全文获取类型
收费全文 | 1853篇 |
免费 | 192篇 |
国内免费 | 74篇 |
专业分类
电工技术 | 27篇 |
综合类 | 103篇 |
化学工业 | 1104篇 |
金属工艺 | 19篇 |
机械仪表 | 30篇 |
建筑科学 | 100篇 |
矿业工程 | 60篇 |
能源动力 | 130篇 |
轻工业 | 45篇 |
水利工程 | 21篇 |
石油天然气 | 121篇 |
武器工业 | 8篇 |
无线电 | 66篇 |
一般工业技术 | 108篇 |
冶金工业 | 115篇 |
原子能技术 | 19篇 |
自动化技术 | 43篇 |
出版年
2024年 | 1篇 |
2023年 | 29篇 |
2022年 | 33篇 |
2021年 | 29篇 |
2020年 | 37篇 |
2019年 | 46篇 |
2018年 | 37篇 |
2017年 | 35篇 |
2016年 | 50篇 |
2015年 | 56篇 |
2014年 | 67篇 |
2013年 | 101篇 |
2012年 | 98篇 |
2011年 | 119篇 |
2010年 | 109篇 |
2009年 | 97篇 |
2008年 | 96篇 |
2007年 | 116篇 |
2006年 | 111篇 |
2005年 | 113篇 |
2004年 | 97篇 |
2003年 | 77篇 |
2002年 | 78篇 |
2001年 | 68篇 |
2000年 | 60篇 |
1999年 | 55篇 |
1998年 | 51篇 |
1997年 | 41篇 |
1996年 | 35篇 |
1995年 | 23篇 |
1994年 | 23篇 |
1993年 | 21篇 |
1992年 | 20篇 |
1991年 | 11篇 |
1990年 | 12篇 |
1989年 | 15篇 |
1988年 | 14篇 |
1987年 | 15篇 |
1986年 | 3篇 |
1985年 | 8篇 |
1984年 | 5篇 |
1983年 | 2篇 |
1982年 | 1篇 |
1980年 | 1篇 |
1959年 | 1篇 |
1951年 | 2篇 |
排序方式: 共有2119条查询结果,搜索用时 15 毫秒
1.
2.
The methanol‐to‐olefins reaction (MTO) was studied in a small‐scale fluidized‐bed reactor over synthesized silicoaluminophosphate (SAPO‐34) catalysts. Mesoporous nanocrystalline SAPO‐34 molecular sieves were synthesized hydrothermally by ultrasonic and microwave‐assisted aging processes in the presence of hexadecyltrimethylammonium bromide (CTAB) and tetradecyldimethyl(3‐trimethoxysilylpropyl)ammonium chloride (TPOAC) as surfactant agents. The Box‐Behnken experimental design method was applied to determine the optimum operating parameters of this process conducted in the fluidized‐bed reactor. The optimum conditions in terms of reaction temperature, ratio of inlet gas velocity to minimum fluidizing velocity, and MeOH weight fraction were evaluated. 相似文献
3.
A hybrid fluidized-bed bioreactor for water purification was proposed and analyzed. It is a novel type of bioreactor characterized by hitherto unknown stationary and dynamic features. Steady-state characteristics of this hybrid bioreactor with external liquid circulation are presented. A quantitative analysis of steady-state properties of the bioreactor was performed with the aid of an original mathematical model developed for a double-substrate aerobic microbiological process. A steady-state analysis of aerobic processes characterized by different oxygen demand was performed. The effect of essential parameters was evaluated, including carbonaceous substrate concentration in the feed stream to the apparatus, aeration intensity, total residence time of a liquid in the bioreactor, and height of the bed of fine carrier particles. 相似文献
4.
Fluctuations and waves in fluidized bed systems: The influence of the air-supply system 总被引:1,自引:0,他引:1
Srdjan Sasic 《Powder Technology》2005,153(3):176-195
A general model of the response of a fluidized bed to disturbances is formulated, and the information provided by the model with respect to the dynamics of the bed, the bed plus the air-plenum and the bed plus the entire air-supply system, is investigated. Expressions given in literature on the fundamental frequency of the bed-plenum system are analyzed, and it is shown that they are a special case of the general model. In order to simulate various types of interaction between the bed and the rest of the system, experiments were performed in a cold fluidized bed unit operated under both non-circulating and circulating conditions. At low velocity, three regimes were identified: the multiple bubble regime with almost no interaction between bed and air-plenum, the single bubble regime with the interaction between bed and air-plenum only, and a regime with numerous irregular bubbles, where the bed interacted with the entire air-supply system. At high fluidization velocity, the exploding bubble regime was identified, with the same dominant frequency as that of the single bubble regime (the interaction with the air-supply system remains at that frequency). The models investigated correctly reproduce the dynamics when the bed is independent of the other parts of the system, or when the bed interacts only with the air-plenum. However, the models are only partially applicable when the bed interacts with the entire air-supply system. The reasons for this are investigated. In the case of system interaction, pressure waves, generated in the bed, interact with pressure pulsations from the air-supply system. This results in a coupled system, which is not covered by the models. Pressure waves resulting from events in the bed, are recognized as the coherent part of the cross power spectra of pressure fluctuations measured in the bed and the air-plenum. 相似文献
5.
Yi‐Hung Chen Ching‐Yuan Chang Wei‐Ling Su Chun‐Yu Chiu Yue‐Hwa Yu Pen‐Chi Chiang Chiung‐Fen Chang Je‐Lueng Shie Chyow‐San Chiou Sally IM Chiang 《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》2005,80(1):68-75
This study investigates the ozonation of CI Reactive Black 5 (RB5) by using the rotating packed bed (RPB) and completely stirred tank reactor (CSTR) as ozone contactors. The RPB, which provides high gravitational force by adjusting the rotational speed, was employed as a novel ozone contactor. The same ozone dosage was separately introduced into either the RPB or the CSTR for the investigation, while the experimental solution was continuously circulated within the apparatus consisting of the RPB and CSTR. The decolorization and mineralization efficiencies of RB5 in the course of ozonation are compared for these two methods. Moreover, the dissolved and off‐gas ozone concentrations were simultaneously monitored for the further analysis. As a result, the ozone mass transfer rate per unit volume of the RPB was significantly higher because of its higher mass transfer coefficient and gas–liquid concentration driving force. Furthermore, ozonation kinetics was found to be independent of the gravitational magnitude of an ozone gas–liquid contactor. Therefore, the results suggest employing RPBs as ozone‐contacting devices with the advantage of volume reduction. The experimental results, which can be used for further modeling of the ozonation process in the RPB, also show the requirement of correct design for the RPB. Consequently, the present study is useful for the understanding of practical application of RPBs. Copyright © 2004 Society of Chemical Industry 相似文献
6.
7.
Pankaj Mathure Ashwin Patwardhan 《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》2005,80(4):413-419
In this study, the mass transfer efficiencies of a novel horizontal rotating packed (h‐RPB) bed and the conventional disc‐type rotating biological contactor (RBC) were studied at four speeds and seven submergences. Pall rings of two different sizes (25, 38 mm), superintalox saddles and a wiremesh spiral bundle were used as packings in the h‐RPB. Volumetric gas–liquid mass transfer coefficients were determined by unsteady state absorption of atmospheric oxygen in de‐aerated water. Power consumption per unit liquid volume has been found for all geometries tested. The oxygen transfer efficiency values for the h‐RPB were found to be 2–5 kg kWh?1 and for the disc RBC were found to be 1–2 kg kWh?1. The performance of the h‐RPB was also compared with other gas–liquid contactors such as surface aerators. The study proves that the h‐RPB is a energy efficient alternative to conventional contactors. Copyright © 2005 Society of Chemical Industry 相似文献
8.
9.
Bench-scale tests were conducted with raw and beneficiated shales in an advanced multi-purpose research reactor. Raw Alabama shale and raw and beneficiated Indiana shales were retorted at 515 °C using hydrogen pressures of 4 and 7 MPa. Shale feed rates were 15 to 34 kg h−1. High oil yields and carbon conversions were achieved in all tests. Oil yield from Alabama shale hydroretorted at 7 MPa was 200% of Fischer assay. Raw and beneficiated Indiana shales hydroretorted at 7 MPa produced oil yields of 170 and 195% of Fischer assay respectively. Total carbon conversions were >70% for all tests conducted at 7 MPa. 相似文献
10.
Different NMR techniques were combined to obtain the structure and velocity information for a systematic investigation of fixed beds with low aspect ratio (tube diameter to particle diamter, dt/dp) in the range 1.4 to 32. The structure of the void space was determined for a variety of packed beds of glass beads or regular and irregular porous pellets by magnetic resonance imaging (MRI). Based on the images the radial distribution of the voids within the bed was obtained. Ordering effects were found even for non‐spherical and polydisperse particles, and a maximum of the fluid density near the tube wall was confirmed for all pellet geometries and sizes. By combining MRI with velocity encoding, velocity profiles and distributions of flow velocity components of a single fluid phase through packed beds have been acquired. The radial velocity distribution follows an oscillatory pattern which largely reflects the ordering of the particles, which can be accessed from the density distribution of the interparticle fluid. Maximum velocities of up to four times the average value were found to occur near the tube wall. This wall effect was observed for all but the smallest particles, where the aspect ratio was dt/dp = 32. Moreover, a visualisation of flow pattern in the presence of packed particles was achieved by using a tagging technique, and the stationary flow field could be identified for an experimental time of several hours. 相似文献