全文获取类型
收费全文 | 3884篇 |
免费 | 166篇 |
国内免费 | 16篇 |
专业分类
电工技术 | 42篇 |
综合类 | 12篇 |
化学工业 | 861篇 |
金属工艺 | 159篇 |
机械仪表 | 78篇 |
建筑科学 | 82篇 |
矿业工程 | 8篇 |
能源动力 | 282篇 |
轻工业 | 281篇 |
水利工程 | 50篇 |
石油天然气 | 32篇 |
无线电 | 474篇 |
一般工业技术 | 908篇 |
冶金工业 | 381篇 |
原子能技术 | 50篇 |
自动化技术 | 366篇 |
出版年
2023年 | 60篇 |
2022年 | 96篇 |
2021年 | 158篇 |
2020年 | 109篇 |
2019年 | 134篇 |
2018年 | 178篇 |
2017年 | 151篇 |
2016年 | 156篇 |
2015年 | 91篇 |
2014年 | 151篇 |
2013年 | 352篇 |
2012年 | 186篇 |
2011年 | 245篇 |
2010年 | 168篇 |
2009年 | 194篇 |
2008年 | 188篇 |
2007年 | 127篇 |
2006年 | 93篇 |
2005年 | 77篇 |
2004年 | 62篇 |
2003年 | 70篇 |
2002年 | 64篇 |
2001年 | 49篇 |
2000年 | 49篇 |
1999年 | 47篇 |
1998年 | 62篇 |
1997年 | 53篇 |
1996年 | 52篇 |
1995年 | 45篇 |
1994年 | 48篇 |
1993年 | 40篇 |
1992年 | 40篇 |
1991年 | 28篇 |
1990年 | 25篇 |
1989年 | 27篇 |
1988年 | 42篇 |
1987年 | 32篇 |
1986年 | 27篇 |
1985年 | 33篇 |
1984年 | 29篇 |
1983年 | 31篇 |
1982年 | 27篇 |
1981年 | 35篇 |
1980年 | 27篇 |
1979年 | 15篇 |
1978年 | 17篇 |
1977年 | 10篇 |
1976年 | 19篇 |
1975年 | 17篇 |
1974年 | 8篇 |
排序方式: 共有4066条查询结果,搜索用时 31 毫秒
1.
Wireless Personal Communications - Internet of Things (IoT) is one of the emerging technologies, which is widely used across the globe. As the idea of a smart city was founded, IoT has been... 相似文献
2.
Wireless Personal Communications - Internet of Things (IoT) offers complex networks of connected devices, which are used to serve in the real-time environment. Interestingly, Wireless Sensor... 相似文献
3.
Dhirendra Kumar Mishra Gopal Pugazhenthi Tamal Banerjee 《International Journal of Hydrogen Energy》2021,46(29):15773-15779
The current work explores the usage of novel synthesized Deep Eutectic Solvent (DES) as a catalyst cum solvent media for the thermal dehydrogenation of chemical hydrides, namely Ammonia Borane (AB) and Ethylene diamine bisborane (EDAB). In the first instance, the quantum chemistry based COSMO-SAC (COnductor like Screening MOdel Segment Activity Coefficient) model was used for the selection of the pertinent solvent. 1-Butyl-3-methylimidazolium methanesulfonate: Imidazole ([BMIM][MeSO3]:[Im]) turned out to be an ideal eutectic mixture with the highest predicted solubility with amine boranes. The DES was synthesized by combining the Hydrogen Bond Acceptor (HBA), namely 1-Butyl-3-methylimidazolium methanesulfonate and Imidazole as Hydrogen Bond Donor (HBD) at a molar ratio of 1:2 and T = 70 °C. The formation of DES was confirmed by recording the NMR spectra. Further, the thermal dehydrogenation study was performed at a vacuum of 4 × 10?2 mbar (gauge pressure) of AB/DES and EDAB/DES systems at 105 °C, where a hydrogen equivalent of 1.40 and 2.55 was produced, respectively. The residual samples were further analyzed through 1H NMR analysis for the reaction mechanism and to confirm the role of Ionic Liquid-based DES as catalyst cum solvent media. 相似文献
4.
ABSTRACTA mathematical model has been developed by coupling genetic algorithm (GA) with heat and material balance equations to estimate rate parameters and solid-phase evolution related to the reduction of iron ore-coal composite pellets in a multi-layer bed Rotary hearth Furnace (RHF). The present process involves treating iron ore-coal composite pellets in a crucible over the hearth in RHF. The various solid phases evolved at the end of the process are estimated experimentally, and are used in conjunction with the model to estimate rate parameters. The predicted apparent activation energy for the wustite reduction step is found to be lower than those of the reduction of higher oxides. The thermal efficiency is found to decrease significantly with an increase in the carbon content of the pellet. Thermal efficiency was also found to increase mildly up to three layers. Multilayer bed remains as a potential design parameter to increase thermal efficiency. 相似文献
5.
Wireless Personal Communications - In this paper the conventional circular patch has been reshaped by two circular arcs with the FR4 Epoxy material for substrate. This is supported by the... 相似文献
6.
7.
8.
Building useful systems with an ability to understand "real" natural language input has long been an elusive goal for Artificial Intelligence. Well-known problems such as ambiguity, indirectness, and incompleteness of natural language inputs have thwarted efforts to build natural language interfaces to intelligent systems. In this article, we report on our work on a model of understanding natural language design specifications of physical devices such as simple electrical circuits. Our system, called KA, solves the classical problems of ambiguity, incompleteness and indirectness by exploiting the knowledge and problem-solving processes in the situation of designing simple physical devices. In addition, KA acquires its knowledge structures (apart from a basic ontology of devices) from the results of its problem-solving processes. Thus, KA can be bootstrapped to understand design specifications and user feedback about new devices using the knowledge structures it acquired from similar devices designed previously.In this paper, we report on three investigations in the KA project. Our first investigation demonstrates that KA can resolve ambiguities in design specifications as well as infer unarticulated requirements using the ontology, the knowledge structures, and the problem-solving processes provided by its design situation. The second investigation shows that KA's problem-solving capabilities help ascertain the relevance of indirect design specifications, and identify unspecified relations between detailed requirements. The third investigation demonstrates the extensibility of KA's theory of natural language understanding by showing that KA can interpret user feedback as well as design requirements. Our results demonstrate that situating language understanding in problem solving, such as device design in KA, provides effective solutions to unresolved problems in natural language processing. 相似文献
9.
10.
Buttari D. Chini A. Meneghesso G. Zanoni E. Moran B. Heikman S. Zhang N.Q. Shen L. Coffie R. DenBaars S.P. Mishra U.K. 《Electron Device Letters, IEEE》2002,23(2):76-78
Pre-metal-deposition reactive ion etching (RIE) was performed on an Al0.3Ga0.7N/AlN/GaN heterostructure in order to improve the metal-to-semiconductor contact resistance. An optimum AlGaN thickness for minimizing contact resistance was determined. An initial decrease in contact resistance with etching time was explained in terms of removal of an oxide surface layer and/or by an increase in tunnelling current with the decrease of the AlGaN thickness. The presence of a dissimilar surface layer was confirmed by an initial nonuniform etch depth rate. An increase in contact resistance for deeper etches was experienced. The increase was related to depletion of the two-dimensional (2-D) electron gas (2-DEG) under the ohmics. Etch depths were measured by atomic force microscopy (AFM). The contact resistance decreased from about 0.45 Ωmm for unetched ohmics to a minimum of 0.27 Ωmm for 70 Å etched ohmics. The initial thickness of the AlGaN layer was 250 Å. The decrease in contact resistance, without excessive complications on device processing, supports RIE etching as a viable solution to improve ohmic contact resistance in AlGaN/GaN HEMTs 相似文献