全文获取类型
收费全文 | 40508篇 |
免费 | 3982篇 |
国内免费 | 2105篇 |
专业分类
电工技术 | 2689篇 |
技术理论 | 3篇 |
综合类 | 2985篇 |
化学工业 | 6032篇 |
金属工艺 | 2437篇 |
机械仪表 | 2715篇 |
建筑科学 | 3302篇 |
矿业工程 | 1285篇 |
能源动力 | 1153篇 |
轻工业 | 2871篇 |
水利工程 | 862篇 |
石油天然气 | 2090篇 |
武器工业 | 409篇 |
无线电 | 4891篇 |
一般工业技术 | 4674篇 |
冶金工业 | 1746篇 |
原子能技术 | 471篇 |
自动化技术 | 5980篇 |
出版年
2024年 | 169篇 |
2023年 | 672篇 |
2022年 | 1237篇 |
2021年 | 1910篇 |
2020年 | 1424篇 |
2019年 | 1049篇 |
2018年 | 1280篇 |
2017年 | 1383篇 |
2016年 | 1219篇 |
2015年 | 1750篇 |
2014年 | 2237篇 |
2013年 | 2584篇 |
2012年 | 2826篇 |
2011年 | 3026篇 |
2010年 | 2577篇 |
2009年 | 2375篇 |
2008年 | 2523篇 |
2007年 | 2251篇 |
2006年 | 2251篇 |
2005年 | 2000篇 |
2004年 | 1302篇 |
2003年 | 1095篇 |
2002年 | 1061篇 |
2001年 | 917篇 |
2000年 | 813篇 |
1999年 | 905篇 |
1998年 | 674篇 |
1997年 | 615篇 |
1996年 | 503篇 |
1995年 | 428篇 |
1994年 | 390篇 |
1993年 | 265篇 |
1992年 | 221篇 |
1991年 | 154篇 |
1990年 | 126篇 |
1989年 | 99篇 |
1988年 | 80篇 |
1987年 | 54篇 |
1986年 | 32篇 |
1985年 | 28篇 |
1984年 | 20篇 |
1983年 | 13篇 |
1982年 | 10篇 |
1981年 | 8篇 |
1980年 | 16篇 |
1979年 | 7篇 |
1974年 | 3篇 |
1970年 | 2篇 |
1969年 | 1篇 |
1959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.
4.
Lin Haicheng Huang Wantong Zhao Kun Qiao Shuang Liu Zheng Wu Jian Chen Xi Ji Shuai-Hua 《Nano Research》2020,13(1):133-137
Nano Research - The isostructural and isoelectronic transition-metal-dichalcogenides 1T-TaS2 and 1T-TaSe2 are layered materials with intricate electronic structures. Combining the molecular beam... 相似文献
5.
Huizhu Cai Bingbing Chen Xiao Zhang Yuchen Deng Dequan Xiao Ding Ma Chuan Shi 《Nano Research》2021,14(1):122-130
Over recent years,catalytic materials of Fe-N-C species have been recognized being active for oxygen reduction reaction(ORR).However,the identification of active site remains challenging as it generally involves a pyrolysis process and mixed components being obtained.Herein Fe3C/C and Fe2N/C samples were synthesized by temperature programmed reduction of Fe precursors in 15%CH4/H2and pure NH3,respectively.By acid leaching of Fe2N/C sample,only single sites of FeN4species were presented,providing an ideal model for identification of catalytic functions of the single sites of FeN4in ORR.A correlation was conducted between the concentration of FeⅡN4in low spin state by Mossbauer spectra and the kinetic current density at 0.8 V in alkaline media,and such a structure-performance correlation assures the catalytic roles of low spin FeⅡN4 species as highly active sites for the ORR. 相似文献
6.
一种北斗联合低轨星座的导航增强方法研究 总被引:1,自引:0,他引:1
单纯依靠北斗导航系统提供定位导航授时服务,存在卫星信号落地功率低、易受遮蔽和阻断的不足。针对此问题,研究了一种北斗联合低轨星座实现导航增强的系统架构;提出了一种新的适应严重遮蔽或干扰条件下,基于到达时间(TOA)和到达频率(FOA)联合观测的定位解算算法;对高中低轨混合星座条件下的覆盖特性和精度衰减因子进行了仿真分析。分析结果表明,用户可见星数平均增加了64.2%,位置精度衰减因子(PDOP)平均改善了28.7%。研究结果可为下一代北斗的论证设计与研制建设提供参考借鉴。 相似文献
7.
Nitrile rubber (NBR) blends with excellent performance have always been a hot research topic in petroleum field. Due to the excellent performance and compatibility of polyamide 6 (PA6), it provides an opportunity for the preparation of high-performance NBR/PA6 blends. In this article, NBR/PA6 blends were prepared by the three-step molding process. Experimentally, it was found that PA6 has a prominent reinforcement effect in NBR matrix. The variation of this mechanical property was investigated from different aspects of the crystal structure, crystallinities, phase morphology, and so on. It can be cleared that the formation of fibrous structure of PA6 phase is the main factor for reinforcement of the polymer blends. Meanwhile, the formation mechanism of the special phase structure induced by the three-step process is deeply expounded and its structural evolution schematic is established. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47472. 相似文献
8.
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
9.
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