全文获取类型
收费全文 | 60920篇 |
免费 | 6310篇 |
国内免费 | 1817篇 |
专业分类
电工技术 | 6367篇 |
综合类 | 4507篇 |
化学工业 | 10404篇 |
金属工艺 | 5774篇 |
机械仪表 | 2762篇 |
建筑科学 | 6061篇 |
矿业工程 | 1321篇 |
能源动力 | 11245篇 |
轻工业 | 2648篇 |
水利工程 | 509篇 |
石油天然气 | 2414篇 |
武器工业 | 326篇 |
无线电 | 1233篇 |
一般工业技术 | 5776篇 |
冶金工业 | 5459篇 |
原子能技术 | 1045篇 |
自动化技术 | 1196篇 |
出版年
2024年 | 225篇 |
2023年 | 725篇 |
2022年 | 1497篇 |
2021年 | 1681篇 |
2020年 | 1811篇 |
2019年 | 1373篇 |
2018年 | 1252篇 |
2017年 | 1494篇 |
2016年 | 1823篇 |
2015年 | 1882篇 |
2014年 | 3657篇 |
2013年 | 3457篇 |
2012年 | 4261篇 |
2011年 | 4546篇 |
2010年 | 3377篇 |
2009年 | 3548篇 |
2008年 | 2759篇 |
2007年 | 4080篇 |
2006年 | 3702篇 |
2005年 | 3321篇 |
2004年 | 2921篇 |
2003年 | 2602篇 |
2002年 | 2373篇 |
2001年 | 2058篇 |
2000年 | 1687篇 |
1999年 | 1355篇 |
1998年 | 1010篇 |
1997年 | 924篇 |
1996年 | 724篇 |
1995年 | 600篇 |
1994年 | 482篇 |
1993年 | 381篇 |
1992年 | 330篇 |
1991年 | 211篇 |
1990年 | 171篇 |
1989年 | 175篇 |
1988年 | 114篇 |
1987年 | 77篇 |
1986年 | 62篇 |
1985年 | 45篇 |
1984年 | 69篇 |
1983年 | 54篇 |
1982年 | 54篇 |
1981年 | 17篇 |
1980年 | 12篇 |
1979年 | 5篇 |
1978年 | 3篇 |
1977年 | 3篇 |
1959年 | 28篇 |
1951年 | 22篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
81.
油井热洗是油田最常用的一种清蜡方法。靖安长6油藏是采油三厂的主力油藏,截至2004年底建成油井1064口,由于长6层原油含蜡量高,油井结蜡严重,通常采用常规热洗方法进行油井清蜡。存在以下两方面问题:一是常规油井热洗方法操作比较复杂,运行动力设施多,热洗费用较高;二是常规洗井油源均来自联合站或接转站,为不同层所采的混合原油,进入地层后,会对地层造成一定程度的伤害。为此,我们认真分析了现有油井热洗工艺的不足,查找了油井热洗费用高的影响因素,结合靖安油田长6油藏丰富的伴生气资源,自主研发了撬装式油井热洗装置,经过现场应用取得了较好的效果。 相似文献
82.
83.
The strength of agglomerates of nickel flash furnace concentrate and dust was determined from experimental observations of agglomerates forming under controlled conditions, combined with mathematical equations from the literature. It was found that the agglomerates had a tensile strength ranging from 0.01 Pa to 38.7 Pa, while inter-particle forces ranged from 2.2 × 10− 12 N to 1.5 × 10− 10 N. These values were compared to the expected magnitude of van der Waals, electrostatic, magnetic and capillary forces within the agglomerates, and it was found that both electrostatic and van der Waals forces are likely to contribute to the cohesion of agglomerates, although sub-micron particles and the presence of sufficiently large asperities on the surface of particles limit the magnitude of van der Waals forces. Magnetic forces are large enough to contribute to the cohesion of dust agglomerates, which is in keeping with the high magnetite content of the recycle dust. It is postulated that electrostatic forces, acting over a longer range than van der Waals forces, may be responsible for initially bringing particles together. The methodology for determining inter-particle forces can be applied to the computer modelling of flash smelting systems, as well as other gas/particle systems such as fluidized beds. 相似文献
84.
This article presents results from a numerical study of pulsating jet impingement heat transfer. The motivation is to seek conditions offering a significant enhancement compared to steady flow impingement drying. The CFD software package FLUENT was used for simulating slot-type pulsating jet impingement flows with confinement. The parameter study included velocity amplitude ratio, mean jet velocity, and pulsation frequency. The distance from nozzle exit to surface was three times the hydraulic diameter of the nozzle. The Reynolds number based on the nozzle hydraulic diameter and jet temperature was 2,460 with a mean jet velocity of 30 m/s, which is the base case of the numerical experiments. Results showed that time-averaged surface heat transfer increased with increasing velocity amplitude for the same mean jet velocity. Large velocity amplitudes helped enhance heat transfer by two mechanisms: high jet velocity during the positive cycle and strong recirculating flows during the negative cycle. For the cases with different mean jet velocities but the same maximum velocity, time-averaged surface heat flux decreased with decreasing mean jet velocity. As for the effects of pulsation frequency, with high-velocity amplitude ratio, time-averaged surface heat fluxes were at the same level regardless of frequency. However, at low-velocity amplitude ratio, high frequency caused stronger recirculating flows resulting in greater heat transfer compared to the cases with a lower frequency. 相似文献
85.
This paper documents the first of the two interrelated studies that were conducted to more fundamentally understand the scalability of flame heat flux, the motivation being that it has been reported that flame heat flux back to the burning surface in bench‐scale experiments is not the same as for large‐scale fires. The key aspect was the use of real scale applied heat flux up to 200kW/m2 which is well beyond that typically considered in contemporary testing. The main conclusions are that decomposition kinetics needs to be included in the study of ignition and the energy balance for steady burning is too simplistic to represent the physics occurring. An unexpected non‐linear trend is observed in the typical plotting methods currently used in fire protection engineering for ignition and mass loss flux data for several materials tested and this non‐linearity is a true material response. Using measured temperature profiles in the condensed phase shows that viewing ignition as an inert material process is inaccurate at predicting the surface temperature at higher heat fluxes. The steady burning temperature profiles appear to be invariant with applied heat flux. This possible inaccuracy was investigated by obtaining the heat of gasification via the ‘typical technique’ using the mass loss flux data and comparing it to the commonly considered ‘fundamental’ value obtained from differential scanning calorimetry measurements. This comparison suggests that the ‘typical technique’ energy balance is too simplified to represent the physics occurring for any range of applied heat flux. Observed bubbling and melting phenomena provide a possible direction of study. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献
86.
热泵热水机组是一种新型热水和供暖产品,它可以从空气、水等环境中吸取能量,热效率高,被公为是传统锅炉、电热水器及燃油(气)热水机组的更新换代环保型产品。详细阐述了以ADμC834芯片为核心的热泵热水机组控制器软硬件系统设计。论述了多路温度数据与压力数据采集、液晶显示等模块的硬件组成及各个模块的工作原理。控制器的软件系统采用前后台架构,用QuickStart平台开发完成。其人机界面系统由按键阵列和TG2401286V2型液晶显示屏组成。 相似文献
87.
The effect of hydrogen heat treatment on impurity contents in aluminum nitride powder of different fineness is studied. Thermodynamic calculations are provided pointing to the possibility of forming gaseous hydrogen compounds with impurity elements. It is established that as a result of treatment the contents of impurity elements, i.e. oxygen, carbon, sulfur, are reduced by a factor of 3-13. The optimum hydrogen heat treatment regime is determined: a temperature of 1323 K and an exposure time of 30 min. 相似文献
88.
地方热电联产企业发展对策的探讨 总被引:2,自引:2,他引:0
介绍了泰州热电企业的运行情况,分析了各热电厂在技术改造、扩大热用户和强化内部考核管理方面的措施,探讨了地方热电企业应采取的对策和发展思路。 相似文献
89.
In this work, we co‐formulated an oil‐borne copper naphthenate/permethrin wood preservative system with synthetic polymer‐based fire‐retardant additives prior to the impregnation of Pinus radiata sapwood. We evaluated what effect, if any, the preservative had upon the fire performance properties of the fire retardants and whether the fire retardants impacted on the fungicidal and termiticidal efficacy of the preservative. The fire retardants included halogenated and phosphorus‐based systems. A mass loss calorimeter, in conjunction with a thermopile, was used to measure the time to ignition and the peak heat release rate (PHRR) from which the fire performance index (FPI) was determined. The preservative properties were evaluated using termite and soil‐block decay bioassays. In summary, we found that the rate of fire growth was reduced when the fire retardants were used in combination with the wood preservative. We also found that the PHRR was a better determinant of fire performance than the FPI. The performance of the wood preservative was enhanced against fungal decay and termite attack when used in combination with the fire retardants. The fire retardants also demonstrated some wood preservative properties of their own. Copyright © 2008 John Wiley & Sons, Ltd. 相似文献
90.
讨论人体新陈代谢发热率及其影响因素;论述节能建筑中舒适的环境温度、空气相对湿度、空气流速以及新鲜空气供给量的最佳值范围;同时考虑皮肤和肺部的显热散热和蒸发潜热散热,建立了传热模型,得出了计算公式。 相似文献