全文获取类型
收费全文 | 235261篇 |
免费 | 32957篇 |
国内免费 | 20122篇 |
专业分类
电工技术 | 26214篇 |
技术理论 | 9篇 |
综合类 | 27079篇 |
化学工业 | 23444篇 |
金属工艺 | 6942篇 |
机械仪表 | 15018篇 |
建筑科学 | 13490篇 |
矿业工程 | 6009篇 |
能源动力 | 5551篇 |
轻工业 | 12384篇 |
水利工程 | 5377篇 |
石油天然气 | 7125篇 |
武器工业 | 2825篇 |
无线电 | 30470篇 |
一般工业技术 | 20463篇 |
冶金工业 | 6709篇 |
原子能技术 | 3202篇 |
自动化技术 | 76029篇 |
出版年
2024年 | 814篇 |
2023年 | 3643篇 |
2022年 | 7063篇 |
2021年 | 9521篇 |
2020年 | 8029篇 |
2019年 | 6979篇 |
2018年 | 7062篇 |
2017年 | 8765篇 |
2016年 | 10663篇 |
2015年 | 12005篇 |
2014年 | 15755篇 |
2013年 | 16162篇 |
2012年 | 16919篇 |
2011年 | 16953篇 |
2010年 | 13785篇 |
2009年 | 14205篇 |
2008年 | 14301篇 |
2007年 | 17021篇 |
2006年 | 15199篇 |
2005年 | 12981篇 |
2004年 | 10262篇 |
2003年 | 9085篇 |
2002年 | 7087篇 |
2001年 | 5776篇 |
2000年 | 5100篇 |
1999年 | 3968篇 |
1998年 | 3169篇 |
1997年 | 2692篇 |
1996年 | 2329篇 |
1995年 | 1953篇 |
1994年 | 1757篇 |
1993年 | 1265篇 |
1992年 | 1060篇 |
1991年 | 839篇 |
1990年 | 758篇 |
1989年 | 638篇 |
1988年 | 434篇 |
1987年 | 305篇 |
1986年 | 271篇 |
1985年 | 263篇 |
1984年 | 258篇 |
1983年 | 202篇 |
1982年 | 179篇 |
1981年 | 101篇 |
1980年 | 127篇 |
1979年 | 65篇 |
1977年 | 47篇 |
1964年 | 39篇 |
1962年 | 67篇 |
1959年 | 60篇 |
排序方式: 共有10000条查询结果,搜索用时 214 毫秒
41.
42.
This article proposes an active balancer, which features bidirectional charge shuttling and adaptive equalization current control, to fast counterbalance the state of charge (SOC) of cells in a lithium-ion battery (LIB) string. The power circuit consists of certain bidirectional buck-boost converters to transfer energy among the different cells back and forth. Owing to the characterization of the open-circuit voltage (OCV) vs SOC in LIB being relatively smooth near the SOC middle range, the SOC-inspected balance strategy can achieve more precise and efficient equilibrium than the voltage-based control. Accordingly, a compensated OCV-based SOC estimation is put forward to take into account the discrepancy of SOC estimation. Besides, the varied-duty-cycle (VDC) and curve-fitting modulation (CFM) methods are devised herein to tackle the problems of slow equalization rate and low balance efficacy, which arise from the diminution in balancing current as the SOC difference between the cells decreases in the later duration of equalization especially. The proposed strategies have taken the battery nonlinear characteristic and circuit parameter nonideality into account and can adaptively modulate the duty cycle with the SOC difference to keep balancing current constant throughout the balancing cycle. Simulated and experimental results are given to demonstrate the feasibility and effectiveness of the same prototype constructed. Compared with the fixed duty cycle and the VDC methods, the proposed CFM has the best balancing efficiency of 81.4%, and the balance time is shortened by 27.1% and 18.6%, respectively. 相似文献
43.
《Ceramics International》2022,48(15):21600-21609
Stereolithography (SL) shows advantages for preparing alumina-based ceramics with complex structures. The effects of the particle size distribution, which strongly influence the sintering properties in ceramic SL, have not been systematically explored until now. Herein, the influence of the particle size distribution on SL-manufactured alumina ceramics was investigated, including bending strength at room temperature, post-sintering shrinkage, porosity, and microstructural morphology. Seven particle size distributions of alumina ceramics were studied (in μm/μm: 30/5, 20/3, 10/2, 5/2, 5/0.8, 3/0.5, and 2/0.3); a coarse:fine particle ratio of 6:4 was maintained. At the same sintering temperature, the degree of sintering was greater for finer particle sizes. The particle size distribution had a larger influence on flexural strength, porosity and shrinkage than sintering temperature when the particle size distribution difference reached 10-fold but was weaker for 10 μm/2 μm, 5 μm/2 μm and 5 μm/0.8 μm. The sintering shrinkage characteristics of cuboid samples with different particle sizes were studied. The use of coarse particles influenced the accuracy of small-scale samples. When the particle size was comparable to the sample width, such as 30 μm/5 μm and 5 mm, the width shrinkage was consistent with the height shrinkage. When the particle size was much smaller than the sample width, such as 2 μm/0.3 μm and 5 mm, the width shrinkage was consistent with the length shrinkage. The results of this study provide meaningful guidance for future research on applications of SL and precise control of alumina ceramics through particle gradation. 相似文献
44.
海胆酮是一种酮式类胡萝卜素,主要从海胆及藻类等海洋生物中提取。本文研究海胆酮对乙酰胆碱酯酶(acetylcholinesterase,AChE)的抑制作用,应用酶动力学、荧光光谱、圆二色光谱和分子对接技术研究海胆酮对AChE的抑制机理,并用淀粉样β蛋白片段25~35(amyloid beta-peptide 25-35,Aβ25-35)诱导大鼠肾上腺嗜铬细胞瘤细胞(PC12细胞)建立阿尔茨海默症(Alzheimer’s disease,AD)模型,研究海胆酮对AD细胞模型氧化应激损伤的作用。结果表明,海胆酮有很强的AChE抑制活性,其半抑制质量浓度为(16.29±0.97)μg/mL,抑制常数Ki为3.82 μg/mL,表现为竞争性抑制;海胆酮可诱导AChE二级结构改变,更容易与AChE活性中心氨基酸Ser200、His440、Trp84和Tyr121结合,阻碍底物碘代硫代乙酰胆碱(acetylthiocholine iodide,ATCI)与酶结合,从而引起酶活力降低。海胆酮能有效抑制Aβ25-35诱导PC12细胞的AChE活力,降低丙二醛含量,增加超氧化物歧化酶、过氧化氢酶和谷胱甘肽过氧化物酶活力,减轻Aβ25-35诱导的PC12细胞氧化应激损伤。本研究基于AChE和氧化应激阐明了海胆酮对AD的潜在作用机制,为海胆酮在功能食品、生物医药等领域的应用提供了数据支持和理论根据。 相似文献
45.
46.
Structural health monitoring system based on multi-agent coordination and fusion for large structure
In practical applications of structural health monitoring technology, a large number of distributed sensors are usually adopted to monitor the big dimension structures and different kinds of damage. The monitored structures are usually divided into different sub-structures and monitored by different sensor sets. Under this situation, how to manage the distributed sensor set and fuse different methods to obtain a fast and accurate evaluation result is an important problem to be addressed deeply. In the paper, a multi-agent fusion and coordination system is presented to deal with the damage identification for the strain distribution and joint failure in the large structure. Firstly, the monitoring system is adopted to distributedly monitor two kinds of damages, and it self-judges whether the static load happens in the monitored sub-region, and focuses on the static load on the sub-region boundary to obtain the sensor network information with blackboard model. Then, the improved contract net protocol is used to dynamically distribute the damage evaluation module for monitoring two kinds of damage uninterruptedly. Lastly, a reliable assessment for the whole structure is given by combing various heterogeneous classifiers strengths with voting-based fusion. The proposed multi-agent system is illustrated through a large aerospace aluminum plate structure experiment. The result shows that the method can significantly improve the monitoring performance for the large-scale structure. 相似文献
47.
One specific class of non-linear evolution equations, known as the Tzitzéica-type equations, has received great attention from a group of researchers involved in non-linear science. In this article, new exact solutions of the Tzitzéica-type equations arising in non-linear optics, including the Tzitzéica, Dodd–Bullough–Mikhailov and Tzitzéica–Dodd–Bullough equations, are obtained using the expa function method. The integration technique actually suggests a useful and reliable method to extract new exact solutions of a wide range of non-linear evolution equations. 相似文献
48.
This paper proposes a method for the coordinated control of power factor by means of a multiagent approach. The proposed multiagent system consists of two types of agent: single feeder agent (F_AG) and bus agent (B_AG). In the proposed system, an F_AG plays as an important role, which decides the power factors of all distributed generators by executing the load flow calculations repeatedly. The voltage control strategies are implemented as the class definition of Java into the system. In order to verify the performance of the proposed method, it has been applied to a typical distribution model system. The simulation results show that the system is able to control very violent fluctuation of the demands and the photovoltaic (PV) generations. 相似文献
49.