全文获取类型
收费全文 | 154576篇 |
免费 | 17980篇 |
国内免费 | 7680篇 |
专业分类
电工技术 | 54751篇 |
技术理论 | 4篇 |
综合类 | 11936篇 |
化学工业 | 10087篇 |
金属工艺 | 3936篇 |
机械仪表 | 7671篇 |
建筑科学 | 10622篇 |
矿业工程 | 3098篇 |
能源动力 | 12977篇 |
轻工业 | 6664篇 |
水利工程 | 3416篇 |
石油天然气 | 3872篇 |
武器工业 | 1327篇 |
无线电 | 17095篇 |
一般工业技术 | 8874篇 |
冶金工业 | 4258篇 |
原子能技术 | 2498篇 |
自动化技术 | 17150篇 |
出版年
2024年 | 861篇 |
2023年 | 2474篇 |
2022年 | 4525篇 |
2021年 | 5350篇 |
2020年 | 5859篇 |
2019年 | 4851篇 |
2018年 | 4469篇 |
2017年 | 5826篇 |
2016年 | 6154篇 |
2015年 | 6663篇 |
2014年 | 10853篇 |
2013年 | 9372篇 |
2012年 | 12160篇 |
2011年 | 12923篇 |
2010年 | 9513篇 |
2009年 | 9612篇 |
2008年 | 9112篇 |
2007年 | 10839篇 |
2006年 | 9429篇 |
2005年 | 7734篇 |
2004年 | 6268篇 |
2003年 | 5095篇 |
2002年 | 4002篇 |
2001年 | 3438篇 |
2000年 | 2798篇 |
1999年 | 2070篇 |
1998年 | 1416篇 |
1997年 | 1152篇 |
1996年 | 1111篇 |
1995年 | 828篇 |
1994年 | 712篇 |
1993年 | 475篇 |
1992年 | 404篇 |
1991年 | 289篇 |
1990年 | 234篇 |
1989年 | 186篇 |
1988年 | 130篇 |
1987年 | 108篇 |
1986年 | 68篇 |
1985年 | 86篇 |
1984年 | 118篇 |
1983年 | 85篇 |
1982年 | 84篇 |
1981年 | 45篇 |
1980年 | 69篇 |
1979年 | 28篇 |
1964年 | 29篇 |
1963年 | 27篇 |
1959年 | 32篇 |
1955年 | 28篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
71.
网络的性能与可靠性已分别得到广泛的研究,然而,怎样分析具有容错机制的环网的性能仍属有待开拓的研究领域,本文提出了一种分析具有自修复机制的多环网络系统的方法,并给出了报文传输时间分布的拉氏变换式,平均等待时间及平均队列长度公式,分析结果可用于评估故障与修复过程对实时令牌环网的实时响应特性的影响,对基于LAN的分布式实时系统设计具有指导意义。 相似文献
72.
三峡电站厂用电结线复杂,使电站运行工作考虑因素增多,只有对设备合理选型,注意安装质量,加强维护,强化运行管理,才能保证用电的安全,实现可靠供电。 相似文献
73.
Packaging engineers need to be able to accurately determine the forces present in the shipping environment in order to protect packaged goods. The purpose of this study was to determine the vertical vibration levels measured in three separate truck-trailer suspension systems; conventional leaf-spring, conventional air-ride and damaged air-ride. The main conclusion reached in this study is that the air-ride suspension when maintained gives lower power density (PD) levels on all road surfaces studied. A damaged air-ride suspension and leaf-spring suspension are very similar in response frequencies, although the damaged air-ride produces higher vibration levels at lower frequencies. 相似文献
74.
Since electronic switching systems usually require very strict reliability requirements as well as good performance objectives, we need to jointly analyse the performance and reliability of switching systems. In this paper, we compare conventional time–space–time switches with single space switches with those with multiple separated space switches, from the viewpoints of reliability and performance. We consider time–space–time switching networks which consist of N incoming time switches, i.e. one NxN space switch, two (N/2)x(N/2) space switches, and four (N/4)x(N/4) space switches. We introduce a Markov reliability model to study the effect of failures and analyse the reliability and performance of three different types of switching networks in terms of average blocking probability and the mean time to unreliable operation, as we vary the offered traffic. As a result, T–S–T switching networks with multiple separated space switches exhibit better performance and reliability than those with single space switches. 相似文献
75.
The bond strength and slip of epoxy-coated reinforcing bars in concrete have been evaluated by carrying out single pullout and double pullout tests. In extended single pullout tests, slip measurements were made while tensile force was applied to reinforcing bars embedded in concrete. In double pullout tests, 20 cycles of load were applied at levels of steel stress between zero and 0·5 times characteristic steel strength. Strains were measured by electrical resistance strain gauges glued inside the bars. Both epoxy-coated and uncoated bars were used in the investigation, to obtain comparative results. The strain gradient along the bar was found to be less for the coated reinforcement. In general, the epoxy coating was found to increase slip in bond and thereby reduce the bond performance of coated bars. 相似文献
76.
77.
This paper presents an efficient method which provides the optimal generation mix and the optimal generation construction process. The approximation method in which the dynamic programming technique and gradient method are combined is applied to determine the optimal generation mix with hydropower generation technologies. The successive approximations dynamic programming (SADP) technique, which is very suitable for high-dimensional multistage decision process problems, is used for obtaining the optimal generation construction process. The effectiveness and feasibility of the developed technique are demonstrated on a practical power system model which has five types of generation technologies including a hydropower generation technology. 相似文献
78.
79.
本法采用同一色谱条件反相高效液相色谱法测定棉铃宝中甲基对硫磷和辛硫磷的含量,方法简单易行,具有较高的精密度和准确度,其回收率分析为甲基对硫磷99.59%,辛硫磷101.0%。 相似文献
80.
G.652光纤上的2.5Gbit/s色散受限系统 总被引:1,自引:0,他引:1
本文根据色散受限中继段长度的计算,对实际工程中1550nm波长2.5Gbit/s系统进行计算比较得出啁啾声引起的色散不容忽视,它使2.5Gbit/s成为色散受限系统。对1310nm波长622Mbit/s系统,当使用多纵模激光器时,往往也会成为色散受限系统。 相似文献