全文获取类型
收费全文 | 44764篇 |
免费 | 5604篇 |
国内免费 | 3942篇 |
专业分类
电工技术 | 4047篇 |
综合类 | 4497篇 |
化学工业 | 6065篇 |
金属工艺 | 2913篇 |
机械仪表 | 3281篇 |
建筑科学 | 3619篇 |
矿业工程 | 1444篇 |
能源动力 | 1391篇 |
轻工业 | 5131篇 |
水利工程 | 1544篇 |
石油天然气 | 1292篇 |
武器工业 | 661篇 |
无线电 | 5132篇 |
一般工业技术 | 4313篇 |
冶金工业 | 1427篇 |
原子能技术 | 804篇 |
自动化技术 | 6749篇 |
出版年
2024年 | 259篇 |
2023年 | 728篇 |
2022年 | 1807篇 |
2021年 | 2393篇 |
2020年 | 1605篇 |
2019年 | 1090篇 |
2018年 | 1187篇 |
2017年 | 1345篇 |
2016年 | 1237篇 |
2015年 | 1980篇 |
2014年 | 2359篇 |
2013年 | 2888篇 |
2012年 | 3767篇 |
2011年 | 3834篇 |
2010年 | 3701篇 |
2009年 | 3451篇 |
2008年 | 3583篇 |
2007年 | 3595篇 |
2006年 | 3308篇 |
2005年 | 2658篇 |
2004年 | 1981篇 |
2003年 | 1309篇 |
2002年 | 1254篇 |
2001年 | 1118篇 |
2000年 | 860篇 |
1999年 | 353篇 |
1998年 | 108篇 |
1997年 | 83篇 |
1996年 | 56篇 |
1995年 | 53篇 |
1994年 | 33篇 |
1993年 | 55篇 |
1992年 | 48篇 |
1991年 | 40篇 |
1990年 | 26篇 |
1989年 | 28篇 |
1988年 | 12篇 |
1987年 | 16篇 |
1986年 | 12篇 |
1985年 | 6篇 |
1984年 | 9篇 |
1983年 | 18篇 |
1982年 | 5篇 |
1981年 | 8篇 |
1980年 | 13篇 |
1979年 | 6篇 |
1965年 | 5篇 |
1959年 | 9篇 |
1958年 | 1篇 |
1951年 | 10篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
Peiying Wang Juanli Zhao Yun Fan Wei Zhang Yuanyuan Cui Liangmiao Zhang Bin Liu Hongqiang Nian Yiran Li 《Ceramics International》2021,47(11):15023-15029
In this work, the composition-dependent point defect types and formation energies of RE2Hf2O7 (RE = La, Ce, Pr, Nd, Pm, Sm, Eu and Gd) as well as the oxygen diffusion behavior are systematically investigated by first-principles calculations. The possible defect reactions and dominant defect complexes under stoichiometric and non-stoichiometric conditions are revealed. It is found that O Frenkel pairs are the predominant defect in stoichiometric pyrochlore hafnates. Hf-RE cation anti-site defects, accompanied by RE vacancies and/or oxygen interstitials, are stable in the non-stoichiometric case of HfO2 excess. On the other hand, RE-Hf anti-site defects together with oxygen vacancies and/or RE interstitials are preferable in the case of RE2O3 excess. The energy barriers for the migration along the VO48f - VO48f pathway of pyrochlore hafnates were calculated to be between 0.81 eV and 0.89 eV. Based on these results, a defect engineering strategy is proposed and the pyrochlore hafnates investigated here are predicted to exhibit potential oxygen ionic conductivity. 相似文献
2.
3.
一次性医用手套是能够防止人们交叉感染的常用防护用品。随着新冠肺炎疫情在全球范围的迅速蔓延,疫情防控一线以及广大普通民众对一次性医用手套的需求与日俱增,其标准也受到广泛关注。本文对中国国家标准涉及一次性使用医用手套的4项产品标准进行了解读,并分析它们与国外同种产品标准间的对应关系以及重点指标的差异。 相似文献
4.
Yuanyuan Zhang Haiyan Lu Bing Wang Zhuo Zhang Xiaorong Lin Zhongzheng Chen Bin Li 《International Journal of Food Science & Technology》2015,50(6):1397-1404
Removal of imidacloprid and acetamiprid in tea infusions by microfiltration membrane using dead‐end model was investigated in the present study. The results showed that microfiltration significantly promoted the removal of both pesticides (P < 0.05) in tea infusions. Furthermore, the extent of removal was strongly influenced by the pore size of membrane, operational pressure and the concentrations of tea infusions. The initial concentration of imidacloprid and acetamiprid showed no significant effect on their removal rates. The maximum removal rates were 79.7% for imidacloprid and 81.9% acetamiprid. The changes in major chemical components of tea infusions after microfiltration were evaluated. The results indicated that microfiltration caused no considerable changes in total polyphenols and total free amino acids, and small but statistically significant losses (6.3–18.0%) of eight catechins and three methylxanthines when filtration volume reached to 200 mL. The present study validated the application of microfiltration as a potentially feasible and promising method for the removal of imidacloprid and acetamiprid residues from tea infusions. 相似文献
5.
6.
提出一种基于随机光栅与高反射布拉格光栅(FBG)相结合的可调谐随机光纤激光器。利用980nm泵浦光源泵浦一段7m长的掺铒光纤(EDF)进行增益放大,由随机光栅提供随机反馈。随机光栅长7cm,具有约10000个折射率修改点,这些点由飞秒激光逐点写入,并沿光纤方向随机分布,两点相邻间隔小于10μm。同时,利用中心波长为1548nm的高反射FBG来组成半开放腔结构,实现了随机激光的输出。实验测得的泵浦阈值功率仅为18mW,斜率效率高达13.2%,并通过改变FBG的中心波长,实现了输出激光波长的可调谐,调谐范围为4.45nm(1548.04~1552.49nm)。得益于半开放式激光腔的设计和EDF的高增益,整个系统具有阈值低、效率高、结构简单等优点。 相似文献
7.
8.
申浩 《苏州科技学院学报(工程技术版)》2015,(2):61-65
解释了跨界借鉴的含义,并阐述了其在建筑立面创新设计中运用的可能性和积极意义。通过案例分析,提出建筑立面跨界借鉴的内容和方式。 相似文献
9.
Chaoxin Li Yi Zhou Yuming Tian Yuanyuan Zhao Kaiyue Wang Guomin Li Yuesheng Chai 《Ceramics International》2019,45(5):5613-5616
Ceramics with mullite whiskers were prepared from coal fly ash and Al2O3 raw materials, with AlF3 used as an additive. The phase structures and microstructures of the ceramics were identified via X-ray diffraction and scanning electron microscopy, respectively. The results show that pickling of coal fly ash is an effective method for enhancing the flexural strength of ceramics. Sintering temperature and AlF3 addition were also key factors influencing the creation of ideal ceramics. The ceramic made from pickled coal fly ash, 6?wt% AlF3, and sintered at 1200?°C, exhibited the highest flexural strength of 59.1?MPa, and had a bulk density of 1.32?g/cm3 and porosity of 26.8%. The results show that ceramic materials made under these conditions are ideal candidates for manufacturing ceramic proppants for the exploitation of unconventional oil and gas resources. 相似文献
10.