全文获取类型
收费全文 | 1950篇 |
免费 | 103篇 |
国内免费 | 86篇 |
专业分类
电工技术 | 38篇 |
综合类 | 28篇 |
化学工业 | 191篇 |
金属工艺 | 31篇 |
机械仪表 | 71篇 |
建筑科学 | 32篇 |
矿业工程 | 13篇 |
能源动力 | 119篇 |
轻工业 | 25篇 |
水利工程 | 13篇 |
石油天然气 | 12篇 |
武器工业 | 7篇 |
无线电 | 249篇 |
一般工业技术 | 179篇 |
冶金工业 | 3篇 |
原子能技术 | 6篇 |
自动化技术 | 1122篇 |
出版年
2024年 | 3篇 |
2023年 | 40篇 |
2022年 | 67篇 |
2021年 | 78篇 |
2020年 | 69篇 |
2019年 | 71篇 |
2018年 | 57篇 |
2017年 | 80篇 |
2016年 | 66篇 |
2015年 | 70篇 |
2014年 | 142篇 |
2013年 | 128篇 |
2012年 | 94篇 |
2011年 | 153篇 |
2010年 | 99篇 |
2009年 | 108篇 |
2008年 | 118篇 |
2007年 | 125篇 |
2006年 | 101篇 |
2005年 | 85篇 |
2004年 | 62篇 |
2003年 | 72篇 |
2002年 | 35篇 |
2001年 | 24篇 |
2000年 | 26篇 |
1999年 | 29篇 |
1998年 | 17篇 |
1997年 | 20篇 |
1996年 | 13篇 |
1995年 | 7篇 |
1994年 | 5篇 |
1993年 | 8篇 |
1992年 | 9篇 |
1991年 | 4篇 |
1990年 | 8篇 |
1989年 | 7篇 |
1988年 | 1篇 |
1986年 | 2篇 |
1985年 | 2篇 |
1984年 | 4篇 |
1983年 | 6篇 |
1982年 | 4篇 |
1981年 | 4篇 |
1980年 | 5篇 |
1979年 | 3篇 |
1978年 | 4篇 |
1977年 | 2篇 |
1976年 | 2篇 |
排序方式: 共有2139条查询结果,搜索用时 15 毫秒
1.
Although hybrid Petri net (HPN) is a popular formalism in modelling hybrid production systems, the HPN model of large scale systems gets substantially complicated for analysis and control due to large dimensionality of such systems. To overcome this problem, a typical approach is to decompose the net into subnets and then control the plant through hierarchical or decentralized structures. Although this concept has been widely discussed in the literature for discrete PNs, there is a lack of research for HPNs. In this paper, a new method of decomposition of first-order hybrid Petri nets (FOHPNs) is proposed first and then the hierarchical control of the subnets through a coordinator is introduced. The advantage of using the proposed approach is validated by an existing example. A sugar milling case study is analysed by using a decomposed FOHPN model and the optimization results are compared against the results of the approaches presented in other papers. Simulation results show not only an improvement in production rate, but also show the ability to control the plant online. In addition, by using the hierarchical control structure for an FOHPN model, it is possible to reduce the cost of communication links, improve the reliability of the system, maintain the plant locally, and partially redesign the system. 相似文献
2.
High dimensionality in real-world multi-reservoir systems greatly hinders the application and popularity of evolutionary algorithms, especially for systems with heterogeneous units. An efficient hierarchical optimization framework is presented for search space reduction, determining the best water distributions, not only between cascade reservoirs, but also among different types of hydropower units. The framework is applied to the Three Gorges Project (TGP) system and the results demonstrate that the difficulties of multi-reservoir optimization caused by high dimensionality can be effectively solved by the proposed hierarchical method. For the day studied, power output could be increased by 6.79 GWh using an optimal decision with the same amount of water actually used; while the same amount of power could be generated with 2.59 × 107 m3 less water compared to the historical policy. The methodology proposed is general in that it can be used for other reservoir systems and other types of heterogeneous unit generators. 相似文献
3.
《Ceramics International》2022,48(17):24840-24849
In this paper, Gd3+ doped V2O5/Ti3C2Tx MXene (GVO/MX) hierarchical architectures have been synthesized by wet chemical approach. As prepared GVO/MX composite, along undoped VO and unsupported GVO were well characterized by XRD, FESEM, EDX, FT-IR and BET techniques. Electrochemical performance of VO, GVO and GVO/MX was evaluated by CV, GCD and EIS measurements. Among the three electrodes, GVO/MX composite exhibited highest electrochemical activity with the optimum specific capacitance of 1024 Fg-1 at 10 mVs?1. The specific capacitance of GVO/MX was ~1.7 and ~3 times higher than unsupported GVO (585 Fg-1) and VO (326 Fg-1), respectively. The cyclic life of GVO/MX with capacitance retention 96.12% was observed at 60 mVs?1. EIS measurements showed reduction in electrochemical impedance for GVO/MX as compared to GVO and VO. The corresponding impedance values of Rct and Resr for GVO/MX were calculated as 18 Ω and 1.8 Ω, respectively. The superior capacitive ability of GVO/MX can be ascribed to its unique morphology, short diffusion path and high surface area of fabricated composite. Considering it, the present work provides a feasible strategy to fabricate highly effective electrode materials for next generation energy storage devices. 相似文献
4.
Novel core-shell-like Ni-supported hierarchical beta zeolite catalysts on bioethanol steam reforming
《International Journal of Hydrogen Energy》2020,45(33):16409-16420
Hierarchical-Beta zeolites have been hydrothermally synthesized by adding a new gemini organic surfactant. The used gemini surfactant play the role of a “pore-forming agents” on the mesoscale, on the same time, providing alkaline environment for the system. With this hierarchical Beta zeolite as the core support, we successfully prepared a shell layer of Ni-containing (22 wt%) petal-like core-shell-like catalyst and applied it to bioethanol steam reforming. At the reaction temperature of 350 °C–550 °C, the conversion rate of ethanol and the selectivity of hydrogen were always above 85% and 70%. After reaction of 100 h on stream at 400 °C, there were not obvious inactivation could be observed on NiNPs/OH-MBeta catalyst. 相似文献
5.
Sahar Hashemi Daryan Jafar Javadpour Alireza Khavandi Mohammad Erfan 《Ceramics International》2018,44(16):19743-19750
Well-ordered and surface engineered hierarchical hydroxyapatite microspheres (HAM) were prepared via a template free hydrothermal process. Ethylene diamine tetra (methylene phosphonic acid) (EDTMP) was used as chelating or regulating agent for the first time in this study. The results indicated the formation of sheet-like particles in the absence of EDTMP. On the other hand, microspheres with radially grown nanorods (HAMNR) or nanosheets (HAMNS) on the surface were obtained (with average diameter of 5?µm) in the presence of EDTMP. X-ray diffraction (XRD) and Fourier transform infrared (FTIR) spectroscopy were used to characterize the crystalline phases in the synthesized samples. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) showed that EDTMP concentration played an important part in regulating the morphology to form well organized microspheres with nanosheets or nanorods on the surface. Brunauer-Emmett-Teller (BET) revealed an increase in the specific surface area with the change in morphology from the HAMNS to HAMNR. Possible mechanisms are proposed to account for the formation of different morphologies based upon thermodynamic and kinetic theories. 相似文献
6.
7.
文章给出将神经网络与矢量量化相结合的两种编码方法,介绍了其原理和实现的算法。经计算机模拟表明,在比特率低于0.3bpp时仍可得到高质量的编码图象。 相似文献
8.
BaXO4 (X = Mo, W) nanobelts and a variety of hierarchical superstructures assembled from the nanobelts have been synthesized in a catanionic reverse‐micelle system. The effects of various factors, such as the mixing ratio (r) between the anionic and cationic surfactants, the temperature, and the presence of polymeric additives, on the formation of the nanobelts and their hierarchical assembly have been examined in detail. In particular, r has been shown to be powerful in modulating the formation and assembly of the BaMoO4 and BaWO4 nanobelts. Architectural control of the penniform nanobelt superstructures has been readily achieved by changing the experimental parameters. A plausible two‐stage growth mechanism has been proposed for the formation of penniform BaXO4 nanobelt superstructures in catanionic reverse micelles. 相似文献
9.
Modelling spatio-temporal environmental data 总被引:1,自引:0,他引:1
Jussi Rasinmki 《Environmental Modelling & Software》2003,18(10):877-Technology
A conceptual model for environmental data is presented with special emphasis on the ability to store spatio-temporal references of the data. Other aspects of the model are the ability to handle hierarchical data and semantics of the measurements. The model was tested with an implementation on an object-relational database management system. As a part of the test implementation, a forestry data set covering 75 years and 4900 hectares was loaded onto the database. 相似文献
10.
Ray tracing has been shown to be an excellent technique for rendering realistic images. However, it is important to reduce the lengthy computation time resulting from the brute-force nature of the original ray-tracing algorithms. In this paper, two ideas are proposed to speep up the well-known hierarchical subdivision method. First, a new hierarchy traversal scheme is described to reduce the number of raybounding volume intersection tests for secondary rays. Then, a plane-sweep method is proposed to make fewer intersection checks for eye rays. Experiments and discussions are presented to prove the feasibility of our methods. 相似文献