全文获取类型
收费全文 | 83113篇 |
免费 | 6159篇 |
国内免费 | 3851篇 |
专业分类
电工技术 | 3200篇 |
技术理论 | 12篇 |
综合类 | 19555篇 |
化学工业 | 8588篇 |
金属工艺 | 2039篇 |
机械仪表 | 4066篇 |
建筑科学 | 9359篇 |
矿业工程 | 1801篇 |
能源动力 | 1486篇 |
轻工业 | 2419篇 |
水利工程 | 1703篇 |
石油天然气 | 1942篇 |
武器工业 | 1038篇 |
无线电 | 7168篇 |
一般工业技术 | 5941篇 |
冶金工业 | 4277篇 |
原子能技术 | 422篇 |
自动化技术 | 18107篇 |
出版年
2024年 | 269篇 |
2023年 | 1051篇 |
2022年 | 1614篇 |
2021年 | 2176篇 |
2020年 | 2312篇 |
2019年 | 1762篇 |
2018年 | 1670篇 |
2017年 | 1963篇 |
2016年 | 2414篇 |
2015年 | 2868篇 |
2014年 | 5765篇 |
2013年 | 5112篇 |
2012年 | 6090篇 |
2011年 | 6964篇 |
2010年 | 6117篇 |
2009年 | 5918篇 |
2008年 | 5212篇 |
2007年 | 5492篇 |
2006年 | 4901篇 |
2005年 | 4060篇 |
2004年 | 3345篇 |
2003年 | 3045篇 |
2002年 | 2567篇 |
2001年 | 1847篇 |
2000年 | 1610篇 |
1999年 | 1222篇 |
1998年 | 804篇 |
1997年 | 674篇 |
1996年 | 565篇 |
1995年 | 529篇 |
1994年 | 428篇 |
1993年 | 363篇 |
1992年 | 336篇 |
1991年 | 250篇 |
1990年 | 198篇 |
1989年 | 213篇 |
1988年 | 173篇 |
1987年 | 106篇 |
1986年 | 116篇 |
1985年 | 90篇 |
1984年 | 97篇 |
1983年 | 70篇 |
1982年 | 84篇 |
1981年 | 53篇 |
1980年 | 37篇 |
1979年 | 45篇 |
1978年 | 35篇 |
1964年 | 39篇 |
1957年 | 36篇 |
1955年 | 62篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
基于支持向量机的多类分类研究 总被引:1,自引:0,他引:1
现今流行的分类方法的重要基础是传统的统计学,前提是要有足够的样本,当样本数目有限时容易出现过学习的问题,导致分类效果不理想。引入支持向量机方法,它基于统计学习理论,采用了结构风险最小化原则代替经验风险最小化原则,较好的解决了小样本学习的问题;又由于采用了核函数思想,把非线性空间的问题转换到线性空间,降低了算法的复杂度。对其相关内容包括优化算法及多类分类问题的解决进行了研究,最后用一个实例说明了该方法的可行性和有效性。 相似文献
82.
Starting from a microscopic Hamiltonian defined on a semi-infinite cubic lattice, and employing a mean-field approximation, the surface parameters relevant for wetting in confined ternary mixtures are derived. These are found in terms of the microscopic coupling constants, and yield a physical interpretation of their origins. In comparison with the standard expression for the surface free-energy density, several new terms arising from the derivation are identified. The influence of the surface parameters on a predicted unbinding transition in a mixture of oil, water, and amphiphile demonstrate that existing results are robust to the addition of the extra surface terms. 相似文献
83.
A. Kaveh V. Kalatjari 《International journal for numerical methods in engineering》2003,58(5):771-791
In this article size/topology optimization of trusses is performed using a genetic algorithm (GA), the force method and some concepts of graph theory. One of the main difficulties with optimization with a GA is that the parameters involved are not completely known and the number of operations needed is often quite high. Application of some concepts of the force method, together with theory of graphs, make the generation of a suitable initial population well‐matched with critical paths for the transformation of internal forces feasible. In the process of optimization generated topologically unstable trusses are identified without any matrix manipulation and highly penalized. Identifying a suitable range for the cross‐section of each member for the ground structure in the list of profiles, the length of the substrings representing the cross‐sectional design variables are reduced. Using a contraction algorithm, the length of the strings is further reduced and a GA is performed in a smaller domain of design space. The above process is accompanied by efficient methods for selection, and by using a suitable penalty function in order to reduce the number of numerical operations and to increase the speed of the optimization toward a global optimum. The efficiency of the present method is illustrated using some examples, and compared to those of previous studies. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
84.
"通信原理"课程教学改革探索 总被引:15,自引:4,他引:11
张水英 《电气电子教学学报》2003,25(5):12-14
针对我院省重点专业“电子信息工程”的必修主干专业基础课程。“通信原理”教学中存在的不利于培养和提高学生分析问题、解决问题的能力的因素,从课程的教学内容、教学手段等方面论述了课程改革的基本构想,并对课程的实践环节——设计性实验的改革进行了探讨。 相似文献
85.
提高EDA实验教学质量的实践与探索 总被引:4,自引:0,他引:4
介绍了一种在教学实践中总结出的行之有效的实验教学实施方式。一方面,将EDA实验教学过程分为实验预习、实验和总结提高三个阶段,为每个阶段规定了任务和要求。另一方面,为确保实验教学质量,需要明确实验任务,严格考核标准,做好讨论与总结。另外还讨论了网站等手段在EDA实验教学中的作用。 相似文献
86.
Requirements engineering in health care: the example of chemotherapy planning in paediatric oncology
Health care is characterized by highly complex processes of patient care that require unusual amount of communication between different health care professionals of different institutions. Sub-optimal processes can significantly impact on the patient’s health, increase the consumption of services and resources and in severe cases can lead to the patient death. For these reasons, requirements engineering for the development of information technology in health care is a complex process as well: without constant and rigorous evaluation, the impact of new systems on the quality of care is unknown and it is possible that badly designed systems significantly harm patients. To overcome these limitations, we present and discuss an approach to requirements engineering that we applied for the development of applications for chemotherapy planning in paediatric oncology. Chemotherapy planning in paediatric oncology is complex and time-consuming and errors must be avoided by all means. In the multi-hospital/multi-trial-centre environment of paediatric oncology, it is especially difficult and time-consuming to analyse requirements. Our approach combines a grounded theory approach with evolutionary prototyping based on the constant development and refinement of a generic domain model, in this case a domain model for chemotherapy planning in paediatric oncology. The prototypes were introduced in medical centres and final results show that the developed generic domain model is adequate. 相似文献
87.
要培养学生的创造力,教师主要起引导作用。应提倡感性的观察方法与理性的表现相结合。从构图阶段开始就应该贯穿创新意念,鼓励学生采用大胆新奇的构图,以独特的视觉去观察对象、设计函面,充分发挥学生的主观能动性。 相似文献
88.
The Industry Council for Development (ICD) is an Industry Non Governmental Organisation established in 1990; it aims to contribute to improving public health through partnership projects on food safety and nutrition. This paper presents ICD’s activities in the past years and explains the reasons why the food industry should have a vested interest in supporting training and education of health professionals in food safety. 相似文献
89.
Recent years have witnessed a rapid growth of interest in the study of the dynamic behavior of replenishment rules of bullwhip effect. We prove that bullwhip effect and butterfly effect share a same the self-oscillation amplifying mechanism that is the ordering decisions the supplier self-oscillation amplify the perturbations brought by the errors in the processing of retailers' demand information. This results as an explicit self-similar structure of the sensitivity of the system to the initial values duty to the nonlinear mechanism. In this paper, the causes process of the bullwhip effect is described as the internal nonlinear mechanism and study on the complexity of bullwhip effect for order-up-to policy under demand signal processing. The methodology is based on fractal and chaotic theory and allows important insights to be gained about the complexity behavior of bullwhip effect. 相似文献
90.