全文获取类型
收费全文 | 42858篇 |
免费 | 3171篇 |
国内免费 | 1645篇 |
专业分类
电工技术 | 1241篇 |
综合类 | 4068篇 |
化学工业 | 4809篇 |
金属工艺 | 1882篇 |
机械仪表 | 919篇 |
建筑科学 | 19705篇 |
矿业工程 | 2458篇 |
能源动力 | 1027篇 |
轻工业 | 2732篇 |
水利工程 | 2361篇 |
石油天然气 | 1216篇 |
武器工业 | 256篇 |
无线电 | 817篇 |
一般工业技术 | 2137篇 |
冶金工业 | 1095篇 |
原子能技术 | 261篇 |
自动化技术 | 690篇 |
出版年
2024年 | 141篇 |
2023年 | 343篇 |
2022年 | 899篇 |
2021年 | 1040篇 |
2020年 | 958篇 |
2019年 | 690篇 |
2018年 | 742篇 |
2017年 | 904篇 |
2016年 | 1005篇 |
2015年 | 1192篇 |
2014年 | 2685篇 |
2013年 | 1856篇 |
2012年 | 2953篇 |
2011年 | 3265篇 |
2010年 | 2859篇 |
2009年 | 2988篇 |
2008年 | 2664篇 |
2007年 | 3416篇 |
2006年 | 3055篇 |
2005年 | 2630篇 |
2004年 | 1992篇 |
2003年 | 1752篇 |
2002年 | 1481篇 |
2001年 | 1281篇 |
2000年 | 1125篇 |
1999年 | 858篇 |
1998年 | 635篇 |
1997年 | 551篇 |
1996年 | 399篇 |
1995年 | 302篇 |
1994年 | 260篇 |
1993年 | 152篇 |
1992年 | 158篇 |
1991年 | 84篇 |
1990年 | 58篇 |
1989年 | 69篇 |
1988年 | 44篇 |
1987年 | 27篇 |
1986年 | 21篇 |
1985年 | 19篇 |
1984年 | 12篇 |
1983年 | 14篇 |
1982年 | 10篇 |
1981年 | 11篇 |
1980年 | 23篇 |
1979年 | 23篇 |
1978年 | 4篇 |
1977年 | 6篇 |
1976年 | 5篇 |
1959年 | 4篇 |
排序方式: 共有10000条查询结果,搜索用时 11 毫秒
1.
Qiqi Peng Xu Jiang Yifan Chen Wei Zhang Jun Jiang Anquan Jiang 《Ceramics International》2021,47(16):22753-22759
Large domain wall (DW) conductivity in an insulating ferroelectric plays an important role in the future nanosensors and nonvolatile memories. However, the wall current was usually too small to drive high-speed memory circuits and other agile nanodevices requiring high output-powers. Here, a large domain-wall current of 67.8 μA in a high on/off ratio of ~4460 was observed in an epitaxial Au/BiFeO3/SrRuO3 thin-film capacitor with the minimized oxygen vacancy concentration. The studies from read current-write voltage hysteresis loops and piezo-response force microscope images consistently showed remaining of partially unswitched domains after application of an opposite poling voltage that increased domain wall density and wall current greatly. A theoretical model was proposed to explain the large wall current. According to this model, the domain reversal occurs with the appearance of head-to-head and tail-to-tail 180° domain walls (DWs), resulting in the formation of highly conductive wall paths. As the applied voltage increased, the domain-wall number increased to enhance the on-state current, in agreement with the measurements of current-voltage curves. This work paves a way to modulate DW currents within epitaxial Au/BiFeO3/SrRuO3 thin-film capacitors through the optimization of both oxygen vacancy and domain wall densities to achieve large output powers of modern domain-wall nanodevices. 相似文献
2.
Ava Kwong Cecilia Y. S. Ho Vivian Y. Shin Chun Hang Au Tsun Leung Chan Edmond S. K. Ma 《International journal of molecular sciences》2021,22(2)
The germline carrier of the BRCA1 pathogenic mutation has been well proven to confer an increased risk of breast and ovarian cancer. Despite BRCA1 biallelic pathogenic mutations being extremely rare, they have been reported to be embryonically lethal or to cause Fanconi anemia (FA). Here we describe a patient who was a 48-year-old female identified with biallelic pathogenic mutations of the BRCA1 gene, with no or very subtle FA-features. She was diagnosed with ovarian cancer and breast cancer at the ages of 43 and 44 and had a strong family history of breast and gynecological cancers. 相似文献
3.
4.
《Food Control》2015
In this work a multicommuted flow system employing copper–4,4′- dipyridyl coordination compound as the solid-phase reagent for the spectrophotometric determination of reducing sugar was developed. The coordination compound was synthesized through a reaction of the 4,4′-dipyridyl and copper (II) nitrate, under hydrothermal conditions. The complex was characterized by infrared spectroscopy (FTIR), power X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive spectrometer (EDS) and thermogravimetric analysis (TGA). Based on the characterization, a multicommuted spectrophotometric procedure for the determination of reducing sugar using copper (II) complex as solid reagent is proposed. The proposed method was based on the redox reaction between a monosaccharide, such as fructose and glucose (reducing sugar) and Cu(II). This reaction, mediated in an alkaline medium, produces a yellow compound that can be determined by absorption electronic spectroscopy (λABS = 420 nm). Under optimum experimental conditions, a linear response ranging from 1.0 to 20.0 g L−1 (R = 0.9978 and n = 5), a detection (3σ criterion) and quantification (10σ criterion) limit estimated at 0.23 and 0.75 g L−1, respectively, a standard deviation relative of 4.7% (n = 7), for a reference solution of 10.0 g L−1 reducing sugar, and a sampling rate of 75 determinations per hour were achieved. The proposed system was applied to the determination of reducing sugars in coconut water and juices. The analysis of ten samples and the application of the t-test to the results found, and those obtained using reference procedures (AOAC), provided no significant differences at a 95% confidence level. This system enabled the analysis of reducing sugar with ease and simplicity, providing a significant economy of the solid reagent (600 μg per determination) and reducing effluent generation. 相似文献
5.
Donghai Xu Peng Feng Yang Wang Wanpeng Yang Yu Wang Shaoyan Sun 《American Institute of Chemical Engineers》2022,68(2):e17472
Corrosion and salt deposition problems severely restrict the industrialization of supercritical water oxidation. Transpiring wall reactor can effectively weaken these two problems by a protective water film. In this work, methanol was selected as organic matter, and the influences of vital structural parameters on water film properties and organic matter removal were studied via numerical simulation. The results indicate that higher than 99% of methanol conversion could be obtained and hardly affected by transpiration water layer, transpiring wall porosity and inner diameter. Increasing layer and porosity reduced reactor center temperature, but inner diameter's influence was lower relatively. Water film temperature reduced but coverage rate raised as layer, porosity, and inner diameter increased. Notably, the whole reactor was in supercritical state and coverage rate was only approximately 85% in the case of one layer. Increasing reactor length affected slightly the volume of the upper supercritical zone but enlarged the subcritical zone. 相似文献
6.
7.
8.
9.
对CFG桩质量缺陷的探讨 总被引:2,自引:2,他引:0
根据具体工程的概况及水文地质条件,分析了CFG桩在地下水位出现大面积缩颈现象和复合地基载荷试验达不到设计要求的原因,并介绍了地基补强措施,以满足工程质量的要求。 相似文献
10.