全文获取类型
收费全文 | 196143篇 |
免费 | 22364篇 |
国内免费 | 16133篇 |
专业分类
电工技术 | 15459篇 |
技术理论 | 28篇 |
综合类 | 29429篇 |
化学工业 | 15749篇 |
金属工艺 | 6265篇 |
机械仪表 | 13296篇 |
建筑科学 | 24417篇 |
矿业工程 | 7808篇 |
能源动力 | 7502篇 |
轻工业 | 7590篇 |
水利工程 | 12457篇 |
石油天然气 | 9608篇 |
武器工业 | 2362篇 |
无线电 | 15117篇 |
一般工业技术 | 15107篇 |
冶金工业 | 7398篇 |
原子能技术 | 1672篇 |
自动化技术 | 43376篇 |
出版年
2024年 | 915篇 |
2023年 | 2500篇 |
2022年 | 4952篇 |
2021年 | 5617篇 |
2020年 | 5982篇 |
2019年 | 5116篇 |
2018年 | 4937篇 |
2017年 | 6331篇 |
2016年 | 7345篇 |
2015年 | 8071篇 |
2014年 | 12910篇 |
2013年 | 11937篇 |
2012年 | 14016篇 |
2011年 | 15224篇 |
2010年 | 12154篇 |
2009年 | 12882篇 |
2008年 | 12499篇 |
2007年 | 14847篇 |
2006年 | 13171篇 |
2005年 | 11421篇 |
2004年 | 9261篇 |
2003年 | 7988篇 |
2002年 | 6310篇 |
2001年 | 5249篇 |
2000年 | 4542篇 |
1999年 | 3408篇 |
1998年 | 2636篇 |
1997年 | 2137篇 |
1996年 | 2006篇 |
1995年 | 1745篇 |
1994年 | 1440篇 |
1993年 | 1043篇 |
1992年 | 882篇 |
1991年 | 645篇 |
1990年 | 542篇 |
1989年 | 492篇 |
1988年 | 318篇 |
1987年 | 205篇 |
1986年 | 167篇 |
1985年 | 136篇 |
1984年 | 143篇 |
1983年 | 72篇 |
1982年 | 78篇 |
1981年 | 73篇 |
1980年 | 69篇 |
1979年 | 66篇 |
1978年 | 26篇 |
1975年 | 15篇 |
1973年 | 13篇 |
1959年 | 18篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
51.
Results from applying the model on a sample of contractors, the majority of whom were international and operating in Egypt, reinforces the credibility of the developed methodology, claim the authors. 相似文献
52.
根据转炉炼钢的物理化学反应机理,从质量平衡和能量平衡的计算出发,通过小参数变动,导出了增量式静态模型中矿石方程和供氧方程的系数。所得结论与新日铁资料基本相符。同时,还进行了炉料和产物的计算,分析了改变废钢比对生产的影响。 相似文献
53.
In this study a thermodynamic model for the phase behavior of aqueous salt+polymer solutions is developed. The model is based on the solution theory of Hill, which included scaling laws for the polymer molecular mass dependence and Pitzer–Debye–Hückel theory. This model was tested for systems composed of two different molecular mass of polyethylene glycols (PEG) and five different inorganic salts. All the model parameters were determined from independent measurements. The agreement between the experimental and predicted phase diagrams by this model is good. 相似文献
54.
S
awomir Lasota 《Theoretical computer science》2002,280(1-2):123-135
We relate two abstract notions of bisimulation, induced by open maps and by coalgebra morphisms, respectively. We show that open maps correspond to coalgebra morphisms for a suitable chosen endofunctor in a category of many sorted sets. This demonstrates that the notion of open-maps bisimilarity is of essentially coalgebraic nature. A central role in our development is played by a category of presheaves, which we show as corresponding to the subcategory of consistent coalgebras with lax cohomomorphisms. 相似文献
55.
56.
Objective: Guided by the extended parallel process model (EPPM), the objective was to assess control processes dominant in influenza behavior decisions. Design: Cross-sectional survey. Results: Response rate was 31% (n=968). Regarding influenza risk, 59% were in danger control. Those in fear control were more likely to report influenza infection (p=.000). In the nonvaccinated, those in fear control were more likely to indicate not knowing where to get the vaccine (p=.016) and that it was unavailable (p=.027), and those in danger control believed they did not need it (p=.023). Zero critical values were more likely to indicate that no health provider recommended the shot (p=.002). Conclusions: Most perceived efficacy to be stronger than threat related to influenza; according to the EPPM, they are aware of their risk but recognize their ability to avert it. For those in danger control, messages should focus on increasing perceptions of severity and susceptibility to positively affect behavior change. For those in fear control, messages should focus on efficacy only. With a critical value of zero, no threat is induced, and a high-threat/high-efficacy approach should be taken. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
57.
U. Reimer
H. -J. Schek
《Data & Knowledge Engineering》1989,4(4):321-352The first part of this paper introduces the basic constructs of a frame representation model and gives a formal definition for them. Subsequently the nested relational model (NF2) is described as an extension of the classical relational model to support relation-valued attributes. In the second part of this paper both models are compared with each other and a mapping of frame representation structures to NF2 structures is specified. The structural similarities between frames and NF2 relations are made clear and it is shown that their main difference is due to the type polymorphism introduced by the concept hierarchy of the frame model. This causes type collisions to occur in the strictly typed NF2 model when frames are directly mapped to NF2 structures. Two solutions to this problem are suggested and compared. The paper concludes with a reformulation of query operations of the frame model in terms of NF2 algebra operations. 相似文献
58.
U. Amato G. Amodeo V. Brandi V. Cuomo D. Ruggi C. Serio V. Silvestrini G. C. Tosato 《国际能源研究杂志》1985,9(1):33-51
In Italy solar thermal energy and energy from biogas are two possible means of reducing dependence on energy imports. Using a multiperiod LP model (MARKAL) the authors assessed the likely potential of both technologies under various circumstances. The study covered the period 1980–2005, in five segments of five years. It focused only on the subsystem of the energy end-uses which can be substituted for by solar thermal and biogas technologies. The overall non-renewable sources which can be saved in 20 years by these technologies total 450 PJ (1 PJ = 101 5 J) if the fuel prices rise at 0 per cent average annual, 1450 PJ if the fuel prices rise at 4.2 per cent average annual, 1860 PJ if the fuel prices rise at 7.2 per cent average annual and 3780 PJ if the fuel prices rise at 15 per cent average annual. However the most competitive technologies appear to be solar water heaters used mainly in the private and commercial sectors and biogas systems used mainly in the agricultural sector. The study was carried out by APRE under ENEA (formerly CNEN) contract and was intended to serve as an analytical basis for establishing an overall development and demonstration strategy for end-use renewable technologies in Italy. 相似文献
59.
在氧化铝生产过程中,熟料折合比是烧结法一项重要的综合性指标,本文通过对熟料折合比的定义、计算公式的剖析,分析了生产过程中影响熟料折合比的主要因素,对有效降低熟料折合比的措施进行了探讨。 相似文献
60.
The objective, strategy, and implementation details of a new undergraduate course, Internet-based Instrumentation and Control, are presented. The course has a companion laboratory that is supported by the National Science Foundation and industry. The combination is offered to senior-level undergraduate engineering students interested in sensing, instrumentation, control, and web programming that want to learn more about the integration of these technologies for solving real-world engineering problems. The course will also be offered to gifted high school seniors with similar interests and can serve as a vehicle to attract them to engineering disciplines. Preliminary assessment of the first offering of the course is encouraging and has shown that the course has achieved success in helping students understand concepts and master basic technologies for developing Internet-based automatic systems. 相似文献