全文获取类型
收费全文 | 17997篇 |
免费 | 1333篇 |
国内免费 | 1568篇 |
专业分类
电工技术 | 1350篇 |
综合类 | 1135篇 |
化学工业 | 6086篇 |
金属工艺 | 563篇 |
机械仪表 | 756篇 |
建筑科学 | 1072篇 |
矿业工程 | 539篇 |
能源动力 | 1649篇 |
轻工业 | 591篇 |
水利工程 | 524篇 |
石油天然气 | 1446篇 |
武器工业 | 296篇 |
无线电 | 211篇 |
一般工业技术 | 892篇 |
冶金工业 | 381篇 |
原子能技术 | 3002篇 |
自动化技术 | 405篇 |
出版年
2024年 | 38篇 |
2023年 | 169篇 |
2022年 | 397篇 |
2021年 | 485篇 |
2020年 | 488篇 |
2019年 | 494篇 |
2018年 | 476篇 |
2017年 | 589篇 |
2016年 | 673篇 |
2015年 | 572篇 |
2014年 | 1023篇 |
2013年 | 1642篇 |
2012年 | 1023篇 |
2011年 | 1278篇 |
2010年 | 973篇 |
2009年 | 1052篇 |
2008年 | 916篇 |
2007年 | 1076篇 |
2006年 | 968篇 |
2005年 | 939篇 |
2004年 | 772篇 |
2003年 | 747篇 |
2002年 | 663篇 |
2001年 | 587篇 |
2000年 | 441篇 |
1999年 | 424篇 |
1998年 | 313篇 |
1997年 | 253篇 |
1996年 | 207篇 |
1995年 | 227篇 |
1994年 | 175篇 |
1993年 | 153篇 |
1992年 | 105篇 |
1991年 | 122篇 |
1990年 | 96篇 |
1989年 | 77篇 |
1988年 | 44篇 |
1987年 | 66篇 |
1986年 | 32篇 |
1985年 | 31篇 |
1984年 | 19篇 |
1983年 | 9篇 |
1982年 | 7篇 |
1981年 | 6篇 |
1980年 | 5篇 |
1979年 | 2篇 |
1978年 | 1篇 |
1975年 | 1篇 |
1959年 | 33篇 |
1951年 | 9篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
51.
Stephan Boden Martina Bieberle Uwe Hampel 《Chemical engineering journal (Lausanne, Switzerland : 1996)》2008,139(2):351-362
Cone-beam type X-ray computed tomography (CBCT) is a potential method to measure three-dimensional phase distributions in vessels. An example for that is the measurement of gas profiles in stirred chemical reactors. Such data are highly valuable for the assessment and evaluation of chemical processes, for optimisation of the reactor and stirrer design, and for evaluation of computational fluid dynamics codes used to model the fluid flow and heat transfer in reactive systems. However, there are considerable difficulties for accurate quantitative measurements due to beam hardening and radiation scattering effects. In a theoretical and experimental work we have investigated the non-linear effects of both physical phenomena and developed a suitable measurement setup as well as calibration and software correction methods to achieve a highly accurate measurement of void fraction profiles with CBCT. 相似文献
52.
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
53.
乙烯裂解炉内传递和反应过程综合数值模拟Ⅱ.反应管内传递和反应过程的数值模拟 总被引:4,自引:0,他引:4
采用乙烯裂解炉传递反应过程综合数学模型中的反应管数学模型,对工业裂解炉反应管进行了系统的数值模拟,得到了反应管内流场、温度场和浓度场的详细信息,揭示了反应管内流动、传热、传质和裂解反应的基本特点。模拟结果表明,沿反应管轴向油气吸热升温,裂解反应加剧,产物产率逐渐发生变化;沿反应管径向存在明显的流体流速和温度的变化,而产物产率的变化不如流体流速和温度的变化明显。通过比较湍流粘度和分子粘度的大小,认为29.975~30mm的径向区域为层流层,层流层的存在使得临近管壁的区域内流体流速和温度变化显著。 相似文献
54.
Adaptation of the microscopic properties of redox catalysts to the type of gas-solid reactor 总被引:1,自引:0,他引:1
Catalysts of selective oxidation usually work in a simultaneous redox mode in reactant/air cofed reactors. The solid must provide selective lattice oxygen according to a kinetic mechanism depending on operating conditions that differ from one reactor to another. Better catalytic performance can be obtained in a recirculating solids reactor because it allows separate optimization of the reduction and oxidation steps. Among the microscopic properties of the catalyst, the crystal morphology is to be taken into account because it influences its reactivity on stream. These considerations lead to a new approach of the catalyst-reaction-reactor trio. 相似文献
55.
本文主要完成了液态金属钠高温沸腾实验回路的应力分析与计算,确定了回路高温区连接管系的布置型式和支吊架系统,是该回路总体设计的重要组成部分。 相似文献
56.
57.
58.
Optimal Conditions for Preparing Ultra-Fine CeO2 Powders in A Submerged Circulative Impinging Stream Reactor 总被引:1,自引:0,他引:1
Cerium carbonate powders were produced in a submerged circulation impinging stream reactor (SCISR) from Ce(NO3)3·6H2O. NH4HCO3 was used as a precipitant in the reaction. Cerium carbonate powders were roasted to produce ultra-fine cerium dioxide (CeO2) powders. The optimal conditions of such production process were obtained by orthogonal and one-factor experiments. The results showed that ultra-fine and narrowly distributed cerium carbonate powders were produced under the optimal flowing conditions. The concentrations of Ce(NO3)3 and NH4HCO3 solutions were 0.25 and 0.3 mol·L-1, respectively. The concentration of PEG4000 added in these two solutions was 4 g·L-1. The stirring ratio, reaction temperature, feeding time, solution pH, reaction time and digestion time were 900 r·min-1, 80 ℃, 20 min, 5~6, 5 min and 1 h, respectively. The final product, CeO2 powders, was obtained by roasting the produced cerium carbonate in air for 3 h at 500 ℃. The finally produced CeO2 powders were torispherical particles with a narrow size distribution of 0.8~2.5 μm. The crystal structure of CeO2 powders belonged to cubic crystal system and its space point group was O5H-FM3M. Under optimal conditions, powders produced by SCISR were finer and more narrowly distributed than that by Stirred Tank Reactor (STR). 相似文献
59.
Athanasios Eftaxias Josep Font Agusti Fortuny Azael Fabregat Frank Stüber 《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》2005,80(6):677-687
The wet air oxidation of phenol over a commercial active carbon catalyst was studied in a trickle bed reactor (TBR) in the temperature and oxygen partial pressure ranges of 120–160 °C and 0.1–0.2 MPa, respectively. The performance of the active carbon was compared in terms of phenol and COD destruction. The weight change of active carbon due to reaction was also measured. Finally, oxic phenol adsorption isotherms were assessed in batch conditions at 25, 125 and 160 °C. In order to use the conversion data obtained from the TBR for a kinetic study, special care was taken to check the kinetic control in the TBR experiments. Several kinetic models including power law or Langmuir–Hinshelwood expressions were considered to describe the catalytic oxidation of phenol over active carbon. The simple power law model with first order dependence on both phenol and oxygen concentration predicted satisfactorily the experimental data not only over the entire range of operating conditions studied, but also outside its validity range. Copyright © 2005 Society of Chemical Industry 相似文献
60.