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   1487024篇
  免费   29234篇
  国内免费   7827篇
电工技术   35129篇
技术理论   4篇
综合类   7874篇
化学工业   262681篇
金属工艺   64962篇
机械仪表   42274篇
建筑科学   45681篇
矿业工程   12038篇
能源动力   51029篇
轻工业   107068篇
水利工程   15162篇
石油天然气   37456篇
武器工业   278篇
无线电   198565篇
一般工业技术   282262篇
冶金工业   156519篇
原子能技术   34170篇
自动化技术   170933篇
  2021年   16244篇
  2020年   12630篇
  2019年   15246篇
  2018年   15972篇
  2017年   15287篇
  2016年   21708篇
  2015年   18187篇
  2014年   29859篇
  2013年   89550篇
  2012年   36246篇
  2011年   48376篇
  2010年   43392篇
  2009年   51858篇
  2008年   45169篇
  2007年   41801篇
  2006年   45066篇
  2005年   39249篇
  2004年   41526篇
  2003年   41690篇
  2002年   40943篇
  2001年   37669篇
  2000年   35898篇
  1999年   34853篇
  1998年   42879篇
  1997年   35830篇
  1996年   32124篇
  1995年   29889篇
  1994年   28141篇
  1993年   27883篇
  1992年   25505篇
  1991年   22682篇
  1990年   23056篇
  1989年   21971篇
  1988年   20524篇
  1987年   18847篇
  1986年   18296篇
  1985年   21539篇
  1984年   21860篇
  1983年   19810篇
  1982年   18902篇
  1981年   18979篇
  1980年   17621篇
  1979年   18149篇
  1978年   17400篇
  1977年   17067篇
  1976年   17943篇
  1975年   15717篇
  1974年   15245篇
  1973年   15321篇
  1972年   12851篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
11.
12.
13.
Gelatin is one of the most important multifunctional biopolymers and is widely used as an essential ingredient in food, pharmaceutical, and cosmetics. Porcine gelatin is regarded as the leading source of gelatin globally then followed by bovine gelatin. Porcine sources are favored over other sources since they are less expensive. However, porcine gelatin is religiously prohibited to be consumed by Muslims and the Jewish community. It is predicted that the global demand for gelatin will increase significantly in the future. Therefore, a sustainable source of gelatin with efficient production and free of disease transmission must be developed. The highest quality of Bovidae-based gelatin (BG) was acquired through alkaline pretreatment, which displayed excellent physicochemical and rheological properties. The utilization of mammalian- and plant-based enzyme significantly increased the gelatin yield. The emulsifying and foaming properties of BG also showed good stability when incorporated into food and pharmaceutical products. Manipulation of extraction conditions has enabled the development of custom-made gelatin with desired properties. This review highlighted the various modifications of extraction and processing methods to improve the physicochemical and functional properties of Bovidae-based gelatin. An in-depth analysis of the crucial stage of collagen breakdown is also discussed, which involved acid, alkaline, and enzyme pretreatment, respectively. In addition, the unique characteristics and primary qualities of BG including protein content, amphoteric property, gel strength, emulsifying and viscosity properties, and foaming ability were presented. Finally, the applications and prospects of BG as the preferred gelatin source globally were outlined.  相似文献   
14.
15.
16.
17.
Garzan oil field is located at the south east of Turkey. It is a mature oil field and the reservoir is fractured carbonate reservoir. After producing about 1% original oil in place (OOIP) reservoir pressure started to decline. Waterflooding was started in order to support reservoir pressure and also to enhance oil production in 1960. Waterflooding improved the oil recovery but after years of flooding water breakthrough at the production wells was observed. This increased the water/oil ratio at the production wells. In order to enhance oil recovery again different techniques were investigated. Chemical enhanced oil recovery (EOR) methods are gaining attention all over the world for oil recovery. Surfactant injection is an effective way for interfacial tension (IFT) reduction and wettability reversal. In this study, 31 different types of chemicals were studied to specify the effects on oil production. This paper presents solubility of surfactants in brine, IFT and contact angle measurements, imbibition tests, and lastly core flooding experiments. Most of the chemicals were incompatible with Garzan formation water, which has high divalent ion concentration. In this case, the usage of 2-propanol as co-surfactant yielded successful results for stability of the selected chemical solutions. The results of the wettability test indicated that both tested cationic and anionic surfactants altered the wettability of the carbonate rock from oil-wet to intermediate-wet. The maximum oil recovery by imbibition test was reached when core was exposed 1-ethly ionic liquid after imbibition in formation water. Also, after core flooding test, it is concluded that considerable amount of oil can be recovered from Garzan reservoir by waterflooding alone if adverse effects of natural fractures could be eliminated.  相似文献   
18.
Ca3Co4O9 is a promising p-type thermoelectric oxide material having intrinsically low thermal conductivity. With low cost and opportunities for automatic large scale production, thick film technologies offer considerable potential for a new generation of micro-sized thermoelectric coolers or generators. Here, based on the chemical composition optimized by traditional solid state reaction for bulk samples, we present a viable approach to modulating the electrical transport properties of screen-printed calcium cobaltite thick films through control of the microstructural evolution by optimized heat-treatment. XRD and TEM analysis confirmed the formation of high-quality calcium cobaltite grains. By creating 2.0 at% cobalt deficiency in Ca2.7Bi0.3Co4O9+δ, the pressureless sintered ceramics reached the highest power factor of 98.0 μWm?1 K-2 at 823 K, through enhancement of electrical conductivity by reduction of poorly conducting secondary phases. Subsequently, textured thick films of Ca2.7Bi0.3Co3.92O9+δ were efficiently tailored by controlling the sintering temperature and holding time. Optimized Ca2.7Bi0.3Co3.92O9+δ thick films sintered at 1203 K for 8 h exhibited the maximum power factor of 55.5 μWm?1 K-2 at 673 K through microstructure control.  相似文献   
19.
Journal of Computer and Systems Sciences International - It is shown that the Lyapunov theorem on the distribution properties of the sum of random variables with different distribution densities...  相似文献   
20.
Multimedia Tools and Applications - Mammograms are the images used by radiologists to diagnose breast cancer. Breast cancer is one of the most common cancers in women. The early detection of breast...  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