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   2632篇
  免费   113篇
  国内免费   7篇
电工技术   27篇
化学工业   424篇
金属工艺   38篇
机械仪表   26篇
建筑科学   74篇
矿业工程   12篇
能源动力   33篇
轻工业   753篇
水利工程   18篇
石油天然气   2篇
无线电   183篇
一般工业技术   470篇
冶金工业   294篇
原子能技术   6篇
自动化技术   392篇
  2023年   21篇
  2022年   16篇
  2021年   47篇
  2020年   32篇
  2019年   31篇
  2018年   56篇
  2017年   61篇
  2016年   101篇
  2015年   71篇
  2014年   90篇
  2013年   155篇
  2012年   138篇
  2011年   122篇
  2010年   120篇
  2009年   110篇
  2008年   136篇
  2007年   107篇
  2006年   91篇
  2005年   64篇
  2004年   60篇
  2003年   46篇
  2002年   60篇
  2001年   28篇
  2000年   28篇
  1999年   32篇
  1998年   96篇
  1997年   54篇
  1996年   54篇
  1995年   18篇
  1994年   16篇
  1993年   21篇
  1992年   13篇
  1976年   19篇
  1937年   11篇
  1936年   29篇
  1935年   32篇
  1934年   21篇
  1933年   21篇
  1932年   16篇
  1931年   25篇
  1930年   24篇
  1929年   20篇
  1928年   46篇
  1927年   36篇
  1926年   14篇
  1925年   23篇
  1915年   16篇
  1913年   49篇
  1912年   28篇
  1907年   13篇
排序方式: 共有2752条查询结果,搜索用时 9 毫秒
81.
Novel fluorinated reactive surfactants were used for the organic modification of monmorillonite clays. These organoclays were used for the preparation of polystyrene?clay nanocomposites by in‐situ free radical polymerization. Reference systems based on hydrocarbon homologous surfmer and nonpolymerizable surfactants were also used to deduce the effect of the fluorine moiety and the polymerizable function on the morphology and thermal stability of the prepared nanocomposites. Different structural parameters of the surfactants were investigated and modulated for the clay modification including: the nature of surfactant (surfmer/classical surfactant, fluorinated, or hydrocarbonated), the length of the fluorinated chain as well as the length of the hydrocarbon spacers linking the ammonium head to the fluorine chain or the polymerizable acrylic function. Wide angle‐X‐ray scattering (WAXD), thermogravimetric analysis (TGA), and electronic microcopies (TEM and SEM) were used to establish a structure‐morphology, thermal properties relationships, and to highlight the key parameters governing the exfoliation process. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42347.  相似文献   
82.
83.
Polymer materials with antimicrobial activity are prepared by UV polymerization of acrylate and methacrylate mixture at room temperature. The antimicrobials are silver acetate and copper (II) acetate, used without pretreatment. Their chemical stability in the acrylate matrix and their effect on the thermal and mechanical properties of the polymer matrix are investigated as a function of their concentration up to 15 wt %. Physico‐chemical, thermal, rheological, and morphological analyses as well as the surveillance of metal salts release in aqueous medium are conducted. A significant decrease in the thermal stability of the salts introduced into the acrylate matrix is observed after UV treatment. The metal salts also have significant effects on the properties of the matrix. A plasticization and densification of the material associated with an aggregation of salts up to the percolation at the highest concentration are highlighted. At equal concentrations, the effects are more pronounced in the presence of copper salts. The latter was released more slowly than silver salts from acrylate material. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43501.  相似文献   
84.
Manufacturing of chemical‐pharmaceutical products is moving increasingly fast on a global scale. Therefore, developing and starting up production facilities fast, with high quality, and at reasonable costs has become extremely challenging. Engineering concepts like modularization, standardization and simultaneous/parallel engineering are discussed as methods for speeding up process design and filing for regulatory approval. Transfer from batch to continuous operation mode of production is pointed out as the key‐issue in such strategies.  相似文献   
85.
Abstract

The objective of this study was to compare spray-dried and freeze-dried extracts of Sennae fructus regarding the stability of the sennosides. Therefore, the influence of the addition of maltodextrin (MD) not only before the drying processes but also during fluidized bed granulation was investigated. Analysis of the hygroscopicities, the simultaneous TGA-DSC-MS data, and the influence of storage revealed that spray-dried extracts are more stable than freeze-dried extracts. The addition of MD led to an even better stability of the extracts. Lower amounts of MD are sufficient if applied onto the surface of the native extract during fluidized bed granulation.  相似文献   
86.
Very high concentrations of polybrominated diphenyl ethers (PBDE) have been reported in fish from Lake Mj?sa in Norway. This study was performed to examine the serum concentrations of PBDE and hexabromocyclododecane (HBCD) in consumers of fish from this lake and to investigate possible relationships between serum concentrations, self-reported fish intake and calculated total dietary PBDE exposure. Serum concentrations of the sum of the seven PBDE (BDE-28, 47, 99, 100, 153, 154 and 183) were significantly higher than those of a reference group of Norwegians eating only food with background levels of contamination (medians: 18 ng/g lipids men, 8.4 ng/g lipids women). The median dietary intake of Sum 7 PBDE was 2549 ng/day (30 ng/kg body weight/day), the highest dietary intake of PBDE reported. The contribution from fish caught from the contaminated lake comprised 98.7% of the total dietary exposure. For men, serum levels of PBDE were strongly correlated with the calculated dietary exposure, except for BDE-209. This suggests that sources other than the diet are important for human BDE-209 exposure. The median serum HBCD concentration was 4.1 and 2.6 ng/g lipids for men and women, respectively, and was also found to be associated with consumption of fish from Lake Mj?sa.  相似文献   
87.
88.
This contribution is concerned with the business value of Radio Frequency Identification (RFID) technology in retail. We present a case study of an RFID project at Galeria Kaufhof, a subsidiary of Metro Group and one of the largest department store chains in Europe. The project encompasses a variety of RFID applications at the intersection of store logistics and customer service. The contribution that our study makes to the literature is threefold. First, we describe an innovative large-scale trial that goes beyond what was done in earlier projects in several respects. The most fundamental difference from previous trials is the full integration of RFID event data with point-of-sale (POS) and master data, which for the first time offers the retailer the opportunity to directly observe and analyse physical in-store processes. Second, the heterogeneity of RFID applications implemented by Kaufhof allows us to theorise about the effects that RFID may have on business processes from an IT value perspective. We develop a conceptual model to explain the different cause-and-effect chains between RFID investments and their impact on firm performance, the role of complementary and contextual factors, and the difficulty of assessing these impacts using objective performance measures. Third, we compare the case to a prior trial conducted by Kaufhof about 5 years earlier. The differences between the lessons that the company learned in the two projects illustrate the impact of technological advances and standardisation efforts in recent years on managerial perceptions of RFID business value, which allows for the derivation of a number of useful implications for practice.  相似文献   
89.
Rod Extrusion of Titanium‐Aluminum Composites The combination of different metals enables the processing of materials with local optimized properties. Thus, the production of metallic composites is associated with high standards in manufacturing technologie. Focus of the following investigations is the rod extrusion process of titanium‐aluminum‐composites. Besides the mechanical properties, the formation of the bonding zone and the mechanisms of adhesion in the bonding zone were investigated. The influence of specimens’ preparation and of different coatings used improve bonding were a matter of particular interest. Whereas coatings of copper or nickel inhibit the formation of a strong bonding due to the formation of oxide layers, sealed titanium cores can reach a mechanical strength of up to 100 MPa after rod extrusion. Compared to other joining technologies, an impairment of the base metal via formation of heat affected zones, pores or grain coarsening does not occur.  相似文献   
90.
The hydrological observation network in the Amazon basin is made of conventional rainfall and water level stations presently maintained by the Agência Nacional de Águas (ANA), the National Agency for Waters. The water level network has long been plagued by difficulties associated with spatial coverage, timely delivery and data errors. Satellite observations are important means for providing hydrologic data with acceptable spatial and temporal resolution, and radar altimeters embarked onboard successive satellites since the early 1970s collect measurements of water level over rivers in a well-defined geodetic reference frame and can be used to address some of these problems. Nowadays, satellite altimetry can be used to collect the time variations of the water levels over many rivers throughout the word, as long as the reach are several hundred meters wide. This ability is particularly interesting in ungauge basins but it can also be used as an independent source of information to cross-check existing gauge series. In the present study, we focus on examples from the Amazon basin where radar altimetry has been used to provide an independent dataset that can be used to support the management of hydrological observation networks by including new data together with conventional field data,  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