全文获取类型
收费全文 | 42150篇 |
免费 | 4249篇 |
国内免费 | 2161篇 |
学科分类
工业技术 | 48560篇 |
出版年
2024年 | 228篇 |
2023年 | 820篇 |
2022年 | 1464篇 |
2021年 | 2079篇 |
2020年 | 1516篇 |
2019年 | 1294篇 |
2018年 | 1385篇 |
2017年 | 1399篇 |
2016年 | 1316篇 |
2015年 | 1818篇 |
2014年 | 2210篇 |
2013年 | 2468篇 |
2012年 | 2757篇 |
2011年 | 2684篇 |
2010年 | 2462篇 |
2009年 | 2306篇 |
2008年 | 2306篇 |
2007年 | 2133篇 |
2006年 | 2078篇 |
2005年 | 1787篇 |
2004年 | 1402篇 |
2003年 | 1424篇 |
2002年 | 1682篇 |
2001年 | 1395篇 |
2000年 | 1093篇 |
1999年 | 997篇 |
1998年 | 687篇 |
1997年 | 625篇 |
1996年 | 574篇 |
1995年 | 462篇 |
1994年 | 376篇 |
1993年 | 313篇 |
1992年 | 217篇 |
1991年 | 164篇 |
1990年 | 158篇 |
1989年 | 118篇 |
1988年 | 79篇 |
1987年 | 48篇 |
1986年 | 51篇 |
1985年 | 20篇 |
1984年 | 22篇 |
1983年 | 19篇 |
1982年 | 22篇 |
1981年 | 12篇 |
1980年 | 31篇 |
1979年 | 6篇 |
1978年 | 5篇 |
1977年 | 13篇 |
1971年 | 4篇 |
1951年 | 9篇 |
排序方式: 共有10000条查询结果,搜索用时 156 毫秒
31.
Multimedia Tools and Applications - Understanding human emotions through facial expressions is key enabling technology for interactive robots. Most approaches of facial expression recognition are... 相似文献
32.
Xuezhi Wang Xue Sun Zhelun Ma Tianbiao Yu Wanshan Wang 《Ceramics International》2018,44(18):22301-22307
Vitrified bond CBN grinding wheels are being widely used due to their superior performance. Also, advantages of vitrified grinding wheels are high elastic modulus, stable chemical property, and low thermal expansion coefficient. Brittleness and low strength are key factors restricting the development of vitrified bond CBN grinding wheels. In this paper, the sintering in a high magnetic field was innovatively introduced into the manufacturing of vitrified bond CBN grinding wheels, and the effects of sintering in a high magnetic field on properties on vitrified bond and vitrified CBN composites were systematically investigated. Vitrified bond was characterized using three-point bending, scanning electron microscopy, X-ray diffraction. It was observed that microstructure of vitrified bond could be changed, grain orientation could be controlled and average grain size could be decreased in a high magnetic field, while vitrified bond strength could be simultaneously improved. High quality vitrified bond could be obtained by appropriately adjusting the strength and direction of high magnetic field. Results demonstrated that vitrified bond properties were improved when the magnetic field strength was 6?T. In order to highlight the high magnetic field effect on the vitrified CBN composites, the ordinary CBN abrasives and nickel plated CBN abrasives were used respectively. Microstructures, bending strengths of vitrified CBN composites were compared in different high magnetic fields. When the magnetic field strength was appropriate (less than 6?T), the binding characteristic of vitrified bond CBN composites with nickel plated CBN abrasives was greatly improved. The highest bending strength value of vitrified CBN composites was 79.5?MPa in 6?T high magnetic field. 相似文献
33.
摘要:为了研究退火温度对镀锌DP980+Z烘烤硬化值的影响,退火温度控制在760~820℃之间,系统分析退火温度对烘烤硬化值的影响。通过准静态拉伸试验机测量烘烤硬化值及抗拉强度,采用lepara试剂对组织中的马氏体进行着色,利用金相显微镜及图像处理软件测量马氏体的体积分数;采用扫描电镜观察DP980+Z的双相组织特点,并且将组织图片通过CAD转化成有限元图进行网格划分,建立代表性体积单元(RVE),通过有限元分析铁素体、马氏体强度对烘烤硬化值的影响。在同样的变形量情况下,DP980+Z的原始屈服强度越高,烘烤硬化值越高。 相似文献
34.
Qiang Wang Lei Shen Tong Xue Gao Cheng Cheng Zhi Huang Hong Jin Fan Yuan Ping Feng 《Advanced functional materials》2021,31(2):2002187
The {100} facet of single-crystalline TiO2(B) is an ideal platform for inserting Li ions, but it is hard to be obtained due to its high surface energy. Here, the single-crystalline TiO2(B) nanobelts from H2Ti3O7 with nearly 70% {100} facets exposed are synthesized, which significantly enhances Li-storage capacity. The first-principle calculations demonstrate an ab in-plane 2D diffusion through the exposed {100} facets. As a consequence, the nanobelts can significantly accommodate Li ions in LiTiO2 formula with specific capacity up to 335 mAh g−1, which is in good agreement with the electrochemical characterizations. Coating with conductive and protective poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate), the cut-off discharge voltage is as low as 0.5 V, leading to a capacity of 160.7 mAh g−1 after 1500 cycles with a retention rate of 66% at 1C. This work provides a practical strategy to increase the Li-ion capacity and cycle stability by tailoring the crystal orientation and nanostructures. 相似文献
35.
Oktaviana Laily Tong Van-Canh Hong Seong-Wook 《Journal of Mechanical Science and Technology》2019,33(2):837-845
Journal of Mechanical Science and Technology - Skidding is a phenomenon that frequently occurs in ball–raceway contact areas of bearings and often leads to their early failure. This paper... 相似文献
36.
37.
Minghuan Wang Xia Chen Wenjun Tong Jiajie Wang Xindi Wang 《The International Journal of Advanced Manufacturing Technology》2020,107(1):157-166
Microdimples as a typical surface texture has been widely used for improving the properties in tribology and heat transfer fields. Ultrasonically assisted 相似文献
38.
Yingchao Hu Wenqiang Liu Yuandong Yang Xianliang Tong Qianjun Chen Zijian Zhou 《Ceramics International》2018,44(14):16668-16677
Li4SiO4 sorbents for high-temperature CO2 removal have drawn extensive attention owing to their potential application in carbon capture and storage (CCS). The major challenge in the application lies in the poor CO2 capture performance under realistic conditions of low CO2 concentrations, owing to the dense structure and poor porosity. In this work, Li4SiO4 sorbents were prepared with porous micromorphologies and large contact areas using a variety of organometallic Li-precursors, achieving fast CO2 sorption kinetics, high capacity and excellent cyclic stability at a low CO2 concentration (15?vol%). It was found that a high conversion of ~?74% was maintained for pure Li4SiO4 even after 100 sorption/desorption cycles. Moreover, by doping with Na2CO3 to reduce the CO2 diffusion resistance, the conversion of the sorbent was further enhanced to 93.2%. The enhancement mechanism of alkali carbonate have been proven here to be ascribed to the formation of the eutectic melt of Li/Na carbonates, the existence and function of which has been confirmed in this study. 相似文献
39.
通过HPT250轧机在技术改造中遇到的一个问题,即滑移系数对冷轧元缝钢管在轧制过程中所起的作用。在实际生产中经过不断的技术研究和改进。使闲置多年的HPT250轧机为钢管公司的生产迭拉起到很大的作用。 相似文献
40.