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   28779篇
  免费   1217篇
  国内免费   108篇
电工技术   371篇
综合类   229篇
化学工业   4846篇
金属工艺   622篇
机械仪表   581篇
建筑科学   962篇
矿业工程   93篇
能源动力   929篇
轻工业   3833篇
水利工程   240篇
石油天然气   150篇
武器工业   6篇
无线电   2235篇
一般工业技术   4078篇
冶金工业   6984篇
原子能技术   237篇
自动化技术   3708篇
  2023年   137篇
  2022年   304篇
  2021年   775篇
  2020年   530篇
  2019年   595篇
  2018年   683篇
  2017年   763篇
  2016年   715篇
  2015年   549篇
  2014年   847篇
  2013年   1398篇
  2012年   1244篇
  2011年   1573篇
  2010年   1149篇
  2009年   1198篇
  2008年   1090篇
  2007年   955篇
  2006年   769篇
  2005年   832篇
  2004年   899篇
  2003年   808篇
  2002年   785篇
  2001年   688篇
  2000年   537篇
  1999年   546篇
  1998年   2269篇
  1997年   1462篇
  1996年   998篇
  1995年   648篇
  1994年   512篇
  1993年   575篇
  1992年   226篇
  1991年   288篇
  1990年   233篇
  1989年   195篇
  1988年   213篇
  1987年   167篇
  1986年   170篇
  1985年   181篇
  1984年   129篇
  1983年   93篇
  1982年   119篇
  1981年   125篇
  1980年   121篇
  1979年   91篇
  1978年   75篇
  1977年   159篇
  1976年   269篇
  1975年   83篇
  1973年   49篇
排序方式: 共有10000条查询结果,搜索用时 343 毫秒
991.
Reduced scale experiments are often employed in engineering because they are much cheaper than real scale testing. Unfortunately, though, it is difficult to design a thermal-hydraulic circuit or equipment in reduced scale capable of reproducing, both accurately and simultaneously, all the physical phenomena that occur in real scale and operating conditions. This paper presents a methodology to designing thermal-hydraulic experiments in reduced scale based on setting up a constrained optimization problem that is solved using genetic algorithms (GAs). In order to demonstrate the application of the methodology proposed, we performed some investigations in the design of a heater aimed to simulate the transport of heat and momentum in the core of a pressurized water reactor (PWR) at 100% of nominal power and non-accident operating conditions. The results obtained show that the proposed methodology is a promising approach for designing reduced scale experiments.  相似文献   
992.
Software engineers of multi‐agent systems (MASs) are faced with different concerns such as autonomy, adaptation, interaction, collaboration, learning, and mobility, which are essentially different from classical concerns addressed in object‐oriented software engineering. MAS developers, however, have relied mostly on object‐oriented design techniques and programming languages, such as Java. This often leads to a poor separation of MAS concerns and in turn to the production of MASs that are difficult to maintain and reuse. This paper discusses software engineering approaches for MASs, and presents a new method for integrating agents into object‐oriented software engineering from an early stage of design. The proposed approach encourages the separate handling of MAS concerns, and provides a disciplined scheme for their composition. Our proposal explores the benefits of aspect‐oriented software development for the incorporation of agents into object‐oriented systems. We also illustrate our aspect‐oriented approach through the Portalware multi‐agent system, a Web‐based environment for the development of e‐commerce portals. Copyright © 2004 John Wiley & Sons, Ltd.  相似文献   
993.
Pertrochanteric femoral fractures are common and intramedullary nailing is an accepted method for their surgical treatment. Accurate placement of the implant is essential to ensure fixation. The conventional technique can require multiple guide wire passes, and relies heavily on fluoroscopy. A computer-assisted planning and navigation system based on two-dimensional fluoroscopy for guide wire placement in the femoral neck has been developed, in order to perform intramedullary pertrochanteric fracture fixation using the proximal femoral nail (PFNA). The planning process was supported by a 'zero-dose C-arm navigation' system. The PFNA was inserted into 12, intact, femoral sawbones guided by the computer-based navigation, and into 12, intact, femoral sawbones using a conventional fluoroscopic-assisted technique. Guide wire and subsequent blade placement in the femoral neck was evaluated. The computer-assisted technique achieved a significant decrease in the number of required fluoroscopic images and in the number of guide wire passes. The obtained average blade placement accuracy in the femoral neck was equivalent to the conventional technique. The operation time was significantly longer in the navigation-assisted group. The addition of computer-assisted planning and surgical guidance to the intramedullary nailing of pertrochanteric femoral fractures offers a number of clinical benefits based on the results of this sawbone study. Further studies including fractured sawbones and cadaver models with extension of the navigation process to all steps of PFNA introduction and with the goal of reducing operation time are indispensable before integration of this navigation system into clinical practice.  相似文献   
994.
The eight current species of bear (Ursidae) are widely distributed throughout Europe, Asia, and America. They are mainly encountered in the northern hemisphere, except for the spectacled bear and the sun bear, which are also found in the south of the equator. Adaptations of the masticatory apparatus (teeth, tongue, and musculature) to diet are one of the factors that imply the greatest structural changes in the cranium. This diet may be carnivorous, herbivorous, melliferous, or insectivorous, with one type of food predominating according to the time of year. The way in which food is eaten determines the morphology of the lingual surface; generally speaking, all bears put their mouth to the food, which, initially, they lick or they let the food stick to their tongue, as occurs when insects are eaten. As in all mammals, a distinction can be made between mechanical and gustatory papillae and the development and distribution of which depend on the species and their eating habits. In this study of the complete tongues of four species of adult bears, we describe the morphology of the lingual surfaces, the different types of papillae, their characteristics, and topographic distribution. It was seen that there were five main types of lingual papillae: filiform, conical, fungiform, foliate, and vallate. Morphology of the microgrooves and pores was similar to that observed in other mammals. In general, there were no great differences among the four species of bears studied, perhaps due to the similarity in the kind of food they consume in captivity.  相似文献   
995.
椭球封头圆柱形爆炸容器振动特性研究   总被引:2,自引:1,他引:2  
对椭球封头圆柱形爆炸容器在中心点爆炸状态下的 19次有效炮实验给予了介绍并对实验结果的壳体振动特性进行了分析。理论和实验分析表明 ,在封闭容器内爆炸冲击载荷具有明显的脉冲激励特征 ;容器壳体的振动频谱主要受前 10阶固有频率的影响 ;随着冲击载荷的增加 ,其壳体的主振频率将趋于相应壳体的呼吸频率 ,其应变增长具有减少的趋势 ;联接螺栓的振动模态主要受相应圆柱壳体和封头轴向振动模态的影响 ,并出现了在时域上其振动模态在圆柱壳振动模态和封头轴向振动模态间跳变的现象。  相似文献   
996.

Definition of the problem

“Medical necessity” (MedN) is the central regulatory concept for decisions about which services are covered by German statutory health insurance. Despite its seeming objectivity and dependence on physicians’ expert judgment, the concept is by no means clearly defined.

Arguments

In this first of five planned papers on the conceptual analysis of MedN from the perspectives of philosophy and ethics of medicine, law, and (social) medicine, the focus lies on systemizing ongoing controversies.

Conclusion

Our goal is to come up with a so far missing foundation for detailed debates. We aim to clarify MedN’s conceptual structure, function, contextuality, and ambiguities as well as the fundamental limits of conceptual investigations for the normative questions at issue of regulating medical services.
  相似文献   
997.
998.

Background

The international recruitment and migration of health workers has long been debated in the health policy literature. This study assesses to what extent the ethics of international recruitment are targeted in existing public health peer-reviewed literature, with a focus on concepts and in-depth consideration within articles. It further critically discusses hidden implications of this discourse regarding equity-creating health policy.

Methods

We conducted a qualitative scoping literature review searching the databases PubMed and Web of Science. Articles were assessed for quality using the Critical Appraisal Skills Program (CASP) checklist for qualitative research. Drawing on a thematic analysis approach, common themes across the sample were identified, coded and analyzed.

Results

A total of 17 articles were included in the analysis after searches and quality appraisal. These articles predominantly targeted nursing professions and physicians, and were written mainly by authors working in the Global North. Thematic analysis revealed that ethics are generally discussed in connection with overviews regarding the situation of health systems as well as regarding inequities between countries. Their focus lies more on migration between countries than between regions within a country. Proposed solutions are usually of an economic nature and range from global financial equalization between countries to national improvements in working conditions. Creative evaluation schemes for these solutions are rarely discussed in depth. Overall, the academic ethics discussion focuses predominantly on the health systems level, and views migration of health workers as problematic.

Conclusions

Our results suggest that academic research operates and aims to inform policy within the current system, without necessarily proposing fundamental changes to the status quo. Thus, an ethics discourse of health workforce recruitment may serve to increase awareness of inequalities without supporting radical change. Further research into intersectional aspects of health worker migration, including gender and ethnicity, may be useful for the discussion on inequities.
  相似文献   
999.
1000.

Definition of the problem

The concept of “ethics” has recently been incorporated into both the 2014 Model Professional Code for Dentists and the current version of the “National Competence-Based Catalog of Learning Objectives in Dental Medicine” (NKLZ, Nationaler Kompetenzbasierter Lernzielkatalog Zahnmedizin). The study presented here addresses the question which relevance this has for the relevance of the new concept accomplished for the dental profession and society.

Arguments

To this end, the societal processes that are related to the autonomous freedom of action of the dental profession are discussed. Therefore the sociological fields of discourse such as profession (and the effect of its constitutive antinomies), trust, education, expertise, practice of treatments and sanction are reviewed for their potential of having connections to each other and serving as a structural frame concerning an ethically reflected acting of the professional. The basis of the professional freedom of action is the trust of society and the individual patient in the professionally acting dentist.

Conclusion

The study arrives at the conclusion that it was a serious omission for many decades not to make young dentists aware of the ethical foundations of dental activity on an institutionally established basis and thus failing to encourage them to constantly reflect their professional expertise in relation to the problems to be solved. This deficit has now been identified. It is absolutely essential to implement an institutionalized structure dealing with ethical questions within the scope of dental medicine.
  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