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   3552篇
  免费   197篇
  国内免费   3篇
电工技术   65篇
综合类   13篇
化学工业   738篇
金属工艺   80篇
机械仪表   63篇
建筑科学   166篇
矿业工程   16篇
能源动力   80篇
轻工业   259篇
水利工程   24篇
石油天然气   1篇
无线电   385篇
一般工业技术   626篇
冶金工业   697篇
原子能技术   26篇
自动化技术   513篇
  2023年   68篇
  2022年   89篇
  2021年   122篇
  2020年   91篇
  2019年   99篇
  2018年   109篇
  2017年   118篇
  2016年   119篇
  2015年   120篇
  2014年   132篇
  2013年   183篇
  2012年   192篇
  2011年   202篇
  2010年   148篇
  2009年   142篇
  2008年   139篇
  2007年   136篇
  2006年   93篇
  2005年   95篇
  2004年   52篇
  2003年   40篇
  2002年   61篇
  2001年   50篇
  2000年   37篇
  1999年   49篇
  1998年   164篇
  1997年   114篇
  1996年   85篇
  1995年   56篇
  1994年   49篇
  1993年   47篇
  1992年   30篇
  1991年   25篇
  1990年   38篇
  1989年   38篇
  1988年   28篇
  1987年   21篇
  1986年   19篇
  1985年   20篇
  1984年   15篇
  1983年   22篇
  1981年   17篇
  1980年   12篇
  1979年   17篇
  1978年   21篇
  1977年   14篇
  1976年   30篇
  1973年   12篇
  1971年   20篇
  1970年   16篇
排序方式: 共有3752条查询结果,搜索用时 10 毫秒
21.
Surveyed 38 rehabilitation counselors to investigate the relationship of experienced burnout to self-concept and job setting. Ss completed the Maslach Burnout Inventory and a questionnaire about their work. The emotional exhaustion component of burnout emerged as the key factor in the results. Emotional exhaustion was related to work overload and a perceived lack of control. It was also linked to dissatisfaction with certain aspects of the job. Findings are consistent with previous theorizing and research on burnout by J. Gaines and J. M. Jermier (see record 1984-10923-001) and C. Maslach and S. E. Jackson (see record 1985-24012-001) and underscore the relevance of this phenomenon for the rehabilitation profession. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
22.
Koch  N. 《Software, IET》2007,1(3):98-111
Software development techniques are continuously evolving with the goal of solving the main problems that still affect the building and maintenance of software systems: time, costs and error-proneness. Model-driven engineering (MDE) approaches aim to reduce at least some of these problems providing techniques for the construction of models and the specification of transformation rules, tool support and automatic generation of code and documentation. The method of resolution of MDE is to first build models, which are independent of the platform, transforming them in later stages to technological-dependent models, and to achieve automatic model and code generation based on transformation rules. Web engineering is a domain where model-driven approaches can be used to address evolution and adaptation of Web software to continuously emerging new platforms and changes in technologies. We present an overview of the development process of the Unified Modelling Language (UML)-based Web engineering (UWE) defined as an MDE approach. The main characteristic of UWE is the use of standards including the UML, XML metadata interchange as model exchange, meta-object facility for metamodelling, model-driven architecture and the transformation language query-view-transformation. We focus on the model transformation aspects of the UWE process.  相似文献   
23.
Integrated model-driven dashboard development   总被引:1,自引:0,他引:1  
Business performance modeling and model-driven business transformation are two research directions that are attracting much attention lately. In this study, we propose an approach for dashboard development that is model-driven and can be integrated with the business performance models. We adopt the business performance modeling framework, and we extend it in order to capture the reporting aspect of the business operation. We describe models that can effectively represent all the elements necessary for the business performance reporting process, and the interactions among them. We demonstrate how all these models can be combined and automatically generate the final solution. We further extend the proposed framework with mechanisms that can detect changes in the models and incrementally update the deployed solutions. Finally, we discuss our experience from the application of our technique in a real-world scenario. This case study shows that our technique can be efficiently applied to and handle changes in the underlying business models, delivering significant benefits in terms of both development time and flexibility.  相似文献   
24.
In many technical devices such as transformers and electrical machines, large differences in geometric dimensions are observed. As a consequence, the generation of a 3D computational grid for the whole device leads to unacceptably large numbers of elements or can even fail. In addition to the commonly applied cartesian or cylindrical symmetries of the overall geometry, the model can be subdivided into parts featuring translational or cylindrical symmetries. Such parts are discretised separately, accounting for the local symmetry, and are then combined with the surrounding 3D model. Excitations and boundary conditions of the submodels are not necessarily symmetric but are expected to be smooth in the direction of the symmetry. Then, the field distribution at the interface is well approximated by a set of spectral elements along the dimension of symmetry. Coupling between the model parts is carried out by means of Lagrange multipliers. A single-phase transformer with thin insulation sheets is taken as an example to illustrate the proposed hybrid discretisation. The cross-section of the cylindrically symmetric part containing thin sheets, is represented by a fine 2D finite-element mesh so that all the geometrical details can be resolved, and the rest of the structure is discretised by a 3D mesh. Nevertheless, a fully 3D field distribution is calculated in all model parts. Only a small number of harmonic functions is needed to account for the azimuthal field variation at the cylindrical interface. Hence, the number of unknowns in the numerical model is reduced significantly, while a high level of accuracy is maintained  相似文献   
25.
Pilot tests were performed with a process combination of electrodialysis and ozonation for the removal of micropollutants and the concentration of nutrients in urine. In continuous and batch experiments, maximum concentration factors up to 3.5 and 4.1 were obtained, respectively. The desalination capacity did not decrease significantly during continuous operation periods of several weeks. Membrane cleaning after 195 days resulted in approximately 35% increase in desalination rate. The Yeast Estrogen Screen (YES), a bioassay that selectively detects oestrogenic compounds, confirmed that about 90% of the oestrogenic activity was removed by electrodialysis. HPLC analysis showed that ibuprofen was removed to a high extent, while other micropollutants were below the detection limit. In view of the fact that ibuprofen is among the most rapidly transported micropollutants in electrodialysis processes, this result indicates that electrodialysis provides an effective barrier for micropollutants. Standardised plant growth tests were performed in the field with the salt solution resulting from the treatment by electrodialysis and subsequent ozonation. The results show that the plant height is comparable to synthetic fertilisers, but the crop yield is slightly lower. The latter is probably caused by volatilisation losses during field application, which can be prevented by improved application technologies.  相似文献   
26.
Ohne Zusammenfassung  相似文献   
27.

The interoperability of proof assistants and the integration of their libraries is a highly valued but elusive goal in the field of theorem proving. As a preparatory step, in previous work, we translated the libraries of multiple proof assistants, specifically the ones of Coq, HOL Light, IMPS, Isabelle, Mizar, and PVS into a universal format: OMDoc/MMT. Each translation presented great theoretical, technical, and social challenges, some universal and some system-specific, some solvable and some still open. In this paper, we survey these challenges and compare and evaluate the solutions we chose. We believe similar library translations will be an essential part of any future system interoperability solution, and our experiences will prove valuable to others undertaking such efforts.

  相似文献   
28.
Online social networks have been gaining increasing economic importance in light of the rising number of their users. Numerous recent acquisitions priced at enormous amounts have illustrated this development and revealed the need for adequate business valuation models. The value of an online social network is largely determined by the value of its users, the relationships between these users, and the resulting network effects. Therefore, the interconnectedness of a user within the network has to be considered explicitly to get a reasonable estimate for its economic value. Established standard business valuation models, however, do not account for these aspects sufficiently. Thus, we propose an economic model for the valuation of online social networks, which takes into account the users’ interconnectedness within the network. Furthermore, we analyze different centrality measures, which can be used to quantify users’ interconnectedness in online social networks and propose a measure which is based on the PageRank-algorithm. Finally, the practical application of the model is illustrated by an example of the European online social network XING.com.  相似文献   
29.
Reflective displays are advantageous in applications requiring low power or daylight readability. However, there are no low‐cost reflective technologies capable of displaying bright colors. By employing photoluminescence to more efficiently use ambient light, we created a prototype display that provides bright, full color in a simple, low‐cost architecture. This prototype includes a novel electrokinetic shutter, a layer that incorporates patterned luminescent red, green, and blue sub‐pixel elements, and a novel optical out‐coupling scheme. The luminescent elements convert otherwise‐wasted portions of the incident spectrum to light in the desired color band, resulting in improved color saturation and lightness. This prototype provides a color gamut that is superior to competing reflective display technologies that utilize color filters in single‐layer side‐by‐side sub‐pixel architectures. The current prototype is capable of switching in <0.5 s; future displays based on an alternative electro‐optic shutter technology should achieve video rate operation. A transflective version of this technology has also been prototyped. The transflective version utilizes its backlight with a power efficiency that is at least three times that of a conventional liquid crystal display. These photoluminescence‐based technologies enable a host of applications ranging from low‐power mobile products and retail pricing signage to daylight readable signage for outdoor advertising segments.  相似文献   
30.
Mechanical alloying was used to synthesize NixZr1–x alloys from mixtures of intermetallic compound powders, and also from mixtures of intermetallic compound powders and pure elemental powders. The mechanically alloyed powders were amorphous in the range 0.24 x 0.85. This range is larger than amorphous alloys produced by the melt-spinning technique and mechanical alloying of elemental crystalline powders. Two-phase mixtures of the amorphous phase and the corresponding crystalline terminal solid solution were formed in the range 0.10 x 0.22, and x=0.90. It is found that the morphological development during mechanical alloying of these powders is different from mechanical alloying using only pure ductile crystalline elemental powders. The thermal stability has been investigated. The enthalpy and activation energy of crystallization for Ni-Zr amorphous powders prepared by mechanical alloying are lower than those for melt-spun samples of the same composition. The crystallization temperature of the mechanically alloyed Ni-Zr amorphous powders is higher than that of meltspun samples in the composition range Ni20Zr80 to Ni33Zr67 and Ni40Zr60 to Ni60Zr40. The presence of tiny crystallites as nucleation centres and high oxygen levels in the mechanically alloyed amorphous alloys might be responsible for the differences in crystallization behaviour. A new crystalline metastable phase was observed during crystallization studies of Ni24Zr76 amorphous powder.  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