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   31920篇
  免费   1271篇
  国内免费   114篇
电工技术   427篇
综合类   232篇
化学工业   5995篇
金属工艺   693篇
机械仪表   702篇
建筑科学   1082篇
矿业工程   97篇
能源动力   1062篇
轻工业   4541篇
水利工程   270篇
石油天然气   165篇
武器工业   6篇
无线电   2385篇
一般工业技术   4711篇
冶金工业   6497篇
原子能技术   264篇
自动化技术   4176篇
  2024年   60篇
  2023年   173篇
  2022年   585篇
  2021年   908篇
  2020年   623篇
  2019年   714篇
  2018年   811篇
  2017年   889篇
  2016年   871篇
  2015年   655篇
  2014年   997篇
  2013年   1698篇
  2012年   1501篇
  2011年   1835篇
  2010年   1370篇
  2009年   1420篇
  2008年   1278篇
  2007年   1119篇
  2006年   892篇
  2005年   913篇
  2004年   968篇
  2003年   870篇
  2002年   857篇
  2001年   750篇
  2000年   574篇
  1999年   561篇
  1998年   2123篇
  1997年   1397篇
  1996年   976篇
  1995年   634篇
  1994年   497篇
  1993年   559篇
  1992年   236篇
  1991年   291篇
  1990年   238篇
  1989年   205篇
  1988年   215篇
  1987年   164篇
  1986年   169篇
  1985年   186篇
  1984年   135篇
  1983年   96篇
  1982年   116篇
  1981年   124篇
  1980年   120篇
  1979年   92篇
  1978年   77篇
  1977年   142篇
  1976年   234篇
  1975年   86篇
排序方式: 共有10000条查询结果,搜索用时 12 毫秒
81.
82.
83.
Inspired by the relational algebra of data processing, this paper addresses the foundations of data analytical processing from a linear algebra perspective. The paper investigates, in particular, how aggregation operations such as cross tabulations and data cubes essential to quantitative analysis of data can be expressed solely in terms of matrix multiplication, transposition and the Khatri–Rao variant of the Kronecker product. The approach offers a basis for deriving an algebraic theory of data consolidation, handling the quantitative as well as qualitative sides of data science in a natural, elegant and typed way. It also shows potential for parallel analytical processing, as the parallelization theory of such matrix operations is well acknowledged.  相似文献   
84.
85.
86.
Fractal dimension applied to plant identification   总被引:2,自引:0,他引:2  
This article discusses methods to identify plants by analysing leaf complexity based on estimating their fractal dimension. Leaves were analyzed according to the complexity of their internal and external shapes. A computational program was developed to process, analyze and extract the features of leaf images, thereby allowing for automatic plant identification. Results are presented from two experiments, the first to identify plant species from the Brazilian Atlantic forest and Brazilian Cerrado scrublands, using fifty leaf samples from ten different species, and the second to identify four different species from genus Passiflora, using twenty leaf samples for each class. A comparison is made of two methods to estimate fractal dimension (box-counting and multiscale Minkowski). The results are discussed to determine the best approach to analyze shape complexity based on the performance of the technique, when estimating fractal dimension and identifying plants.  相似文献   
87.
This paper reports results of research into the definition of requirements for new consumer products––specifically, electro-mechanical products. The research dealt with the derivation of design requirements that are demonstrably aligned with stakeholder needs. The paper describes a comprehensive process that can enable product development teams to deal with statements of product requirements, as originally collected through market research activities, in a systematic and traceable manner from the early, fuzzy front end, stages of the design process. The process described has been based on principles of systems engineering. A case study from its application and evaluation drawn from the power sector is described in this paper. The case study demonstrates how the process can significantly improve product quality planning practices through revision of captured product requirements, analysis of stakeholder requirements and derivation of design requirements. The paper discusses benefits and issues from the use of the process by product development teams, and identifies areas for further research. Finally, the conclusions drawn from the reported research are presented.
Vassilis AgouridasEmail:
  相似文献   
88.
89.
Ribeiro AB  Caleya RF  Santos JL 《Applied optics》1995,34(28):6481-6488
Progressive ladder topology is studied by consideration of its properties of power budget and coupler tailoring. Optimization criteria are addressed for lossless and real systems, and their basic characteristics are compared with other topologies. Numerical results are presented, and an experiment is described for the case in which the network supports interferometric and intensity (with referentiation) fiber-optic-based sensors.  相似文献   
90.
Bacterial populations associated with poultry processing were determined on neck skin samples, equipment surfaces and environmental samples by replicate surveys. Aerobic plate counts, Enterobacteriaceae counts, Enterobacteriaceae counts and Pseudomonas counts were performed by standard procedures and the prevalence of Listeria, presumptive Salmonella and Staphylococcus aureus determined. Statistically significant (P < 0.05) increases in counts of all types of bacteria were obtained on product samples as a result of processing. Although bacterial counts on neck skin samples decreased by 0.3 to 0.4 log CFU g-1 after spray washing of carcasses, subsequent spinchilling and packaging of whole carcasses resulted in 0.7 to 1.2 log CFU g-1 increases. Bacterial numbers on equipment surfaces, however, decreased significantly from the "dirty" to the "clean" areas of the abattoir. Transport cages, "rubber fingers", defeathering curtains, shackles and conveyor belts repeatedly showed aerobic plate counts in excess of 5.0 log CFU 25 cm-2. Aerobic plate counts of scald tank and spinchiller water were 2 log CFU ml-1 higher than those of potable water samples. Bacterial numbers of the air in the "dirty" area were higher than those of the "clean" area. Listeria, presumptive Salmonella and Staphylococcus aureus were isolated from 27.6, 51.7 and 24.1% of all product samples, respectively, and Listeria and Staphylococcus aureus were also isolated from selected equipment surfaces.  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