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   728篇
  免费   10篇
  国内免费   7篇
电工技术   17篇
综合类   6篇
化学工业   127篇
金属工艺   22篇
机械仪表   29篇
建筑科学   17篇
矿业工程   1篇
能源动力   46篇
轻工业   29篇
水利工程   3篇
石油天然气   1篇
武器工业   1篇
无线电   163篇
一般工业技术   137篇
冶金工业   56篇
原子能技术   3篇
自动化技术   87篇
  2024年   1篇
  2023年   1篇
  2022年   11篇
  2021年   9篇
  2020年   2篇
  2019年   4篇
  2018年   10篇
  2017年   5篇
  2016年   7篇
  2015年   10篇
  2014年   17篇
  2013年   60篇
  2012年   25篇
  2011年   28篇
  2010年   29篇
  2009年   34篇
  2008年   38篇
  2007年   27篇
  2006年   22篇
  2005年   20篇
  2004年   26篇
  2003年   33篇
  2002年   22篇
  2001年   30篇
  2000年   16篇
  1999年   25篇
  1998年   27篇
  1997年   21篇
  1996年   29篇
  1995年   14篇
  1994年   16篇
  1993年   26篇
  1992年   10篇
  1991年   18篇
  1990年   16篇
  1989年   13篇
  1988年   11篇
  1987年   7篇
  1986年   4篇
  1985年   3篇
  1984年   5篇
  1983年   6篇
  1982年   1篇
  1981年   1篇
  1980年   1篇
  1979年   1篇
  1977年   2篇
  1974年   1篇
排序方式: 共有745条查询结果,搜索用时 15 毫秒
111.
112.
We observed temporal fading on 1.9 GHz fixed wireless channels during short-term measurements at 107 different locations in a suburban macrocell environment characterized by flat terrain and heavy foliage in order to determine how the rate of fading varies with average wind speed and distance. For each location, we estimated: (1) the Ricean K-factor using a momentbased estimator and (2) an equivalent Doppler frequency which is related to the maximum Doppler frequency by a factor that depends upon the shape of the Doppler spectrum. We did so by fitting the measured level crossing rate (LCR) and average fade duration (AFD) distributions to expressions normally justified for mobile wireless links using a method recently proposed by Feick, Valenzuela and Ahumada (2007). As has been observed at other sites, the Ricean K-factor decreased with both average wind speed and distance. However, we found that the equivalent Doppler frequency was effectively uncorrelated with wind speed and noticeably increased with distance. Similar measurements at other sites will be required to determine the extent to which these trends are affected by foliage density and tower height.  相似文献   
113.
We report on an on-site 500 RT cooling tower ozone treatment process, in which chemicals other than ozone itself were completely eliminated. Ozone in an amount leading to less than 0.1 ppm of dissolved ozone was continuously introduced via side-stream injection into the circulating water returning from the chiller. The ozonated water was initially made to flow from the distributor to the filler in order to eliminate the growth of algae, and then to the chiller to reduce the corrosion and the fouling in the water. Positive ions such as Ca+2 and Mg+2 in the circulating water were precipitated by chelating them with carboxylic acids formed by the oxidation of organic compounds. We observed that using an ozone dosage of 0.1 ppm resulted in a colony-forming unit (CFU) less than 2 × 103 /mL. With that well-controlled CFU, corrosion controlling and scale reducing were achieved as well.  相似文献   
114.
Ce0.9Gd0.1O1.95 ceramics were prepared using a simple and effective process in this study. Without any prior calcination, the mixture of raw materials was pressed and sintered directly. The reaction of the raw materials occurred during the heating up period by passing the calcination stage in the conventional solid-state reaction method. More than 99.5% of theoretical density was obtained for Ce0.9Gd0.1O1.95 sintering at 1500–1600 °C. Fine grains (<1 μm) formed in pellets sintered at 1450 °C. The homogeneity of grains increased with the sintering temperature. The grains grew to >4.5 μm in pellets sintered at 1600 °C. The reactive-sintering process is proved to be a simple and effective method in preparing Ce0.9Gd0.1O1.95 ceramics for solid electrolyte application.  相似文献   
115.
Low-temperature synthesis of BiNbO4 ceramics using reaction-sintering process was investigated. Orthorhombic BiNbO4 phase together with minor triclinic BiNbO4 phase were found in the pellets. The phase transition temperature in BiNbO4 with 0.5 wt% CuO addition was lowered from 960 °C via traditional route to 880 °C when the reaction-sintering process was used. After 920 °C sintering for 4 and 6 h, densities 6.8–6.85 g/cm3 (94% of the theoretical value) were obtained. The abnormal grain growth in BiNbO4 via traditional route was not observed in this study.  相似文献   
116.
This paper discusses the role of government mortgage guarantee schemes in housing policy. It explores different types of government mortgage guarantee scheme, which play different roles, in eight countries. Mortgage guarantee schemes interfere in the mortgage market in order to improve access to mortgages. Such guarantees can be shaped as self-supporting instruments or as subsidies. If the latter is the case the issue of competition and a level playing field is relevant. This paper explores the US and the Dutch guarantee models in depth in order to answer the question of whether these schemes are unsubsidised mortgage market instruments or subsidised programmes. It concludes by reflecting on the meaning of the outcomes in the context of EU competition policy.  相似文献   
117.
智勇  刘乃仓 《化肥设计》2009,47(6):46-48
简述了甲醇装置甲醇分离器的基本结构和技改前存在的问题,介绍了复合型高效捕沫器的基本原理以及应用于甲醇分离器的实际效果,分析了技改中有待解决的问题和原因。技改效果表明,采用复合型高效捕沫器后,甲醇分离器的分离效率由28.9%提高至94.4%;技改投资为30万元/套,投资回收期为2个月。  相似文献   
118.
Dyslipidemia is characterized by increasing plasma levels of low-density lipoprotein-cholesterol (LDL-C), triglycerides (TGs) and TG-rich lipoproteins (TGRLs) and is a major risk factor for the development of atherosclerotic cardiovascular disorders (ASCVDs). It is important to understand the metabolic mechanisms underlying dyslipidemia to develop effective strategies against ASCVDs. Angiopoietin-like 3 (ANGPTL3), a member of the angiopoietin-like protein family exclusively synthesized in the liver, has been demonstrated to be a critical regulator of lipoprotein metabolism to inhibit lipoprotein lipase (LPL) activity. Genetic, biochemical, and clinical studies in animals and humans have shown that loss of function, inactivation, or downregulated expression of ANGPTL3 is associated with an obvious reduction in plasma levels of TGs, LDL-C, and high-density lipoprotein-cholesterol (HDL-C), atherosclerotic lesions, and the risk of cardiovascular events. Therefore, ANGPTL3 is considered an alternative target for lipid-lowering therapy. Emerging studies have focused on ANGPTL3 inhibition via antisense oligonucleotides (ASOs) and monoclonal antibody-based therapies, which have been carried out in mouse or monkey models and in human clinical studies for the management of dyslipidemia and ASCVDs. This review will summarize the current literature on the important role of ANGPTL3 in controlling lipoprotein metabolism and dyslipidemia, with an emphasis on anti-ANGPTL3 therapies as a potential strategy for the treatment of dyslipidemia and ASCVDs.  相似文献   
119.
A method is presented for the analysis of dynamic positron emission tomography (PET) data using sparse Bayesian learning. Parameters are estimated in a compartmental framework using an over-complete exponential basis set and sparse Bayesian learning. The technique is applicable to analyses requiring either a plasma or reference tissue input function and produces estimates of the system's macro-parameters and model order. In addition, the Bayesian approach returns the posterior distribution which allows for some characterisation of the error component. The method is applied to the estimation of parametric images of neuroreceptor radioligand studies.   相似文献   
120.
Journal of Real-Time Image Processing - Due to the effect of lighting and complex background, most visual hand gesture recognition systems work only under restricted environments. Here, we propose...  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