全文获取类型
收费全文 | 40350篇 |
免费 | 4985篇 |
国内免费 | 3199篇 |
专业分类
电工技术 | 4834篇 |
技术理论 | 1篇 |
综合类 | 4457篇 |
化学工业 | 3183篇 |
金属工艺 | 3099篇 |
机械仪表 | 2931篇 |
建筑科学 | 2819篇 |
矿业工程 | 1676篇 |
能源动力 | 1782篇 |
轻工业 | 1151篇 |
水利工程 | 1334篇 |
石油天然气 | 5225篇 |
武器工业 | 600篇 |
无线电 | 5096篇 |
一般工业技术 | 4555篇 |
冶金工业 | 1329篇 |
原子能技术 | 746篇 |
自动化技术 | 3716篇 |
出版年
2024年 | 89篇 |
2023年 | 608篇 |
2022年 | 1063篇 |
2021年 | 1269篇 |
2020年 | 1299篇 |
2019年 | 1145篇 |
2018年 | 1020篇 |
2017年 | 1453篇 |
2016年 | 1538篇 |
2015年 | 1650篇 |
2014年 | 2301篇 |
2013年 | 2336篇 |
2012年 | 2980篇 |
2011年 | 3203篇 |
2010年 | 2382篇 |
2009年 | 2399篇 |
2008年 | 2158篇 |
2007年 | 2744篇 |
2006年 | 2583篇 |
2005年 | 2179篇 |
2004年 | 1873篇 |
2003年 | 1701篇 |
2002年 | 1355篇 |
2001年 | 1119篇 |
2000年 | 1067篇 |
1999年 | 924篇 |
1998年 | 721篇 |
1997年 | 645篇 |
1996年 | 573篇 |
1995年 | 454篇 |
1994年 | 407篇 |
1993年 | 270篇 |
1992年 | 208篇 |
1991年 | 168篇 |
1990年 | 163篇 |
1989年 | 164篇 |
1988年 | 92篇 |
1987年 | 45篇 |
1986年 | 30篇 |
1985年 | 22篇 |
1984年 | 28篇 |
1983年 | 13篇 |
1982年 | 19篇 |
1981年 | 12篇 |
1980年 | 11篇 |
1979年 | 8篇 |
1959年 | 9篇 |
1958年 | 3篇 |
1955年 | 3篇 |
1951年 | 7篇 |
排序方式: 共有10000条查询结果,搜索用时 19 毫秒
1.
本文主要总结了新冠疫情期间作者的电磁场理论课程在线教学经验。对比分析了录播和直播的优缺点后,选择录播教学方式。基于超星网络教学平台,展示了录播网络教学的具体措施,包括网上答疑和学习效果检查以及在线批改作业等。给出了网络教学可以为线下教学继续使用的方法和手段,为疫情结束后的正常教学提供了新的网络教学补充措施。 相似文献
2.
3.
目的 对某福利院一起肠炎沙门菌食源性疾病进行调查和溯源,为研究相关食源性疾病提供参考。方法采用流行病学、食品卫生学和脉冲场凝胶电泳(PFGE)同源性分析等方法,分析本次食源性疾病事件。结果 确认本次事件中病例23名,患病率5.65%(23/407);现场采集病例肛拭子15份和厨房工作人员肛拭子3份、留样菜品3份、水果2份以及冰棒1份,其中从11份病例肛拭子中检出肠炎沙门菌,PFGE结果显示11株肠炎沙门菌的DNA条带图谱相似性为96.4%,聚类分析为同一型,结合流行病学调查,初步判断菌株来自同一克隆系。结论 综合流行病学、食品卫生学和实验室检测结果,确定为一起肠炎沙门菌引起的食源性疾病,福利院应加强对特殊人群的饮食安全管理,制定相应的食源性疾病突发事件应急处理预案,防止此类事故再发生。 相似文献
4.
The ceramic joining using electric field (E-field) has garnered significant research attention due to the decreased joining barrier and enhanced reliability. However, the underlying mechanism of E-field assisted joining remains unclear. Herein, we report the rapid joining of alumina ceramics using a small current. Moreover, the E-field is applied in both perpendicular and parallel directions to the faying surfaces, demonstrating a significant difference in terms of joint strength. These results indicate that the E-field generates defects and promotes the joining process by facilitating ionic diffusion. 相似文献
5.
《Ceramics International》2022,48(10):13719-13731
Li0.04Ca0.96-xSiO3:Smx orange?red emitting phosphors were synthesized using the sol-gel method. X-ray diffraction, Rietveld refinement of XRD patterns, Fourier transform infrared spectroscopy and ?uorescence spectrophotometry were used to characterize the crystal structure, sites of cationic Ca and luminescence properties of the prepared phosphors. The relationship of the different Ca sites in the matrix with the luminescence properties was analysed. The results indicate that the prepared phosphors reveal a β-CaSiO3 phase with a monoclinic crystal structure and space Group P21/a. As the Sm3+ concentration increases, the unit cell volume of phosphors and the Ca–O band lengths of different Ca sites decrease due to substitution of Ca2+ by smaller Sm3+ ions. By excitation at 404 nm, Li0.04Ca0.96-xSiO3:Smx phosphors exhibit warm orange?red light, corresponding to the electron transitions from 4G5/2 → 6H5/2 (567 nm), 4G5/2 → 6H7/2 (605 nm) and 4G5/2 → 6H9/2 (651 nm) of Sm3+. The concentration quenching phenomenon appears at Sm3+ concentrations beyond 0.02. The refinement results demonstrate that three cationic Ca sites, named Ca1, Ca2 and Ca3, exist in the β-CaSiO3 host lattice. The Ca2+ ions at Ca1 and Ca2 sites are coordinated with six oxygen ions, leading to the same coordination number (CN). The Ca2+ ion located at Ca3 site has seven coordination numbers. The Ca1 site possesses a smaller lattice distortion and better symmetry than those of Ca2 and Ca3 sites. However, the Ca3 site exhibits the largest lattice distortion and poor symmetry. The Sm3+ present in symmetric Ca1 sites in the matrix illustrates the strong emission intensity, long luminescence lifetimes and good thermal stability. 相似文献
6.
In recent years, the light field (LF) as a new imaging modality has attracted wide interest. The large data volume of LF images poses great challenge to LF image coding, and the LF images captured by different devices show significant differences in angular domain. In this paper we propose a view prediction framework to handle LF image coding with various sampling density. All LF images are represented as view arrays. We first partition the views into reference view (RV) set and intermediate view (IV) set. The RVs are rearranged into a pseudo sequence and directly compressed by a video encoder. Other views are then predicted by the RVs. To exploit the four dimensional signal structure, we propose the linear approximation prior (LAP) to reveal the correlation among LF views and efficiently remove the LF data redundancy. Based on the LAP, a distortion minimization interpolation (DMI) method is used to predict IVs. To robustly handle the LF images with different sampling density, we propose an Iteratively Updating depth image based rendering (IU-DIBR) method to extend our DMI. Some auxiliary views are generated to cover the target region and then the DMI calculates reconstruction coefficients for the IVs. Different view partition patterns are also explored. Extensive experiments on different types LF images also valid the efficiency of the proposed method. 相似文献
7.
《Ceramics International》2021,47(24):34521-34528
Aiming at the problem that power density and energy density are difficult to obtain simultaneously under low field, a novel composition (1-x)Na0·5Bi0·5TiO3-xBaZn1/3Ta2/3O3((1-x)NBT-xBZT) was designed and fabricated via solid-state methods. With the addition of BZT, the crystal lattice, structural symmetry, grain size, and dense degree were all increased proved by XRD, Raman, and Archimedes drainage method et al. Because of the enhancement of relaxor behavior, the x=0.10 sample displayed a high permittivity εr of 2871±15% and a low dielectric loss tan δ ≤ 0.025 in the wide temperature range of 60–400 oC. This ceramic also showed maximum recoverable energy density Wd (2.07 J/cm3) with high efficiency η (71.5%) under a low field of 150 kV/cm. Moreover, pulse discharge testing proved that this ceramic possessed both a significant discharge energy density WD (0.96 J/cm3) and a record high power density PD (108.54 MW/cm3). This work provided a promising material for high power and energy applications. 相似文献
8.
Can Ercan S. Esra Safran Artuğ Türkmenoğlu Uğur Karabakal 《Journal of surfactants and detergents》2021,24(1):139-147
Garzan oil field is located at the south east of Turkey. It is a mature oil field and the reservoir is fractured carbonate reservoir. After producing about 1% original oil in place (OOIP) reservoir pressure started to decline. Waterflooding was started in order to support reservoir pressure and also to enhance oil production in 1960. Waterflooding improved the oil recovery but after years of flooding water breakthrough at the production wells was observed. This increased the water/oil ratio at the production wells. In order to enhance oil recovery again different techniques were investigated. Chemical enhanced oil recovery (EOR) methods are gaining attention all over the world for oil recovery. Surfactant injection is an effective way for interfacial tension (IFT) reduction and wettability reversal. In this study, 31 different types of chemicals were studied to specify the effects on oil production. This paper presents solubility of surfactants in brine, IFT and contact angle measurements, imbibition tests, and lastly core flooding experiments. Most of the chemicals were incompatible with Garzan formation water, which has high divalent ion concentration. In this case, the usage of 2-propanol as co-surfactant yielded successful results for stability of the selected chemical solutions. The results of the wettability test indicated that both tested cationic and anionic surfactants altered the wettability of the carbonate rock from oil-wet to intermediate-wet. The maximum oil recovery by imbibition test was reached when core was exposed 1-ethly ionic liquid after imbibition in formation water. Also, after core flooding test, it is concluded that considerable amount of oil can be recovered from Garzan reservoir by waterflooding alone if adverse effects of natural fractures could be eliminated. 相似文献
9.
《Ceramics International》2022,48(14):20062-20069
Photocatalytic N2 fixation is a promising and sustainable manufacturing process of ammonia (NH3); however, the NH3 production rate by this method is very low, thus severely restricting further application of this sustainable technology. Therefore, developing an efficient photocatalyst for N2 fixation under mild conditions is urgently required. Herein, ferroelectric Bi2WO6 materials with different surface oxygen defects were prepared, and the concentration of corresponding defects was controlled by adjusting the thermal reduction time. The abundant oxygen defects in Bi2WO6 can provide more reactive sites to promote the effective adsorption of N2, and the photogenerated charge carrier can be efficiently separated benefiting from the internal electric field. These would weaken the N2 triple bond and reduce the activation energy barrier for the conversion of N2 to NH3 under mild conditions. In the absence of sacrificial agents and cocatalysts, the optimized Bi2WO6 with oxygen defects shows an indigenous NH3 yield of 132.175 μmol·g-1·L-1·h-1, which is more than two times higher than that of the original Bi2WO6. Surprisingly, the Bi2WO6 with oxygen defects produced more than eight times NH3 (471.13 μmol·g-1·L-1·h-1) than that of the original Bi2WO6 when assisted by an external magnetic field, thus providing a new perspective for further enhancing the N2 fixation performance. 相似文献
10.