全文获取类型
收费全文 | 9240篇 |
免费 | 1246篇 |
国内免费 | 1285篇 |
专业分类
电工技术 | 1313篇 |
综合类 | 1165篇 |
化学工业 | 180篇 |
金属工艺 | 152篇 |
机械仪表 | 622篇 |
建筑科学 | 175篇 |
矿业工程 | 104篇 |
能源动力 | 140篇 |
轻工业 | 91篇 |
水利工程 | 106篇 |
石油天然气 | 38篇 |
武器工业 | 96篇 |
无线电 | 1649篇 |
一般工业技术 | 414篇 |
冶金工业 | 324篇 |
原子能技术 | 142篇 |
自动化技术 | 5060篇 |
出版年
2024年 | 15篇 |
2023年 | 134篇 |
2022年 | 162篇 |
2021年 | 220篇 |
2020年 | 291篇 |
2019年 | 306篇 |
2018年 | 261篇 |
2017年 | 367篇 |
2016年 | 450篇 |
2015年 | 440篇 |
2014年 | 591篇 |
2013年 | 815篇 |
2012年 | 704篇 |
2011年 | 778篇 |
2010年 | 594篇 |
2009年 | 643篇 |
2008年 | 639篇 |
2007年 | 689篇 |
2006年 | 549篇 |
2005年 | 522篇 |
2004年 | 422篇 |
2003年 | 343篇 |
2002年 | 262篇 |
2001年 | 250篇 |
2000年 | 207篇 |
1999年 | 154篇 |
1998年 | 135篇 |
1997年 | 112篇 |
1996年 | 95篇 |
1995年 | 89篇 |
1994年 | 90篇 |
1993年 | 87篇 |
1992年 | 62篇 |
1991年 | 60篇 |
1990年 | 51篇 |
1989年 | 29篇 |
1988年 | 12篇 |
1987年 | 17篇 |
1986年 | 8篇 |
1985年 | 12篇 |
1984年 | 14篇 |
1983年 | 21篇 |
1982年 | 10篇 |
1981年 | 7篇 |
1980年 | 8篇 |
1979年 | 5篇 |
1965年 | 3篇 |
1964年 | 6篇 |
1962年 | 4篇 |
1958年 | 4篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
Hua Yang Shi-Xiao Wei Han Chen Lang Chen Chak-Tong Au Ting-Liang Xie Shuang-Feng Yin 《American Institute of Chemical Engineers》2022,68(10):e17810
A high-throughput (105.5 g/h) passive four-stage asymmetric oscillating feedback microreactor using chaotic mixing mechanism was developed to prepare aggregated Barium sulfate (BaSO4) particles of high primary nanoparticle size uniformity. Three-dimensional unsteady simulations showed that chaotic mixing could be induced by three unique secondary flows (i.e., vortex, recirculation, and oscillation), and the fluid oscillation mechanism was examined in detail. Simulations and Villermaux–Dushman experiments indicate that almost complete mixing down to molecular level can be achieved and the prepared BaSO4 nanoparticles were with narrow primary particle size distribution (PSD) having geometric standard deviation, σg, less than 1.43 when the total volumetric flow rate Qtotal was larger than 10 ml/min. By selecting Qtotal and reactant concentrations, average primary particle size can be controlled from 23 to 109 nm as determined by microscopy. An average size of 26 nm with narrow primary PSD (σg = 1.22) could be achieved at Qtotal of 160 ml/min. 相似文献
2.
目前的搜索引擎仍然存在“重形式,轻语义”的问题,无法做到对搜索关键词和文本的深层次语义理解,因此语义检索成为当前搜索引擎中亟需解决的问题。为了提高搜索引擎的语义理解能力,该文提出一种语义相关度的计算方法。首先,标注了金融类新闻标题实体与新闻正文语义相关度语料1万条,然后建立新闻实体与正文语义相关度计算的BERTCA(Bidirectional Encoder Representation from Transformers Co-Attention)模型,通过使用BERT预训练模型,综合考虑细粒度的实体和粗粒度的正文的语义信息,然后经过协同注意力,实现实体与正文的语义匹配,不仅能计算出金融新闻实体与新闻正文之间的相关度,还能根据相关度阈值来判定相关度类别,实验表明该模型在1万条标注语料上准确率超过95%,优于目前主流模型,最后通过具体搜索示例展示了该模型的优秀性能。 相似文献
3.
焦炉生产是典型的大惯性、非线性、时变快的复杂系统,以“火落温度”为基础的焦炉前反馈热工控制系统,通过立火道温度自动测量与人工测温相关性分析、粗煤气温度测量与火落判断、标准温度的优化等运行实践,达到了自动火落时间判断、标准温度指导、加热和燃烧优化、高低温炉号判别等目的,对于稳定炉温、降低回炉煤气消耗、提高焦炭质量以及推进焦化企业技术进步具有重要意义。 相似文献
4.
The , and mixed dynamic output feedback control of Markov jump linear systems in a partial observation context is studied through an iterative approach. By partial information, we mean that neither the state variable x(k) nor the Markov chain θ(k) are available to the controller. Instead, we assume that the controller relies only on an output y(k) and a measured variable coming from a detector that provides the only information of the Markov chain θ(k). To solve the problem, we resort to an iterative method that starts with a state‐feedback controller and solves at each iteration a linear matrix inequality optimization problem. It is shown that this iterative algorithm yields to a nonincreasing sequence of upper bound costs so that it converges to a minimum value. The effectiveness of the iterative procedure is illustrated by means of two examples in which the conservatism between the upper bounds and actual costs is significantly reduced. 相似文献
5.
This paper proposes a signal feedback interference topology to control the characteristics of a coupled line bandpass filter. Control is carried out by varying the ratio of the transmission line parameters of the forward and the feedback couplers. The topology produces a compact filter that does not require a complicated design or fabrication. The results of the insertion and return losses show that the feedback‐controlled design has desirable features in terms of the design frequency, fractional bandwidth, stopband rejection level, roll‐off rate and insertion loss. The test results of the fabricated prototype achieved good agreement with the simulation results of the ideal transmission line design model. Several microwave, modern wireless and mobile/satellite communication systems may benefit from such a filter design due to its compactness and flexibility. 相似文献
6.
In collaborative crowdsourcing communities for open innovation, users generate and submit ideas as idea co‐creators. Firms then select and implement valuable ideas for new product development. Despite the popularity and success of these open innovation communities, relatively little is known about the factors that determine the implementation of the user‐generated ideas. Based on research on individual creativity, we propose a conceptual model integrating users' previous experience, idea presentation characteristics and feedback valence to explain the likelihood of idea implementation. We validate our research model with a panel data analysis of 43 550 ideas submitted by 16 360 users in the MIUI new product development community hosted by Xiaomi, a large electronics manufacturing company in China. We find an inverted U‐shaped relationship between users' past successful experience and idea implementation. Furthermore, the length of ideas is positively associated with the likelihood of idea implementation. There is also an inverted U‐shaped relationship between supporting evidence and idea implementation. Finally, we demonstrate the negative effect of positive feedback and the positive effect of negative feedback on idea implementation. These findings offer rich insights to understand the phenomenon of open innovation better. Theoretical and practical implications are discussed. 相似文献
7.
针对尾撑式风洞模型强方向性振动问题,基于异位配置加速度负反馈控制器对风洞模型振动主动控制方法进行研究。首先,通过模态分析得到系统低阶模态振动的强方向性并基于系统特性设计了具有结构耦合性的内嵌压电陶瓷作动器的风洞模型振动主动控制系统。然后,基于异位配置NAF控制器分别设计了针对第二阶模态和前两阶模态的单模态NAF控制算法和双模态NAF控制算法。最后,进行了实验验证,结果表明:双模态NAF控制算法控制效果较好,前两阶模态阻尼比分别提高近13倍和近40倍,镇定时间分别缩短近11s和近26s。 相似文献
8.
9.
ABSTRACTThis paper deals with asymptotic stabilisation of a class of nonlinear input-delayed systems via dynamic output feedback in the presence of disturbances. The proposed strategy has the structure of an observer-based control law, in which the observer estimates and predicts both the plant state and the external disturbance. A nominal delay value is assumed to be known and stability conditions in terms of linear matrix inequalities are derived for fast-varying delay uncertainties. Asymptotic stability is achieved if the disturbance or the time delay is constant. The controller design problem is also addressed and a numerical example with an unstable system is provided to illustrate the usefulness of the proposed strategy. 相似文献
10.