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   2306篇
  免费   259篇
  国内免费   242篇
化学   250篇
晶体学   6篇
力学   215篇
综合类   1篇
数学   35篇
物理学   251篇
无线电   2049篇
  2024年   10篇
  2023年   20篇
  2022年   37篇
  2021年   73篇
  2020年   50篇
  2019年   22篇
  2018年   35篇
  2017年   85篇
  2016年   81篇
  2015年   85篇
  2014年   110篇
  2013年   122篇
  2012年   133篇
  2011年   200篇
  2010年   144篇
  2009年   176篇
  2008年   183篇
  2007年   235篇
  2006年   214篇
  2005年   165篇
  2004年   157篇
  2003年   193篇
  2002年   97篇
  2001年   71篇
  2000年   28篇
  1999年   20篇
  1998年   18篇
  1997年   11篇
  1996年   5篇
  1995年   7篇
  1994年   4篇
  1993年   4篇
  1991年   1篇
  1990年   1篇
  1989年   8篇
  1987年   1篇
  1982年   1篇
排序方式: 共有2807条查询结果,搜索用时 187 毫秒
71.
An innovative process for the adsorption of the hydrophobic Basil-Oil (BO) into the hydrophilic food byproduct chitosan (CS) and the development of an advanced low-density polyethylene/chitosan/basil-oil (LDPE/CS_BO) active packaging film was investigated in this work. The idea of this study was the use of the BO as both a bioactive agent and a compatibilizer. The CS was modified to a CS_BO hydrophobic blend via a green evaporation/adsorption process. This blend was incorporated directly in the LDPE to produce films with advanced properties. All the obtained composite films exhibited improved packaging properties. The film with 10% CS_BO content exhibited the best packaging properties, i.e., 33.0% higher tensile stress, 31.0% higher water barrier, 54.3% higher oxygen barrier, and 12.3% higher antioxidant activity values compared to the corresponding values of the LDPE films. The lipid oxidation values of chicken breast fillets which were packaged under vacuum using this film were measured after seven and after fourteen days of storage. These values were found to be lower by around 41% and 45%, respectively, compared with the corresponding lipid oxidation values of pure LDPE film.  相似文献   
72.
We demonstrate the proof-of-principle of a new separation concept for micrometer-sized particles in a structured microfluidic device. Under the action of externally applied, periodic voltage-pulses two different species of like-charged polystyrene beads are observed to simultaneously migrate into opposite directions. Based on a theoretical model of the particle motion in the microdevice that shows good agreement with the experimental measurements, the underlying separation mechanism is identified and explained. Potential biophysical applications, such as cell sorting, are briefly addressed.  相似文献   
73.
The present study deals with the development of a liquid microextraction procedure for enhancing the sensitivity of the determination of 2‐methyl‐4‐isothiazolin‐3‐one and 5‐chloro‐2‐methyl‐4‐isothiazolin‐3‐one in adhesives. The procedure involves a three‐phase hollow‐fiber liquid‐phase microextraction using a semipermeable polypropylene membrane, which contained 1‐octanol as the organic phase in the pores of the membrane. The donor and acceptor phases are aqueous acidic and alkaline media, respectively, and the final liquid phase (acceptor) is analyzed by HPLC coupled with diode array detection. The most appropriate conditions were extraction time 20 min, stirring speed 1400 rpm, extraction temperature 50°C. The quantification limits of the method were 0.123 and 0.490 μg/g for 2‐methyl‐4‐isothiazolin‐3‐one and 5‐chloro‐2‐methyl‐4‐isothiazolin‐3‐one, respectively. Three different adhesive samples were successfully analyzed. The procedure was compared to direct analysis using ultra high pressure liquid chromatography coupled with TOF‐MS, where the identification of the compounds and the quantification values were confirmed.  相似文献   
74.
This study aims to optimize the formulation of composite films based on chicken skin gelatin with incorporation of rice starch (10–20%, w/w) and curcumin (0.03–0.10%, w/v). The effect of their interaction on film's tensile strength (TS), elongation at break (EAB), water vapor permeability (WVP) and antioxidant properties (DPPH%) were investigated using a response surface methodology-central composite design (RSM-CCD). The optimized film formulation was further validated to indicate the validity of the prediction model. The optimum conditions of the film were selected with incorporation of rice starch at 20% (w/w) and curcumin at 0.03% (w/v). The optimized film formulation has revealed better mechanical properties with low WVP value and good antioxidant activity. The results showed that optimized composite films formulation based on chicken skin gelatin with the incorporation of rice starch and curcumin has proving good validation of model prediction and can be effectively utilized in food packaging industry.  相似文献   
75.
The development of antimicrobial food packaging is needed for food preservation and quality maintenance. Silver nanoparticles (AgNPs) have been widely used as an antimicrobial agent in food packaging technologies. However, the risks associated with their potential migration into foods are a major concern. This paper comprehensively reviews the use of AgNPs in food packaging technologies. The application of AgNPs in food packaging technologies has been regulated by the United States Food and Drug Administration and the European Food Safety Authority. The addition of AgNPs into food packaging can improve their barrier, mechanical, and antibacterial properties, as well as maintain the quality of foods. Migration of AgNPs from food packaging into foods is still a concern as it has implications for human health associated with their toxicity properties. A study on the toxicological properties of AgNPs released from food packaging needs to be carried out intensively to ensure their safety before being widely implemented. Moreover, comprehensive economic evaluation to implement AgNPs in food packaging is needed as such a study is missing in the literature.  相似文献   
76.
新型低驱动电压电子纸显示单元的研究   总被引:1,自引:0,他引:1  
研制了一种基于介质上电润湿(electrowetting-on-dielectric,EWOD)的新型低驱动电压电子纸反射式显示单元器件.本文分析了器件的工作原理以及性能影响因素,并提出用优化的氮化硅与碳氟聚合物复合介质层来改善器件的驱动电压.实验证实,器件在15V低电压驱动下成功实现了"开启"、"关闭"功能,其"开启"、"关闭"响应时间小于1/30s.  相似文献   
77.
电子整机的微小型化体现在其尺寸小、厚度薄、重量轻上,体现在它们的高性能、多功能、高可靠、便携化、卡片化上;而达到这些性能的关键及基础是适应电子整机需要的微电子封装技术的不断进步,用先进封装技术“武装”各类电子整机。二者密切结合、相互促进、协同发展、共同提高,引领着电子整机微小型化发展的大趋势。文章沿着微电子发展的脉络论述了二者向更高阶段发展的必由之路。  相似文献   
78.
<正>Packaging of MEMS ( micro-electro-mechanical system ) devices poses more challenges than conventional IC packaging, since the performance of the MEMS devices is highly dependent on packaging processes. A Land Grid Array ( LGA ) package is introduced for MEMS technology based linear multi-axis accelerometers. Finite element modeling is conducted to simulate the warpage behavior of the LGA packages. A method to correlate the package warpage to matrix block warpage has been developed. Warpage for both package and sensor substrate are obtained. Warpage predicted by simulation correlates very well with experimental measurements. Based on this validated method, detailed design analysis with different package geometrical variations are carried out to optimize the package design. With the optimized package structure, the packaging effect on accelerometer signal performance is well controlled.  相似文献   
79.
张军  贾宏  陈旭 《电子与封装》2006,6(8):33-36
各向异性导电胶膜(ACF)的玻璃转化温度T_g是它的一个重要性能参数,用差示扫描热示计(DSC)分别测定商用各向异性导电胶膜固化前和固化后的玻璃转化温度,并确定不同的固化时间对它的玻璃转化温度的影响,以及高温高湿(85℃,85%RH)环境对它的玻璃转化温度影响,得到各向异性导电胶玻璃转化温度下降是其粘接强度下降的原因之一。  相似文献   
80.
随着微电子封装技术的发展,各向异性导电胶作为一种绿色的连接材料,广泛应用于电子产品中。文中主要介绍各向异性导电胶互连器件的粘接原理和影响其可靠性的各种因素,如粘接工艺参数、外界环境的干扰、各向异性导电胶的物理特性等。  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