全文获取类型
收费全文 | 23445篇 |
免费 | 2445篇 |
国内免费 | 1414篇 |
专业分类
电工技术 | 3001篇 |
综合类 | 1610篇 |
化学工业 | 2431篇 |
金属工艺 | 2123篇 |
机械仪表 | 1455篇 |
建筑科学 | 1890篇 |
矿业工程 | 564篇 |
能源动力 | 2029篇 |
轻工业 | 1504篇 |
水利工程 | 386篇 |
石油天然气 | 580篇 |
武器工业 | 188篇 |
无线电 | 2051篇 |
一般工业技术 | 2154篇 |
冶金工业 | 2713篇 |
原子能技术 | 941篇 |
自动化技术 | 1684篇 |
出版年
2024年 | 77篇 |
2023年 | 315篇 |
2022年 | 563篇 |
2021年 | 762篇 |
2020年 | 827篇 |
2019年 | 732篇 |
2018年 | 625篇 |
2017年 | 794篇 |
2016年 | 907篇 |
2015年 | 843篇 |
2014年 | 1568篇 |
2013年 | 1599篇 |
2012年 | 1877篇 |
2011年 | 1951篇 |
2010年 | 1427篇 |
2009年 | 1438篇 |
2008年 | 1195篇 |
2007年 | 1579篇 |
2006年 | 1492篇 |
2005年 | 1129篇 |
2004年 | 964篇 |
2003年 | 882篇 |
2002年 | 727篇 |
2001年 | 591篇 |
2000年 | 540篇 |
1999年 | 418篇 |
1998年 | 289篇 |
1997年 | 236篇 |
1996年 | 193篇 |
1995年 | 157篇 |
1994年 | 124篇 |
1993年 | 96篇 |
1992年 | 57篇 |
1991年 | 54篇 |
1990年 | 44篇 |
1989年 | 38篇 |
1988年 | 16篇 |
1987年 | 15篇 |
1986年 | 13篇 |
1985年 | 21篇 |
1984年 | 33篇 |
1983年 | 28篇 |
1982年 | 20篇 |
1981年 | 10篇 |
1980年 | 13篇 |
1975年 | 1篇 |
1966年 | 1篇 |
1964年 | 1篇 |
1959年 | 18篇 |
1951年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 78 毫秒
1.
2.
Mehdi Hosseini Abadshapoori 《亚洲传热研究》2021,50(2):1056-1072
Increasing the heat capacity of heat exchangers is a crucial need for modern devices. The thermal conductivity of the usual fluids and the Nusselt (Nu) number of flows containing such fluids are two bottlenecks in the way of increasing heat delivery in the heat exchangers. For this reason, nanofluids have been introduced. The effect of utilizing a Cu-water nanofluid as a coolant of two hot pipes in a square cavity is investigated numerically with a two-component lattice Boltzmann method. The volume fraction of nanoparticles is assumed to be constant (0.03) while the Richardson (Ri) number varies from 0.02 to 20. Results show that the effectiveness of nanoparticles is better observed in the natural convection mode. However, sedimentation is also very probable at high Ri numbers, which significantly reduces the effectiveness of the nanoparticles. Configurations which produce a natural convection stream similar to the forced convection one as well as the configurations with high spacing and hence, low heat stream interactions, are the best choices for a uniform heat rate from the pipes. 相似文献
3.
The slight-alkalization of generator internal cooling water (GICW) is widely used to inhibit the corrosion of hollow copper conductor and thereby ensure the safe operation of the generator. CO2 inleakage is increasingly identified as a potential security risk for GICW system. In this paper, the influence of CO2 inleakage on the slight-alkalization of GICW was theoretically discussed. Based on the equilibriums of the CO2-NaOH-H2O system, CO2 inleakage saturation was derived to quantify the amount of the dissolved CO2 in GICW. This parameter can be directly calculated with the measured conductivity and the [Na+] of GICW. The influence of CO2 inleakage on the slight-alkalization conditioning of GICW and the measurement of its water quality parameters were then analyzed. The more severe the inleakage, the narrower the water quality operation ranges of GICW, resulting in the more difficult the slight-alkalization conditioning of GICW. The temperature calibrations of the conductivity and the pH value of GICW show non-linear correlations with the amount of CO2 inleakage and the NaOH dosage. This study provides insights into the influence of CO2 inleakage on the slight-alkalization of GICW, which can serve as the theoretical basis for the actual slight-alkalization when CO2 inleakage occurs. 相似文献
4.
5.
6.
摘要:为了研究300M超高强钢在中性盐雾环境中的腐蚀行为及腐蚀机制,采用失重法,宏观、微观腐蚀形貌分析,三维表面轮廓分析及电化学分析的研究方法,来表征腐蚀实验现象并进行分析。结果表明:300M超高强钢在中性盐雾环境中的腐蚀产物为FeOOH、Fe2O3、Fe(OH)3和Fe3O4;腐蚀速率随着腐蚀时间逐渐降低,腐蚀后期(72h)腐蚀速率降低50%;腐蚀初期以点蚀为主,点蚀坑通过横向扩展,逐渐发展为后期的均匀腐蚀,腐蚀表面形貌呈沟壑状;外腐蚀层对基体的保护能力很弱,Cr元素在锈层靠近基体的一侧偏聚使内腐蚀层具有一定的抗腐蚀性。 相似文献
7.
针对现有海量点云可视化方法存在索引构建时间长、内存占用大等问题,研究一种八叉树索引结合OSG分页结点的快速可视化方法,可在占用较小内存的基础上快速建立点云索引并实时调度。采用八叉树索引结构对海量点云进行数据组织,建立各层级的八叉树结点并以文件映射的方式分块保存,对结点文件重组织转换为支持OSG渲染引擎的多分辨率点云数据。采用基于OSG分页结点的实时调度技术,对海量点云进行高质量可视化。与目前两款主流的点云数据处理商业软件进行实验对比分析,结果表明所提方法具有索引建立速度快、内存占用小等优点,同时可视化交互更加流畅,适用于各种配置计算机下海量点云数据的调度管理与实时可视化。 相似文献
8.
随着互联网的高速发展,引发了网络流量、电信骨干网流量急速增长,使得网络容量的提升迫在眉睫。目前,100G 系统已经商用,超100G系统能够更有效地解决流量和网络带宽持续增长带来的压力,本文主要介绍新型单模光纤的特性以及探讨基于新型单模光纤的传输技术。 相似文献
9.
A flower‐shaped ultra‐wideband fractal antenna is presented. It comprises a fourth iterative flower‐shaped radiator, asymmetrical stub‐loaded feeding line, and coplanar quarter elliptical ground planes. A wide operating band of 12.12 GHz (4.58‐16.7 GHz) for S 11 ≤ ? 10 dB is achieved along with an overall antenna footprint of 15.7 × 11.4 mm2. In addition, other desirable characteristics, that is, omnidirectional radiation patterns, peak gain upto 5 dB, and fidelity factor more than 75% are achieved. A good agreement exists between the simulation and measured results. The obtained results illustrate that this antenna has wide operating range and compact dimensions than available structures. 相似文献
10.
This paper presented the exergoeconomic evaluation of the developed desiccant-evaporative air-conditioning system. The developed system was evaluated based on the steady-state conditions at different regeneration and reference temperatures. The exergoeconomic evaluation method was implemented to the system components and the whole system to evaluate the exergy efficiency, exergy destruction ratios, cost rates, relative cost differences and exergoeconomic factors. The regeneration and reference temperatures affected the exergy efficiencies, exergy destruction ratios, cost rates, relative cost differences and exergoeconomic factors. The desiccant wheel, heating coil and evaporative cooler had a high cost rate (investment cost, operation and maintenance cost, and exergy destruction cost). The exit air fan, outdoor air fan and evaporative cooler had a high relative cost difference. The exit air fan, outdoor air fan and secondary heat exchanger had a high exergoeconomic factor. Replacement of the desiccant wheel with a higher dehumidification performance could decrease the high cost rate. A higher efficiency evaporative cooler and heating coil were needed. Cheaper air fans (outdoor air fans and exit air fans) were needed. 相似文献