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   80251篇
  免费   7900篇
  国内免费   4855篇
电工技术   5103篇
技术理论   4篇
综合类   9022篇
化学工业   9301篇
金属工艺   2256篇
机械仪表   3260篇
建筑科学   20696篇
矿业工程   4438篇
能源动力   3915篇
轻工业   5356篇
水利工程   5409篇
石油天然气   3046篇
武器工业   690篇
无线电   3545篇
一般工业技术   7149篇
冶金工业   4090篇
原子能技术   670篇
自动化技术   5056篇
  2024年   763篇
  2023年   1216篇
  2022年   1970篇
  2021年   2499篇
  2020年   2417篇
  2019年   1965篇
  2018年   1769篇
  2017年   2229篇
  2016年   2366篇
  2015年   2535篇
  2014年   4779篇
  2013年   4386篇
  2012年   5476篇
  2011年   5846篇
  2010年   4512篇
  2009年   4809篇
  2008年   4317篇
  2007年   5692篇
  2006年   5241篇
  2005年   4804篇
  2004年   4054篇
  2003年   3574篇
  2002年   2999篇
  2001年   2374篇
  2000年   1998篇
  1999年   1592篇
  1998年   1197篇
  1997年   991篇
  1996年   807篇
  1995年   746篇
  1994年   562篇
  1993年   432篇
  1992年   357篇
  1991年   261篇
  1990年   243篇
  1989年   211篇
  1988年   168篇
  1987年   140篇
  1986年   102篇
  1985年   82篇
  1984年   92篇
  1983年   49篇
  1982年   42篇
  1981年   48篇
  1980年   41篇
  1979年   68篇
  1978年   19篇
  1976年   21篇
  1975年   22篇
  1974年   19篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
11.
《Drying Technology》2007,25(12):1949-1958
A mathematical model for through drying of paper at constant pressure drop was developed. The model is based on physical properties; hence, basis weight, pressure drop, drying air temperature, pore size distribution, initial gas fraction, and tortuosity are important input parameters to the model. The model was solved for different combinations of the variables basis weight, drying air temperature, and pressure drop corresponding to industrial conditions and the results were compared with data from bench-scale experiments. The simulations show that the drying rate curve is very sensitive to the air flow rate and that correctly modeling the correlation between pressure drop and air flow rate is the most important factor for a successful model for through drying. The model was tuned by adjusting the parameters initial gas fraction and tortuosity in order to give the best possible fit to experimental data. For a given basis weight and pressure drop, different drying air temperatures resulted in relatively constant values of the fitted parameters. This means that the model can well predict the effects of changes in drying air temperature based on a tuning of the model performed at the same basis weight and pressure drop. However, for a given basis weight, an increase in pressure drop yielded fitted parameters that were somewhat different; i.e., a lower initial gas fraction and a higher tortuosity, a change that increases the resistance to air flow. This implies that the correlation between pressure drop and air flow rate in the model does not quite capture the nonlinear relationship shown by the experiments.  相似文献   
12.
Jerzy   WIGO&#x 《Drying Technology》1996,14(2):271-288
Typical methods of dehumidification of air circulating in the dehumidifying driers (indirect and direct cooler and partial exchange of the air) were analysed. Energy aspect of cooler operation was evaluated. The method for minimization of unit thermal energy consumption in a dehumidifying drier by the optimal selection of the cooler point was also given. Methods of the heat recovery of heat conveyed in a cooler lending to save energy (heat regeneration. expansion and compression of the air, a dehumidifier) were analysed. It was indicated that introduction of dehumidifiers into contemporary wood driers caused significant improvement of energy aspects of their operation  相似文献   
13.
Phase separation during polymerization was studied in a model system consisting of a diepoxide based on diglycidyl ether of bisphenol A (DGEBA), variable amounts of ethylenediamine (EDA) and the mass of castor oil (CO) necessary to obtain a mass fraction equal to 0-15 in a final system where the stoichiometric ratio of amine to epoxy equivalents, r, was equal to 1. A two-step polymerization process was performed by curing first a system with r = 0-5, during variable times before phase separation, and then carrying the system to r = 1. Thermodynamic analysis of samples with different r values led to a linear relationship between the Flory-Huggins interaction parameter and r. The concentration (P) and average size (D?) of dispersed-phase particles followed opposite trends, i.e. P increased while D? decreased, when either r was increased or the time of curing in the first step of a two-step process was decreased. This was explained by assuming that the competition between nucleation and growth was determined by the viscosity at the cloud point, ηcp. Low values of ηcp favoured growth over nucleation and led to fewer but larger particles.  相似文献   
14.
Experimental tests showed that poststrike elevation in tongue-flicking rate (PETF) and strike-induced chemosensory searching (SICS) in the gila monster last longer than reported for any other lizard. Based on analysis of numbers of tongue-flicks emitted in 5-min intervals, significant PETF was detected in all intervals up to and including minutes 41–45. Using 10-min intervals, PETF lasted though minutes 46–55. Two of eight individuals continued tongue-flicking throughout the 60 min after biting prey, whereas all individuals ceased tongue-flicking in a control condition after minute 35. The apparent presence of PETF lasting at least an hour in some individuals suggests that there may be important individual differences in duration of PETF. PETF and/or SICS are present in all families of autarchoglossan lizards studied except Cordylidae, the only family lacking linguallly mediated prey chemical discrimination. However, its duration is known to be greater than 2-min only in Helodermatidae and Varanidae, the living representatives of Varanoidea. That prolonged PETF and SICS are typical of snakes provides another character supporting a possible a varanoid ancestry for Serpentes. Analysis of 1-min intervals showed that PETF occurred in the first minute. A review of the literature suggests that a pause in tongue-flicking and delay of searching movements are absent in lizards and the few nonvenomous colubrid snakes tested. The delayed onset of SICS may be a specific adaptation of some viperid snakes to allow potentially dangerous prey to be rendered harmless by venom following voluntary release after envenomation and preceding further physical contact with the prey.  相似文献   
15.
Book Review     
《Expert Systems》2002,19(1):53-55
  相似文献   
16.
本文采用粒子追踪理论对水平管中粒子流动状态进行了数值模拟.文中提出了一种新的粒子碰撞模型,并忽略粒子的旋转和扬力,仅考虑气流阻力和重力对粒子的影响,在输送量为9.13×10~3kg/s,混合比约0.3的条件下,通过数值计算得知:由于粒子间的碰撞,使得异径粒子的速度趋向平均化;粒子间的碰撞是粒子悬浮的原因之一;粒子的浓度沿管轴向是随时间而发生变化的.  相似文献   
17.
Provides the biography of Dante Cicchetti and announces that he has received the APA Award for Distinguished Senior Career Contributions to Psychology in the Public Interest (2004) for his seminal role in bridging theory, research, and practice by fostering the emergence and coalescence of the field of developmental psychopathology. A selected bibliography is also provided. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
18.
介绍首钢2号高炉大修采用的新技术、开炉操作和投产以来的生产情况。  相似文献   
19.
空气压缩机无油润滑在山脚树矿的应用   总被引:1,自引:1,他引:0  
山脚树矿有5台1966年上海生产的4L—20/8空气压缩机,运行很不经济,利用聚四氟乙烯合成材料制成活塞环,全部实现无油润滑运转,取得了良好的经济效益。  相似文献   
20.
对职业教育的大众性问题进行了论述、实证分析和理论、政策、改革等思考。  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