首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   56457篇
  免费   5998篇
  国内免费   2551篇
电工技术   6317篇
综合类   5806篇
化学工业   5621篇
金属工艺   1605篇
机械仪表   3044篇
建筑科学   3276篇
矿业工程   1346篇
能源动力   1587篇
轻工业   2678篇
水利工程   1160篇
石油天然气   2182篇
武器工业   765篇
无线电   7770篇
一般工业技术   5582篇
冶金工业   1946篇
原子能技术   865篇
自动化技术   13456篇
  2025年   394篇
  2024年   1095篇
  2023年   1083篇
  2022年   1495篇
  2021年   1709篇
  2020年   2104篇
  2019年   1946篇
  2018年   1695篇
  2017年   2134篇
  2016年   2369篇
  2015年   2412篇
  2014年   3220篇
  2013年   3758篇
  2012年   3845篇
  2011年   3965篇
  2010年   2877篇
  2009年   2991篇
  2008年   2838篇
  2007年   3339篇
  2006年   3103篇
  2005年   2549篇
  2004年   2138篇
  2003年   1998篇
  2002年   1666篇
  2001年   1466篇
  2000年   1248篇
  1999年   948篇
  1998年   754篇
  1997年   670篇
  1996年   537篇
  1995年   454篇
  1994年   386篇
  1993年   324篇
  1992年   235篇
  1991年   219篇
  1990年   159篇
  1989年   138篇
  1988年   105篇
  1987年   99篇
  1986年   72篇
  1985年   75篇
  1984年   57篇
  1983年   41篇
  1982年   44篇
  1981年   34篇
  1980年   33篇
  1979年   25篇
  1978年   17篇
  1964年   13篇
  1956年   12篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
1.
In this work it is presented a study on the residence time distribution (RTD) of particles in a co-current pilot-plant spray dryer operated with a rotary atomization system. A nuclear technique is applied to investigate the RTD responses of spray dryers. The methodology is based on the injection of a radioisotope tracer in the feed stream followed by the monitoring of its concentration at the outlet stream. The experiments were performed during the drying of aqueous suspensions of gadolinium oxide. The RTD responses obtained experimentally presented good reproducibility, indicating that the technique applied is well suited to investigating fluid-dynamics of spray dryers. In addition to the experimental investigation, a mathematical model was used to describe the RTD experimental curves.  相似文献   
2.
In the present study of gas–liquid contactors, mean residence/contact time was calculated from knowledge of superficial velocity and the gas phase hold-up, for various gas rates and impeller geometry and speeds, and compared with values obtained from RTD measurements. A new correlation, involving Flow Number, Froude Number, system geometry and the physical properties, is proposed. This uses the authors data and those available in literature.  相似文献   
3.
《IIE Transactions》2007,39(9):879-898
We study an inventory system that consists of two demand classes. The orders in the first class need to be satisfied immediately, whereas the orders in the second class are to be filled in a given demand lead time. The two classes are also of different criticality. For this system, we propose a policy that rations the non-critical orders. Under a one-for-one replenishment policy with backordering and for Poisson demand arrivals for both classes, we first derive expressions for the service levels of both classes. The service level for the critical class is an approximation, whereas the service level for the non-critical class is exact. We then conduct a computational study to show that our approximation works reasonably, the benefits of rationing can be substantial, and the incorporation of demand lead time provides more value when the demand class with demand lead time is the critical class. The research is motivated by the spare parts service system of a major capital equipment manufacturer that faces two types of demand. For this company, the critical down orders need to be satisfied immediately, while the less critical maintenance orders can be satisfied after a fixed demand lead time. We conduct a case study with 64 representative parts and show that significant savings (as much as 14% on inventory on hand) are possible through incorporation of demand lead times and rationing.  相似文献   
4.
This article presents experimental results for spouted bed drying of sawdust, carried out in a full-scale as well as in a laboratory-scale dryer using air as well as steam as drying media. The aim is to present design parameters for a spouted-bed sawdust dryer that can be used by the industry in designing full-scale dryers. A hydrodynamically stable spouted jet spouted bed was obtained. The heat transfer characteristics of the bed were represented in terms of a volumetric heat transfer coefficient (VHC). When sawdust is dried in a spouted bed, the mean VHC is increasing up to fiber saturation level (20-25% wb) from 40 to 110 W/m3 K. The VHC decreases with the residence time and with an increased static bed height. Gas temperature profiles are also presented for the bottom part of the drying chamber.  相似文献   
5.
6.
With a view to evaluate the effects of hydraulic retention time and volatile solids loading rate on methane production using water hyacinth, experiments were conducted in a 160 dm3 capacity, well-mixed continuous digestion unit at ambient temperature. The optimal design of biogas plant using water hyacinth was elucidated, to provide a unit giving a maximum methane yield of 0.16 nm3 kg?1 volatile solids added, which was 60% greater than the conventional plant using cowdung. The calculations of optimal design factors were based on reactor size, hydraulic retention time and volatile solids loading rate; considerations were made of capital cost, running costs and operational revenue.  相似文献   
7.
8.
Hydrolysis of Fe(OH)SO4 was carried out in the presence of metallic iron in order to prevent the formation of iron(III) oxides with strongly bonded sulphate. Under the conditions of the experiment, the products were found to be mixtures of ?-Fe2O3 and α-FeOOH. The occluded sulphate, if any, could be easily washed out with water. The hydrolysis reaction passes through an equilibrium state before coming to completion. The entropy with enthalpy of the hydrolysis corresponding to the equilibrium state were found to be 4 e.u. and 0·5 kJ/mol, respectively. The activation energy of the hydrolysis reaction was found to be 21 kJ/mol.  相似文献   
9.
10.
Equipment was developed to measure the time for complete gelling of sodium alginate fibres in calcium chloride solution, taken as the time to achieve maximum tensile strength. The effects of fibre diameter, alginate concentration, alginate composition and calcium chloride concentration on gelling time were investigated. A diffusional model, developed to predict the gelling time, agreed with experimental results except for the effect of calcium ion concentration which was modelled empirically.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号