全文获取类型
收费全文 | 38246篇 |
免费 | 2209篇 |
国内免费 | 2151篇 |
专业分类
电工技术 | 711篇 |
技术理论 | 2篇 |
综合类 | 8445篇 |
化学工业 | 3530篇 |
金属工艺 | 382篇 |
机械仪表 | 1605篇 |
建筑科学 | 3553篇 |
矿业工程 | 281篇 |
能源动力 | 145篇 |
轻工业 | 336篇 |
水利工程 | 257篇 |
石油天然气 | 129篇 |
武器工业 | 96篇 |
无线电 | 5260篇 |
一般工业技术 | 788篇 |
冶金工业 | 471篇 |
原子能技术 | 47篇 |
自动化技术 | 16568篇 |
出版年
2024年 | 75篇 |
2023年 | 330篇 |
2022年 | 737篇 |
2021年 | 1044篇 |
2020年 | 950篇 |
2019年 | 531篇 |
2018年 | 497篇 |
2017年 | 545篇 |
2016年 | 792篇 |
2015年 | 1249篇 |
2014年 | 3080篇 |
2013年 | 2103篇 |
2012年 | 3262篇 |
2011年 | 4054篇 |
2010年 | 3363篇 |
2009年 | 2870篇 |
2008年 | 2440篇 |
2007年 | 2713篇 |
2006年 | 2312篇 |
2005年 | 1918篇 |
2004年 | 1552篇 |
2003年 | 1468篇 |
2002年 | 1197篇 |
2001年 | 888篇 |
2000年 | 752篇 |
1999年 | 531篇 |
1998年 | 326篇 |
1997年 | 238篇 |
1996年 | 187篇 |
1995年 | 129篇 |
1994年 | 93篇 |
1993年 | 75篇 |
1992年 | 46篇 |
1991年 | 35篇 |
1990年 | 31篇 |
1989年 | 29篇 |
1988年 | 29篇 |
1987年 | 11篇 |
1986年 | 19篇 |
1985年 | 5篇 |
1984年 | 15篇 |
1983年 | 9篇 |
1982年 | 8篇 |
1972年 | 4篇 |
1966年 | 5篇 |
1962年 | 5篇 |
1959年 | 4篇 |
1957年 | 4篇 |
1956年 | 3篇 |
1955年 | 9篇 |
排序方式: 共有10000条查询结果,搜索用时 125 毫秒
31.
32.
In recent years, the Industry 4.0 concept brings new demands and trends in different areas; one of them is distributing computational power to the cloud. This concept also introduced the Reference Architectural Model for Industry 4.0 (RAMI 4.0). The efficiency of data communications within the RAMI 4.0 model is a critical issue. Aiming to evaluate the efficiency of data communication in the Cloud Based Cyber-Physical Systems (CB-CPS), this study analyzes the periods and data amount required to communicate with individual hierarchy levels of the RAMI 4.0 model. The evaluation of the network properties of the communication protocols eligible for CB-CPS is presented. The network properties to different cloud providers and data centers’ locations have been measured and interpreted. To test the findings, an architecture for cloud control of laboratory model was proposed. It was found that the time of the day; the day of the week; and data center utilization have a negligible impact on latency. The most significant impact lies in the data center distance and the speed of the communication channel. Moreover, the communication protocol also has impact on the latency. The feasibility of controlling each level of RAMI 4.0 through cloud services was investigated. Experimental results showed that control is possible in many solutions, but these solutions mostly cannot depend just on cloud services. The intelligence on the edge of the network will play a significant role. The main contribution is a thorough evaluation of different cloud providers, locations, and communication protocols to provide recommendations sufficient for different levels of the RAMI 4.0 architecture. 相似文献
33.
非测绘专业"测量学"课程的探讨 总被引:4,自引:0,他引:4
探讨了非测绘专业中测量学课程教学改革的问题,结合我院实际情况,从教学内容、教材的选用、教学方法、实验实习教学环节等方面进行讨论,希望能起到一定的借鉴作用。 相似文献
34.
The influence of network density on the strain hardening behaviour of amorphous polymers is studied. The network density of polystyrene is altered by blending with poly(2,6-dimethyl-1,4-phenylene-oxide) and by cross-linking during polymerisation. The network density is derived from the rubber-plateau modulus determined by dynamic mechanical thermal analysis. Subsequently uniaxial compression tests are performed to obtain the intrinsic deformation behaviour and, in particular, the strain hardening modulus. At room temperature, the strain hardening modulus proves to be proportional to the network density, irrespective of the nature of the network, i.e. physical entanglements or chemical cross-links. With increasing temperature, the strain hardening modulus is observed to decrease. This decrease appears to be related to the influence of thermal mobility of the chains, determined by the distance to the glass-transition temperature (T−Tg). 相似文献
35.
36.
主要对各国3G许可证与使用技术标准的抽绑政策.各国对2G/3G网络漫游的管制规定。以及3G网络之间共享的种类及实施方式等方面做了详尽的讲解,并进行比较和分析。 相似文献
37.
提出在县市级广电宽带数据网络的建设过程中,要着眼业务发展,突出高扩展性,构建基于标准、扩展灵活的主干网,实现网络建设的可持续性发展,并结合实际,从核心设备、端口、中继带宽、网络业务4个方面对扩展能力进行了阐述. 相似文献
38.
M. J. O’Sullivan C. G. Walker M. L. O’Sullivan T. D. Thompson A. B. Philpott 《Telecommunication Systems》2006,33(4):353-376
The problem of designing fibre-optic networks for local-access telecommunications generates (at least) three non-trivial subproblems.
In the first of these subproblems one must determine how many fibre-optic cables (fibres) are required at either end of a
street. In the next subproblem a minimum-cost network must be designed to support the fibres. The network must also provide
distinct paths from either end of the street to the central exchange(s). Finally, the fibre-optic cables must be placed in
protective covers. These covers are available in a number of different sizes, allowing some flexibility when covering each
section of the network. In this paper we describe a dynamic programming (DP) formulation for finding a minimum-cost (protective)
covering for the network (the third of the subproblems). This problem is a generalised set covering problem with side constraints
and is further complicated by the introduction of fixed and variable welding costs. The DP formulation selects covers along
each arc (in the network), but cannot exactly model the fixed costs and so does not guarantee optimality. We also describe
an integer programming (IP) formulation for assessing the quality of the DP solutions. The cost of the networks constructed
by the IP model is less than those designed using the DP model, but the saving is not significant for the problems examined
(less than 0.1%). This indicates that the DP model will generally give very good solutions. Furthermore, as the problem dimensions
grow, DP gives significantly better solution times than IP. 相似文献
39.
通过对广州市电视台综合信息平台网络系统的应用现状及安全风险进行分析,提出基于网络层、系统层、用户层和安全策略管理全方位的网络信息安全体系. 相似文献
40.
在介绍宽带无线移动发展趋势所采用的新技术的基础上,论述了宽带无线移动通信网络优化及相关发展策略的一些问题。 相似文献