全文获取类型
收费全文 | 48413篇 |
免费 | 4613篇 |
国内免费 | 2718篇 |
专业分类
电工技术 | 3161篇 |
技术理论 | 4篇 |
综合类 | 3685篇 |
化学工业 | 7457篇 |
金属工艺 | 3040篇 |
机械仪表 | 3401篇 |
建筑科学 | 3807篇 |
矿业工程 | 1850篇 |
能源动力 | 1436篇 |
轻工业 | 3691篇 |
水利工程 | 1146篇 |
石油天然气 | 2571篇 |
武器工业 | 533篇 |
无线电 | 5425篇 |
一般工业技术 | 5168篇 |
冶金工业 | 2337篇 |
原子能技术 | 663篇 |
自动化技术 | 6369篇 |
出版年
2024年 | 174篇 |
2023年 | 731篇 |
2022年 | 1392篇 |
2021年 | 2095篇 |
2020年 | 1513篇 |
2019年 | 1271篇 |
2018年 | 1452篇 |
2017年 | 1611篇 |
2016年 | 1485篇 |
2015年 | 2068篇 |
2014年 | 2556篇 |
2013年 | 3074篇 |
2012年 | 3413篇 |
2011年 | 3592篇 |
2010年 | 3295篇 |
2009年 | 3105篇 |
2008年 | 3176篇 |
2007年 | 2972篇 |
2006年 | 2756篇 |
2005年 | 2367篇 |
2004年 | 1705篇 |
2003年 | 1432篇 |
2002年 | 1516篇 |
2001年 | 1252篇 |
2000年 | 1042篇 |
1999年 | 947篇 |
1998年 | 680篇 |
1997年 | 562篇 |
1996年 | 508篇 |
1995年 | 426篇 |
1994年 | 379篇 |
1993年 | 271篇 |
1992年 | 219篇 |
1991年 | 151篇 |
1990年 | 100篇 |
1989年 | 91篇 |
1988年 | 93篇 |
1987年 | 55篇 |
1986年 | 44篇 |
1985年 | 25篇 |
1984年 | 16篇 |
1983年 | 9篇 |
1982年 | 18篇 |
1981年 | 13篇 |
1980年 | 13篇 |
1979年 | 14篇 |
1977年 | 7篇 |
1976年 | 7篇 |
1959年 | 6篇 |
1947年 | 5篇 |
排序方式: 共有10000条查询结果,搜索用时 187 毫秒
1.
Wireless Networks - Geolocation is important for many emerging applications such as disaster management and recommendation system. In this paper, we propose a multilayer recognition model (MRM) to... 相似文献
2.
3.
Jincheng Yu Yabin Chang Ewa Jakubczyk Bing Wang Feridoon Azough Robert Dorey Robert Freer 《Journal of the European Ceramic Society》2021,41(9):4859-4869
Ca3Co4O9 is a promising p-type thermoelectric oxide material having intrinsically low thermal conductivity. With low cost and opportunities for automatic large scale production, thick film technologies offer considerable potential for a new generation of micro-sized thermoelectric coolers or generators. Here, based on the chemical composition optimized by traditional solid state reaction for bulk samples, we present a viable approach to modulating the electrical transport properties of screen-printed calcium cobaltite thick films through control of the microstructural evolution by optimized heat-treatment. XRD and TEM analysis confirmed the formation of high-quality calcium cobaltite grains. By creating 2.0 at% cobalt deficiency in Ca2.7Bi0.3Co4O9+δ, the pressureless sintered ceramics reached the highest power factor of 98.0 μWm?1 K-2 at 823 K, through enhancement of electrical conductivity by reduction of poorly conducting secondary phases. Subsequently, textured thick films of Ca2.7Bi0.3Co3.92O9+δ were efficiently tailored by controlling the sintering temperature and holding time. Optimized Ca2.7Bi0.3Co3.92O9+δ thick films sintered at 1203 K for 8 h exhibited the maximum power factor of 55.5 μWm?1 K-2 at 673 K through microstructure control. 相似文献
4.
燕麦为西藏自治区典型牧草之一,由于种植区地域辽阔,灌溉试验结果受限,西藏燕麦主要种植区的灌溉定额尚不明确。本文在西藏燕麦主要种植区内选取28个典型站点进行资料收集,遵循农业气候相似原则进行区域划分,基于水量平衡法揭示了西藏燕麦主要种植区灌溉定额的空间分布特征,并根据统计学原理分析了其影响因素。研究表明:燕麦主要种植区的灌溉定额呈由西藏中部至东部呈现先递增后递减的趋势,50%水文年下的燕麦灌溉定额在56~265 mm之间变化。降雨量是影响研究区内燕麦灌溉定额的主要因素(R2为0.515),ET0次之(R2为0.152);其它气象因素中,日照时数对研究区燕麦灌溉定额影响较大(R2为0.462),且呈正相关关系;相对湿度对燕麦灌溉定额影响较小。西藏燕麦主要种植区的灌溉定额及其空间分布可为西藏自治区灌溉用水管理提供支撑。 相似文献
5.
6.
KH550, KH560, CTAB, and F127 were adopted to modify silicon (Si) to improve the dispersity and stability of Si in the polyacrylonitrile/dimethyl sulfoxide (PAN/DMSO) polymer solutions. The influence of surfactants on rheological behaviors of PAN/DMSO/Si blending polymer solutions was investigated by an advanced solution and melt rotation rheometer. The homogeneity and stability were also studied. The results showed that the surfactants could change the viscosity dependence of blending polymer solutions on shear rate, temperature and storage time by increase the steric hindrance of Si. Among the four solutions, PAN/DMSO/Si blending polymer solution with F127 exhibited the lowest viscosity, activation energy and the smallest structural viscosity index and exhibited the trend close to the Newtonian fluids. Moreover, PAN/DMSO/Si blending polymer solution with F127 exhibited the best dispersity and stability, indicating its best physical properties and machinability. 相似文献
7.
全膜电容器边缘处的电场畸变是影响电容器元件击穿的重要因素之一.为研究浸渍情况和压紧系数对全膜电容器电场分布的影响,对电容器端部进行建模,通过改变浸渍情况和压紧系数,计算不同参数下电容器端部的电场分布情况,结果表明:未浸渍情况下电场最大值集中在折边处两侧,浸渍情况下场强在折边圆弧处分布较为均匀.同时发现,在浸渍情况下增大压紧系数K可以明显改善全膜电容器端部电场的分布情况. 相似文献
8.
基于冲击破碎技术对截割滚筒结构进行了优化设计,将其设计为振动形式.利用MATLAB软件对截割滚筒中关键的偏心锤结构进行了优化设计.利用COMSOL软件对行星齿轮结构固有频率进行分析,发现工作频率远小于固有频率,不会发生共振问题.将设计的新型截割滚筒应用到煤矿工程实践中,采煤效率显著提升. 相似文献
9.
Peng Li Haibin Jiang Ariel Barr Zhichu Ren Rui Gao Hua Wang Weiwei Fan Meifang Zhu Guiyin Xu Ju Li 《Advanced functional materials》2021,31(51):2105845
Mercury, lead, and cadmium are among the most toxic and carcinogenic heavy metal ions (HMIs), posing serious threats to the sustainability of aquatic ecosystems and public health. There is an urgent need to remove these ions from water by a cheap but green process. Traditional methods have insufficient removal efficiency and reusability. Structurally robust, large surface-area adsorbents functionalized with high-selectivity affinity to HMIs are attractive filter materials. Here, an adsorbent prepared by vulcanization of polyacrylonitrile (PAN), a nitrogen-rich polymer, is reported, giving rise to PAN-S nanoparticles with cyclic π-conjugated backbone and electronic conductivity. PAN-S can be coated on ultra-robust melamine (ML) foam by simple dipping and drying. In agreement with hard/soft acid/base theory, N- and S-containing soft Lewis bases have strong binding to Hg2+, Pb2+, Cu2+, and Cd2+, with extraordinary capture efficiency and performance stability. Furthermore, the used filters, when collected and electrochemically biased in a recycling bath, can release the HMIs into the bath and electrodeposit on the counter-electrode as metallic Hg0, Pb0, Cu0, and Cd0, and the PAN-S@ML filter can then be reused at least 6 times as new. The electronically conductive PAN-S@ML filter can be fabricated cheaply and holds promise for scale-up applications. 相似文献
10.
Xinming Ren Beiyue Ma Gaofeng Fu Fan Qian Guoqi Liu Jingkun Yu Yawei Li 《Ceramics International》2021,47(14):19959-19969
The recycling of solid waste is a win-win solution for humans and nature. For this purpose, magnesite tailings and silicon kerf waste were employed to prepare MgO–Mg2SiO4 composite ceramics by solid-state reaction synthesis in the present work. Then, effects of sintering temperature and raw material ratio on as-prepared ceramics were systematically studied. As-prepared ceramics showed improvement in their relative density (from 47.55%–68.12% to 90.96%–95.25%) and cold compressive strength (from 7.34–118.66 MPa to 303.39–546.65 MPa) with the increase in sintering temperature from 1300 to 1600 °C. In addition, it was found that Si promoted synthesis process of Mg2SiO4 phase through transient liquid phase sintering and Fe2O3 accelerated sintering process through activation sintering. Consequently, the presence of Mg2SiO4 phase effectively improved the density and strength of MgO–Mg2SiO4 composite ceramic, while reducing its thermal conductivity. This work provides a potential reutilization strategy for magnesite tailings, and as-prepared products are expected to be applied in fields of construction, metallurgy, and chemical industry. 相似文献