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   19544篇
  免费   1614篇
  国内免费   755篇
电工技术   556篇
综合类   1420篇
化学工业   4131篇
金属工艺   1042篇
机械仪表   357篇
建筑科学   1671篇
矿业工程   945篇
能源动力   478篇
轻工业   3874篇
水利工程   539篇
石油天然气   1288篇
武器工业   45篇
无线电   743篇
一般工业技术   1203篇
冶金工业   1558篇
原子能技术   111篇
自动化技术   1952篇
  2024年   96篇
  2023年   246篇
  2022年   536篇
  2021年   599篇
  2020年   651篇
  2019年   605篇
  2018年   581篇
  2017年   691篇
  2016年   727篇
  2015年   745篇
  2014年   1249篇
  2013年   1324篇
  2012年   1483篇
  2011年   1512篇
  2010年   1099篇
  2009年   1024篇
  2008年   895篇
  2007年   1136篇
  2006年   1014篇
  2005年   876篇
  2004年   847篇
  2003年   707篇
  2002年   554篇
  2001年   443篇
  2000年   402篇
  1999年   317篇
  1998年   255篇
  1997年   203篇
  1996年   185篇
  1995年   177篇
  1994年   142篇
  1993年   108篇
  1992年   91篇
  1991年   75篇
  1990年   52篇
  1989年   45篇
  1988年   39篇
  1987年   26篇
  1986年   24篇
  1985年   24篇
  1984年   16篇
  1983年   7篇
  1982年   16篇
  1981年   13篇
  1980年   8篇
  1979年   6篇
  1964年   4篇
  1960年   3篇
  1959年   3篇
  1958年   3篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
1.
《石油化工》2015,44(4):506
采用便携式微量水分析仪和库仑法微量水分析仪测定了乙烯、丙烯试样中的微量水含量,对试样的传输系统、进样量的控制、液体试样的气化和水标准气体的制备方法进行了改进,优化了测试条件。以低吸附惰性管线和小死体积单进单出的不锈钢减压器为试样传输系统,缩短了测试时间。采用液态烃闪蒸气化取样进样器气化液体试样并准确控制试样的进样量,可避免液体试样渐次气化对水含量测定结果的影响及对采样钢瓶大小的限制。采用渗透管发生器制备水标准气体,可验证分析结果的准确度。采用库仑法微量水分析仪测定水含量时,试样流量选择600 m L/min较适宜,开封保存15 d之内的卡尔·费休试剂对测定结果无影响。采用便携式微量水分析仪测定水含量时,选择试样流量在400~800 m L/min之间较适宜。两种仪器的测量结果相近,稳定性好,准确度高,回收率在102%~107%之间,相对偏差小于10%。  相似文献   
2.
概述了氢的主要工业生产方法和实际应用,详细介绍了氯碱氢三级脱水工艺过程,并运用在线分析手段,准确显示了干燥过程中的氯碱氢水分含量变化规律。  相似文献   
3.
本文对运营商信息安全集中管控架构演进和信息安全管控策略面临的问题进行了深入分析,提出了信息安全集中管控架构的演进方向建议及对信息安全监控策略工作优化的若干意见。  相似文献   
4.
Al、Mo含量对铸造钛合金力学性能的影响   总被引:1,自引:0,他引:1  
运用正交实验 ,考察了Al、Mo含量对Ti Al Mo 1Zr系铸造钛合金力学性能的影响。试验结果表明 :随Al、Mo含量提高 ,铸造合金的强度增加 ,塑性和冲击韧性降低 ,但Al、Mo的交互作用却使合金塑性提高 ,强度和冲击韧性降低  相似文献   
5.
As the surface properties of the drying materials are very important not only for the drying rate but also for the quality change during drying, the effects of surface concentration on the drying behavior of liquid foods (sugar solutions) were investigated by isothermal drying experiments and by numerical calculation experiments. The isothermal drying experiments with gelled sugar solution systems (sucrose and maltodextrin) were carried out at various relative humidity (RH) values (RH = 0 to 84%). Separate experiments were carried out for determination of the desorption isotherms.

The isothermal drying curves of sugar solutions at RH = 0 to 51% were very similar. Numerical simulations also showed that the drying curves of these sugars at the surface concentration = 0 and 0.1 are almost the same, although the concentration distributions are different.

When a small amount of gelatin was added to sugar solutions, the drying rate decreased remarkably as the gelatin might form a thin film (skin) near the surface, and consequently the retention of ethanol increased.  相似文献   
6.
过氧化甲乙酮合成研究   总被引:1,自引:0,他引:1  
论述了过氧化甲乙酮的合成方法,用阳离子交换树脂催化剂代替传统的无机酸催化剂。考察了离子交换树脂用量、反应温度对反应产率、活性氧含量的影响及溶剂对产品稳定性的影响。  相似文献   
7.
Previous work has shown that the enzymatic hydrolysis of sugarcane bagasse could be greatly enhanced by peracetic acid (PAA) pretreatment. There are several factors affecting the enzymatic digestibility of the biomass, including lignin and hemicelluloses content, cellulose crystallinity, acetyl group content, accessible surface area and so on. The objective of this work is to analyze the mechanism of the enhancement of enzymatic digestibility caused by PAA pretreatment. Delignification resulted in an increase of the surface area and reduction of the irreversible absorption of cellulase, which helped to increase the enzymatic digestibility. The Fourier transform infrared (FTIR) spectrum showed that the absorption peaks of aromatic skeletal vibrations were weakened or disappeared after PAA pretreatment. However, the infrared crystallization index (N.O'KI) was increased. X‐ray diffraction (XRD) analysis indicated that the crystallinity of PAA‐treated samples was increased owing to the partial removal of amorphous lignin and hemicelluloses and probable physical change of cellulose. The effect of acetyl group content on enzymatic digestibility is negligible compared with the degree of delignification and crystallinity. The results indicate that enhancement of enzymatic digestibility of sugarcane bagasse by PAA pretreatment is achieved mainly by delignification and an increase in the surface area and exposure of cellulose fibers. Copyright © 2008 Society of Chemical Industry  相似文献   
8.
Industrial pelletizing of sawdust was carried out as a designed experiment in the factors: sawdust moisture content, fractions of fresh pine, stored pine and spruce. The process parameters and response variables were energy consumption, pellet flow rate, pellet bulk density, durability and moisture content. The final data consisted of twelve industrial scale runs. Because of the many response variables, data evaluation was by principal component analysis of a 12 × 9 data matrix. The two principal component model showed a clustering of samples, with a good reproducibility of the center points. It also showed a positive correlation of energy consumption, bulk density and durability all negatively correlated to flow rate and moisture content. The stored pine was more related to high durability and bulk density. The role of the spruce fraction was unclear. The design matrix, augmented with the process parameters was a 12 × 6 matrix. Partial least squares regression showed excellent results for pellet moisture content and bulk density. The model for durability was promising. A 12 × 21 data matrix of fatty- and resin acid concentrations measured by GC–MS showed the differences between fresh and stored pine very clearly. The influence of the spruce fraction was less clear. However, the influence of the fatty- and resin acids on the pelletizing process could not be confirmed, indicating that other differences between fresh and stored pine sawdust have to be investigated. This work shows that it is possible to design the pelletizing process for moderate energy consumption and high pellet quality.  相似文献   
9.
本文介绍了一种F级高云母含量云母带,它的主要特点是云母含量高达48%以上,具有良好的长时间耐电热老化性能,适用于高压电机主绝缘多胶模压工艺要求,该云母带的应用对提高电机绝缘水平和延长电机使用寿命具有重要意义。  相似文献   
10.
针对锅炉飞灰含碳置影响因素复杂.实时测量难度大.精度低,提出了一种基于遗传神经网络的预测方法,并用于某电厂,结果表明,该方法是有效的。  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