全文获取类型
收费全文 | 46776篇 |
免费 | 3410篇 |
国内免费 | 2338篇 |
专业分类
电工技术 | 2360篇 |
技术理论 | 16篇 |
综合类 | 5573篇 |
化学工业 | 5522篇 |
金属工艺 | 1593篇 |
机械仪表 | 1642篇 |
建筑科学 | 8210篇 |
矿业工程 | 2735篇 |
能源动力 | 1619篇 |
轻工业 | 3701篇 |
水利工程 | 2408篇 |
石油天然气 | 3390篇 |
武器工业 | 195篇 |
无线电 | 2484篇 |
一般工业技术 | 3688篇 |
冶金工业 | 2878篇 |
原子能技术 | 558篇 |
自动化技术 | 3952篇 |
出版年
2024年 | 174篇 |
2023年 | 603篇 |
2022年 | 1055篇 |
2021年 | 1258篇 |
2020年 | 1220篇 |
2019年 | 1200篇 |
2018年 | 1029篇 |
2017年 | 1167篇 |
2016年 | 1297篇 |
2015年 | 1416篇 |
2014年 | 2435篇 |
2013年 | 2365篇 |
2012年 | 2902篇 |
2011年 | 3263篇 |
2010年 | 2596篇 |
2009年 | 2743篇 |
2008年 | 2476篇 |
2007年 | 3137篇 |
2006年 | 2976篇 |
2005年 | 2737篇 |
2004年 | 2264篇 |
2003年 | 2108篇 |
2002年 | 1775篇 |
2001年 | 1521篇 |
2000年 | 1312篇 |
1999年 | 1015篇 |
1998年 | 708篇 |
1997年 | 616篇 |
1996年 | 530篇 |
1995年 | 490篇 |
1994年 | 382篇 |
1993年 | 305篇 |
1992年 | 245篇 |
1991年 | 167篇 |
1990年 | 170篇 |
1989年 | 152篇 |
1988年 | 126篇 |
1987年 | 96篇 |
1986年 | 70篇 |
1985年 | 61篇 |
1984年 | 50篇 |
1983年 | 24篇 |
1982年 | 26篇 |
1981年 | 38篇 |
1980年 | 29篇 |
1979年 | 31篇 |
1977年 | 17篇 |
1976年 | 18篇 |
1975年 | 20篇 |
1974年 | 17篇 |
排序方式: 共有10000条查询结果,搜索用时 12 毫秒
111.
本文介绍了冷却器盘管破裂泄漏的情况,分析了失效破坏的原因,并提出防止冷却器盘管破裂泄漏的措施。 相似文献
112.
为了利用分数阶累加算子在灰色短期预测中的高效性能,首次将分数阶累加算子引入变异时序回归模型以期取得更高的预测精度。主要方法如下:首先取湖北省链子崖某监测点1978—1987年的十年数据作为训练集并使用引力搜索算法确定最佳分数阶累加阶数,而1988—1993年的六年数据作为验证集验证提出的模型;其次对比了经典灰色模型GM(1,1)、分数阶累加灰色模型、变异时序回归模型TSGM(1,1)三种灰色模型。结果如下:首先修正了陈西江等人变异时序回归模型仿真时出现的错误,其次表明了相比于其他的模型,基于引力搜索算法的分数阶累加时序回归模型在进行灰色长期预测中具有较高的预测精度。因此,通过分数阶累加算子提高了灰色理论中长期预测模型的精度,为灰色长期预测提供了指导。 相似文献
113.
S. R. Dargar L. J. Groven J. J. Swiatkiewicz J. A. Puszynski 《International Journal of Self-Propagating High-Temperature Synthesis》2007,16(3):125-132
The primary objective of this investigation was focused on in-situ densification of SHS composites synthesized from nanoreactants.
Simultaneous combustion synthesis and densification technique was utilized and it was found to be an effective method to form
dense intermetallic-ceramic composites. In this research study, two nanoreactant energetic systems, Al-TiO2 and Ni-Al-Al2O3, were explored. In-situ combustion synthesis and densification experiments were conducted in a uniaxial press with densification
pressures up to 200 MPa and preheating capability of 1500K. The experiments were conducted in both vacuum and Ar atmosphere.
Samples of titanium aluminides-alumina composites with density in the range of 95–98% have been obtained at a preheating temperature
of 860°C and pressure of 100 MPa. Reactants and SHS-produced materials were characterized by SEM, XRD, BET, and DSC/TGA. In
addition, more fundamental studies of the reaction kinetics as a function of average particle size of aluminum nanopowders
were conducted using DSC.
相似文献
114.
Student academic underachievement is a concern of paramount importance in Europe, where around 15% of the students in the last high school courses do not achieve the minimum knowledge academic requirement. In this paper, we propose a model based on a system of differential equations to study the dynamics of the students’ academic performance in the German region of the North Rhine-Westphalia. This approach is supported by the idea that both good and bad study habits, are a mixture of personal decisions and influence of classmates. This model allows us to forecast the student academic performance by means of confidence intervals over the next few years. 相似文献
115.
The main purpose of this paper is to investigate the optimal replenishment lot size of supplier and optimal production rate of manufacturer under three levels of trade credit policy for supplier–manufacturer–retailer supply chain. The supplier provides a fixed credit period to settle the accounts to the manufacturer, while the manufacturer gives a fixed credit period to settle the account to the retailer and the retailer, in turn, also offers a credit period to each of its customers to settle the accounts. We assume that the supplier supplies the raw material to the manufacturer and sends back the defective raw materials to the outside supplier after completion of inspection at one lot with a sales price. The system always produces good items in the model. Also, we consider the idle times of supplier and manufacturer. Finally, numerical examples are provided to illustrate the behaviour and application of the model with graphical simulation. 相似文献
116.
S. Chaturvedi C. Dunne Z. Ashktorab R. Zachariah B. Shneiderman 《Computer Graphics Forum》2014,33(8):52-68
An important part of network analysis is understanding community structures like topological clusters and attribute‐based groups. Standard approaches for showing communities using colour, shape, rectangular bounding boxes, convex hulls or force‐directed layout algorithms remain valuable, however our Group‐in‐a‐Box meta‐layouts add a fresh strategy for presenting community membership, internal structure and inter‐cluster relationships. This paper extends the basic Group‐in‐a‐Box meta‐layout, which uses a Treemap substrate of rectangular regions whose size is proportional to community size. When there are numerous inter‐community relationships, the proposed extensions help users view them more clearly: (1) the Croissant–Doughnut meta‐layout applies empirically determined rules for box arrangement to improve space utilization while still showing inter‐community relationships, and (2) the Force‐Directed layout arranges community boxes based on their aggregate ties at the cost of additional space. Our free and open source reference implementation in NodeXL includes heuristics to choose what we have found to be the preferable Group‐in‐a‐Box meta‐layout to show networks with varying numbers or sizes of communities. Case study examples, a pilot comparative user preference study (nine participants), and a readability measure‐based evaluation of 309 Twitter networks demonstrate the utility of the proposed meta‐layouts. 相似文献
117.
118.
119.
This paper discusses the adoption of a pluralist theoretical framework – one that is also multiparadigmatic – for conducting and publishing information system (IS) research. The discussion is illustrated by a single case study involving the Australian cotton industry. The theoretical framework is informed by three sociological theories, each with its particular paradigmatic assumptions: structuration theory as a meta‐theory, and diffusion of innovations and gender relations as lower‐level theories from notionally opposing paradigms. Theoretical pluralism helped to produce rich findings, illuminating both the social nature of women farmers' roles, the materiality of the cotton farming context, the characteristics of the decision support systems in use and the recursive way in which human agency and institutional pressures shape each other. Because users of so‐called divergent paradigms often face criticism based on the incommensurability issue, one of the main contributions of this paper is to discuss the value of a pluralist and multiparadigmatic theoretical framework in dealing with complex IS social phenomena. 相似文献
120.
"网络营销"课程知识体系须随着互联网应用的出现和普及而逐渐得到完善,为此提出了该课程的教学改革实施方案。网络营销课程的教学始终要以实践应用为主导,在教学过程中采用案例教学、任务驱动、结合竞赛、学科互动、团队合作等方法。考核应采用灵活分配学分比例的办法。最终使得学生能够将课堂上的知识灵活地运用到工作当中。 相似文献