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   2418篇
  免费   51篇
  国内免费   4篇
电工技术   13篇
综合类   6篇
化学工业   61篇
金属工艺   11篇
机械仪表   23篇
建筑科学   33篇
矿业工程   2篇
能源动力   10篇
轻工业   28篇
水利工程   28篇
石油天然气   1篇
无线电   90篇
一般工业技术   75篇
冶金工业   1982篇
原子能技术   3篇
自动化技术   107篇
  2022年   6篇
  2021年   4篇
  2020年   9篇
  2018年   20篇
  2017年   5篇
  2016年   9篇
  2015年   18篇
  2014年   15篇
  2013年   38篇
  2012年   20篇
  2011年   19篇
  2010年   23篇
  2009年   17篇
  2008年   23篇
  2007年   21篇
  2006年   22篇
  2005年   27篇
  2004年   16篇
  2003年   20篇
  2002年   23篇
  2001年   19篇
  2000年   18篇
  1999年   75篇
  1998年   653篇
  1997年   394篇
  1996年   247篇
  1995年   118篇
  1994年   96篇
  1993年   103篇
  1992年   16篇
  1991年   26篇
  1990年   24篇
  1989年   26篇
  1988年   32篇
  1987年   20篇
  1986年   17篇
  1985年   20篇
  1984年   2篇
  1983年   3篇
  1982年   12篇
  1981年   10篇
  1980年   16篇
  1978年   4篇
  1977年   45篇
  1976年   103篇
  1975年   5篇
  1974年   2篇
  1973年   2篇
  1972年   2篇
  1955年   4篇
排序方式: 共有2473条查询结果,搜索用时 15 毫秒
71.
Residuals of facial paralysis consist of a great variety of cosmetic and functional anomalies which differ in quality and/or quantity. An internationally standardized evaluation of such defects is mandatory for the assessment of the results of different therapeutic procedures. In the present study, a system has been developed to record the results of facial paralysis following therapy. Such a system does not require specialized training, instrumentation or require significant time for completion. A clearly-defined "Yes-No" evaluation criteria is established which creates a high interscorer reliability. The usefulness of this scoring system was tested by three examiners on 42 patients following facial nerve surgery, with an obtained interscorer reliability of 93%.  相似文献   
72.
In semiconductor manufacturing, the accurate placement of circuit components ensures the proper functioning of microelectronic circuits. This is often subject to photolithography, an optical technique that transfers circuit patterns from photomasks to silicon wafers. Sources of placement error include aberration and misalignment between different levels, and we focus on the former. Aberration is an optical phenomenon that often degrades imaging system performance. Since aberration differs from one imaging system to another, a photomask design that minimizes the aberration-induced placement error is desired. In this paper, we discuss the optimization process of a general one-dimensional mask pattern under a general illumination condition. The constraint is a known population mean of the root mean square aberrations for the imaging systems under consideration. To apply the theory, we search for the optimal parameters for two common mask designs: alternating phase-shifting masks (PSMs) and attenuated PSMs. The theoretical results are compared with those from a Monte Carlo analysis on a large set of imaging systems. These results are indicative to mask manufacturers and circuit designers of increasing manufacturability of circuits.  相似文献   
73.
Rule induction is an important part of learning in expert systems. Rules can help managers make more effective decisions and gain insight into the relationships between decision variables. We present a logic-based approach to rule induction in expert systems which is simple, robust and consistent. We also derive bounds on levels of certainty for combining rules. We apply our approach to the development of rules for the entry decisions of new products. We then discuss how the logic-based approach of rule induction can be used to create a decision support system and the methodology to create such a system.  相似文献   
74.
A PDES/STEP-based information model for computer-aided process planning   总被引:8,自引:0,他引:8  
Computer Aided Process Planning (CAPP) constitutes one of the most essential elements in Computer Integrated Manufacturing (CIM). Although many CAPP systems have been reported in literature during the last two decades, few of them are compatible enough to integrate easily with other systems in the CIM environment. One major reason is the lack of an effective method to represent the information required by CAPP, and to unify such information with the information of other systems in the CIM environment. Indeed, this problem has received relatively inadequate attention in the recent research of CAPP systems. In this paper, an information model for CAPP is developed by using the object-oriented modeling and the Product Data Exchange Step/STandard of Exchange Product data (PDES/STEP) techniques. The model consists of the part information model, the process plan information model, and the production resource information model. The EXPRESS language or the EXPRESS-G diagram is used to represent these models. Indeed, the proposed information model will greatly improve the CAPP system's capability of effective integration with other systems in the CIM environment, and, ultimately, to facilitate the implementation of the whole CIM strategy in manufacturing enterprises.  相似文献   
75.
用激光脉冲沉积(PLD)法在MgO(001)衬底上成功地生长、制备出了外延铌酸锶钡钠(SCNN)电光薄膜.对生长制备出的SCNN电光薄膜用X射线衍射对其微观结构进行了测量研究;X射线衍射结果显示生长在MgO(001)衬底上的SCNN电光薄膜是外延膜;对生长在MgO(001)衬底上的外延SCNN电光薄膜在200~900nm光谱范围的透射光谱进行了测量研究,通过对薄膜透射光谱的振荡曲线分析计算得到了SCNN电光薄膜的光学常数,结果发现外延SCNN电光薄膜的折射率符合单电子模型.  相似文献   
76.
This article provides an ethnography and analysis of the revival of the tradition of indigenous water buffalo cheese and milk product consumption in Shunde, Guangdong. Contrary to the widely held belief that dairy products are not part of the traditional Chinese diet, water buffalo cheese and milk products have been part of the food systems of Guangdong for centuries. But in the past 30 years, these indigenous milk products have been reinvented as a kind of culinary heritage, supplemented by new forms and practices. The popularity of water buffalo milk products in Shunde today has come about as a result of marketing by various agents, including cheese makers, milk merchants, chefs and the government in post-Mao China. Furthermore, the culture of milk consumption in Shunde today has been shaped by both the forces of post-reform economic development, international cultural institutions, the changing perceptions of members of different social classes, and modernity. The reinvented tradition of milk products provides people of different social classes with new ways of consuming milk products and of conducting social interactions.  相似文献   
77.
Jianping Tu  Wei Shih  Henry Mak 《传热工程》2017,38(17):1429-1438
A concept of using energy storage material (ESM) or phase change material (PCM) to enhance the heat transfer dissipation by a conventional compact fin-based heat sink is demonstrated. An actual design is developed, fabricated, and tested to demonstrate the heat transfer enhancement. The heat sink is light weight (made with Aluminum) and miniature in size with a total fin length of 26 mm. Test results demonstrated that under a high peak load (4.4 W/cm2) and low duty power cycle (30/55 on/off ratio with a period of 85 sec), the peak temperature at the heating surface with the ESM/PCM heat sink is 5°C lower than that of a conventional heat sink. At the tip of the fin, the peak temperature with the ESM/PCM heat sink is 3°C lower than that of a conventional heat sink. When the external heat transfer coefficient increases (with increase air velocity), the impact of the PCM/ESM on the heat transfer performance is less. A numerical model, based on COMSOL, is developed to provide a theoretical understanding of the experimental observation.  相似文献   
78.
Systemic lupus erythematosus (SLE) is an immune-complex-mediated multi-systemic autoimmune condition of multifactorial etiology, which mainly affects young women. It is currently believed that the onset of SLE and lupus flares are triggered by various environmental factors in genetically susceptible individuals. Various environmental agents and toxicants, such as cigarette smoke, alcohol, occupationally- and non-occupationally-related chemicals, ultraviolet light, infections, sex hormones and certain medications and vaccines, have been implicated to induce SLE onset or flares in a number case series, case-control and population-based cohort studies and very few randomized controlled trials. Here, we will describe some of these recognized environmental lupus triggering and perpetuating factors and explain how these factors potentially bias the immune system towards autoimmunity through their interactions with genetic and epigenetic alterations. Further in-depth exploration of how potentially important environmental factors mechanistically interact with the immune system and the genome, which trigger the onset of SLE and lupus flares, will certainly be one of the plausible steps to prevent the onset and to decelerate the progress of the disease.  相似文献   
79.
The reactive and refractory metals zirconium, titanium, tantalum and niobium have been in commercial production and industrial application over the last 30 years and more. With growing experience, there has been progressive improvement in process and equipment designs in the industrial practice. There has also been a continuous drive to develop entirely new processes, and to diversify the applications of these metals. The paper reviews the present status and the emerging trends, and places the Indian work in the global perspective.  相似文献   
80.
In this paper discrete-time bilinear systems are considered. Necessary and sufficient conditions are developed which ensure that for any constant input in an unbounded control domain, the trajectories of the system tend to the origin as time increases.  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