全文获取类型
收费全文 | 554830篇 |
免费 | 43993篇 |
国内免费 | 24142篇 |
专业分类
电工技术 | 34062篇 |
技术理论 | 80篇 |
综合类 | 63082篇 |
化学工业 | 61779篇 |
金属工艺 | 22731篇 |
机械仪表 | 36769篇 |
建筑科学 | 86099篇 |
矿业工程 | 28291篇 |
能源动力 | 17499篇 |
轻工业 | 34075篇 |
水利工程 | 24580篇 |
石油天然气 | 24588篇 |
武器工业 | 6356篇 |
无线电 | 35622篇 |
一般工业技术 | 43709篇 |
冶金工业 | 27071篇 |
原子能技术 | 4590篇 |
自动化技术 | 71982篇 |
出版年
2024年 | 1427篇 |
2023年 | 5834篇 |
2022年 | 10656篇 |
2021年 | 14440篇 |
2020年 | 14455篇 |
2019年 | 11393篇 |
2018年 | 10835篇 |
2017年 | 13370篇 |
2016年 | 16214篇 |
2015年 | 17924篇 |
2014年 | 35267篇 |
2013年 | 30739篇 |
2012年 | 38723篇 |
2011年 | 41665篇 |
2010年 | 32669篇 |
2009年 | 33658篇 |
2008年 | 31024篇 |
2007年 | 38812篇 |
2006年 | 35464篇 |
2005年 | 31086篇 |
2004年 | 26003篇 |
2003年 | 23454篇 |
2002年 | 19128篇 |
2001年 | 16068篇 |
2000年 | 13513篇 |
1999年 | 10762篇 |
1998年 | 8133篇 |
1997年 | 7067篇 |
1996年 | 6175篇 |
1995年 | 5131篇 |
1994年 | 4427篇 |
1993年 | 3262篇 |
1992年 | 2764篇 |
1991年 | 2068篇 |
1990年 | 1736篇 |
1989年 | 1560篇 |
1988年 | 1136篇 |
1987年 | 814篇 |
1986年 | 590篇 |
1985年 | 588篇 |
1984年 | 546篇 |
1983年 | 399篇 |
1982年 | 356篇 |
1981年 | 248篇 |
1980年 | 227篇 |
1979年 | 161篇 |
1978年 | 92篇 |
1977年 | 98篇 |
1976年 | 71篇 |
1975年 | 74篇 |
排序方式: 共有10000条查询结果,搜索用时 18 毫秒
131.
Fault detection and isolation in water distribution networks is an active topic due to the nonlinearities of flow propagation and recent increases in data availability due to sensor deployment. Here, we propose an efficient two-step data driven alternative: first, we perform sensor placement taking the network topology into account; second, we use incoming sensor data to build a network model through online dictionary learning. Online learning is fast and allows tackling large networks as it processes small batches of signals at a time. This brings the benefit of continuous integration of new data into the existing network model, either in the beginning for training or in production when new data samples are gathered. The proposed algorithms show good performance in our simulations on both small and large-scale networks. 相似文献
132.
针对互联网中恶意域名攻击事件频发,现有域名检测方法实时性不强的问题,提出一种基于词法特征的恶意域名快速检测算法。该算法根据恶意域名的特点,首先将所有待测域名按照长度进行正则化处理后赋予权值;然后利用聚类算法将待测域名划分成多个小组,并利用改进的堆排序算法按照组内权值总和计算各域名小组优先级,根据优先级降序依次计算各域名小组中每一域名与黑名单上域名之间的编辑距离;最后依据编辑距离值快速判定恶意域名。算法运行结果表明,基于词法特征的恶意域名快速检测算法与单一使用域名语义和单一使用域名词法的恶意域名检测算法相比,准确率分别提高1.7%与2.5%,检测速率分别提高13.9%与6.8%,具有更高的准确率和实时性。 相似文献
133.
一种北斗联合低轨星座的导航增强方法研究 总被引:1,自引:0,他引:1
单纯依靠北斗导航系统提供定位导航授时服务,存在卫星信号落地功率低、易受遮蔽和阻断的不足。针对此问题,研究了一种北斗联合低轨星座实现导航增强的系统架构;提出了一种新的适应严重遮蔽或干扰条件下,基于到达时间(TOA)和到达频率(FOA)联合观测的定位解算算法;对高中低轨混合星座条件下的覆盖特性和精度衰减因子进行了仿真分析。分析结果表明,用户可见星数平均增加了64.2%,位置精度衰减因子(PDOP)平均改善了28.7%。研究结果可为下一代北斗的论证设计与研制建设提供参考借鉴。 相似文献
134.
《Intermetallics》2015
The site preferences of co-alloying elements (Mo–Ta, Mo–Re, Mo–Cr) in Ni3Al are studied using first-principles calculations, and the effects of these alloying elements on the elastic properties of Ni3Al are evaluated by elastic property calculations. The results show that the Mo–Ta, Mo–Re and Mo–Cr atom pairs all prefer Al–Al sites and the spatial neighbor relation of substitution sites almost has no influence on the site preference results. Furthermore, the Young's modulus of Ni3Al increases much higher by substituting Al–Al sites with co-alloying atoms, among which Mo–Re has the best strengthening effect. The enhanced chemical bondings between alloying atoms and their neighbor host atoms are considered to be the main strengthening mechanism of the alloying elements in Ni3Al. 相似文献
135.
文章通过对黑龙江省高效节水现状,存在问题的分析,结合黑龙江省高效节水发展的支撑能力,阐述黑龙江省节水增粮目标、任务及总体布局,为黑龙江省2012—2015年节水增粮实施提供依据。 相似文献
136.
In this paper, we introduce an optimization strategy in order to comprehensively quantify the impact of availability and maintenance notions during the early stages of synthesis and design of a new natural gas combined cycle power plant. A detailed state-space approach is thoroughly discussed, where influence of maintenance funds on each component's repair rate is directly assessed.In this context, analysis of the reliability characteristics of the system is centered at two designer-adopted parameters, which largely influence the obtained results: the number of components which may fail independently at the same time, and the number of simultaneous failure/repair events.Then, optimal solutions are evaluated as the availability-related parameters and the amount of resources assigned for maintenance actions are varied across a wide range of feasible values, which enable obtaining more accurate and detailed estimations of the expected economic performance for the project when compared with traditional economic evaluation approaches. 相似文献
137.
Robert Brooke Manrico Fabretto Samuel Pering Eliza Switalska Lachlan Reeks Drew Evans Peter Murphy 《应用聚合物科学杂志》2015,132(26)
A study using three different pairs of electrochromic polymers (ECPs) synthesized onto plaques by means of a modified vapor phase polymerization (VPP) technique is presented. Restriction of the respective polymerization times, allowed both faster and slower polymerizing monomers to be controlled, and produced blended plaques with visually diffuse interfaces. The ECPs within the blended plaques retain their individual electrochromic behavior and when encapsulated into an electrochromic device, show outstanding optical switching performance with little degradation evident over 10,000 cycles, coupled with a switching time of the order of 1 second. Blends also allow multiple diffuse color changes within an electrochromic device, due to the difference in oxidation potentials of the individual ECPs, making them candidates for adaptive camouflage use. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42158. 相似文献
138.
139.
Controllability and observability of multi-agent systems with heterogeneous and switching topologies
ABSTRACTThis paper focuses on controllability and observability of multi-agent systems with heterogeneous and switching topologies, where the first- and the second-order information interaction topologies are different and switching. First, based on the controllable state set, a controllability criterion is obtained in terms of the controllability matrix corresponding to the switching sequence. Next, by virtue of the subspace sequence, two necessary and sufficient algebraic conditions are established for controllability in terms of the system matrices corresponding to all the possible topologies. Furthermore, controllability is considered from the graphic perspective. It is proved that the system is controllable if the union graph of all the possible topologies is controllable. With respect to observability, two sufficient and necessary conditions are derived by taking advantage of the system matrices and the corresponding invariant subspace, respectively. Finally, some simulation examples are worked out to illustrate the theoretical results. 相似文献
140.
与传统比例-积分-微分(PID)控制方法相比,滑模控制(SMC)方法可以比较容易地将不确定性纳入控制器设计中,从而增强系统的鲁棒性。探索了SMC技术在运载器主动段姿态控制中的工程应用,首先通过分析基于趋近律的SMC系统,提出了降低不连续切换项系数的需求,然后研究了基于干扰上界的SMC方法。三通道小偏差仿真结果验证了两种方法的控制效果,表明第2种控制器的鲁棒性更好,稳态误差小,同时发动机喷管摆角需求较小。 相似文献