全文获取类型
收费全文 | 777篇 |
免费 | 48篇 |
专业分类
电工技术 | 22篇 |
综合类 | 3篇 |
化学工业 | 166篇 |
金属工艺 | 12篇 |
机械仪表 | 27篇 |
建筑科学 | 12篇 |
能源动力 | 60篇 |
轻工业 | 31篇 |
水利工程 | 11篇 |
石油天然气 | 1篇 |
无线电 | 78篇 |
一般工业技术 | 190篇 |
冶金工业 | 58篇 |
原子能技术 | 4篇 |
自动化技术 | 150篇 |
出版年
2024年 | 6篇 |
2023年 | 19篇 |
2022年 | 36篇 |
2021年 | 40篇 |
2020年 | 37篇 |
2019年 | 33篇 |
2018年 | 42篇 |
2017年 | 58篇 |
2016年 | 56篇 |
2015年 | 23篇 |
2014年 | 33篇 |
2013年 | 61篇 |
2012年 | 39篇 |
2011年 | 47篇 |
2010年 | 45篇 |
2009年 | 33篇 |
2008年 | 14篇 |
2007年 | 21篇 |
2006年 | 18篇 |
2005年 | 14篇 |
2004年 | 11篇 |
2003年 | 18篇 |
2002年 | 12篇 |
2001年 | 6篇 |
2000年 | 6篇 |
1999年 | 6篇 |
1998年 | 8篇 |
1997年 | 10篇 |
1996年 | 3篇 |
1995年 | 3篇 |
1994年 | 4篇 |
1993年 | 8篇 |
1992年 | 7篇 |
1991年 | 3篇 |
1990年 | 3篇 |
1989年 | 3篇 |
1988年 | 5篇 |
1987年 | 9篇 |
1983年 | 2篇 |
1982年 | 2篇 |
1981年 | 3篇 |
1980年 | 4篇 |
1979年 | 3篇 |
1978年 | 1篇 |
1977年 | 2篇 |
1976年 | 1篇 |
1974年 | 1篇 |
1973年 | 1篇 |
1971年 | 1篇 |
1970年 | 2篇 |
排序方式: 共有825条查询结果,搜索用时 15 毫秒
31.
Majority of the products can be assembled in several ways that means the same final product can be realized by different sequences of assembly operations. Different degree of difficulty is associated with each sequence of assembly operation and such difficulties are caused by the different mechanical constraints forced by the different sequences of operations. In the past, few notable attempts have been made to represent and enumerate the degree of difficulty associated with an assembly sequence (in the form of triangular fuzzy number) by using the concept of assembly graph. However, such representation schemes do not possess the capabilities to model the user's reasoning and preferences. In this research, an intelligent Petri net model that combines the abilities of modelling, planning and performance evaluation for assembly operation is presented. This modelling tool can represent the issues concerning degree of difficulty associated with assembly sequences. The proposed mechanism is enhanced expert high-level colored fuzzy Petri net (EEHLCFPN) that is a hybrid of knowledge-based system and colored Petri net. An example encompassing assembly of subassemblies is considered to efficiently delineate the modelling capabilities of proposed hybrid petri net model. 相似文献
32.
The paper reports an investigation into the effect of interfacial friction law during the forging of a powder circular disc
with large slenderness ratio(L/D), between two flat dies. The deformation pattern during the operation is influenced by many factors, which interact with each
other in a complex manner. The relative velocity between the work piece material and the die surface, together with high interfacial
pressure and/or deformation modes, creates the conditions essential for adhesion in addition to sliding. The decisive factors
are the interfacial conditions, initial relative density of the preform and geometry of the preform. An attempt has been made
to determine the most realistic interfacial friction law and die pressures developed during such forging using an upper bound
approach. The results so obtained are presented graphically and discussed critically to illustrate the interaction of various
interfacial friction laws involved. 相似文献
33.
34.
Valuable metal extraction technology from thermal power plant fly ash is limited. In the present study, aluminium is extracted from fly ash as highly pure aluminium sulphate (>99.0%) by leaching with sulphuric acid, followed by pre-concentration and successive crystallization. Two types of fly ashes from different sources, i.e., Talcher Thermal Power Station (TTPS) and Vedanta Aluminium Company Limited (VAL) were chosen for comparative study on the extraction of aluminium as aluminium sulphate. The product is characterized by powder X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and thermogravimetric analysis (TGA). Purity of aluminium sulphate was also investigated by inductively coupled plasma–optical emission spectrometry (ICP–OES). The extraction efficiency of aluminium depends on the varied solid-to-liquid ratio (fly ash : 18 mol/L H2SO4, g/mL) and particle size of fly ashes. Physico-chemical analysis indicates that the obtained product is Al2(SO4)3·18H2O, having low iron content (0.08%). 相似文献
35.
Himadri Sekhar Samanta Samit Kumar Ray Paramita Das Nayan Ranjan Singha 《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》2012,87(5):608-622
BACKGROUND: Low energy and less expensive membrane based separation of acetic acid‐water mixtures would be a better alternative to conventional separation processes. However, suitable acid resistant membranes are still lacking. Thus, the objective of the present study was to develop mixed matrix membrane (MMM) which would allow high flux and water selectivity over a wide range of feed concentrations of acid in water. RESULTS: Three MMMs, namely PANBA0.5, PANBA1.5 and PANBA3 were made by emulsion copolymerization of acrylonitrile (AN) and butyl acrylate (BA) with 5.5:1 comonomer ratio and in situ incorporation of 0.5, 1.5 and 3 wt%, sodium montmorilonite (Na‐MMT) nanofillers, respectively. For a feed concentration of 99.5 wt% of acid in water the membranes show good permeation flux (2.61, 3.19, 3.97 kg m?2 h?1 µm?1, for PANBA0.5, PANBA1.5 and PANBA3 membrane, respectively) and very high separation factors for water (1473, 1370, 1292 for PANBA0.5, PANBA1.5 and PANBA3 membrane, respectively) at 30 °C. Similarly for a dilute acid–water solution, i.e. for 71.6 wt% acid the membrane showed a very high thickness normalize flux (8.67, 9.44, 11.56 kg m?2 h?1 µm?1, for PANBA0.5, PANBA1.5 and PANBA3 membrane, respectively) and good water selectivity (101.7, 95.3, 79 for PANBA0.5, PANBA1.5 and PANBA3 membrane, respectively) at the same feed temperature. The permeation ratio, permeability, diffusion coefficient and activation energy for permeation of the membranes were also estimated. CONCLUSION: Unlike most of the reported membranes, the present MMMs allowed high flux and selectivity over a wide range of feed concentrations. These membranes may also be effective for separating other similar organic‐water mixtures. Copyright © 2012 Society of Chemical Industry 相似文献
36.
37.
Biobutanol: science,engineering, and economics 总被引:1,自引:0,他引:1
Among several liquid alternative fuels, biobutanol has shown great promise because of its very similar properties to gasoline. This review provides an overview of research activities in acetone–butanol–ethanol (ABE) fermentation over the past two and a half decades. We have addressed seven important facets of ABE fermentation, viz. biochemistry, microbial cultures, alternative substrates, solvent recovery, fermentation mode and reactor designs, mathematical modeling, and economics. Development of mutant strains having higher yield, selectivity and tolerance to inhibition, and search for cheap alternative substrates for fermentation are most important thrust areas in biobutanol production. New and efficient processes have been developed for in situ removal and recovery of the ABE solvents. Several rigorous kinetic and physiological models for fermentation have been formulated, which form useful tool for optimization of the process. These research activities have been reviewed in this paper. Finally, we have summarized studies on the economic viability of large‐scale ABE fermentation processes employing various process designs, substrates, and microbial cultures. With the use of new strains, inexpensive substrates, and superior reactor designs, economic potential of ABE fermentation has been found to be highly attractive. Research efforts in science, engineering, and economics of ABE fermentation have brought biobutanol close to commercialization as liquid alternate fuel. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
38.
In this paper, the relationship between the number of unit-cells used in the design of a frequency selective surface (FSS) and its expected directivity is established. The relationship between the number of FSS unit-cells and the directivity is based on the planer microstrip patch array antenna design concept where the unit-cell is treated as the superstrate illuminated by the source. To validate the proposed technique, the analytical value of the directivity has been compared with that of ray-tracing method. The directivity of antenna is calculated for two different planar array configurations at 600 GHz. The results of numerical analysis are compared to that of the full-wave electromagnetic simulator CST Microwave Studio and results are comparable. Further, the directivity computed by this proposed technique has also been compared with that of the reported in literatures. 相似文献
39.
Jnyana Ranjan Pati Subhajit Dutta Philippe Eliaers Pinakeswar Mahanta Pradip Kumar Chatterjee 《Drying Technology》2016,34(9):1073-1084
The intensification of interfacial mass, heat, and momentum transfer makes vortex chambers potentially interesting for the efficient drying of paddy, allowing shorter drying times and/or more compact equipment. The presence of a shell introduces particular challenges. Intraparticle diffusion limitations are strong and may reduce the advantage from intensified interfacial mass and heat transfer and the efficiency of air usage. Furthermore, high shear and normal stresses in the fast rotating particle bed may cause damage to the paddy shell, posing problems for transport and storage. With these specific aspects in mind, the use of vortex chambers for paddy drying is experimentally evaluated. 相似文献
40.
One possibility presented by novel communication technologies is the ability for remotely located experts to provide guidance to others who are performing difficult technical tasks in the real world, such as medical procedures or engine repair. In these scenarios, video views and other visual information seem likely to be useful in the ongoing negotiation of shared understanding, or common ground, but actual results with experimental systems have been mixed. One difficulty in designing these systems is achieving a balance between close-up shots that allow for discussion of detail and wide shots that allow for orientation or establishing a mutual point of focus in a larger space. Achieving this balance can be difficult without disorienting or overloading task participants. In this article we present results from two experiments involving three automated camera control systems for remote repair tasks. Results show that a system providing both detailed and overview information was superior to systems providing only one or the other in terms of performance but that some participants preferred the detail-only system. 相似文献