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   1486905篇
  免费   26963篇
  国内免费   7845篇
电工技术   35348篇
技术理论   5篇
综合类   7391篇
化学工业   271797篇
金属工艺   64524篇
机械仪表   42084篇
建筑科学   46364篇
矿业工程   11777篇
能源动力   50328篇
轻工业   112479篇
水利工程   14952篇
石油天然气   38331篇
武器工业   367篇
无线电   196725篇
一般工业技术   280054篇
冶金工业   146217篇
原子能技术   33926篇
自动化技术   169044篇
  2021年   16032篇
  2020年   12109篇
  2019年   14818篇
  2018年   15300篇
  2017年   14597篇
  2016年   21222篇
  2015年   17809篇
  2014年   29148篇
  2013年   88445篇
  2012年   35821篇
  2011年   48030篇
  2010年   42978篇
  2009年   51347篇
  2008年   44991篇
  2007年   42227篇
  2006年   45313篇
  2005年   39525篇
  2004年   41200篇
  2003年   41031篇
  2002年   40323篇
  2001年   36855篇
  2000年   35486篇
  1999年   34068篇
  1998年   39167篇
  1997年   35864篇
  1996年   33077篇
  1995年   29358篇
  1994年   27742篇
  1993年   27590篇
  1992年   25987篇
  1991年   22938篇
  1990年   23312篇
  1989年   22381篇
  1988年   20924篇
  1987年   19197篇
  1986年   18532篇
  1985年   21874篇
  1984年   22259篇
  1983年   20186篇
  1982年   19179篇
  1981年   19280篇
  1980年   17842篇
  1979年   18480篇
  1978年   17695篇
  1977年   17115篇
  1976年   17742篇
  1975年   15957篇
  1974年   15509篇
  1973年   15553篇
  1972年   13044篇
排序方式: 共有10000条查询结果,搜索用时 8 毫秒
241.
242.
Many e-commerce companies collect users’ personal data for marketing purposes despite privacy concerns. Information-collecting companies often offer a monetary reward to users to alleviate privacy concerns and ease the collection of personal information. This study focused on the negative effects of monetary rewards on both information privacy concerns (IPC) and information disclosure. A survey approach was used to collect data and 370 final responses were analysed using a two-way analysis of variance and a binomial logistic regression model. The results show that monetary rewards increase IPC when an information-collecting company requires sensitive information. Additional results indicate that building trust is a more effective way of collecting personal data. This study identifies how organisations can best execute information-collection activities and contributes additional insights for academia and practitioners.  相似文献   
243.
The design of a microstrip‐fed annular‐ring slot antenna (ARSA) with circular polarization (CP) radiation is initially studied. To obtain CP radiation with broad 3‐dB axial ratio (AR) bandwidth that can cover the WiMAX 2.3 GHz (2305–2320 MHz, 2345–2360 MHz) and WLAN 2.4 GHz (2400–2480 MHz) bands, a novel technique of extending an inverted L‐shaped slot from the bottom section of the annular‐ring is proposed. To suppress the harmonic modes induced by the CP ARSA, the technique of integrating a defected ground structure into the annular‐ring slot is further introduced. From the measured results, 10‐dB impedance bandwidth and 3‐dB AR bandwidth of 44.86 and 9.68% were achieved by the proposed harmonic suppressed CP ARSA. Furthermore, average gain and radiation efficiency of ~4.7 dBic and 71%, respectively, were also exhibited across the bands of interest. © 2014 Wiley Periodicals, Inc. Int J RF and Microwave CAE 25:337–345, 2015.  相似文献   
244.
245.
The efficient substitution of sucrose by a sweetener in beverages requires the application of some sensory techniques. First, one must determine the concentrations of the sweeteners under study, equivalent in sweetness to the ideal sucrose concentration. In addition, it is fundamental to determine which is most similar to sucrose. The objectives of this study were to determine the ideal sweetness for espresso coffee and the equivalent concentrations in sweetness of different sweeteners, as well as characterise the time–intensity profile of each sweetener in relation to sweetness. The sweeteners evaluated were sucralose, aspartame, neotame, a cyclamate/saccharin mixture (2:1) and stevia. The sucrose concentration considered ideal by consumers was 12.5% (w/v), and the equivalent concentrations of the sweeteners were 0.0159% for sucralose, 0.0549% for aspartame, 0.0016% for neotame, 0.0359% for the cyclamate/saccharin mixture and 0.0998% for stevia. The time–intensity analysis indicated that possibly the sweeteners neotame, aspartame and sucralose would be the best substitutes for sucrose.  相似文献   
246.
247.
248.
249.
Enhancement of the dissolution rate of the poorly water-soluble hypoglycemic agent, gliclazide, by the aid of lyophilization was investigated. Mannitol, sodium lauryl sulfate (SLS) and polyvinyl pyrrolidone (PVP-k-30) were employed in different weight ratios (43%, 56% and 64% w/w, respectively) as water-soluble excipients in the formulation. Lyophilized systems were found to exhibit extremely higher in vitro dissolution rate compared to the unprocessed drug powder. Solid state characterization of the lyophilized systems using X-ray powder diffraction, Fourier transform infrared spectroscopy and differential scanning calorimetry techniques revealed that dissolution enhancement was attributable to transformation of gliclazide from the crystalline to an amorphous state in the solid dispersion formed during the lyophilization process. The gastrointestinal absorption and hypoglycemic effect of the lyophilized gliclazide/SLS system were investigated following oral administration to Albino rabbits. Cmax and area under the plasma concentration–time curve of gliclazide (AUC0–12) after administration of the lyophilized formulations were significantly higher than those obtained after administration of the unprocessed gliclazide.  相似文献   
250.
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