全文获取类型
收费全文 | 22217篇 |
免费 | 1419篇 |
国内免费 | 1022篇 |
专业分类
电工技术 | 665篇 |
综合类 | 1752篇 |
化学工业 | 2282篇 |
金属工艺 | 5666篇 |
机械仪表 | 1035篇 |
建筑科学 | 1952篇 |
矿业工程 | 566篇 |
能源动力 | 336篇 |
轻工业 | 566篇 |
水利工程 | 188篇 |
石油天然气 | 508篇 |
武器工业 | 158篇 |
无线电 | 666篇 |
一般工业技术 | 1836篇 |
冶金工业 | 4991篇 |
原子能技术 | 83篇 |
自动化技术 | 1408篇 |
出版年
2024年 | 72篇 |
2023年 | 217篇 |
2022年 | 472篇 |
2021年 | 475篇 |
2020年 | 568篇 |
2019年 | 427篇 |
2018年 | 386篇 |
2017年 | 546篇 |
2016年 | 610篇 |
2015年 | 591篇 |
2014年 | 1243篇 |
2013年 | 1150篇 |
2012年 | 1555篇 |
2011年 | 1699篇 |
2010年 | 1325篇 |
2009年 | 1282篇 |
2008年 | 993篇 |
2007年 | 1543篇 |
2006年 | 1435篇 |
2005年 | 1174篇 |
2004年 | 1010篇 |
2003年 | 948篇 |
2002年 | 852篇 |
2001年 | 811篇 |
2000年 | 696篇 |
1999年 | 598篇 |
1998年 | 422篇 |
1997年 | 360篇 |
1996年 | 261篇 |
1995年 | 217篇 |
1994年 | 184篇 |
1993年 | 128篇 |
1992年 | 96篇 |
1991年 | 87篇 |
1990年 | 56篇 |
1989年 | 51篇 |
1988年 | 32篇 |
1987年 | 23篇 |
1986年 | 13篇 |
1985年 | 13篇 |
1984年 | 6篇 |
1983年 | 7篇 |
1982年 | 7篇 |
1981年 | 3篇 |
1980年 | 4篇 |
1973年 | 2篇 |
1964年 | 2篇 |
1961年 | 2篇 |
1958年 | 1篇 |
1951年 | 1篇 |
排序方式: 共有10000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.
Waveguide configurations of hierarchical system are proposed as new microstructures for composites in absorbing enhancement. Supercritical fluid (SCF) one-pot exfoliation of layered graphite and manganese oxide mixing materials is developed to obtain a hierarchical system, containing graphene nanosheets (GNS) and exfoliated manganese oxides (EMO) in different sizes. Composites with GNS–EMO embedded in epoxy resin matrix are produced for a design of dielectric and magnetic loss integrated absorber. Volume fraction of GNS–EMO in composites is given for an optimal quantity of resin epoxy in fixation and formation. The effect of mixing ratios between electric and magnetic components is provided for the design of dielectric and magnetic loss integrated absorbers. Frequency shifting phenomena are revealed in the component adjusting course. Excluding the offsetting sizes, reflection loss of composites is enhanced as thickness increases. Synergistic effect of electric and magnetic coordinated materials demonstrates the superiority of micro-waveguide structures in GNS–EMO composite absorber. 相似文献
3.
针对传统的小区内开环功率控制算法通常以提升本小区的吞吐量性能为目标,忽略了当前小区用户对邻小区用户同频干扰的问题,为提升边缘用户性能的同时兼顾系统整体性能,提出了一种LTE系统小区间上行联合功率控制(UJPC)算法。该算法采用单基站三扇区为系统模型,以最优化系统吞吐量比例公平函数为目标,首先根据最小信干噪比(SINR)约束值和用户最大发射功率这两个约束条件得到相应的数学优化模型,然后采用连续凸近似的方法求解优化问题得出各个基站所管辖的小区内所有用户的最优发射功率。仿真结果表明,与基准的开环功控方案相比,联合功控方案在保证系统平均频谱利用率的情况下能够较大幅度地提高小区边缘频谱利用率,其最佳性能增益能达到50%。 相似文献
4.
5.
放置过滤器浇注系统的设计 总被引:3,自引:1,他引:2
综述了常用的网型、芯型、泡沫陶瓷过滤器的研究和应用情况。指出应根据过滤器类型,确定其在浇注系统中的安放位置并相应改变该处的结构和截面积,以便在使用过滤器净化金属的同时,保证充型速度不变。 相似文献
6.
通过分析钢水在结晶器内凝固的不均匀性及对钢水结晶的热量平衡计算,讨论连铸中间包钢水温度、结晶器冷却水流量及进出水温差对拉坯速度的影响。 相似文献
7.
8.
María P. Albano Liliana B. Garrido 《Journal of Materials Synthesis and Processing》2002,10(4):211-218
Si3N4powders coated with 6 wt% Y2O3and 4 wt% Al2O3were prepared by coprecipitation. The resulting powders were dispersed in water at different pH values and with addition of various amounts of ammonium polyacrylate (NH4PA) to produce 32 vol% slips. The influence of the amount of NH4PA solution added and pH on the rheological properties of 32 vol% coated Si3N4slips were studied. In addition, the sintered density of cast samples was determined and related to the degree of slip dispersion. The adsorption of the NH4PA on the coated particle surface was rather high and the surface became saturated near 0.86 mg/m2at pH 9.2. High NH4PA concentrations (1.7–3 wt%) were necessary to obtain well dispersed 32 vol% coated Si3N4slips at pH 9.2. The best stabilization was obtained with the addition of 2.3 wt% NH4PA; in this condition, the viscosity reached a minimum value of 35 mPa.s at 100 s–1. The slip viscosity increased with increasing pH from 9.2 to 10.2. Slips with low viscosities gave a more dense packing of cast samples and consequently higher sintered density values. 相似文献
9.
10.
耿鑫明 《机械制造与自动化》2002,(2):6-8
针对中国压铸行业的现状和存在的问题 ,以及当前的机遇和面临的挑战 ,论述了中国压铸工业进入 2 1世纪所面临的新形势及应采取的对策 相似文献