全文获取类型
收费全文 | 14819篇 |
免费 | 1248篇 |
国内免费 | 9篇 |
专业分类
电工技术 | 99篇 |
综合类 | 9篇 |
化学工业 | 5702篇 |
金属工艺 | 184篇 |
机械仪表 | 359篇 |
建筑科学 | 521篇 |
矿业工程 | 24篇 |
能源动力 | 415篇 |
轻工业 | 3760篇 |
水利工程 | 127篇 |
石油天然气 | 83篇 |
无线电 | 576篇 |
一般工业技术 | 1990篇 |
冶金工业 | 756篇 |
原子能技术 | 50篇 |
自动化技术 | 1421篇 |
出版年
2024年 | 49篇 |
2023年 | 198篇 |
2022年 | 1008篇 |
2021年 | 1118篇 |
2020年 | 470篇 |
2019年 | 484篇 |
2018年 | 544篇 |
2017年 | 598篇 |
2016年 | 622篇 |
2015年 | 500篇 |
2014年 | 661篇 |
2013年 | 1056篇 |
2012年 | 998篇 |
2011年 | 1100篇 |
2010年 | 841篇 |
2009年 | 781篇 |
2008年 | 725篇 |
2007年 | 680篇 |
2006年 | 520篇 |
2005年 | 389篇 |
2004年 | 336篇 |
2003年 | 304篇 |
2002年 | 276篇 |
2001年 | 175篇 |
2000年 | 116篇 |
1999年 | 147篇 |
1998年 | 189篇 |
1997年 | 147篇 |
1996年 | 138篇 |
1995年 | 101篇 |
1994年 | 79篇 |
1993年 | 81篇 |
1992年 | 76篇 |
1991年 | 59篇 |
1990年 | 41篇 |
1989年 | 39篇 |
1988年 | 47篇 |
1987年 | 33篇 |
1986年 | 48篇 |
1985年 | 42篇 |
1984年 | 31篇 |
1983年 | 26篇 |
1982年 | 21篇 |
1981年 | 20篇 |
1980年 | 28篇 |
1979年 | 23篇 |
1978年 | 22篇 |
1977年 | 16篇 |
1976年 | 17篇 |
1975年 | 13篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
61.
Sinéad C. Mac Namara Maria M. Garlock David P. Billington 《Canadian Metallurgical Quarterly》2007,21(2):152-156
Steam generator replacement at nuclear power plants requires large construction openings in nuclear containment structures. This study examines the effects of such openings placed in a 61?cm (2?ft) thick dome of a shield building. The dome is cast in two layers, and the limiting cases of the two layers acting as one and the lower layer carrying the entire load are considered. Without openings, the stresses due to dead load in the structure are very low when compared to the material strength. With openings, the loads are easily redistributed around the opening, and the maximum stresses for the conservative case are between three and four and one-half times larger than in the original structure with no openings. The extent of the affected area around the holes is relatively small. Smooth corners in the openings are necessary to avoid high local stress concentrations. 相似文献
62.
63.
Bonto-Kane Maria Vicente A. Chin Alvin Mc Carthy Sheila Srikulwong Mayuree Timmins Paul J. 《Pervasive Computing, IEEE》2007,6(4)
Pervasive computing is as much about the user as it is about the technology. So, the Fifth International Conference on Pervasive Computing emphasized desirability rather than just feasibility. Featured themes included user benefits, human-computer interaction, group and social interactions, context awareness, finding and positioning people and objects, and personal privacy. 相似文献
64.
65.
Ronald R. Delyser Sheila S. Thompson Jerry Edelstein Corinne Lengsfeld Albert J. Rosa Paul J. Rullkoetter Robert Whitman Margaret Whitt 《工程教育杂志》2003,92(3):269-273
A team of faculty members at the University of Denver changed the learning environment in key courses in the Department of Engineering from predominately teacher centered to student centered. Through this funded project new grading methods were implemented, classrooms were renovated and wired with studio layouts to facilitate learning, the Engineering Circuits Laboratory was rewired and instrumented for automated data acquisition and reporting, and two new pedagogical approaches were developed. At the onset of the project, six goals were established related to student learning. The introduction of industry standard hardware and software provided students with unprecedented hands‐on experience and project related activities stimulated faculty innovations in other current and future courses. Assessment results indicate that the new grading system improved the clarity of expectations for students before assignments were given resulting in increased reported motivation for learning in many courses. Even though course GPAs did not always reflect higher achievement on graded work, faculty members firmly believe that deeper understanding was achieved because more complex material was assimilated. 相似文献
66.
Marcos de Carvalho Barcellos Alcino Palermo de Aguiar Mônica Regina Marques Palermo de Aguiar Luiz Claudio de Santa Maria 《Polymer Bulletin》2005,55(1-2):61-70
Summary This article deals with the handy synthesis of sulfonyl resins, which were produced by the treatment of a commercial sulfonic resin (Lewatit VPOC1812® based at divinylbenzene (DVB) and styrene (STY). The preliminary chemical modification was based on the reaction of the Lewatit VPOC1812® with thionyl chloride aiming to produce the sulfonyl chloride groups. The best conditions to obtain the sulfonyl chloride groups were: SOCl2/SO3H (molar ratio) =13 at 79 °C during 72 h. The resin chlorinated was afterward treated with urea, thiourea or guanidine. The functionalized resins with urea, thiourea or guanidine were produced with 56, 68 and 93% yield, respectively. The commercial and modified resins were characterized by apparent density, swelling degree, elemental analysis (CHNS), FTIR, optical microscopy (OM) and scanning electron microscopy (SEM). 相似文献
67.
Scale selection using three different representations for images 总被引:1,自引:0,他引:1
J. Martinez-Baena J. A. García J. Fdez-Valdivia Rosa Rodriguez-Sanchez 《Pattern recognition letters》1997,18(14):1453-1467
68.
69.
Trends in Hydrological Parameters of a Southern Brazilian Watershed and its Relation to Human Induced Changes 总被引:5,自引:1,他引:4
Moraes Jorge M. Pellegrino Giampaolo Q. Ballester Maria V. Martinelli Luiz A. Victoria Reynaldo L. Krusche Alex V. 《Water Resources Management》1998,12(4):295-311
The Piracicaba river basin is a subtropical watershed located in the southeastern region of Brazil. With an area of 12 400 km2, the basin is a typical example of new landscape resulting from development in tropical and sub-tropical regions: establishment of intensive industrial and agricultural processes were followed by significant population growth and water management. This scenario has led to significant increase in water demand and decrease in water quality. The main objective of this study is the detection of changes in the patterns of flow and precipitation in the basin, and its possible relation to man-induced changes. Statistical analyses were performed on records of precipitation, evapotranspiration and streamflow, from 1947 to 1991. Precipitation and evapotranspiration totals showed significant increasing trends for the entire basin. From eight streamflow gauge stations, half showed significant decreasing trend. The most probable cause of such trends is the export of water from the basin to the metropolitan region of São Paulo city. 相似文献
70.
Jos M. Moreno Maria A. Aramendía Alberto Marinas Jos M. Marinas Francisco J. Urbano 《Applied catalysis. B, Environmental》2005,59(3-4):275-283
The liquid-phase hydrodechlorination of 3-chloropyridine and chlorobenzene has been studied over alkali-modified zirconia-supported palladium catalysts. The modification of the ZrO2 with alkali metal carbonates improves the catalytic activity of the final palladium catalyst. Therefore, the larger the ionic radii (Li+ < Na+ < K+), the greater the catalytic activity (TOF) of the palladium catalyst. For 3-chloropyridine, hydrodechlorination proceeds without catalyst deactivation. This is explained as the result of the interaction of reaction products (pyridine and HCl) forming pyridinium chloride, thus avoiding the detrimental effect of HCl on the palladium particles. Catalytic hydrodechlorination of chlorobenzene over Pd catalysts exhibits an initial catalytic activity (TOF) much lower than that of 3-chloropyridine and the Pd catalysts deactivate as the reaction proceeds. Finally, chlorobenzene hydrodehalogenation has also been carried out in the presence of an equimolecular amount of pyridine resulting in a decrease in the initial reaction rate on the one hand, but also in an increase in final conversion on the other. 相似文献