全文获取类型
收费全文 | 3131篇 |
免费 | 39篇 |
国内免费 | 23篇 |
专业分类
电工技术 | 17篇 |
综合类 | 3篇 |
化学工业 | 197篇 |
金属工艺 | 14篇 |
机械仪表 | 27篇 |
建筑科学 | 54篇 |
矿业工程 | 5篇 |
能源动力 | 27篇 |
轻工业 | 74篇 |
水利工程 | 9篇 |
石油天然气 | 7篇 |
无线电 | 131篇 |
一般工业技术 | 173篇 |
冶金工业 | 2269篇 |
原子能技术 | 18篇 |
自动化技术 | 168篇 |
出版年
2022年 | 8篇 |
2021年 | 13篇 |
2020年 | 11篇 |
2019年 | 15篇 |
2018年 | 18篇 |
2017年 | 18篇 |
2016年 | 21篇 |
2015年 | 20篇 |
2014年 | 17篇 |
2013年 | 62篇 |
2012年 | 29篇 |
2011年 | 53篇 |
2010年 | 32篇 |
2009年 | 45篇 |
2008年 | 28篇 |
2007年 | 31篇 |
2006年 | 33篇 |
2005年 | 35篇 |
2004年 | 26篇 |
2003年 | 32篇 |
2002年 | 19篇 |
2001年 | 25篇 |
2000年 | 22篇 |
1999年 | 86篇 |
1998年 | 737篇 |
1997年 | 421篇 |
1996年 | 242篇 |
1995年 | 167篇 |
1994年 | 133篇 |
1993年 | 142篇 |
1992年 | 40篇 |
1991年 | 57篇 |
1990年 | 47篇 |
1989年 | 48篇 |
1988年 | 31篇 |
1987年 | 39篇 |
1986年 | 38篇 |
1985年 | 33篇 |
1984年 | 15篇 |
1983年 | 12篇 |
1982年 | 15篇 |
1981年 | 11篇 |
1980年 | 26篇 |
1978年 | 12篇 |
1977年 | 44篇 |
1976年 | 89篇 |
1975年 | 11篇 |
1974年 | 7篇 |
1973年 | 10篇 |
1971年 | 7篇 |
排序方式: 共有3193条查询结果,搜索用时 218 毫秒
1.
Thin Film Thermoelectric Metal–Organic Framework with High Seebeck Coefficient and Low Thermal Conductivity 下载免费PDF全文
2.
3.
4.
Castro M. Foster R.S. Gunn K. Roberts E.B. 《Engineering Management, IEEE Transactions on》2003,50(3):297-306
The virtual agency concept is now used within the United States Government as an alliance approach to manage large research and development (R&D) processes across departments. This paper examines the history of the virtual agency concept and its important characteristics. The paper identifies the potential benefits and associated risks involved in managing R&D within a virtual agency. Three cases are examined where the virtual agency concept has been applied to R&D programs: the High Performance Computing and Communications initiative, the Next Generation Internet, and the Partnership for a New Generation of Vehicles. The case studies indicate that the R&D process is attempting to balance formal process controls with the agility to adapt rapidly to new research opportunities. Virtual agencies can be used to improve organizational efficiency, improve knowledge transfer, increase interoperability through standards, provide better alignment of agency missions with national policy, and introduce increased flexibility into the R&D process. At the same time, the virtual agency concept has major risks including inefficiencies due to organizational complexity, the danger of collective myopia, the problem of adopting standards too early, the difficulty of reaching objectives in a loose organizational structure, and the problem of properly balancing the tension between agency mission objectives and national policy agendas. 相似文献
5.
Lead content of rice collected from various areas in the world 总被引:1,自引:0,他引:1
ZW Zhang CS Moon T Watanabe S Shimbo M Ikeda 《Canadian Metallurgical Quarterly》1996,191(1-2):169-175
Rice samples consumed by local populations were collected between 1990 and 1995 in 17 areas in the world, mostly from Asia (10 areas), but also from 7 areas outside of Asia. In total, 1528 samples were obtained (about one half from Japan) and were analyzed for lead (Pb) by electrothermal atomic absorption spectrometry. When the Pb contents in rice samples were classified into 10 areas in Asia, the highest and the lowest geometric means (GMs) were for Indonesia (38 ng/g) and Australia (2 ng/g), respectively. Among 7 regions outside Asia, the GM was highest for Spain (58 ng/g) and the lowest for the USA. (3 ng/g). Moreover, inter-regional differences were significant, when more than 100 samples from one area were divided into 3-9 regions and GMs for regions were compared. There was a marked difference in Pb contents in rice by areas and regions in the world. Nevertheless, comparison by area of the present results with those reported in literature show that there has been no substantial reduction in Pb in rice in the past decade either in Japan or elsewhere in the world. 相似文献
6.
7.
Pre-transplant nephrectomy was done in a 25-year-old man for calculous pyelonephritis using a retroperitoneal laparoscopic approach with a newly devised ligature applicator-dissector- kidney retractor. 相似文献
8.
E Bazopoulou-Kyrkanidou P Neou CS Bartsocas S Kyrkanides I Fanourakis 《Canadian Metallurgical Quarterly》1995,6(3):227-232
PURPOSE: To select ideal radiologic projections for mapping and ablation of tachycardias of right ventricular outflow tract (RVOT). METHODS: Ten hearts from human corpses were studied utilizing radiopaque material to identify the pulmonary valve and three distinct sites on this valve: septal anterior (A), septal posterior (P) and free-wall (L). Next, the hearts were filmed in the frontal plane and in oblique projections with 15 degrees increments to the right and to the left. The projections in which the sites were lateralized on the valve, eased radiologic interpretation and were considered ideal for mapping and ablation. Depending on the proximity of the sites to the lateral extremes of the pulmonary valve, the projections were considered ideal ( ), intermediary (++) and inadequate (+). RESULTS: Projections [table: see text] CONCLUSION: The A site of RVOT was best indicated in the 60 and 45 degrees left anterior oblique projections; the 0 degree postero anterior projection was best for mapping the P site; the L region was best explored in the 60 degrees right anterior oblique projection. 相似文献
9.
10.
Determination of the relative amounts of free and complexed manganese ions in aqueous solution by nuclear magnetic resonance. 总被引:1,自引:0,他引:1
The ratio of the transverse relaxation rate to the longitudinal relaxation rate of water protons (T1/T2) at 90 MHz can be used to determine the relative amounts of free Mn2+ ions (the hexaquo ion) and chelated manganese ions when both species are present in the same aqueous solution. This technique is demonstrated for simple aqueous solutions containing known concentrations of both the free Mn2+ ion and a manganese(III) porphyrin. The accuracy of the method is found to be +/- 7.3% for the solutions considered in this report. The determinations of the relative amounts of the free Mn2+ ion and the manganese(III) porphyrin by this T1/T2 method are shown to agree well with those determined by nuclear magnetic resonance dispersion profiles. The theoretical basis of this ratio method as well as the scope and limitations in its application to aqueous solutions containing both free Mn2+ ions and chelated manganese species other than manganese(III) porphyrins are also discussed. This work demonstrates a unique use of NMR as a means for the quantitative analysis of manganese in which the effects of the metal ion on the solvent, and not the metal itself, are observed. 相似文献