全文获取类型
收费全文 | 40202篇 |
免费 | 5632篇 |
国内免费 | 3609篇 |
专业分类
电工技术 | 9491篇 |
技术理论 | 2篇 |
综合类 | 3810篇 |
化学工业 | 1905篇 |
金属工艺 | 545篇 |
机械仪表 | 2823篇 |
建筑科学 | 1239篇 |
矿业工程 | 582篇 |
能源动力 | 3576篇 |
轻工业 | 504篇 |
水利工程 | 1452篇 |
石油天然气 | 1003篇 |
武器工业 | 376篇 |
无线电 | 3980篇 |
一般工业技术 | 3259篇 |
冶金工业 | 655篇 |
原子能技术 | 141篇 |
自动化技术 | 14100篇 |
出版年
2024年 | 240篇 |
2023年 | 738篇 |
2022年 | 1273篇 |
2021年 | 1509篇 |
2020年 | 1699篇 |
2019年 | 1460篇 |
2018年 | 1308篇 |
2017年 | 1751篇 |
2016年 | 1801篇 |
2015年 | 1938篇 |
2014年 | 2816篇 |
2013年 | 3168篇 |
2012年 | 3148篇 |
2011年 | 3272篇 |
2010年 | 2333篇 |
2009年 | 2588篇 |
2008年 | 2478篇 |
2007年 | 2657篇 |
2006年 | 2211篇 |
2005年 | 1866篇 |
2004年 | 1545篇 |
2003年 | 1229篇 |
2002年 | 1013篇 |
2001年 | 881篇 |
2000年 | 780篇 |
1999年 | 615篇 |
1998年 | 458篇 |
1997年 | 435篇 |
1996年 | 368篇 |
1995年 | 317篇 |
1994年 | 270篇 |
1993年 | 200篇 |
1992年 | 200篇 |
1991年 | 171篇 |
1990年 | 137篇 |
1989年 | 108篇 |
1988年 | 75篇 |
1987年 | 39篇 |
1986年 | 33篇 |
1985年 | 39篇 |
1984年 | 53篇 |
1983年 | 30篇 |
1982年 | 30篇 |
1981年 | 27篇 |
1980年 | 32篇 |
1979年 | 31篇 |
1978年 | 19篇 |
1977年 | 21篇 |
1976年 | 7篇 |
1975年 | 6篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
72.
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
73.
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
74.
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
75.
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
76.
J.S. Sánchez 《Pattern recognition》2004,37(7):1561-1564
Instance-based learning methods like the nearest neighbour classifier generally suffer from the indiscriminate storage of all training instances, resulting in large memory requirements and slow execution speed. In this paper, new training set size reduction methods based on prototype generation and space partitioning are proposed. Experimental results show that the new algorithms achieve a very high reduction rate with still an important classification accuracy. 相似文献
77.
78.
动态多目标决策问题的灰色分析方法 总被引:2,自引:0,他引:2
将用于固定时间截面下静态多目标决策的灰色关联理论推广到动态情形,引入局部理想最优效果和整体理想最优效果的概念,提出一种新型的动态多目标决策问题的灰色关联模型,并通过算例说明该方法的合理可行性。 相似文献
79.
探讨了中国3G牌照何时发放、发放数量、牌照与标准是否捆绑、3G产业链如何搭建、频率如何分配、市场容量和终端等问题,并对此提出了建设性的意见。 相似文献
80.
Berrin-Wasserman Stacy; Winnick Wilma A.; Borod Joan C. 《Canadian Metallurgical Quarterly》2003,17(3):429
Does sentence generation and/or stimulus emotionality enhance verbal memory in patients with neurological impairment? This question was addressed by testing 40 patients with unilateral stroke (20 with left-brain and 20 with right-brain damage) and 20 healthy control participants for recall and recognition of 48 target words. During encoding, emotional and nonemotional words were either presented in sentences (read condition) or used to form sentences (generate condition). Both word emotionality and generative processing improved memory performance in all groups. The authors suggest that a similar influence (i.e., cognitive activation) underlies both of these memory-enhancing effects, although the putative origins of the 2 effects are quite different. Neuropsychological underpinnings and clinical implications of these phenomena are discussed. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献