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   5287篇
  免费   92篇
  国内免费   20篇
电工技术   267篇
综合类   7篇
化学工业   1006篇
金属工艺   158篇
机械仪表   101篇
建筑科学   78篇
矿业工程   2篇
能源动力   108篇
轻工业   289篇
水利工程   8篇
石油天然气   18篇
无线电   555篇
一般工业技术   1045篇
冶金工业   1289篇
原子能技术   162篇
自动化技术   306篇
  2023年   18篇
  2022年   51篇
  2021年   99篇
  2020年   38篇
  2019年   56篇
  2018年   59篇
  2017年   61篇
  2016年   77篇
  2015年   57篇
  2014年   89篇
  2013年   185篇
  2012年   175篇
  2011年   235篇
  2010年   160篇
  2009年   161篇
  2008年   176篇
  2007年   186篇
  2006年   155篇
  2005年   164篇
  2004年   147篇
  2003年   139篇
  2002年   109篇
  2001年   105篇
  2000年   104篇
  1999年   134篇
  1998年   540篇
  1997年   289篇
  1996年   218篇
  1995年   165篇
  1994年   130篇
  1993年   117篇
  1992年   78篇
  1991年   80篇
  1990年   65篇
  1989年   70篇
  1988年   51篇
  1987年   59篇
  1986年   63篇
  1985年   59篇
  1984年   54篇
  1983年   37篇
  1982年   43篇
  1981年   46篇
  1980年   44篇
  1979年   33篇
  1978年   31篇
  1977年   28篇
  1976年   73篇
  1975年   18篇
  1974年   14篇
排序方式: 共有5399条查询结果,搜索用时 15 毫秒
101.
Fat bloom in chocolate is a substantial problem that affects its sensory properties, such as texture and appearance. This phenomenon is because of diffuse light reflection on a roughened surface of chocolate, caused by structural changes of fat crystals subjected to various temperature conditions. The purpose of this study is to characterize the fat bloom formed through gradual two-step cooling after exposure to temperatures (35–37 °C) slightly above the cocoa butter Form βV melting point (33.8 °C). To clarify the fat bloom formation process, the structural changes in cocoa butter and on the chocolate surface, at the dynamic thermal condition for bloom formation, was investigated using X-ray diffraction (XRD), fluorescence light microscopy, and scanning electron microscopy (SEM). The results revealed that an entirely light brown fat bloom occurred, even in the absence of the Form βVI or other polymorphic transformation. Microscopic observation showed that the light brown appearance was because of the porous structure on the chocolate surface. This porous structure was formed by liquid oil moving inside of chocolate from the surface. The formation of a coarse network and the subsequent de-oiling, because of movement of unsolidified liquid fat into the chocolate, appeared to be the main causes of bloom formation. Therefore, a coarsened fat network and oil movement besides the conventional principles of polymorphic transformation of cocoa butter should be considered.  相似文献   
102.
Alloy 903 and Alloy 909 are well-known Fe-Co-Ni-Al-Ti-Nb alloys with controlled low thermal expan-sion, but they have some properties that can be improved. To improve stress-accelerated grain boundary oxidation embrittlement of Alloy 903 and instability of theγ phase of alloy 909, two new alloys with good stress-rupture ductility, high creep-rupture strength, high tensile strength at high temperature, and good controlled thermal expansion were developed. These property improvements were accomplished by the combination of optimizing the Fe-Co-Ni ratio of the matrix and stabilizing theγ phase with the addition of aluminum.  相似文献   
103.
The structure of internal oxide layers in decarburized sheet was studied using a newly developed electrochemical method. Dissolving potential profiles indicated the amount of fayalite (Fe2SiO4) and silica (SiO2) in the layers. The quantitative data for the contents of fayalite and silica in the internal oxide layers can be easily obtained by this method.  相似文献   
104.
105.
106.
107.
The plasmodium of Physarum polycephalum is a unicellular and multinuclear giant amoeba that has an amorphous cell body. To clearly observe how the plasmodium makes decisions in its motile and exploratory behaviours, we developed a new experimental system to pseudo-discretize the motility of the organism. In our experimental space that has agar surfaces arranged in a two-dimensional lattice, the continuous and omnidirectional movement of the plasmodium was limited to the stepwise one, and the direction of the locomotion was also limited to four neighbours. In such an experimental system, a cellular automata-like system was constructed using the living cell. We further analysed the exploratory behaviours of the plasmodium by duplicating the experimental results in the simulation models of cellular automata. As a result, it was revealed that the behaviours of the plasmodium are not reproduced by only local state transition rules; and for the reproduction, a kind of historical rule setting is needed.  相似文献   
108.
We have developed a two‐way multi‐view 2‐D/3‐D display combining a liquid crystal lens and horizontally and vertically x times‐density pixels (HVxDP) arrangement. The two‐way multi‐view display features the same display resolution in 2‐D and 3‐D modes and a quite small color moiré for landscape and portrait, respectively, when using the HVxDP arrangement. In this paper, we realized suitable 3‐D properties for achieving a good balance between 3‐D moiré and 3‐D crosstalk for landscape and portrait by a two‐way liquid crystal lens with two kinds of focal lengths for the edge part and the center part of the lens.  相似文献   
109.
MOEA/D is one of the promising evolutionary algorithms for multi- and many-objective optimization. To improve the search performance of MOEA/D, this work focuses on the solution update method in the conventional MOEA/D and proposes its alternative, the chain-reaction solution update. The proposed method is designed to maintain and improve the variable (genetic) diversity in the population by avoiding duplication of solutions in the population. In addition, the proposed method determines the order of existing solutions to be updated depending on the location of each offspring in the objective space. Furthermore, when an existing solution in the population is replaced by a new offspring, the proposed method tries to reutilize the existing solution for other search directions by recursively performing the proposed chain-reaction update procedure. This work uses discrete knapsack and continuous WFG4 problems with 2–8 objectives. Experimental results using knapsack problems show the proposed chain-reaction update contributes to improving the search performance of MOEA/D by enhancing the diversity of solutions in the objective space. In addition, experimental results using WFG4 problems show that the search performance of MOEA/D can be further improved using the proposed method.  相似文献   
110.
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