全文获取类型
收费全文 | 6156篇 |
免费 | 132篇 |
国内免费 | 49篇 |
专业分类
电工技术 | 179篇 |
综合类 | 150篇 |
化学工业 | 652篇 |
金属工艺 | 170篇 |
机械仪表 | 417篇 |
建筑科学 | 849篇 |
矿业工程 | 159篇 |
能源动力 | 640篇 |
轻工业 | 280篇 |
水利工程 | 31篇 |
石油天然气 | 137篇 |
武器工业 | 91篇 |
无线电 | 449篇 |
一般工业技术 | 1373篇 |
冶金工业 | 268篇 |
原子能技术 | 67篇 |
自动化技术 | 425篇 |
出版年
2024年 | 5篇 |
2023年 | 43篇 |
2022年 | 73篇 |
2021年 | 89篇 |
2020年 | 94篇 |
2019年 | 72篇 |
2018年 | 75篇 |
2017年 | 113篇 |
2016年 | 121篇 |
2015年 | 117篇 |
2014年 | 304篇 |
2013年 | 354篇 |
2012年 | 350篇 |
2011年 | 520篇 |
2010年 | 405篇 |
2009年 | 410篇 |
2008年 | 321篇 |
2007年 | 437篇 |
2006年 | 406篇 |
2005年 | 328篇 |
2004年 | 260篇 |
2003年 | 279篇 |
2002年 | 247篇 |
2001年 | 163篇 |
2000年 | 127篇 |
1999年 | 133篇 |
1998年 | 93篇 |
1997年 | 62篇 |
1996年 | 63篇 |
1995年 | 48篇 |
1994年 | 44篇 |
1993年 | 24篇 |
1992年 | 26篇 |
1991年 | 24篇 |
1990年 | 13篇 |
1989年 | 23篇 |
1988年 | 14篇 |
1987年 | 8篇 |
1986年 | 6篇 |
1985年 | 5篇 |
1984年 | 8篇 |
1983年 | 3篇 |
1982年 | 2篇 |
1981年 | 4篇 |
1979年 | 3篇 |
1978年 | 3篇 |
1958年 | 6篇 |
1956年 | 2篇 |
1955年 | 1篇 |
1954年 | 1篇 |
排序方式: 共有6337条查询结果,搜索用时 187 毫秒
21.
本文采用 2只扩散杯 ,一只选择渗透率较大的滤膜 ,使2 2 2 Rn和2 2 0 Rn能很容易的进入。另一只选择渗透率较小的滤膜 ,该滤膜只允许2 2 2 Rn进入 ,半衰期较短的2 2 0 Rn被阻挡在外面。通过不同滤膜扩散率的差异 ,改变探测器的空气交换率 ,从而达到同时测量2 2 2 Rn和2 2 0 Rn的目的 相似文献
22.
Air cleaning as a means of mitigating the risks arising from exposure to indoor radon progeny has been evaluated in a single-family house in the north eastem US. using an automated, semi-continuous activity-weighted size distribution measurement system. The measurements included radon concentration, condensation nuclei count, and activity-weighted size distribution of radon decay products. Measurements were made in the house with and without an operating air filtration system and with various particle sources common to normal indoor activities operating. Aerosols were generated by running water in a shower, candle burning, cigarette smoking, vacuuming, opening doors, and cooking. Using a room model, the changes in attachment rates, average attachment diameters, and deposition rates of the unattached fraction with and without the air cleaning system were calculated. In the presence of active aerosol sources, the air filtration unit typically reduced the concentration of particles within the hour following the end of particle generation. After candle burning, cigarette smoking, and vacuuming in the bedroom, the reductions of PAEC by air filtration are about 60% with the air filtration system operating in the bedroom. During cooking in the kitchen, the reductions of PAEC in the bedroom with the air filtration system were about 40%. However, for all cases the dose reductions were smaller than the particle and PAEC reductions. For those particles that were generated within the bedroom, there was a 20% to 50% reduction in dose. In the case of cooking where the door was open and particles infiltrated from the rest of the house, the dose reduction was only 5% on average and appears to be insignificant. Thus, the dose reductions were h e r than the reductions in activity concentration, but there were no cases where the estimated dose actually increased. 相似文献
23.
李智慧 《石油化工安全环保技术》2003,19(4):44-46,22
对催柴加氢装置分馏系统空冷存在的问题进行了剖析,认为两塔回流温度不能同时满足工艺需要的主要原因是2台空冷共用风机造成的,并对改造方案进行了比较。 相似文献
24.
户式中央空调发展方向的探讨 总被引:2,自引:1,他引:1
本文描述了我国户式中央空调的发展现状,分析了三种户式中央空调各自的特点,提出了把风管式机组作为我国户式中央空调的发展方向。 相似文献
25.
通过几个典型事例的分析、判断和处理,介绍了该厂怎样利用91l型数采器对2D12—100/8型空压机运行状态进行监测,以预报早期故障,为设备检修提供指导. 相似文献
26.
《Drying Technology》2007,25(5):831-839
Residence time distributions for an aqueous solution of 10% sodium chloride in a spouted bed dryer of inert particles were determined using the stimulus-response technique. Glass and polyethylene beads with diameters 2.6 and 3.4 mm were used as inert bodies in a cylindrical column of 14.0 cm diameter and 60° conical base. The effects of inert bodies load, air, and paste flow rates on the mean residence times and RTD were determined following 23 factorial designs. The RTD could be correlated to the perfect mixing cell model with R2 varying from 0.8684 to 0.9815. The mean residence times in CSBD varied from 10.8 to 13.9 and 10.7 to 13.3 min for glass and polyethylene beads, respectively. For both inert particles, mean residence times increased with bed height and decreased with paste feed rates. Also, terms of interaction among the factors were significant in some cases, showing a complex behavior of paste residence times. Equations obtained by response surface regression could predict mean residence times on glass and polyethylene beads with deviations lower than ±10%. 相似文献
27.
28.
The medium coking coal fines of − 0.5 mm from Jharia coal field were taken for this investigation. The release analysis of the composite coal reveals that yield is very low at 10.0% ash, about 25% at 14% ash and 50% at 17% ash level. The low yield is caused by the presence of high ash finer fraction. The size-wise ash analysis of − 0.5 mm coal indicated that − 0.5 + 0.15 mm fraction contains less ash than − 0.15 mm fraction. Thus, the composite feed was split into − 0.5 + 0.15 mm and − 0.15 mm fractions and subjected to flotation separately. The low ash bearing fraction (− 0.5 + 0.15 mm) was subjected to two stages collectorless flotation to achieve the concentrate with 10% ash. The cleaner concentrate (18.9%) with 10% ash was recovered which has an application in metallurgical industries. The concentrate of 30.2% yield with 12.5% ash could be achieved in one stage collectorless flotation which is suitable for use in coke making as sweetener. As the − 0.15 mm fraction contains relatively high ash, collector aided flotation using sodium silicate was performed to get a concentrate of 23.6% yield with about 17% ash. The blending of this product with cleaner tail obtained from − 0.5 + 0.15 mm produces about 35.0% yield with 17% ash and that can be utilized for coke making. The reject from the two fractions can be used for conventional thermal power plant or cement industries using a 23.5% ash after one stage collector aided flotation and the final tailings produced content ash of 61.6% can be used for fluidization combustion bed (FBC). This eventually leads to complete utilization of coal. 相似文献
29.
30.
关于空调水系统节能的探讨 总被引:6,自引:0,他引:6
以空调冷冻水系统的节能为例 ,探讨空调系统节能的途径、存在的问题及解决办法 相似文献