全文获取类型
收费全文 | 47112篇 |
免费 | 5777篇 |
国内免费 | 3138篇 |
专业分类
电工技术 | 16223篇 |
综合类 | 3924篇 |
化学工业 | 2530篇 |
金属工艺 | 2649篇 |
机械仪表 | 2350篇 |
建筑科学 | 2934篇 |
矿业工程 | 1202篇 |
能源动力 | 1868篇 |
轻工业 | 887篇 |
水利工程 | 1638篇 |
石油天然气 | 2781篇 |
武器工业 | 330篇 |
无线电 | 6801篇 |
一般工业技术 | 3095篇 |
冶金工业 | 1398篇 |
原子能技术 | 1520篇 |
自动化技术 | 3897篇 |
出版年
2024年 | 88篇 |
2023年 | 580篇 |
2022年 | 1014篇 |
2021年 | 1315篇 |
2020年 | 1423篇 |
2019年 | 1193篇 |
2018年 | 1147篇 |
2017年 | 1736篇 |
2016年 | 1855篇 |
2015年 | 2064篇 |
2014年 | 3097篇 |
2013年 | 2769篇 |
2012年 | 3694篇 |
2011年 | 4143篇 |
2010年 | 2982篇 |
2009年 | 3171篇 |
2008年 | 3040篇 |
2007年 | 3697篇 |
2006年 | 3158篇 |
2005年 | 2548篇 |
2004年 | 2041篇 |
2003年 | 1715篇 |
2002年 | 1380篇 |
2001年 | 1202篇 |
2000年 | 962篇 |
1999年 | 765篇 |
1998年 | 558篇 |
1997年 | 485篇 |
1996年 | 452篇 |
1995年 | 363篇 |
1994年 | 317篇 |
1993年 | 237篇 |
1992年 | 186篇 |
1991年 | 144篇 |
1990年 | 101篇 |
1989年 | 115篇 |
1988年 | 70篇 |
1987年 | 50篇 |
1986年 | 33篇 |
1985年 | 30篇 |
1984年 | 25篇 |
1983年 | 12篇 |
1982年 | 13篇 |
1981年 | 12篇 |
1980年 | 11篇 |
1978年 | 3篇 |
1976年 | 2篇 |
1975年 | 2篇 |
1961年 | 3篇 |
1959年 | 13篇 |
排序方式: 共有10000条查询结果,搜索用时 218 毫秒
61.
Space heating and cooling represent 63% of total building energy demand. In the present study, the concept of concrete foundation piles was used as an underground storage medium. This system requires no additional drilling costs or space, unlike conventional boreholes. A laboratory-scaled experiment facility was designed to experimentally investigate the thermal response of a concrete pile during the charging and discharging processes. The amount of energy stored and released during each process was evaluated. A flow rate parametric study was also conducted to explore the effect of the laminar and turbulent flow behavior. In order to complement the experimental study, an extensive CFD model was developed and compared with the experimental data. There was good agreement between the numerical and experimental results for each process at different flow rates. The results revealed that increasing the flow rate increases not only the heat rejection and extraction but also the storage efficiency. 相似文献
62.
《Journal of the European Ceramic Society》2020,40(6):2390-2395
ZnO-Bi2O3 based varistor ceramics doped with C3N4 were fabricated via solid state method. Experimental results show that C3N4 additive acts as an inhibitor in ZnO grain growth, and the average grain size decreases from 10.2–7.1 μm. The varistor breakdown voltage gradient increases from 222.3–282.3 V/mm, and the nonlinear coefficient increases from 51.9–58.2 with the increase of C3N4 content from 0 to 3.0 wt%. The C3N4-added samples exhibited smaller residual voltage ratio and better surge current withstanding capability. It is proposed that the C3N4-doping leads to substitution of nitrogen for oxygen in the grain boundary region, forming acceptor type defects. The acceptor type defects act as electron traps, increasing the barrier height from 1.31 to 1.50 eV and the depletion layer width from 54.9–61.8 nm, which increases the nonlinearity, and the surge current performances of the C3N4 doped ZnO varistor ceramics are improved. 相似文献
63.
深入分析了氯碱化工企业10kV电力系统相间短路故障原因,并提出了抑制短路电流的措施,有效解决了因相间短路故障导致的大面积停电事故和变压器烧毁事故等疑难问题。 相似文献
64.
疲劳断裂是金属结构中的主要失效形式,而金属结构中的早期疲劳断裂信号通常难以检测。TOA方法是常用的声发射定位源方法,但是声波传播过程中波速变换和路径的复杂性对其结果影响很大。运用Delta T声发射源定位方法,用断铅实验模拟声发射源,用AIC信息准则对到达时间进行优化,通过使用差值求源点坐标和图像处理的方法,求得声发射源坐标。通过在平板上的实验,比较两种源定位方法在不同结构中的定位结果,分析定位误差,结果表明图像处理方法更为优秀。 相似文献
65.
采用综合应用理论分析、现场实测的方法,对山西汾西集团曙光煤矿1226高瓦斯综采工作面瓦斯来源进行了分析,提出并实施了分区段“风排+煤层钻孔抽放+裂隙带钻孔抽放”的联合瓦斯抽采技术。现场监测结果显示:1226综采工作面上隅角瓦斯浓度控制在0.45%~0.75%,回风流中瓦斯浓度控制在了0.44%~0.75%,瓦斯治理效果明显改善。 相似文献
66.
Bin Zhang Xin Yang Liang Chen Jinyu Chao Jia Teng Qing Wang 《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》2020,95(8):2052-2068
Microplastics are emerging persistent pollutants that have been extensively detected in aqueous environments. Yet, scientists have little knowledge of microplastic pollution in soils. This study reviewed over 60 articles, with the following objectives: (i) to discuss sources and the global distribution of microplastics in soils; (ii) to evaluate current extraction techniques and analytical methods for microplastics in soils; and (iii) to comprehensively assess their adverse impacts on soils and soil organisms. Moreover, this review highlights the lack of research into microplastic contamination in soils as a significant knowledge gap. Research into the fate, sources and analytical techniques of soil microplastics and the interactions between soil organisms, soils and microplastics is essential in order to underpin management decisions aimed at safeguarding the ecological integrity of our soils. © 2020 Society of Chemical Industry 相似文献
67.
68.
《Ceramics International》2020,46(10):16472-16479
(Pb1-xLax) (Zr0.92Ti0.08)1-x/4O3 (PLZT x/92/8, x = 3, 5 and 7 at%) ceramics with compositions near the antiferroelectric (AFE)-ferroelectric (FE) phase boundary were fabricated by a solid-state reaction method. The effect of lanthanum content on the conduction behaviors and relaxation processes has been investigated. It was verified that the main phase with orthorhombic structure was formed in all compositions. The increase of lanthanum substitution resulted in an enhancement of diffuse phase transition. Impedance analysis suggested that the ac conductivity decreased with increasing lanthanum content. Moreover, thermally stimulated depolarization current study was utilized to establish the correlation between defect structures and relaxation processes. It showed three peaks with distinct characteristics, which originated from dipole orientation, oxygen vacancy migration and phase transition respectively. The oxygen vacancy-related defects induced by lanthanum doping were mainly responsible for the variation of conduction behaviors and relaxation processes. 相似文献
69.
在COB(Chip On Board)LED光组件制造领域,点胶、测试和补粉关键工艺基本以手工或半自动为主。为了保证COB LED产品质量一致性、提高生产效率,研制了一种COB自动在线点胶测试及补粉一体机,实现点胶、测试、补粉生产工序的自动化生产。阐述了其工艺流程及设计总体方案,提出了荧光粉量修补方法,修正初次点胶量,实现动态调节,减少人工干预。经实验验证,该一体机可以提高点胶工艺的自动化程度,具有运行速度快、可靠性好、性能稳定等特点。 相似文献
70.
Shibendu Mahata Rajib Kar Durbadal Mandal 《International Journal of Circuit Theory and Applications》2020,48(9):1554-1560
In this letter, the optimal rational approximation of fractional-order bandpass Butterworth filter (FOBBF) is presented. The transfer function of the FOBBF is decomposed into a multiplication of first-order and second-order terms. As a result, the design stability conditions can be easily satisfied using only the variable boundary constraints. The proposed technique generalizes the symmetric fractional-order roll-off characteristic as only a special case of the asymmetric one. Several examples are presented to validate the modeling efficacy. 相似文献