全文获取类型
收费全文 | 49765篇 |
免费 | 4224篇 |
国内免费 | 1970篇 |
专业分类
电工技术 | 12361篇 |
技术理论 | 1篇 |
综合类 | 4240篇 |
化学工业 | 4416篇 |
金属工艺 | 1523篇 |
机械仪表 | 3245篇 |
建筑科学 | 6196篇 |
矿业工程 | 2147篇 |
能源动力 | 3687篇 |
轻工业 | 2189篇 |
水利工程 | 779篇 |
石油天然气 | 1656篇 |
武器工业 | 774篇 |
无线电 | 2890篇 |
一般工业技术 | 4602篇 |
冶金工业 | 2555篇 |
原子能技术 | 362篇 |
自动化技术 | 2336篇 |
出版年
2024年 | 224篇 |
2023年 | 575篇 |
2022年 | 1090篇 |
2021年 | 1386篇 |
2020年 | 1558篇 |
2019年 | 1101篇 |
2018年 | 1047篇 |
2017年 | 1426篇 |
2016年 | 1398篇 |
2015年 | 1530篇 |
2014年 | 3236篇 |
2013年 | 2776篇 |
2012年 | 3725篇 |
2011年 | 3800篇 |
2010年 | 2652篇 |
2009年 | 2813篇 |
2008年 | 2612篇 |
2007年 | 3452篇 |
2006年 | 3227篇 |
2005年 | 2827篇 |
2004年 | 2437篇 |
2003年 | 2265篇 |
2002年 | 1832篇 |
2001年 | 1459篇 |
2000年 | 1188篇 |
1999年 | 934篇 |
1998年 | 680篇 |
1997年 | 553篇 |
1996年 | 441篇 |
1995年 | 388篇 |
1994年 | 300篇 |
1993年 | 192篇 |
1992年 | 182篇 |
1991年 | 123篇 |
1990年 | 90篇 |
1989年 | 87篇 |
1988年 | 62篇 |
1987年 | 43篇 |
1986年 | 31篇 |
1985年 | 20篇 |
1984年 | 50篇 |
1983年 | 56篇 |
1982年 | 29篇 |
1981年 | 10篇 |
1980年 | 9篇 |
1975年 | 3篇 |
1959年 | 4篇 |
1956年 | 3篇 |
1955年 | 3篇 |
1954年 | 4篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
21.
风管摩擦阻力的直接计算方法 总被引:2,自引:1,他引:1
提出用高精度的反映密度、黏度和温度关系的经验公式和Colebrook公式计算风管摩擦阻力系数的方法。分析和算例表明,用该方法计算,计算结果比采用常用工程设计方法更为准确,为应用计算机进行风道设计提供了直接、简便的方法。 相似文献
22.
A model is presented for drying of a single porous particle with superheated steam and humid air. Experimental data for spherical porous ceramic particle reported in the literature were used for the validation of the model. An inversion temperature at which the evaporation rates within superheated steam and humid air are equal was predicted. The effect of thermophysical properties of the particle (permeability 10-14 - 10-17 m2, diameter 3 × 10-3 - 10 × 10-3 m) and operating variables (gas mass flux 0.26 - 0.78 kg m-2 s-1, drying agent temperature 120-200°C) is tested. The inversion temperature is shown to be affected by the thermophysical properties of the porous particle and of the drying agent. 相似文献
23.
Jean‐Marc Aldric Philippe Thonart 《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》2008,83(10):1401-1408
BACKGROUND: In the framework of biological processes used for waste gas treatment, the impact of the inoculum size on the start‐up performance needs to be better evaluated. Moreover, only a few studies have investigated the behaviour of elimination capacity and biomass viability in a two‐phase partitioning bioreactor (TPPB) used for waste gas treatment. Lastly, the impact of ethanol as a co‐substrate remains misunderstood. RESULTS: Firstly, no benefit of inoculation with a high cellular density (>1.5 g L?1) was observed in terms of start‐up performance. Secondly, the TPPB was monitored for 38 days to characterise its behaviour under several operational conditions. The removal efficiency remained above 63% for an inlet concentration of 7 g isopropylbenzene (IPB) m?3 and at some time points reached 92% during an intermittent loading phase (10 h day?1), corresponding to a mean elimination capacity of 4 × 10?3 g L?1 min?1 (240 g m?3 h?1) for a mean IPB inlet load of 6.19 × 10?3 g L?1 min?1 (390 g m?3 h?1). Under continuous IPB loading, the performance of the TPPB declined, but the period of biomass acclimatisation to this operational condition was shorter than 5 days. The biomass grew to approximately 10 g L?1 but the cellular viability changed greatly during the experiment, suggesting an endorespiration phenomenon in the bioreactor. It was also shown that simultaneous degradation of IPB and ethanol occurred, suggesting that ethanol improves the biodegradation process without causing oxygen depletion. CONCLUSION: A water/silicone oil TPPB with ethanol as co‐substrate allowed the removal of a high inlet load of IPB during an experiment lasting 38 days. Copyright © 2008 Society of Chemical Industry 相似文献
24.
蓄热式均热炉生产中存在问题的分析及解决方案 总被引:1,自引:0,他引:1
介绍了高温空气燃烧技术在均热炉上的应用情况,对应用中出现的问题进行了分析,并提出了解决方案。 相似文献
25.
26.
阐述了电接点压力表补水泵定压系统的一些应用问题 ,给出了电接点压力表定压点的上、下限计算公式 ,并提出了该系统补给水泵、补给水箱及安全阀的设计选型方法 相似文献
27.
This paper describes an effective analysis of magnetic shielding based on homogenization. The analyses become time‐consuming if the problems include the magnetic substances having fine structure. The homogenization of the structure makes it possible to analyze effectively the magnetic fields. The authors introduce a method to estimate the effective permeability of the homogenized substance. This method can be applied to any periodic structure made of magnetic substance. The magnetic shielding effects by the structures against direct‐current (DC) fields generated by electric railways are analyzed by using the present method. As a result, it is found that the overhead way and the protective fence near the railway work as a magnetic shield, whose effects can be improved by appropriate arrangement of those constructions. © 2007 Wiley Periodicals, Inc. Electr Eng Jpn, 160(4): 7–15, 2007; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20310 相似文献
28.
陈余万 《大庆石油地质与开发》2003,22(1):44-46
江苏油田的庄 2、韦 2油田属强水敏油田 ,采用热 (水 )洗油井和化学清防蜡效果较差 ,两油田每年因洗井造成地层污染影响的产量损失在 5 0 0 0t以上 ,约占油田产量的 4 5 %。根据集肤效应 ,采用油管电热清蜡技术 ,在含水小于 6 0 %、井斜小于 4 0°的油井上可正常使用 ,一般通电加热 4 0~ 80min后 ,油井井口温度能达到 5 0℃左右 ,最高可达到 6 5℃以上 ,连续加热 5~ 6h即可达到清蜡目的 ,电热清蜡为周期 6 0~ 90d。影响电热清蜡主要指标因素是油井的产液量 ,产液量越小 ,所需要的加热电流和加热电压也越小 ,井口温度达到最高值越低 ,清蜡效果越差。试验的 7口井平均年度投入产出比达到 1∶5 ,经济效益和社会效益十分明显。 相似文献
29.
难处理金矿石加石灰焙烧焙砂中CaS的消除 总被引:4,自引:0,他引:4
介绍了用空气氧化预浸加石灰焙烧焙砂中的CaS,以消除其对金氰化的影响。预浸后金的氰化浸出率可从58%提高到80%以上。 相似文献
30.
Kevin Yale Teichman 《Indoor air》1994,4(3):202-211
Deciding between the different policy approaches available for reducing human exposures to indoor pollutants is an exceptionally complex task. These options can range from waiting until more definitive information is available to enacting regulatory standards, with many variations in between. This paper presents some of the factors policy-makers must consider in establishing indoor air quality policies, and the role researchers should play in ensuring that indoor air policies are based on the best available scientific information. 相似文献