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   329624篇
  免费   25502篇
  国内免费   13152篇
电工技术   19035篇
技术理论   53篇
综合类   29921篇
化学工业   45735篇
金属工艺   18836篇
机械仪表   16676篇
建筑科学   44832篇
矿业工程   18247篇
能源动力   10752篇
轻工业   27193篇
水利工程   13678篇
石油天然气   16688篇
武器工业   4192篇
无线电   22383篇
一般工业技术   23053篇
冶金工业   19033篇
原子能技术   2145篇
自动化技术   35826篇
  2024年   1366篇
  2023年   3962篇
  2022年   7924篇
  2021年   10257篇
  2020年   10039篇
  2019年   7208篇
  2018年   6817篇
  2017年   8750篇
  2016年   10341篇
  2015年   11286篇
  2014年   22445篇
  2013年   19011篇
  2012年   23732篇
  2011年   25865篇
  2010年   19490篇
  2009年   19989篇
  2008年   17831篇
  2007年   22106篇
  2006年   20382篇
  2005年   17697篇
  2004年   14951篇
  2003年   13239篇
  2002年   10781篇
  2001年   8881篇
  2000年   7282篇
  1999年   5707篇
  1998年   4007篇
  1997年   3394篇
  1996年   2767篇
  1995年   2327篇
  1994年   1875篇
  1993年   1340篇
  1992年   1102篇
  1991年   792篇
  1990年   641篇
  1989年   609篇
  1988年   347篇
  1987年   278篇
  1986年   242篇
  1985年   248篇
  1984年   192篇
  1983年   153篇
  1982年   84篇
  1981年   85篇
  1980年   98篇
  1979年   46篇
  1978年   26篇
  1977年   25篇
  1964年   25篇
  1959年   34篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
31.
The aim of this study was to design a modified atmosphere package for a mixed vegetable salad consisting of 75 g of cut carrot, 55 g of cut cucumber, 20 g of sliced garlic and 50 g of whole green pepper. Respiration data of all the components were combined with film permeability data to predict package atmospheres and design optimal packages for experimental testing for improved shelf-life of the produce. The optimal package avoided minimum O2 and maximum CO2 tolerance limits, and chilling injury temperatures for any component. A pouch form package made of 27 mm low density polyethylene developed a modified atmosphere of 2.0–2.1% O2 and 5.5–5.7% CO2, which was beneficial for all components and provided better quality retention than other test packages.  相似文献   
32.
This paper highlights the possibility of inverse gas chromatography for the surface characterization of common fillers (CaCO3, talc, SiO2,) for paints and coatings. Divided solids are described, on the one hand, by the dispersive component of their surface energy and, on the other, by a specific parameter indicating their acid-base interaction potential. The role of the surface morphology at a molecular level is also examined. It is demonstrated that steric effects play an important role in the adsorption of probes on lamellar solids like talc. The consequences of surface treatments as well as examples of practical applications are also reported.  相似文献   
33.
分析了目前公用交换电话网(PSTN)中存在的问题和下一代网络(NGN)的优越性,分析了NGN中的关键技术媒体网关控制技术,探讨了媒体网关控制技术在Alcatel5020MGC中的实际应用,讨论了Alcatel5020MGC的软硬件系统架构。最后强调了在PSTN向NGN发展过程中基于演进产品的方法的重要性。  相似文献   
34.
Vibro-fluidized beds are widely used in drying sticky powders and agglomerated materials as milk powder. Using a vibro-fluidized laboratory scale dryer, this work is aiming at analyzing preliminarily the effect of its operational variables on the drying kinetics and characteristics of whole milk powder. The full-factorial design technique with three replications at the central point has been employed to generate data and correlations to quantify the effect of inlet air temperature, air flow rate, and vibration bed amplitude on the drying curves and the milk powder properties related to its faster reconstitution in water (as tapped density, Hausner cohesion ratio, agglomerate size distribution, and internal pore concentration). Results obtained are analyzed and discussed to identify the adequate operation condition for final drying whole milk powder in vibro-fluidized beds, assuring a high product quality.  相似文献   
35.
The laboratory scale anaerobic–anoxic–aerobic (A2O) process fed with synthetic brewage wastewater was designed to investigate the effects of changing feed C/P ratio on the performance of biological nutrient removal (BNR) processes. In the experiment, the influent chemical oxygen demand (COD) concentration was kept at approximately 300 mg L?1 while the total phosphorus concentration was varied to obtain the desired C/P ratio. Results showed that when the C/P ratio was lower than 32, phosphorus removal efficiency increased as C/P ratio increased linearly, while when the C/P ratio was higher than 32, the P removal efficiency was maintained at 90–98%, and effluent P concentration was lower than 0.5 mg L?1. However, regardless of the C/P ratio, excellent COD removal (90% or higher) and good total nitrogen removal (75–84%) were maintained throughout the experiments. It was also found that very good linear correlation was obtained between COD uptake per unit P released in the anaerobic zone and C/P ratio. In addition, the P content in the wasted activated sludge increased with the decrease in the C/P ratio. Based on the results, it was recommended that the wastewater C/P ratio and its effects be incorporated into BNR design and operational procedures, appropriate C/P ratios were used to achieve the effluent treatment goals. Copyright © 2005 Society of Chemical Industry  相似文献   
36.
暖通空调工程设计常见问题   总被引:1,自引:0,他引:1  
陈钦益 《暖通空调》2004,34(10):68-72,120
通过对施工图审查工作进行总结,指出了暖通空调和防火防排烟设计中存在的问题及防火规范本身的一些不足。  相似文献   
37.
Molecular dynamical simulation has been carried out to investigate the structure and dynamics of a dipolar fluid under strong shear. Dipolar fluid consists of polarizable particles, which have an induced dipole moment in the applied field direction. Shear stress is perpendicular to the field direction. When shear stress is small, the flow has a flowing-chain structure. If shear stress increases to pass a critical value, flowing-chain structure changes to flowing layer structure. Each layer is parallel to the flow direction and shear direction. Within one layer, particles form strings in the flow direction.  相似文献   
38.
39.
Thermal history and solute precipitation behavior of suspended solution droplets of sodium chloride (NaCl), magnesium sulphate (MgSO4), and zirconium hydroxychloride (ZrO(OH)Cl) evaporating at atmospheric and reduced pressures are studied. Experimental measurements on the variation of droplet diameter, solution concentration, and temperature during the evaporation period are presented and discussed. The results of solute precipitation behavior in solution droplets observed under an optical microscope are displayed and discussed. Results indicate that reducing the pressure (∼ 33 kPa) results in a change in the solution droplet evaporation rate, but the thermal histories of a particular solution droplet are similar at the atmospheric and reduced pressures. At atmospheric and reduced pressures used in this study, the d2 law for solution droplets is valid at early stages of the evaporation and before the solute precipitation initiates. Drying of MgSO4 and ZrO(OH)Cl solution droplets results in the formation of spherical particles, whereas drying of spherical NaCl solution droplets results in the formation of cubic particles.  相似文献   
40.
李建宏 《信息技术》2002,(1):65-65,67
针对企业集团分权化管理的缺点,设计出一套利用互联网络技术实现企业集团财务集中控制的模式,给出了模式的图示及说明。  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