全文获取类型
收费全文 | 21740篇 |
免费 | 2135篇 |
国内免费 | 1048篇 |
专业分类
电工技术 | 1155篇 |
综合类 | 1237篇 |
化学工业 | 6929篇 |
金属工艺 | 1618篇 |
机械仪表 | 822篇 |
建筑科学 | 624篇 |
矿业工程 | 511篇 |
能源动力 | 2299篇 |
轻工业 | 2118篇 |
水利工程 | 128篇 |
石油天然气 | 924篇 |
武器工业 | 572篇 |
无线电 | 1208篇 |
一般工业技术 | 2728篇 |
冶金工业 | 1156篇 |
原子能技术 | 226篇 |
自动化技术 | 668篇 |
出版年
2024年 | 40篇 |
2023年 | 478篇 |
2022年 | 553篇 |
2021年 | 789篇 |
2020年 | 769篇 |
2019年 | 736篇 |
2018年 | 665篇 |
2017年 | 819篇 |
2016年 | 777篇 |
2015年 | 701篇 |
2014年 | 1118篇 |
2013年 | 1163篇 |
2012年 | 1343篇 |
2011年 | 1577篇 |
2010年 | 1255篇 |
2009年 | 1180篇 |
2008年 | 1084篇 |
2007年 | 1402篇 |
2006年 | 1310篇 |
2005年 | 1122篇 |
2004年 | 1069篇 |
2003年 | 876篇 |
2002年 | 809篇 |
2001年 | 629篇 |
2000年 | 546篇 |
1999年 | 413篇 |
1998年 | 298篇 |
1997年 | 269篇 |
1996年 | 199篇 |
1995年 | 185篇 |
1994年 | 168篇 |
1993年 | 101篇 |
1992年 | 114篇 |
1991年 | 82篇 |
1990年 | 60篇 |
1989年 | 45篇 |
1988年 | 49篇 |
1987年 | 23篇 |
1986年 | 15篇 |
1985年 | 21篇 |
1984年 | 20篇 |
1983年 | 9篇 |
1982年 | 14篇 |
1981年 | 4篇 |
1980年 | 7篇 |
1979年 | 7篇 |
1977年 | 2篇 |
1976年 | 2篇 |
1973年 | 1篇 |
1951年 | 3篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
61.
The in-situ fabrication of an electron-blocking layer between the Ba-containing anode and the ceria-based electrolyte is an effective approach in suppressing the internal electronic leakage in ceria-based solid oxide fuel cell (SOFC). To improve the thickness of the electron-blocking layer and to research the effect of the layer thickness on the improvement of SOFC, a Ba-containing compound (0.6NiO-0.4BaZr0.1Ce0.7Y0.2O3-δ) modified by Y stabilized zirconia (YSZ) was employed as a composite anode in this research. SEM analyses demonstrated that the thickness of the interlayer can be simply controlled by regulating the proportion of YSZ at anode. The in-situ formed interlayer in the cell with the anode modified by 20?mol% YSZ possesses a thickness of 0.9?µm which is more suitable for the cell achieving an enhanced performance. 相似文献
62.
Paola Cristina Cajas Daza Rodrigo Arbey Muñoz Meneses Ana Candida Martins Rodrigues Cosme Roberto Moreira da Silva 《Ceramics International》2018,44(12):13699-13705
Doped CeGdO and codoped CeGdOSmO compositions were synthesized, giving rise to nanoparticulate powders. Ionic conductivities at bulk and grain boundaries of the sintered samples were determined, exhibiting increased conductivity in the samaria-codoped samples. Scanning electron microscopy (SEM) showed a significant reduction in the grain size of samaria-codoped electrolytes. This reduced grain size of the codoped samples caused a reduction in Schottky barrier height, increasing oxygen vacancy concentration in the space-charge layer of the grain boundary and culminating in greater ionic conductivity in the boundary region. For the gadolinium doped samples, high resolution transmission electron microscopy images at grains showed the presence of large cluster of defects (nanodomains), hindering the movement of charge carriers and reducing ionic conductivity. However, the samaria-codoped system displayed better homogeneity at atomic level, resulting in reduced oxygen vacancy ordering and, consequently, smaller nanodomains and higher bulk (grain) conductivity. The reduced grain sizes and smaller nanodomains caused by codoping favor the ionic conductivity of ceria-based ceramics, doped with gadolinia and codoped with samaria. 相似文献
63.
The impact of total solid (TS) content in combination with the feed rate and air inlet temperature on the survival of Lactobacillus paracasei ssp. paracasei F19 after spray drying in a skim milk matrix has been investigated and correlated with the capsule size. Depending on the experimental conditions, the survival rates ranged from 64 to 0.2%. The higher the air inlet temperature, the lower was the survival rate and an inversely correlation between the TS content and particle size has been determined. These results clearly indicate that process stress analyses and product-related characteristics must not be regarded separately. 相似文献
64.
Lin Ge Yiheng Gu Yanli Zhang Xueyan Li Qing Ni Lucun Guo 《Journal of the European Ceramic Society》2018,38(6):2553-2561
In this work, five different metal-oxide additives (metal?=?Ba, Co, Fe, Li, and Mn) were examined as sintering aids and SiO2 impurity scavengers for Ce0.8Sm0.2O1.9 (SDC). 2?mol% additives were loaded into the SDC with ~150?ppm (moderately impure) and ~2000?ppm (highly impure) SiO2. Ba-, Co-, Fe- and Mn-oxides showed comparative sintering-aid effect on both moderately- and highly-impure SDC specimens, but the sintering-assisting effect of Li-oxide was completely neutralized in highly impure SDC. Regarding electrical property, the deleterious effect of 2000?ppm SiO2 impurity on the grain-boundary conduction of SDC can be effectively alleviated by adding Ba-, Co-, Fe-, or Mn-oxides. Microstructure analysis revealed that Ba-oxide reacted directly with SiO2 and consequently enhanced grain-boundary conduction. By contrast, with the addition of Co-, Fe-, and Mn-oxides, the improved grain-boundary conductions of impure SDC were related to the scavenging reactions between Si, Ca (another original impurity) and Sm components. 相似文献
65.
GCr15钢微织构表面固体润滑性能研究 总被引:2,自引:0,他引:2
为研究不同表面处理方式对PTFE/GCr15钢配副表面摩擦学性能的影响,采用Nd:YAG纳秒激光器对GCr15轴承钢下试样表面进行激光织构加工,并以纳米MoS_2固体润滑剂作为润滑介质,以黏结有PTFE自润滑衬垫的圆柱销作为上试样进行对摩试验。研究发现:PTFE自润滑衬垫与微织构GCr15摩擦副在干摩擦条件下摩擦因数较低,仅为0.137,而在纳米MoS_2固体润滑剂润滑条件下,其摩擦因数进一步下降为0.123,且波动较小。通过EDS分析表明,表面微织构、聚四氟乙烯衬垫与纳米MoS_2润滑介质三者具有协同润滑减摩效应,可摩擦副表面生成一层由PTFE与纳米MoS_2材料组成的致密、平滑复合润滑膜,有效改善对摩副之间的润滑特性。研究表明,通过表面激光织构技术与固体自润滑技术(添加纳米MoS_2)的有效集成融合,可进一步改善PTFE/GCr15钢配副的润滑性能。 相似文献
66.
67.
《International Journal of Hydrogen Energy》2020,45(15):8994-9003
Methanol crossover is still a significant barrier to the commercialization of direct methanol fuel cells with wide-used Nafion® membrane. Herein, molecular sieve is introduced into the design of polymer electrolyte membrane to alleviate methanol crossover. The UZM-9 zeolite with an intermediate window size of 0.42 nm can effectively separate hydrated methanol (ca. 1.10 nm) and hydrated proton (ca. 0.23 nm). The methanol diffusion rate through the membrane is effectively suppressed after modified with UZM-9, which is about four times lower than the origin Nafion® membrane. The resulted peak power density reached 80 mW cm−2 with 2 mol L−1 methanol solution feed, which is 2.5-fold higher than that of direct methanol fuel cell with commercial Nafion® membrane. These results open a promising route to alleviate methanol crossover in direct methanol fuel cells. 相似文献
68.
69.
国民经济的很多工业生产领域中产生了大量的含钒固体废弃物,对其回收利用意义重大。介绍了从废钒催化剂、锅炉灰、含钒沥青、拜尔淤泥和低钒钢渣等含钒固体废弃物中提钒方法的研究进展及其发展趋势,重点介绍了从固体废弃物中提钒的原理和各种方法的最新进展。并就涉及固体废弃物提钒各工艺的可操作性、成本、经济效益和环境污染问题分别进行了阐述。 相似文献
70.
文章研发了一款适用于机器人教育教学的多功能、多用途、普适性的19自由度的小型仿人机器人,主要完成了该机器人的机械结构设计与控制系统构建工作[1]。所设计的机器人机械结构可靠性高、工艺性好、结构紧凑、样式新颖;所构建的机器人控制系统鲁棒性高、稳定性好、控制准确、反应迅速,圆满地实现了预期的设计任务。通过对优缺点的综合对比,得出组合式构型方案在功能性、实用性和稳定性等方面具有明显优势,有望通过后续软件系统的开发提高其运动效能,真正在青少年机器人教育中发挥重要作用[2]。 相似文献