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   4541篇
  免费   67篇
  国内免费   5篇
电工技术   48篇
综合类   6篇
化学工业   802篇
金属工艺   93篇
机械仪表   57篇
建筑科学   272篇
矿业工程   55篇
能源动力   122篇
轻工业   407篇
水利工程   61篇
石油天然气   27篇
武器工业   1篇
无线电   286篇
一般工业技术   649篇
冶金工业   1199篇
原子能技术   35篇
自动化技术   493篇
  2022年   30篇
  2021年   49篇
  2020年   34篇
  2019年   45篇
  2018年   53篇
  2017年   39篇
  2016年   51篇
  2015年   26篇
  2014年   71篇
  2013年   275篇
  2012年   140篇
  2011年   223篇
  2010年   181篇
  2009年   146篇
  2008年   217篇
  2007年   196篇
  2006年   209篇
  2005年   209篇
  2004年   170篇
  2003年   138篇
  2002年   108篇
  2001年   83篇
  2000年   90篇
  1999年   102篇
  1998年   136篇
  1997年   94篇
  1996年   95篇
  1995年   76篇
  1994年   87篇
  1993年   75篇
  1992年   70篇
  1991年   52篇
  1990年   75篇
  1989年   74篇
  1988年   57篇
  1987年   59篇
  1986年   55篇
  1985年   59篇
  1984年   80篇
  1983年   50篇
  1982年   70篇
  1981年   64篇
  1980年   50篇
  1979年   44篇
  1978年   35篇
  1977年   35篇
  1976年   31篇
  1975年   28篇
  1974年   28篇
  1973年   27篇
排序方式: 共有4613条查询结果,搜索用时 15 毫秒
1.
A series of studies of top European and other firms has revealed patterns of design management associated with commercial success. Firms that invest resources and professional expertise in product and industrial design in traditional and new industries have been commercially more successful than firms that pay less attention to these aspects of design. As an industry matures there is a shift in emphasis from design associated with technological innovation, to designs supporting technical improvements, and then to supporting user needs, fashion and product variants. These issues are illustrated through the history of the evolution of the bicycle.  相似文献   
2.
3.
The monolithic integration of components holds promise to increase network functionality and reduce packaging expense. Integration also drives down yield due to manufacturing complexity and the compounding of failures across devices. Consensus is lacking on the economically preferred extent of integration. Previous studies on the cost feasibility of integration have used high-level estimation methods. This study instead focuses on accurate-to-industry detail, basing a process-based cost model of device manufacture on data collected from 20 firms across the optoelectronics supply chain. The model presented allows for the definition of process organization, including testing, as well as processing conditions, operational characteristics, and level of automation at each step. This study focuses on the cost implications of integration of a 1550-nm DFB laser with an electroabsorptive modulator on an InP platform. Results show the monolithically integrated design to be more cost competitive over discrete component options regardless of production scale. Dominant cost drivers are packaging, testing, and assembly. Leveraging the technical detail underlying model projections, component alignment, bonding, and metal-organic chemical vapor deposition (MOCVD) are identified as processes where technical improvements are most critical to lowering costs. Such results should encourage exploration of the cost advantages of further integration and focus cost-driven technology development.  相似文献   
4.
Food products can be high‐pressure processed (HPP) either in bulk or prepackaged in flexible or semi‐rigid packaging materials. In the latter case the packaging material is subjected, together with the food, to high‐pressure treatment. A number of studies have been performed to quantify the effects of high‐pressure processing on the physical and barrier properties of the packaging material, since the integrity of the package during and after processing is of paramount importance to the safety and quality of the food product. This article reviews the results of published research concerning the effect of HPP on packaging materials. Copyright © 2004 John Wiley & Sons, Ltd.  相似文献   
5.
6.
MAN is but a part of the universe; his capabilities make him a significant link, in the cycle of life. To ensure this life, man must live in harmony with his environment. Recently, a disharmony has been discovered which could have grave effects upon the existence of man. It appears that man in his great thrust forward is destroying his own environment. The gravity of this threat to man's own existence carries some intrinsic problems of its own: man must allow his reason rather than his emotion to take command.  相似文献   
7.
8.
Gurton KP  Bruce CW 《Applied optics》1995,34(15):2822-2828
Asystem has been developed to measure the absorption cross section for a single carbon fiber at 35 GHz as a functio of length, orientation, and diameter. Typical lengths of the fibers considered ranged from 1 to 20 mm, and diameters ranged from 3 to 8 μm. The results were compared with the modified integra equation calculations of Waterman and Pedersen that describe the scattering and absorption behavior for a wire of finite length and conductivity. Good agreement was found for all lengths, orientations, and diameters studied.  相似文献   
9.
Reducing environmental impacts and obtaining economic benefits based on utilisation of waste materials are drivers for the implementation of cleaner production policies and technologies in food processing industries. Starch is a very versatile material with a wide range of applications in the food, pharmaceutical, textile, paper, cosmetic and construction industries. In Ethiopia, starch is widely used in the textile industry. To meet the starch demand, the country imports approximately 45% of the starch used in the country. Consequently, it is imperative to find additional sources of starch that could substitute for the amount of starch that is currently being imported. Mango seeds, a waste material that is disposed of after consumption of mangos, were studied for potential use as an alternative resource for starch production. The results showed that starch extraction from mango seeds was facile and a good quality product was obtained. The present study is concerned with a techno-economic analysis for industrial production of starch from mango seeds. The study shows that extraction of starch from waste mango seeds is feasible: the project is financially viable with an accounting rate of return of 83% and a break-even analysis of 78% with a payback period of 2 years.  相似文献   
10.
Odin the Allfather had in his service two great ravens. These ravens' names were Hugin (Thought) and Munin (Memory) and every morning at dawn they would fly off over Midgard (the world) in search of news and information to learn more about humans and their activities. At sundown, they would return to Odin where they would perch one on each of Odin's shoulders, and whisper into his ears all that they had seen and heard.Experience, stored in the brain as memory, is the raw material for intelligence and thought. It has been suggested that at sundown (i.e., during sleep) the brain adjusts its own synaptic matrix to enable adaptive responses to future events by a process of gradient descent optimization, involving repeated reactivations of recent and older memories and gradual adjustment of the synaptic weights. Memory retrieval, thought, and the generation of adaptive behavioral responses involve globally coordinated trajectories through the neuronal state-space, mediated by appropriate synaptic linkages. Artificial neural networks designed to implement even the most rudimentary forms of memory and knowledge extraction and adaptive behavior incorporate massively and symmetrically interconnected nodes; yet, in the cerebral cortex, the probability of a synaptic connection between any two arbitrarily chosen cells is on the order of 10−6, i.e., so close to zero that a naive modeler might neglect this parameter altogether. The probability of a symmetric connection is even smaller (10−12). How then, are thought and memory even possible? The solution appears to have been in the evolution of a modular, hierarchical cortical architecture, in which the modules are internally highly connected but only weakly interconnected with other modules. Appropriate inter-modular linkages are mediated indirectly via common linkages with higher level modules collectively known as association cortex. The hippocampal formation in the temporal lobe is the highest level of association cortex. It generates sequentially coupled patterns unique to the location and content of experience, but which do not contain the actual stored data. Rather, the patterns serve as pointers or ‘links’ to the data. Spontaneous reactivation of these linking patterns during sleep may enable the retrieval of recent sequences of experience stored in the lower levels of the cortex and the gradual extraction of knowledge from them. In this essay I explore these ideas, their implications, and the neuroscientific evidence for them.  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