全文获取类型
收费全文 | 21392篇 |
免费 | 2489篇 |
国内免费 | 1343篇 |
专业分类
电工技术 | 1677篇 |
技术理论 | 1篇 |
综合类 | 1641篇 |
化学工业 | 2665篇 |
金属工艺 | 1393篇 |
机械仪表 | 1393篇 |
建筑科学 | 1569篇 |
矿业工程 | 693篇 |
能源动力 | 585篇 |
轻工业 | 1697篇 |
水利工程 | 524篇 |
石油天然气 | 835篇 |
武器工业 | 274篇 |
无线电 | 2598篇 |
一般工业技术 | 2156篇 |
冶金工业 | 2068篇 |
原子能技术 | 305篇 |
自动化技术 | 3150篇 |
出版年
2024年 | 151篇 |
2023年 | 392篇 |
2022年 | 808篇 |
2021年 | 1245篇 |
2020年 | 878篇 |
2019年 | 637篇 |
2018年 | 745篇 |
2017年 | 809篇 |
2016年 | 720篇 |
2015年 | 1024篇 |
2014年 | 1388篇 |
2013年 | 1446篇 |
2012年 | 1652篇 |
2011年 | 1713篇 |
2010年 | 1442篇 |
2009年 | 1293篇 |
2008年 | 1396篇 |
2007年 | 1280篇 |
2006年 | 1129篇 |
2005年 | 882篇 |
2004年 | 608篇 |
2003年 | 412篇 |
2002年 | 390篇 |
2001年 | 345篇 |
2000年 | 249篇 |
1999年 | 208篇 |
1998年 | 501篇 |
1997年 | 316篇 |
1996年 | 225篇 |
1995年 | 149篇 |
1994年 | 146篇 |
1993年 | 161篇 |
1992年 | 51篇 |
1991年 | 41篇 |
1990年 | 26篇 |
1989年 | 26篇 |
1988年 | 25篇 |
1987年 | 42篇 |
1986年 | 17篇 |
1985年 | 22篇 |
1984年 | 6篇 |
1983年 | 8篇 |
1982年 | 8篇 |
1981年 | 14篇 |
1980年 | 29篇 |
1978年 | 5篇 |
1977年 | 32篇 |
1976年 | 99篇 |
1975年 | 6篇 |
1955年 | 4篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
Changbai Long Ning Ji Li Yang Wenjie Zhou Kun Zheng Wei Ren Laijun Liu 《Journal of the European Ceramic Society》2021,41(6):3369-3378
With co-substitution of (Li0.5Sm0.5) at A site and W at B site, the electrical properties of modified Ca0.92(Li0.5Sm0.5)0.08Bi2Nb2-xWxO9 [(CLS)BN-xW, x = 0, 0.015 and 0.03] piezoceramics with ultrahigh Curie temperature (TC) of > 930 °C were enhanced dramatically. The increased resistivity induced by the co-substitution ensure them to be polarized under an enough high field. Combined with the increase of spontaneous ferroelectric polarization (PS), the significant enhancements in the piezoelectric, dielectric and ferroelectric properties can be obtained in the composition x = 0.015. Furthermore, the piezoelectric activity (d33) and bulk resistivity (ρb) of (CLS)BN-0.015 W can be further enhanced at an appropriate sintering temperature. This optimum composition sintered at 1170 °C shows ultrahigh TC of ~948 °C, d33 of ~17.3 pC/N and ρb of ~6.9 MΩ cm at 600 °C, which are comparable to those of the reported high-temperature Aurivillius piezoceramics with TC > 850 °C. 相似文献
2.
3.
In this study, 30 subjects were exposed to different combinations of air temperature (Ta: 24, 27, and 30°C) and CO2 level (8000, 10 000, and 12 000 ppm) in a high-humidity (RH: 85%) underground climate chamber. Subjective assessments, physiological responses, and cognitive performance were investigated. The results showed that as compared with exposure to Ta = 24°C, exposure to 30°C at all CO2 levels caused subjects to feel uncomfortably warm and experience stronger odor intensity, while increased mental effort and greater intensity of acute health symptoms were reported. However, no significant effects of Ta on task performance or physiological responses were found. This indicated that subjects had to exert more effort to maintain their performance in an uncomfortably warm environment. Increasing CO2 from 8000 to 12 000 ppm at all Ta caused subjects to report higher rates of headache, fatigue, agitation, and feeling depressed, although the results were statistically significant only at 24 and 27°C. The text typing performance and systolic blood pressure (SBP) decreased significantly at this exposure, whereas diastolic blood pressure (DBP) and thermal discomfort increased significantly. These effects suggest higher arousal/stress. No significant interaction effect of Ta and CO2 concentration on human responses was identified. 相似文献
4.
Process object is the instance of process. Vertexes and edges are in the graph of process object. There are different types of the object itself and the associations between object. For the large-scale data, there are many changes reflected. Recently, how to find appropriate real-time data for process object becomes a hot research topic. Data sampling is a kind of finding c hanges o f p rocess o bjects. There i s r equirements f or s ampling to be adaptive to underlying distribution of data stream. In this paper, we have proposed a adaptive data sampling mechanism to find a ppropriate d ata t o m odeling. F irst o f all, we use concept drift to make the partition of the life cycle of process object. Then, entity community detection is proposed to find changes. Finally, we propose stream-based real-time optimization of data sampling. Contributions of this paper are concept drift, community detection, and stream-based real-time computing. Experiments show the effectiveness and feasibility of our proposed adaptive data sampling mechanism for process object. 相似文献
5.
6.
7.
Although Mg alloy possesses high specific strength, low density, and good biocompatibility, poor corrosion resistance hinders its further applications. In the present study, an innovative protective layer against corrosion was prepared on the AZ31 Mg alloy via alkali pretreatment followed by vanillic acid treatment. The alkali pretreatment supplied –OH for the AZ31 Mg alloy surface to react with vanillic acid. The vanillic acid treatment played a crucial role in enhancing the corrosion resistance due to the excellent ability to act as a barrier and retard aqueous solution penetration, which effectively isolated the underlying Mg alloy from the corrosive environment. The corrosion current density of alkali and vanillic acid-treated Mg alloy (AZ31V) almost showed two orders of magnitude lower values in comparison with that of the AZ31 Mg alloy, and the corrosion potential of AZ31V Mg alloy increased from −1.41 to −1.25 V. The immersion tests proved that there was no occurrence of severe corrosion. Hence, the alkali pretreatment and vanillic acid treatment may represent a promising method to improve the corrosion resistance of Mg alloy. 相似文献
8.
9.
针对辽河油区超稠油采油污水的特点,采用Fenton试剂催化氧化,对采油污水处理进行研究。实验研究及现场应用结果表明,此方法对污水的CODCr具有良好的去除效果。处理后污水经过简单生化,进一步降解污染物,能够实现稳定迭标排放,且具有能耗低、运行成本低和操作简单等特点。 相似文献
10.
气动贯通式潜孔锤反循环连续取心取样钻进新技术在河南钼矿中应用 总被引:4,自引:0,他引:4
三道庄钼矿勘探生产中钻遇的地层非常复杂,采用其他方法均无法实现钻进,经过分析比较,决定采用贯通式潜孔锤反循环连续取心(样)钻进新技术来解决该地层钻进难、成孔难、取样难等三大问题。文章从钻进技术特点、工作原理等方面对该技术进行详细分析,得出其具有钻进效率高、岩心(样)采取率高、成孔质量好等突出优点。并介绍了钻进主要设备机具的配套、施工工序、操作要点、遇到问题的解决方法等。在河南钼矿露天采石场应用该项技术,有效避免了塌孔和卡钻事故,工程进展顺利、质量好、岩心(样)采取率在98%以上,取得了良好的效果。针对在生产试验中遇到的某些问题,作者提出了一些改进建议。 相似文献