全文获取类型
收费全文 | 97036篇 |
免费 | 7940篇 |
国内免费 | 5182篇 |
专业分类
电工技术 | 1987篇 |
技术理论 | 6篇 |
综合类 | 8135篇 |
化学工业 | 5445篇 |
金属工艺 | 20685篇 |
机械仪表 | 5068篇 |
建筑科学 | 21722篇 |
矿业工程 | 2030篇 |
能源动力 | 1460篇 |
轻工业 | 1871篇 |
水利工程 | 1276篇 |
石油天然气 | 2790篇 |
武器工业 | 583篇 |
无线电 | 4908篇 |
一般工业技术 | 10839篇 |
冶金工业 | 17493篇 |
原子能技术 | 1568篇 |
自动化技术 | 2292篇 |
出版年
2024年 | 269篇 |
2023年 | 975篇 |
2022年 | 2197篇 |
2021年 | 2482篇 |
2020年 | 2787篇 |
2019年 | 2156篇 |
2018年 | 1866篇 |
2017年 | 2843篇 |
2016年 | 3034篇 |
2015年 | 3395篇 |
2014年 | 5905篇 |
2013年 | 5375篇 |
2012年 | 6936篇 |
2011年 | 7982篇 |
2010年 | 6118篇 |
2009年 | 6371篇 |
2008年 | 5257篇 |
2007年 | 6688篇 |
2006年 | 5974篇 |
2005年 | 4949篇 |
2004年 | 4150篇 |
2003年 | 3591篇 |
2002年 | 3131篇 |
2001年 | 2724篇 |
2000年 | 2394篇 |
1999年 | 1964篇 |
1998年 | 1571篇 |
1997年 | 1457篇 |
1996年 | 1206篇 |
1995年 | 930篇 |
1994年 | 830篇 |
1993年 | 577篇 |
1992年 | 486篇 |
1991年 | 371篇 |
1990年 | 303篇 |
1989年 | 247篇 |
1988年 | 174篇 |
1987年 | 115篇 |
1986年 | 88篇 |
1985年 | 53篇 |
1984年 | 46篇 |
1983年 | 33篇 |
1982年 | 39篇 |
1981年 | 22篇 |
1980年 | 48篇 |
1979年 | 6篇 |
1978年 | 3篇 |
1975年 | 4篇 |
1959年 | 23篇 |
1951年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
11.
《Oil and Energy Trends》2020,45(1):56-58
Currency exchanges rates – updated monthly. Economic indicators of industrial production. Countries included: France, Germany, Italy, the United Kingdom, the United States, Canada, Japan (Total G-7), Eurozone and Total EU-28 (Total OECD). Updated monthly. Economic indicators of car registration in the United States, Canada, France, Germany, Italy, Poland, Spain, Turkey, the United Kingdom, Japan, Republic of Korea and Other OECD (Total OECD-30). Updated monthly. Monthly averages of crude steel production in thousand metric tons for the United States, Canada, Brazil, Mexico, Austria, Belgium, Czech Republic, France, Germany, Italy, Netherlands, Poland, Spain, Sweden, Turkey, the United Kingdom, Russia, Ukraine, South Africa, Iran, China, India, Japan, Republic of Korea, Taiwan and Australia. 相似文献
12.
13.
《Oil and Energy Trends》2020,45(5):56-58
Currency exchanges rates – updated monthly. Economic indicators of industrial production. Countries included: France, Germany, Italy, the United Kingdom, the United States, Canada, Japan (Total G-7), Eurozone and Total EU-28 (Total OECD). Updated monthly. Economic indicators of car registration in the United States, Canada, France, Germany, Italy, Poland, Spain, Turkey, the United Kingdom, Japan, Republic of Korea and Other OECD (Total OECD-30). Updated monthly. Monthly averages of crude steel production in thousand metric tons for the United States, Canada, Brazil, Mexico, Austria, Belgium, Czech Republic, France, Germany, Italy, Netherlands, Poland, Spain, Sweden, Turkey, the United Kingdom, Russia, Ukraine, South Africa, Iran, China, India, Japan, Republic of Korea, Taiwan and Australia. 相似文献
14.
15.
16.
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
17.
《Journal of the European Ceramic Society》2020,40(10):3577-3584
In this work, the grain boundaries composition of the polycrystalline CaCu3Ti4O12 (CCTO) was investigated. A Focused Ion Beam (FIB)/lift-out technique was used to prepare site-specific thin samples of the grain boundaries interface of CCTO ceramics. Scanning transmission electron microscopy (STEM) coupled with energy dispersive X-ray spectrometry (EDXS) and Electron Energy Loss Spectroscopy (EELS) systems were used to characterize the composition and nanostructure of the grain and grain boundaries region. It is known that during conventional sintering, discontinuous grain growth occurs and a Cu-rich phase appears at grain boundaries. This Cu-rich phase may affect the final dielectric properties of CCTO but its structure and chemical composition remained unknown. For the first time, this high-resolution FIB-TEM-STEM study of CCTO interfacial region highlights the composition of the phases segregated at grain boundaries namely CuO, Cu2O and the metastable phase Cu3TiO4. 相似文献
18.
Rectangular section control technology(RSCT)was introduced to achieve high-precision profile control during silicon steel rolling.The RSCT principle and method were designed,and the whole RSCT control strategy was developed.Specifically,RSCT included roll contour design,rolling technology optimization,and control strategy development,aiming at both hot strip mills(HSMs)and cold strip mills(CSMs).Firstly,through the high-performance variable crown(HVC)work roll optimization design in the upper-stream stands and the limited shifting technology for schedule-free rolling in the downstream stands of HSMs,a hot strip with a stable crown and limited wedge,local spot,and single wave was obtained,which was suitable for cold rolling.Secondly,an approximately rectangular section was obtained by edge varying contact(EVC)work roll contour design,edge-drop setting control,and closed loop control in the upper-stream stands of CSMs.Moreover,complex-mode flatness control was realized by coordinating multiple shape-control methods in the downstream stands of CSMs.In addition,the RSCT approach was applied in several silicon-steel production plants,where an outstanding performance and remarkable economic benefits were observed. 相似文献
19.
对鞍钢股份无缝钢管厂连轧机前毛管坯横移装置存在的设计缺陷进行了分析,并提出改进方案,将原横移装置由高架轨道横移机构及上下升降链传动装置,改进为地面轨道横移系统及同步旋转臂实现取管、放管过程。实施后消除了生产故障,缩短了轧制周期,降低生产成本。 相似文献
20.
Muntasir Hashim Farnoosh Farhad David Smyth‐Boyle Robert Akid Xiang Zhang Philip J. Withers 《工业材料与腐蚀》2019,70(11):2009-2019
The environmental performance of 316L grade stainless steel, in the form of tensile specimens containing a single corrosion pit with various aspect ratios, under cyclic loading in aerated chloride solutions is investigated in this study. Results from environmental tests were compared and contrasted with those obtained using finite element analysis (FEA). Fractography of the failed specimens obtained from experiments revealed that fatigue crack initiation took place at the base of the shallow pit. The crack initiation shifted towards the shoulder and the mouth of the pit for pits of increasing depth. This process is well predicted by FEA, as the strain contour maps show that strain is the highest around the centric strip of the pit. However, for shallow pits, local strain is uniformly distributed around that strip but begins to concentrate more towards the shoulder and the mouth region for increasingly deep pits. 相似文献