全文获取类型
收费全文 | 7133篇 |
免费 | 19篇 |
专业分类
电工技术 | 5篇 |
化学工业 | 111篇 |
金属工艺 | 17篇 |
机械仪表 | 6篇 |
建筑科学 | 28篇 |
矿业工程 | 1篇 |
能源动力 | 14篇 |
轻工业 | 61篇 |
水利工程 | 4篇 |
石油天然气 | 2篇 |
无线电 | 70篇 |
一般工业技术 | 95篇 |
冶金工业 | 6662篇 |
原子能技术 | 3篇 |
自动化技术 | 73篇 |
出版年
2021年 | 5篇 |
2020年 | 9篇 |
2019年 | 6篇 |
2018年 | 6篇 |
2017年 | 10篇 |
2016年 | 8篇 |
2015年 | 4篇 |
2014年 | 18篇 |
2013年 | 22篇 |
2012年 | 20篇 |
2011年 | 20篇 |
2010年 | 14篇 |
2009年 | 16篇 |
2008年 | 14篇 |
2007年 | 21篇 |
2006年 | 24篇 |
2005年 | 33篇 |
2004年 | 19篇 |
2003年 | 26篇 |
2002年 | 19篇 |
2001年 | 14篇 |
2000年 | 16篇 |
1999年 | 169篇 |
1998年 | 1972篇 |
1997年 | 1155篇 |
1996年 | 789篇 |
1995年 | 415篇 |
1994年 | 362篇 |
1993年 | 404篇 |
1992年 | 65篇 |
1991年 | 115篇 |
1990年 | 112篇 |
1989年 | 103篇 |
1988年 | 116篇 |
1987年 | 93篇 |
1986年 | 87篇 |
1985年 | 65篇 |
1983年 | 17篇 |
1982年 | 36篇 |
1981年 | 51篇 |
1980年 | 60篇 |
1978年 | 28篇 |
1977年 | 183篇 |
1976年 | 361篇 |
1975年 | 14篇 |
1969年 | 3篇 |
1968年 | 3篇 |
1966年 | 3篇 |
1955年 | 4篇 |
1954年 | 3篇 |
排序方式: 共有7152条查询结果,搜索用时 406 毫秒
91.
92.
93.
94.
95.
A model describing the maximum clock frequency (FMAX) distribution of a microprocessor is derived and compared with wafer sort data for a recent 0.25-μm microprocessor. The model agrees closely with measured data in mean, variance, and shape. Results demonstrate that within-die fluctuations primarily impact the FMAX mean and die-to-die fluctuations determine the majority of the FMAX variance. Employing rigorously derived device and circuit models, the impact of die-to-die and within-die parameter fluctuations on future FMAX distributions is forecast for the 180, 130, 100, 70, and 50-nm technology generations. Model predictions reveal that systematic within-die fluctuations impose the largest performance degradation resulting from parameter fluctuations. Assuming a 3σ channel length deviation of 20%, projections for the 50-nm technology generation indicate that essentially a generation of performance gain can be lost due to systematic within-die fluctuations. Key insights from this work elucidate the recommendations that manufacturing process controls be targeted specifically toward sources of systematic within-die fluctuations, and the development of new circuit design methodologies be aimed at suppressing the effect of within-die parameter fluctuations 相似文献
96.
97.
M. E. Stevenson S. L. Lowrie R. D. Bowman B. A. Bennett 《Journal of Failure Analysis and Prevention》2002,2(4):55-60
Cold cracking of structural steel weldments is a well-characterized, well-documented, and well-understood failure mechanism.
Extensive effort has been put forth to recognize the welding and materials selection parameters that are conducive to cold
cracking; however, these engineering efforts have not fully eliminated the occurrence of such failures. This article describes
cold cracking failure specifically related to the construction industry. This particular failure was successfully identified
prior to final erection of the structural member, and the weld was successfully reworked. These actions potentially prevented
a serious catastrophic event that could have occurred have occurred either later in the construction process or possibly during
the use of the building. Individual welding parameters, such as electrode/wire selection, joint design, and pre/postheating,
played a role in the failure, and a number of human factors relating to the actual fabrication practices also contributed
to the failure process. 相似文献
98.
This paper investigates the effect of the waterproofing sleeve on the calibration of kilovoltage photon beams (50-300 kV). The sleeve effect correction factor, ps has been calculated using the Monte Carlo method as the ratios of the air kerma in an air cavity of a cylindrical chamber without the waterproofing sleeve to that with a sleeve. Three sleeve materials have been studied, PMMA, nylon and polystyrene. The calculations were carried out using the EGS4 (Electron Gamma Shower version 4) code system with the application of a correlated-sampling variance-reduction technique. The results show that the sleeve correction factor for 1-mm thick nylon and polystyrene sleeves, ps varies from 0.992 to 1.000 and from 0.981 to 1.000, respectively, for the same beam quality range. The ps factor varies with sleeve thickness, beam quality and phantom depth. No significant dependence of the ps factor on field size and source-surface distance has been found. Measurements for PMMA, nylon and polystyrene sleeves of various thicknesses have also been carried out and show excellent agreement with Monte Carlo calculations. 相似文献
99.
The settling rates and adsorption isotherms produced by a variety of suites of cationic polyelectrolytes in 3% kaolin suspensions were measured. Settling rates increased with molar mass even for low-mass, high-charge polymers. The very high settling rates produced by cationic copolymers of acrylamide decreased as the charge density of the polymer used increased. Hydrolysis of unbuffered polymers occurred over time and produced large changes in the effectiveness of the polymers. This is attributed to conformational changes. © 1994 John Wiley & Sons, Inc. 相似文献
100.
P Dhordain O Albagli RJ Lin S Ansieau S Quief A Leutz JP Kerckaert RM Evans D Leprince 《Canadian Metallurgical Quarterly》1997,94(20):10762-10767