全文获取类型
收费全文 | 91739篇 |
免费 | 11254篇 |
国内免费 | 6103篇 |
专业分类
电工技术 | 15355篇 |
技术理论 | 5篇 |
综合类 | 8518篇 |
化学工业 | 5789篇 |
金属工艺 | 3243篇 |
机械仪表 | 6298篇 |
建筑科学 | 12865篇 |
矿业工程 | 2861篇 |
能源动力 | 5050篇 |
轻工业 | 3410篇 |
水利工程 | 4005篇 |
石油天然气 | 4942篇 |
武器工业 | 1679篇 |
无线电 | 8092篇 |
一般工业技术 | 6929篇 |
冶金工业 | 2599篇 |
原子能技术 | 781篇 |
自动化技术 | 16675篇 |
出版年
2024年 | 360篇 |
2023年 | 1253篇 |
2022年 | 2588篇 |
2021年 | 3119篇 |
2020年 | 3364篇 |
2019年 | 2805篇 |
2018年 | 2551篇 |
2017年 | 3430篇 |
2016年 | 3782篇 |
2015年 | 4095篇 |
2014年 | 6234篇 |
2013年 | 5604篇 |
2012年 | 7444篇 |
2011年 | 7893篇 |
2010年 | 5910篇 |
2009年 | 5986篇 |
2008年 | 5493篇 |
2007年 | 6316篇 |
2006年 | 5528篇 |
2005年 | 4627篇 |
2004年 | 3673篇 |
2003年 | 2951篇 |
2002年 | 2504篇 |
2001年 | 2109篇 |
2000年 | 1763篇 |
1999年 | 1349篇 |
1998年 | 1087篇 |
1997年 | 886篇 |
1996年 | 845篇 |
1995年 | 696篇 |
1994年 | 542篇 |
1993年 | 396篇 |
1992年 | 354篇 |
1991年 | 230篇 |
1990年 | 230篇 |
1989年 | 175篇 |
1988年 | 111篇 |
1987年 | 72篇 |
1986年 | 66篇 |
1985年 | 52篇 |
1984年 | 49篇 |
1983年 | 26篇 |
1981年 | 28篇 |
1980年 | 78篇 |
1979年 | 55篇 |
1965年 | 26篇 |
1964年 | 34篇 |
1959年 | 33篇 |
1956年 | 29篇 |
1955年 | 32篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
141.
3G系统的安全策略分析 总被引:1,自引:0,他引:1
介绍了当前3G系统面临的各种威胁和针对3G的攻击方法,如对非授权数据的非法获取、对数据完整性的攻击和对业务的非法访问攻击等.分析了3G系统的安全体系结构和安全特性的优缺点. 相似文献
142.
We have previously investigated effects of radiation levels on power quality of a number PV-grid interactive systems in Thailand, in terms of harmonics and voltage variation at the point of common coupling (PCC). In this paper, we focus on the nature of components of complex power (actual, reactive and apparent power) of inverter output of a PV-grid interactive system due to low radiation, below 400 W/m2. The system being investigated has an array of 4.2 kWp and representative of roof top units. It is observed that a PV array supplies increasing real power, in magnitude and as percentage of complex power, at high values of radiation. At low radiation level when the array does not provide enough output power, reactive power is drawn from distribution transformer and fed into an inverter and loads. Based on results from the test site and long term radiation data of Bangkok, we then estimate energy available from low radiation from a hypothetical PV-grid interactive unit in Bangkok of a similar size. It can be seen that for a tropical climate like Thailand a significant amount of energy, 20–30% of radiation energy, is in the form of reactive power. Methods must be devised to capture this low radiation energy and converted into real power form. 相似文献
143.
144.
采用正交试验对汽轮机叶片用X20Cr13钢进行了热处理工艺研究,以获得该钢的最佳热处理工艺,并在回火后以不同的速度冷却,以揭示冷却速度对钢的回火脆性的影响。结果,X20Cr13钢的最佳热处理工艺为900℃油淬或风冷,670℃回火,风冷。 相似文献
145.
针对影响强磁防蜡器两个性能指标的关键要素进行分析,设计并制造了专用的模具和采用水浸式焊接新工艺,提高了产品性能,产品质量的稳定性有了可靠的保证,同时加工成本也有较大幅度的下降。 相似文献
146.
Many approaches have been proposed to enhance software productivity and reliability. These approaches typically fall into three categories: the engineering approach, the formal approach and the knowledge-based approach. But the optimal gain in software productivity cannot be obtained if one relies on only one of these approaches. This paper describes the work in knowledge-based software engineering conducted by the authors for the past 10 years. The final goal of the research is to develop a paradigm for software engineering which integrates the three approaches mentioned above. A knowledge-based tool which can support the whole process of software development is provided in this paper. 相似文献
147.
Gomatofu (sesame tofu) is one of the traditional Japanese healthy foods and is representative of all shojin (vegetarian) dishes. Gomatofu, one of the mixed gels consisting of kudzu (arrowroot) starch and sesame, possesses an extremely unusual textural characteristic which is soft, smooth, and springy. The textural properties are greatly influenced by preparation, ingredients and roasting conditions of sesame seeds. Hence there are many kinds of sesame materials which can be used to prepare gomatofu such as white, black, huskless or not and roasted or unroasted sesame materials, in this study, the effects of these materials on the physical properties of gomatofu were studied. The sample of Ra-W prepared with unroasted huskless sesame seed had the least hardness, but mouthfeel of this sample were the highest. The samples of Ro-B and Ro-W prepared with roasted husk (black and white) sesame seed were evaluated to have the best palatability because of their superior springiness. It was clarified that different kinds of sesame materials affected the forming of structure and physical properties of gomatofu, because the chemical components were different from varieties of sesame materials. 相似文献
148.
149.
150.
Triple tangent flank milling of ruled surfaces 总被引:3,自引:0,他引:3
Cornelia Menzel 《Computer aided design》2004,36(3):289-296
This paper presents a positioning strategy for flank milling ruled surfaces. It is a modification of a positioning method developed by Bedi et al. [Comput Aided Des 35 (2003) 293]. A cylindrical cutting tool is initially positioned tangential to the two boundary curves on a ruled surface. Optimization is used to move these tangential points to different curves on the ruled surface to reduce the error. A second optimization step is used to additionally make the tool tangent to a rule line, further reducing the error and resulting in a tool position, where the tool is positioned tangential to two guiding rails and one rule line. The resulting surface has 88% less under cutting than the method of Bedi et al. 相似文献