直薄壁件逐点沉积过程中温度场的有限元模型,用等价导热系数和焓值法处理了固一液耦合热传导问题和固液混合区的焓.模拟结果真实地反映了沉积316L不锈钢直薄壁件的温度场特征.通过对模拟结果的分析得出,在高温阶段(700℃以上)熔池的平均冷却速率达到10^3℃/s数量级,在240℃以下的冷却速率仅为10℃/s数量级.基板的温度变化经历温度上升、温度平稳、温度下降3个阶段;在温度下降阶段,基板中的热传导对熔池冷却速率影响很小.有限元模拟结果与已有文献的实验测量数据吻合很好. 相似文献