全文获取类型
收费全文 | 296785篇 |
免费 | 28315篇 |
国内免费 | 15053篇 |
专业分类
电工技术 | 60764篇 |
技术理论 | 23篇 |
综合类 | 25943篇 |
化学工业 | 17210篇 |
金属工艺 | 9573篇 |
机械仪表 | 21963篇 |
建筑科学 | 35124篇 |
矿业工程 | 8332篇 |
能源动力 | 12363篇 |
轻工业 | 8583篇 |
水利工程 | 7704篇 |
石油天然气 | 10978篇 |
武器工业 | 3006篇 |
无线电 | 31288篇 |
一般工业技术 | 21037篇 |
冶金工业 | 7893篇 |
原子能技术 | 3681篇 |
自动化技术 | 54688篇 |
出版年
2024年 | 1309篇 |
2023年 | 3591篇 |
2022年 | 6697篇 |
2021年 | 8060篇 |
2020年 | 9041篇 |
2019年 | 7125篇 |
2018年 | 6648篇 |
2017年 | 8724篇 |
2016年 | 9709篇 |
2015年 | 10833篇 |
2014年 | 21047篇 |
2013年 | 17341篇 |
2012年 | 22362篇 |
2011年 | 23920篇 |
2010年 | 18709篇 |
2009年 | 18822篇 |
2008年 | 18231篇 |
2007年 | 21677篇 |
2006年 | 18669篇 |
2005年 | 16008篇 |
2004年 | 13143篇 |
2003年 | 11591篇 |
2002年 | 9059篇 |
2001年 | 7634篇 |
2000年 | 6317篇 |
1999年 | 4768篇 |
1998年 | 3566篇 |
1997年 | 2964篇 |
1996年 | 2596篇 |
1995年 | 2066篇 |
1994年 | 1731篇 |
1993年 | 1175篇 |
1992年 | 946篇 |
1991年 | 771篇 |
1990年 | 544篇 |
1989年 | 484篇 |
1988年 | 362篇 |
1987年 | 277篇 |
1986年 | 195篇 |
1985年 | 239篇 |
1984年 | 264篇 |
1983年 | 210篇 |
1982年 | 204篇 |
1981年 | 90篇 |
1980年 | 75篇 |
1979年 | 72篇 |
1978年 | 40篇 |
1977年 | 41篇 |
1976年 | 22篇 |
1959年 | 34篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
111.
裂齿矩形翅片板翅式换热器优化设计的分析 总被引:2,自引:0,他引:2
对裂齿矩形翅片板翅式换热器中的裂齿矩形翅片的传热效率作了分析,并以单位质量材耗的换热能力最大为目标函数,分析研究了在不同雷诺数(Re)的操作条件下裂齿矩形翅片间角度、翅片厚、长度、宽度及极厚之间的关系。结果表明:在气体换热的场合下,当Re在某一范围时翅片可有效地起到强化传热的作用。当板厚为5mm,翅片厚为3mm,翅片间夹角为45°~70°,Re为2×10~3~8×10~3,最佳翅片纵向间距与翅片长度和翅片厚度乘积的平方根的比为1.5~2.5,最佳翅片尺寸系数为3~5时,传热强化效果较好。 相似文献
112.
说明了在异步串行通信(RS-232)的工作方式下,对所接收的数据进行接收、处理,丢弃乱码,并进行保存的可靠方法,并给出了相关的VC 语言程序. 相似文献
113.
Chris Harty 《Building Research & Information》2005,33(6):512-522
An alternative approach to understanding innovation is made using two intersecting ideas. The first is that successful innovation requires consideration of the social and organizational contexts in which it is located. The complex context of construction work is characterized by inter-organizational collaboration, a project-based approach and power distributed amongst collaborating organizations. The second is that innovations can be divided into two modes: 'bounded', where the implications of innovation are restricted within a single, coherent sphere of influence, and 'unbounded', where the effects of implementation spill over beyond this. Bounded innovations are adequately explained within the construction literature. However, less discussed are unbounded innovations, where many firms' collaboration is required for successful implementation, even though many innovations can be considered unbounded within construction's inter-organizational context. It is argued that unbounded innovations require an approach to understand and facilitate the interactions both within a range of actors and between the actors and technological artefacts. The insights from a sociology of technology approach can be applied to the multiplicity of negotiations and alignments that constitute the implementation of unbounded innovation. The utility of concepts from the sociology of technology, including 'system building' and 'heterogeneous engineering', is demonstrated by applying them to an empirical study of an unbounded innovation on a major construction project (the new terminal at Heathrow Airport, London, UK). This study suggests that 'system building' contains outcomes that are not only transformations of practices, processes and systems, but also the potential transformation of technologies themselves. 相似文献
114.
Cathy Lawson Douglas C. Montgomery 《Quality and Reliability Engineering International》2006,22(8):971-984
Variation exists in all processes. Significant work has been done to identify and remove sources of variation in manufacturing processes resulting in large returns for companies. However, business process optimization is an area that has a large potential return for a company. Business processes can be difficult to optimize due to the nature of the output variables associated with them. Business processes tend to have output variables that are binary, nominal or ordinal. Examples of these types of output include whether a particular event occurred, a customer's color preference for a new product and survey questions that assess the extent of the survey respondent's agreement with a particular statement. Output variables that are binary, nominal or ordinal cannot be modeled using ordinary least‐squares regression. Logistic regression is a method used to model data where the output is binary, nominal or ordinal. This article provides a review of logistic regression and demonstrates its use in modeling data from a business process involving customer feedback. Copyright © 2006 John Wiley & Sons, Ltd. 相似文献
115.
116.
Seog Geun Kang 《ETRI Journal》2006,28(2):235-238
In this letter, a block code that minimizes the peak‐to‐average power ratio (PAPR) of orthogonal frequency division multiplexing (OFDM) signals is proposed. It is shown that peak envelope power is invariant to cyclic shift and codeword inversion. The systematic encoding rule for the proposed code is composed of searching for a seed codeword, shifting the register elements, and determining codeword inversion. This eliminates the look‐up table for one‐to‐one correspondence between the source and the coded data. Computer simulation confirms that OFDM systems with the proposed code always have the minimum PAPR. 相似文献
117.
118.
Non-pinched, minimum energy solutions are important class of distillation designs that offer the potential advantage of a better trade-off between capital investment and operating costs. In this paper, two important tasks associated with non-pinched distillation designs are studied. Thus the novel contributions of this work to the literature are
- (1) A comprehensive methodology for finding non-pinched minimum energy designs.
- (2) Understanding of the reasons for the existence of non-pinched distillation designs.
119.
Porous carbon nanofibers are synthesized by CVD method from acetylene with use of iron-containing catalysts. Activation of the nanofibers in melted potassium hydroxide results in increasing surface area from initial 300–400 m2 g−1 to 1700 m2 g−1. As follows from XRD data, activated nanofibers do not contain regular packages of graphene layers, but retain high electric conductivity. Deposition of copper improves electrochemical hydrogen storing characteristics of carbon nanofibers. Carbon nanomaterials obtained can be used as hydrogen storing materials in batteries instead of hydride forming metals. 相似文献
120.