全文获取类型
收费全文 | 409981篇 |
免费 | 24839篇 |
国内免费 | 12944篇 |
专业分类
电工技术 | 18736篇 |
技术理论 | 56篇 |
综合类 | 21434篇 |
化学工业 | 66926篇 |
金属工艺 | 22871篇 |
机械仪表 | 23895篇 |
建筑科学 | 27786篇 |
矿业工程 | 11461篇 |
能源动力 | 10874篇 |
轻工业 | 21995篇 |
水利工程 | 6527篇 |
石油天然气 | 23277篇 |
武器工业 | 2606篇 |
无线电 | 45079篇 |
一般工业技术 | 54645篇 |
冶金工业 | 20806篇 |
原子能技术 | 3465篇 |
自动化技术 | 65325篇 |
出版年
2024年 | 1289篇 |
2023年 | 5212篇 |
2022年 | 8871篇 |
2021年 | 12549篇 |
2020年 | 9829篇 |
2019年 | 8013篇 |
2018年 | 22047篇 |
2017年 | 22314篇 |
2016年 | 18264篇 |
2015年 | 12779篇 |
2014年 | 16099篇 |
2013年 | 19387篇 |
2012年 | 23114篇 |
2011年 | 31128篇 |
2010年 | 26856篇 |
2009年 | 23459篇 |
2008年 | 24322篇 |
2007年 | 24764篇 |
2006年 | 18456篇 |
2005年 | 17356篇 |
2004年 | 11438篇 |
2003年 | 10256篇 |
2002年 | 8658篇 |
2001年 | 7574篇 |
2000年 | 8185篇 |
1999年 | 9709篇 |
1998年 | 8205篇 |
1997年 | 6795篇 |
1996年 | 6405篇 |
1995年 | 5347篇 |
1994年 | 4389篇 |
1993年 | 3097篇 |
1992年 | 2503篇 |
1991年 | 1983篇 |
1990年 | 1504篇 |
1989年 | 1232篇 |
1988年 | 1028篇 |
1987年 | 681篇 |
1986年 | 535篇 |
1985年 | 342篇 |
1984年 | 243篇 |
1983年 | 204篇 |
1982年 | 196篇 |
1981年 | 129篇 |
1980年 | 130篇 |
1979年 | 67篇 |
1976年 | 55篇 |
1965年 | 49篇 |
1955年 | 63篇 |
1954年 | 68篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
971.
Investigation into the magnets with different squareness of hysteresis loop (SHL) reveals that the microstructure of sintered NdFeB magnets has great effects on the SHL of the magnets. The abnormal grain growth deteriorates the SHL seriously. The shape of the grain and the grain boundary affect the intensity of demagnetization field, and consequently on the SHL. The added elements have effects on the phase structures and distributions in the magnets, which influences the uniform of demagnetization field. 相似文献
972.
Lusheng Wang 《Algorithmica》2007,48(2):127
This special issue contains six selected papers that were presented at the 11th Annual International Computing and Combinatorics
Conference (COCOON 2005), held in Kunming, Yunnan, China on August 16–19, 2005. This year we obtained 353 submissions and
96 of them were accepted for presentation at the conference. These six selected papers represent several areas in theoretical
computer science, including complexity, computational biology, computational finance, and network algorithms. We thank the
authors for submitting and revising their work, and PC members and referees for their careful reviewing. 相似文献
973.
Because of the widespread increasing application of Web services and autonomic computing, self-adaptive software is an area gaining increasing importance. Control theory provides a theoretical foundation for self-adaptive software. In this paper, we propose the use of the supervisory control theory of discrete event dynamic systems (DEDS) to provide a rigorous foundation for designing software for reactive systems. This paper focuses in particular on design of software with an attractivity requirement. It studies this problem using the polynomial dynamic system (PDS) model of DEDS. A necessary and sufficient condition for software existence and two algorithms for such software design are presented. 相似文献
974.
Chi-Chang Wang 《International Communications in Heat and Mass Transfer》2005,32(10):1337-1349
This research discusses the impacts of the surface area that the wavy surface gets more than the flat plate upon the aerosol particle deposition. Starting from the full Navier–Stokes equation, the mathematical analysis takes the thermophoretic motion formed by the temperature gradient and the fluid thermal expansion into consideration, and converts the governing equations into the boundary layer equation by the simple coordinate transformation and non-similarity method, and then works out these equations by the Spline Alternating-Direction Implicit method (SADI). The numerical value result reveals that the average deposition effect of the wavy plate is greater than the flat plate and that the increasing rate is nearly equal to the value obtained by dividing the surface area that the wavy plate gets more than the flat plate by 2.2. 相似文献
975.
Tingfang Hu Jinpeng Chen Haiyan Wang Jun Min Wei 《Petroleum Science and Technology》2006,24(12):1477-1484
Etherification reaction of FCC light gasoline over Hβ zeolite was investigated to decrease the light olefins in motor gasoline while enhancing octane. Etherification activity of several molecular sieve catalysts for FCC light gasoline was studied in a fixed-bed reactor. The influence of pore-enlarging agent (PEG) with different molecular weight, binder (γ-Al2O3), and peptizing agent (HNO3) in the shaping process on etherification activity of Hβ zeolite was studied. The impregnating ways of precursor of oxides and the order of extruding and impregnating were also investigated. The results show that the activity of extruded Hβ zeolite before impregnating precursor of oxides is higher than the reverse order. The best shaping condition obtained was PEG-4000 10%, γ-Al2O3 20%, and HNO3 10%. At the optimal reaction condition, the conversion of tert-olefins reached the peak. 62.93%, the yield of TAME, is also high and the technology can be applied to industry as well. 相似文献
976.
Shui-Jinn Wang Shiue-Lung Chen Kai-Ming Uang Wei-Chi Lee Tron-Min Chen Chao-Hsuing Chen Bor-wen Liou 《Photonics Technology Letters, IEEE》2006,18(10):1146-1148
In this study, the performance of vertical-structured high-power GaN-based light-emitting diodes (VM-LEDs) with a transparent and low-resistant indium-zinc oxide (IZO) film as a current spreading layer (CSL) was investigated. Nickel electroplating and patterned laser liftoff techniques were employed for the transfer of sapphire substrate to nickel substrate. The novel IZO CSL atop n-side-up VM-LEDs offering benefits of superior current spreading ability, larger extraction efficiency, and lower forward voltage drop was demonstrated. As compared to the regular LED without IZO CSL, the use of an IZO CSL with an optimum thickness of around 300 nm leads to an increase in light output power by 97.1 (67.8)% and a decrease in forward voltage drop by 4.9 (15.5)% under an injection current of 350 (800) mA. 相似文献
977.
Kuo‐Hsiung Wang Tzong‐Ming Wu Yeng‐Fong Shih Chien‐Ming Huang 《Polymer Engineering and Science》2008,48(9):1833-1839
The water bamboo husk is one of major agricultural wastes in Taiwan. In this study, the powder obtained from the water bamboo husk was added to poly(lactic acid) (PLA) to form novel reinforced biodegradable composites. Morphologies, mechanical properties, and heat resistance of these water bamboo powder reinforced composites were investigated. The results indicate that the char yields were increased as plant powder was incorporated to PLA. In addition, the mechanical properties were also enhanced due to the addition of powders. The increments of storage moduli of PLA were about 50–200%. Moreover, the increments of loss moduli of PLA were about 70–200%. On the other hand, the Tg of PLA was slightly decreased by the addition of powder, and this may improve the brittle characteristics of PLA. Furthermore, this type of reinforced PLA would be more environmental friendly than the artificial additive‐reinforced one. POLYM. ENG. SCI., 2008. © 2008 Society of Plastics Engineers 相似文献
978.
Dielectric anisotropy phenomenon of coal was detectable by many dielectric measurements. The paper presented that it was attributed to coal interior moisture distribution. A new model describing interior moisture distribution was developed basing on microstructure observation of coal. In the model, coal interior moisture distribution was analyzed and simulated numerically, the relationship between interior moisture distribution and coal dielectric property was constructed, the character of the permittivity varying with moisture content had also been studied and coal dielectric anisotropy was deduced. Corresponding experiment results were well satisfied with the model analysis, demonstrating that the interior moisture content could cause coal dielectric anisotropy. 相似文献
979.
980.
In this study, crisp and fuzzy multiple-goal optimization approaches are respectively introduced to design an optimal biocompatible solvent to a two-stage extractive fermentation with cell recycling for ethanol production. When designing a biocompatible solvent for the extractive fermentation process, many issues, such as extractive efficiency, conversion, amount of solvent utilized and so on, have to be considered. An interactive multiple-goal design procedure is introduced to determine a trade-off result in order to satisfy such contradicted goals. Both approaches could be iterated to solve the interactive multiple-goal design problem in order to yield a trade-off result. However, the crisp optimization design is a tedious task that requires the designer to provide various pairs of the upper bounds for the design problem to obtain the corresponding solution. The fuzzy optimization approach is able to be trade-off several goals simultaneously and to yield the overall satisfactory grade for the product/process design problem. 相似文献