全文获取类型
收费全文 | 556篇 |
免费 | 42篇 |
国内免费 | 3篇 |
专业分类
电工技术 | 8篇 |
化学工业 | 162篇 |
金属工艺 | 11篇 |
机械仪表 | 7篇 |
建筑科学 | 11篇 |
能源动力 | 20篇 |
轻工业 | 41篇 |
水利工程 | 3篇 |
无线电 | 53篇 |
一般工业技术 | 126篇 |
冶金工业 | 40篇 |
原子能技术 | 9篇 |
自动化技术 | 110篇 |
出版年
2024年 | 2篇 |
2023年 | 15篇 |
2022年 | 30篇 |
2021年 | 34篇 |
2020年 | 26篇 |
2019年 | 35篇 |
2018年 | 37篇 |
2017年 | 29篇 |
2016年 | 27篇 |
2015年 | 26篇 |
2014年 | 26篇 |
2013年 | 34篇 |
2012年 | 20篇 |
2011年 | 35篇 |
2010年 | 14篇 |
2009年 | 22篇 |
2008年 | 19篇 |
2007年 | 21篇 |
2006年 | 13篇 |
2005年 | 7篇 |
2004年 | 7篇 |
2003年 | 7篇 |
2002年 | 10篇 |
2001年 | 9篇 |
2000年 | 7篇 |
1999年 | 4篇 |
1998年 | 6篇 |
1997年 | 11篇 |
1996年 | 9篇 |
1995年 | 4篇 |
1994年 | 11篇 |
1993年 | 8篇 |
1992年 | 2篇 |
1990年 | 2篇 |
1987年 | 2篇 |
1986年 | 4篇 |
1985年 | 3篇 |
1984年 | 3篇 |
1983年 | 4篇 |
1982年 | 4篇 |
1981年 | 3篇 |
1980年 | 1篇 |
1977年 | 2篇 |
1976年 | 2篇 |
1975年 | 2篇 |
1974年 | 1篇 |
1972年 | 1篇 |
排序方式: 共有601条查询结果,搜索用时 15 毫秒
81.
E. A. Medina S Venugopal W. G. Frazier S Medeiros W. M. MulHns A Chaudhary R. D. Irwin R Srinivasan J. C. Malas 《Journal of Materials Engineering and Performance》1996,5(6):743-752
A new process design method for controlling microstructure development during hot metal deformation processes is presented.
This approach is based on modern control theory and involves state- space models for describing the material behavior and
the mechanics of the process. The challenge of effectively controlling the values and distribution of important microstructural
features can now be systematically formulated and solved in terms of an optimal control problem. This method has been applied
to the optimization of grain size and certain process parameters such as die geometry profile and ram velocity during extrusion
of plain carbon steel. Various case studies have been investigated, and experimental results show good agreement with those
predicted in the design stage. 相似文献
82.
83.
84.
Routing is a process of selecting a path in a network for delivering a packet from source node to destination node. Successful delivery of a message is a challenge, and therefore, this paper proposes an algorithm for a wireless network called Optimized Routing in wireless networks using Machine Learning (ORuML), which uses machine learning algorithm namely, K‐nearest neighbor (KNN), Support Vector Machine (SVM), and Multinomial Logistic Regression (MLR), to predict the network type of the source and destination nodes. The ML model is trained by using characteristic features of a node collected in real time such as battery power utilization, available internal storage, IP address, and range of a node. Intuitively, the MLR should outperform KNN and SVM in terms of accuracy and Area under ROC Curve (AUC). The proposed algorithm determines whether the source and destination nodes are co‐located and also, determines the best neighboring hop for efficient routing. 相似文献
85.
Abhinav Anand Matteo L. Zaffalon Graziella Gariano Andrea Camellini Marina Gandini Rosaria Brescia Chiara Capitani Francesco Bruni Valerio Pinchetti Margherita Zavelani‐Rossi Francesco Meinardi Scott A. Crooker Sergio Brovelli 《Advanced functional materials》2020,30(4)
Ternary I‐III‐VI2 nanocrystals (NCs), such as CuInS2, are receiving attention as heavy‐metals‐free materials for solar cells, luminescent solar concentrators (LSCs), LEDs, and bio‐imaging. The origin of the optical properties of CuInS2 NCs are however not fully understood. A recent theoretical model suggests that their characteristic Stokes‐shifted and long‐lived luminescence arises from the structure of the valence band (VB) and predicts distinctive optical behaviours in defect‐free NCs: the quadratic dependence of the radiative decay rate and the Stokes shift on the NC radius. If confirmed, this would have crucial implications for LSCs as the solar spectral coverage ensured by low‐bandgap NCs would be accompanied by increased re‐absorption losses. Here, by studying stoichiometric CuInS2 NCs, it is revealed for the first time the spectroscopic signatures predicted for the free band‐edge exciton, thus supporting the VB‐structure model. At very low temperatures, the NCs also show dark‐state emission likely originating from enhanced electron‐hole spin interaction. The impact of the observed optical behaviours on LSCs is evaluated by Monte Carlo ray‐tracing simulations. Based on the emerging device design guidelines, optical‐grade large‐area (30×30 cm2) LSCs with optical power efficiency (OPE) as high as 6.8% are fabricated, corresponding to the highest value reported to date for large‐area devices. 相似文献
86.
This article presents a new dual C‐shaped rectangular dielectric resonator (DR) based antenna for generation of wideband circularly polarized (CP) radiation. The proposed antenna comprises of a pair of C‐shaped rectangular dielectric DR and a metal strip with a coaxial probe. By utilization of a metal strip at the side surface of C‐shaped rectangular DR, the wideband CP radiation is achieved from the proposed dielectric resonator antenna (DRA). Fundamental orthogonal modes (TExδ11 and TEy1δ1) are excited using the rectangular DRA with a metal strip for the generation of CP fields. The proposed antenna with dual C‐shaped rectangular CP DRA provides the measured ?10 dB reflection coefficient bandwidth of 30.07% (3.22 GHz‐4.36 GHz) with measured 3‐dB axial ratio bandwidth of 14.81% (3.25 GHz‐3.77 GHz) at the boresight. The proposed antenna covers the useful Wi‐MAX band. 相似文献
87.
Jillian Aurisano Abhinav Kumar Abeer Alsaiari Barbara Di Eugenio Andrew Johnson 《Computer Graphics Forum》2020,39(3):229-240
This paper describes results from an observational, exploratory study of visual data exploration in a large, multi-view, flexible canvas environment. Participants were provided with a set of data exploration sub-tasks associated with a local crime dataset and were instructed to pose questions to a remote mediator who would respond by generating and organizing visualizations on the large display. We observed that participants frequently posed requests to cast a net around one or several subsets of the data or a set of data attributes. They accomplished this directly and by utilizing existing views in unique ways, including by requesting to copy and pivot a group of views collectively and posing a set of parallel requests on target views expressed in one command. These observed actions depart from multi-view flexible canvas environments that typically provide interfaces in support of generating one view at a time or actions that operate on one view at a time. We describe how participants used these ‘cast-a-net’ requests for tasks that spanned more than one view and describe design considerations for multi-view environments that would support the observed multi-view generation actions. 相似文献
88.
A coaxial probe fed wideband circularly polarized antenna using unequal and adjacent‐slided rectangular dielectric resonators for WLAN applications 下载免费PDF全文
In this article, a coaxial probe fed wideband circularly polarized antenna has been designed and investigated using unequal and adjacent‐slided rectangular dielectric resonators radiating in broadside direction (Φ = 0°, θ = 0°). Wi‐Fi wireless network use radio signal either in 2.4 or 5 GHz band. Owing to high rush in 2.4 GHz band, the proposed antenna is designed for 5 GHz (5.15‐5.825 GHz) WLAN band. The proposed design uses fundamental orthogonal modes and excited in two individual rectangular dielectric resonators to achieve wide axial‐ratio bandwidth (below 3 dB). Measured input reflection coefficient (below ?10 dB) and axial ratio bandwidth (below 3 dB) of 26.07% (5.27‐6.85 GHz) and 26.85% (5.32‐6.97 GHz) has been attained, respectively, in this proposed antenna. The measured far‐field patterns such as gain and radiation patterns are showing consistent performance throughout the working band. 相似文献
89.
Circularly polarized rectangular DRA coupled through orthogonal slot excited with microstrip circular ring feeding structure for Wi‐MAX applications 下载免费PDF全文
In this article, a wideband circularly polarized rectangular dielectric resonator antenna (RDRA) coupled through orthogonal slots and excited with a new microstrip circular ring has been investigated. Circular polarization has been achieved by using plus shaped (+) slot on the ground plane and excited through a new microstrip circular ring feed. TE11δ mode has been excited in the RDRA which has been confirmed through the distribution of E ‐field and dielectric waveguide model (DWM) method of RDRA. Circularly polarized (CP) RDRA offering measured ?10 dB input impedance bandwidth of 20.79% (centered at 3.27 GHz) and 3 dB axial ratio bandwidth in broadside direction of 12.09% (centered at 3.39 GHz), respectively. From the CP radiation pattern, proposed design confirms that right ‐ handed CP (RHCP) in broadside direction. The difference between RHCP field and left ‐ handed CP (LHCP) field are above ?26 dB in operational band. In addition, the proposed CP antenna offers stable gain and radiation efficiency in working bands and it is suitable for IEEE 802.16e/d Wi‐MAX (3.3‐3.7 GHz) band. 相似文献
90.
Investigation of higher order modes excitation through F‐shaped slot in rectangular dielectric resonator antenna for wideband circular polarization with broadside radiation characteristics 下载免费PDF全文
In this article, a wideband circularly polarized rectangular dielectric resonator antenna (RDRA) with broadside radiation characteristics has been proposed. By using modified ground plane having an F‐shaped slot, the proposed structure able to generates three sets of modes i.e., fundamental as well as higher order modes. To obtained circular polarization, an orthogonal mode (TE113) in the RDRA has been generated by using the F‐shaped slot on the modified ground plane. The resonance frequency of fundamental mode (TE111) in the rectangular dielectric resonator (DR) has been calculated by using dielectric waveguide model method. The same has been confirmed through E‐field distribution in RDRA. Here, wide axial ratio (AR) bandwidth of the proposed antenna is due to the generation of and modes. It is observed that input impedance bandwidth has been broadening with a pair of excited modes ( and modes) in the proposed antenna structure. All these modes have been excited and merged to form a wide input impedance bandwidth and wide AR bandwidth of the designed antenna. The proposed antenna shows measured input reflection coefficient (S11 < ?10 dB) of 50.55% and measured AR bandwidth (AR < 3 dB) of 14.28%. The designed antenna shows left‐handed circular polarization in broadside direction and offering an average gain and radiation efficiency of 4.29 dBic and 92.22% respectively. 相似文献