全文获取类型
收费全文 | 5825篇 |
免费 | 388篇 |
国内免费 | 213篇 |
专业分类
电工技术 | 95篇 |
综合类 | 226篇 |
化学工业 | 1620篇 |
金属工艺 | 215篇 |
机械仪表 | 164篇 |
建筑科学 | 248篇 |
矿业工程 | 44篇 |
能源动力 | 135篇 |
轻工业 | 162篇 |
水利工程 | 122篇 |
石油天然气 | 46篇 |
武器工业 | 31篇 |
无线电 | 259篇 |
一般工业技术 | 769篇 |
冶金工业 | 994篇 |
原子能技术 | 37篇 |
自动化技术 | 1259篇 |
出版年
2023年 | 79篇 |
2022年 | 80篇 |
2021年 | 103篇 |
2020年 | 145篇 |
2019年 | 120篇 |
2018年 | 120篇 |
2017年 | 198篇 |
2016年 | 202篇 |
2015年 | 161篇 |
2014年 | 245篇 |
2013年 | 383篇 |
2012年 | 247篇 |
2011年 | 438篇 |
2010年 | 273篇 |
2009年 | 336篇 |
2008年 | 335篇 |
2007年 | 349篇 |
2006年 | 346篇 |
2005年 | 288篇 |
2004年 | 285篇 |
2003年 | 234篇 |
2002年 | 226篇 |
2001年 | 173篇 |
2000年 | 110篇 |
1999年 | 110篇 |
1998年 | 108篇 |
1997年 | 73篇 |
1996年 | 63篇 |
1995年 | 56篇 |
1994年 | 44篇 |
1993年 | 35篇 |
1992年 | 36篇 |
1991年 | 30篇 |
1990年 | 45篇 |
1989年 | 35篇 |
1988年 | 33篇 |
1987年 | 30篇 |
1986年 | 23篇 |
1985年 | 30篇 |
1984年 | 29篇 |
1983年 | 15篇 |
1982年 | 22篇 |
1981年 | 13篇 |
1980年 | 10篇 |
1979年 | 10篇 |
1978年 | 6篇 |
1977年 | 7篇 |
1976年 | 6篇 |
1957年 | 6篇 |
1955年 | 13篇 |
排序方式: 共有6426条查询结果,搜索用时 0 毫秒
121.
This paper studies a supply system for a retailer who orders a single product from one manufacturer. Orders filled by the manufacturer pass through multiple transportation stages before reaching the retailer. Each stage represents either a physical location or a step in the delivery process. The lead time for a new order depends on the location of shipments against prior orders in transit. Shipments are not allowed to cross over in time. Thus, the movement of each shipment depends on the movements of shipments ahead of it and the resulting congestion. The retailer is able to track shipments as they move through the transportation channel. The retailer adopts an ordering policy that minimises the sum of his one-period holding and shortage costs, using available status information of shipments already in transit. The case where practical constraints prevent the retailer from obtaining a complete status of shipments at all stages in the transportation channel is considered. The methodology developed evaluates the value of partial shipment tracking information, and uses it to determine the optimal placement of a limited number of tracking devices. The methodology can also be used to evaluate the cost–benefit of placing additional tracking devices in the supply system. 相似文献
122.
To successfully manage today’s complex production systems it is essential to study operators’ perception of the system. The paper presents perceived production complexity assessed at seven manufacturing companies with the CompleXity Index (CXI) method. While other methods have measured product variants, layout, work content, tools and information items, CXI combines them into three areas. These three complexity areas (Station design, Work variance and Disturbance handling) help to create an understanding of the complex system by visualising how they contribute to complexity, and show the need to support the operators’ ability to handle the varying work. 相似文献
123.
Evaporation‐ and Solution‐Process‐Feasible Highly Efficient Thianthrene‐9,9′,10,10′‐Tetraoxide‐Based Thermally Activated Delayed Fluorescence Emitters with Reduced Efficiency Roll‐Off 下载免费PDF全文
124.
125.
Sheng-Long Lee Chun-Hung Yen Yu-Chih Tzeng Jo-Kuang Nieh Hui-Yun Bor Gung-Hui Liu 《Materials and Manufacturing Processes》2018,33(8):867-872
Trace amount (0.3?wt%) of scandium is added to Al–5.6Mg–0.7Mn alloy to form uniformly distributed Al3Sc precipitates for producing a fine-grained and stable microstructure at high temperature through cross-channel extrusion process. Superplasticity and hot workability of the Sc-containing Al–5.6Mg–0.7Mn alloy, after extrusion, are also examined. The result indicates that Al–5.6Mg–0.7Mn alloys with and without 0.3?wt% Sc after extrusion of six passes at 300°C, fine-grained structures were observed with grain sizes of 1–2?µm and improvement of mechanical properties. Furthermore, Al3Sc phase can effectively retard recrystallization to increase the thermal stability and remain equiaxed. The elongation of Al–5.6Mg–0.7Mn alloy with Sc addition to failure is extended to 873% maximum at high temperature of 450°C at strain rate of 1?×?10?1?s?1after six passes in the CCEP. 相似文献
126.
The stability of a class of Markov Jump Linear Systems characterized by piecewise-constant transition rates and system dynamics is investigated. For these Switching Markov Jump Linear Systems, mean square stability is analyzed through the time evolution of the second-order moment of the state. The main result is a sufficient condition that guarantees mean square stability under constraints on the dwell-time between switching instants. An alternative condition based on Kronecker calculus is worked out. It is shown that both the stability criteria admit an LMI implementation. 相似文献
127.
梁富伟 《数字社区&智能家居》2011,(5)
该文采用B/S架构技术,依据现代化饭店信息管理业务需求,进行了饭店管理模拟教学系统的研究,以方便饭店管理专业的学生进行现代化饭店行业业务流程的学习和模拟实践。 相似文献
128.
129.
Annett Schwamborn Hubertina ThillmannMaria Opfermann Detlev Leutner 《Computers in human behavior》2011,27(1):89-93
This study investigated, whether learning from science texts can be enhanced by providing learners with different forms of visualizations (pictures) in addition to text. One-hundred-two 9th and 10th graders read a computer-based text on chemical processes of washing and answered questions on cognitive load (mental effort, perceived difficulty) and comprehension (retention, transfer, drawing). Instruction varied according to a 2 × 2-factorial design with ‘learner-generated pictures’ (yes, no) and ‘provided pictures’ (yes, no) as factors. Results indicate positive main effects of provided pictures on all three comprehension measures and negative main effects on both cognitive load measures. Additional analyses revealed a mediation effect of perceived difficulty on retention and transfer, that is learning with provided pictures decreased cognitive load and enhanced comprehension. Furthermore, results show a positive main effect of learner-generated pictures on drawing and mental effort, but no mediation effect. Taken together, computer-based learning with provided pictures enhances comprehension as it seems to promote active processing while reducing extraneous cognitive processing. Learners, generating pictures, however, seem to have less cognitive resources available for essential and generative processing, resulting in reduced comprehension. These results are in line with cognitive load theory, cognitive theories of multimedia learning, and generative theories of learning. 相似文献
130.
Gaussian process (GP) models form an emerging methodology for modelling nonlinear dynamic systems which tries to overcome certain limitations inherent to traditional methods such as e.g. neural networks (ANN) or local model networks (LMN).The GP model seems promising for three reasons. First, less training parameters are needed to parameterize the model. Second, the variance of the model's output depending on data positioning is obtained. Third, prior knowledge, e.g. in the form of linear local models can be included into the model. In this paper the focus is on GP with incorporated local models as the approach which could replace local models network.Much of the effort up to now has been spent on the development of the methodology of the GP model with included local models, while no application and practical validation has yet been carried out. The aim of this paper is therefore twofold. The first aim is to present the methodology of the GP model identification with emphasis on the inclusion of the prior knowledge in the form of linear local models. The second aim is to demonstrate practically the use of the method on two higher order dynamical systems, one based on simulation and one based on measurement data. 相似文献