全文获取类型
收费全文 | 199085篇 |
免费 | 2142篇 |
国内免费 | 636篇 |
专业分类
电工技术 | 4114篇 |
综合类 | 124篇 |
化学工业 | 27029篇 |
金属工艺 | 7541篇 |
机械仪表 | 5490篇 |
建筑科学 | 4059篇 |
矿业工程 | 747篇 |
能源动力 | 4717篇 |
轻工业 | 14440篇 |
水利工程 | 1698篇 |
石油天然气 | 2844篇 |
武器工业 | 7篇 |
无线电 | 27411篇 |
一般工业技术 | 37626篇 |
冶金工业 | 45632篇 |
原子能技术 | 3576篇 |
自动化技术 | 14808篇 |
出版年
2021年 | 1265篇 |
2019年 | 1300篇 |
2018年 | 2143篇 |
2017年 | 2125篇 |
2016年 | 2194篇 |
2015年 | 1495篇 |
2014年 | 2640篇 |
2013年 | 7984篇 |
2012年 | 4491篇 |
2011年 | 6170篇 |
2010年 | 4969篇 |
2009年 | 5829篇 |
2008年 | 6185篇 |
2007年 | 6235篇 |
2006年 | 5683篇 |
2005年 | 5345篇 |
2004年 | 5275篇 |
2003年 | 5120篇 |
2002年 | 4927篇 |
2001年 | 5340篇 |
2000年 | 4939篇 |
1999年 | 5468篇 |
1998年 | 15717篇 |
1997年 | 10367篇 |
1996年 | 7973篇 |
1995年 | 5816篇 |
1994年 | 5053篇 |
1993年 | 5061篇 |
1992年 | 3400篇 |
1991年 | 3284篇 |
1990年 | 3242篇 |
1989年 | 3056篇 |
1988年 | 2795篇 |
1987年 | 2241篇 |
1986年 | 2316篇 |
1985年 | 2627篇 |
1984年 | 2324篇 |
1983年 | 2075篇 |
1982年 | 1916篇 |
1981年 | 2059篇 |
1980年 | 1800篇 |
1979年 | 1670篇 |
1978年 | 1666篇 |
1977年 | 2031篇 |
1976年 | 2724篇 |
1975年 | 1426篇 |
1974年 | 1372篇 |
1973年 | 1317篇 |
1972年 | 1126篇 |
1971年 | 958篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
The early history of the IEEE Microwave Theory and Techniques Society (IEEE MTT-S) is summarized since its founding in 1952, and all administrative committee members and presidents are listed. Some of the more recent changes resulting from growth and multinational participation are described. Publications are discussed with editors listed for this Transactions, the IEEE Microwave and Wireless Components Letters, the IEEE Microwave Newsletter, and IEEE Microwave Magazine. The chronological evolution of the IEEE MTT-S's awards is presented, including a listing of all award winners. Distinguished lecturers and microwave symposia sites and chairpersons are also discussed. Early technology trends are described 相似文献
82.
Depletion and hillock formation were examined in-situ in a scanning electron microscope (SEM) during electromigration of bamboo
Al interconnect segments. Hillocks formed directly at the anode ends of the segments by epitaxial addition of Al at the bottom
Al/TiN interface. Depletion occurred nonuniformly from the cathode end and stopped once the distance between the leading void
and the hillock reached the critical length for electromigration at the given current density. A modified equation for the
drift velocity is proposed, which includes the effect of nonuniform depletion and predicts that interconnects with nonuniform
depletion are more reliable than those with uniform depletion. 相似文献
83.
Test Case Generation as an AI Planning Problem 总被引:6,自引:0,他引:6
Adele E. Howe Anneliese von Mayrhauser Richard T. Mraz 《Automated Software Engineering》1997,4(1):77-106
While Artificial Intelligence techniques have been applied to a variety of software engineering applications, the area of automated software testing remains largely unexplored. Yet, test cases for certain types of systems (e.g., those with command language interfaces and transaction based systems) are similar to plans. We have exploited this similarity by constructing an automated test case generator with an AI planning system at its core. We compared the functionality and output of two systems, one based on Software Engineering techniques and the other on planning, for a real application: the StorageTek robot tape library command language. From this, we showed that AI planning is a viable technique for test case generation and that the two approaches are complementary in their capabilities. 相似文献
84.
Development of a recurrent Sigma-Pi neural network rainfall forecasting system in Hong Kong 总被引:1,自引:1,他引:0
At the moment, weather forecasting is still an art — the experience and intuition of forecasters play a significant role in determining the quality of forecasting. This paper describes the development of a new approach to rainfall forecasting using neural networks. It deals with the extraction of information from radar images and an evaluation of past rain gauge records to provide shortterm rainfall forecasting. All of the meteorological data were provided by the Royal Observatory of Hong Kong (ROHK). Preprocessing procedures were essential for this neural network rainfall forecasting. The forecast of the rainfall was performed every half an hour so that a storm warning signal can be delivered to the public in advance. The network architecture is based on a recurrent Sigma-Pi network. The results are very promising, and this neural-based rainfall forecasting system is capable of providing a rain storm warning signal to the Hong Kong public one hour ahead. 相似文献
85.
PURPOSE: To report the disappearance of traumatic macular hole in three eyes of three patients. METHODS: Clinical data of the patients were reviewed. RESULTS: The three patients were relatively young, ranging in age from 12 to 18 years old. In one eye of each patient, a small traumatic macular hole was observed at the first visit. Visual acuities ranged from 20/100 to 20/40. The macular holes resolved spontaneously 3 to 4 months after the trauma, and final visual acuity improved to 20/20 in all patients. CONCLUSION: Small traumatic macular holes in young patients can resolve spontaneously, and this can be associated with good visual recovery. 相似文献
86.
H Asahara K Fujisawa T Kobata T Hasunuma T Maeda M Asanuma N Ogawa H Inoue T Sumida K Nishioka 《Canadian Metallurgical Quarterly》1997,40(5):912-918
Green fluorescent protein (GFP) is increasingly being used in plant biology from the cellular level to whole plant level. At the cellular level, GFP is being used as an in vivo reporter to assess frequency of transient and stable transformation. GFP has also proven to be an invaluable tool in monitoring trafficking and subcellular localization of protein. At the organ level and up, many exciting applications are rapidly emerging. The development of brighter GFP mutants with more robust folding properties has enabled better macroscopic visualization of GFP in whole leaves and plants. One interesting example has been the use of GFP to monitor virus movement in and among whole plants. GFP is also emerging as a powerful tool to monitor transgene movement and transgenic plants in the field. In a proof-of-concept study, tobacco was transformed with a modified version of the GFP gene controlled by a constitutive (35S) promoter. GFP expression in progeny plants ranged from 0% to 0.5%, and approximately 0.1% GFP was the minimal amount needed for unambiguous macroscopic detection. GFP is the first truly in vivo reporter system useful in whole plants, and we project its usefulness will increase even further as better forms of GFP genes become available. 相似文献
87.
To meet the criteria of role accountability, nursing competence and ongoing staff development, an improved peer-evaluation system was designed to continuously monitor these new roles. This peer-evaluation process converts evaluation input into data, giving staff a visual picture of how their performance compares within their peer group. This peer-evaluation process was designed as a tool to assist in staff growth and development, not as a punitive system. 相似文献
88.
89.
The aim of this paper is to give a general quantitative requirement which the loop gain must satisfy in order to stabilize a given unstable (possibly nonlinear and time-varying) plant, namely that the gain must exceed one. 相似文献
90.
J Westhuyzen AD Cochrane PJ Tesar T Mau DB Cross MP Frenneaux FA Khafagi SJ Fleming 《Canadian Metallurgical Quarterly》1997,113(5):942-948
Augmentation of antioxidant defenses may help protect tissues against ischemia-reperfusion injury associated with operations involving cardiopulmonary bypass. In this study we examined the effect of pretreating patients with alpha-tocopherol (vitamin E) and ascorbic acid (vitamin C) or placebo on injury to the myocardium. Seventy-six subjects undergoing elective coronary artery bypass grafting participated in a prospective, double-blind, placebo-controlled randomized trial, receiving either placebo or both 750 IU dl-alpha-tocopherol per day for 7 to 10 days and 1 gm ascorbic acid 12 hours before the operation. Plasma alpha-tocopherol concentrations, raised fourfold by supplementation, fell by 70% after the operation in the supplemented group and to negligible levels in the placebo group. There were no significant differences between the groups with respect to release of creatine kinase MB isoenzyme over 72 hours, nor in the reduction of the myocardial perfusion defect determined by thallium 201 uptake. Electrocardiography provided no evidence of a benefit from antioxidant supplementation. Thus the supplementation regimen prevented the depletion of the primary lipid soluble antioxidant in plasma, but provided no measurable reduction in myocardial injury after the operation. 相似文献