全文获取类型
收费全文 | 433893篇 |
免费 | 28639篇 |
国内免费 | 16053篇 |
专业分类
电工技术 | 21606篇 |
技术理论 | 45篇 |
综合类 | 27123篇 |
化学工业 | 70018篇 |
金属工艺 | 25077篇 |
机械仪表 | 25181篇 |
建筑科学 | 29662篇 |
矿业工程 | 12150篇 |
能源动力 | 10701篇 |
轻工业 | 27293篇 |
水利工程 | 7942篇 |
石油天然气 | 23696篇 |
武器工业 | 2795篇 |
无线电 | 47257篇 |
一般工业技术 | 54183篇 |
冶金工业 | 20938篇 |
原子能技术 | 3850篇 |
自动化技术 | 69068篇 |
出版年
2024年 | 1455篇 |
2023年 | 5565篇 |
2022年 | 9854篇 |
2021年 | 13857篇 |
2020年 | 10430篇 |
2019年 | 8547篇 |
2018年 | 22758篇 |
2017年 | 23092篇 |
2016年 | 19153篇 |
2015年 | 14394篇 |
2014年 | 17654篇 |
2013年 | 21069篇 |
2012年 | 25578篇 |
2011年 | 33887篇 |
2010年 | 29856篇 |
2009年 | 26108篇 |
2008年 | 26928篇 |
2007年 | 27043篇 |
2006年 | 20156篇 |
2005年 | 18761篇 |
2004年 | 13012篇 |
2003年 | 11795篇 |
2002年 | 10406篇 |
2001年 | 8901篇 |
2000年 | 8918篇 |
1999年 | 9442篇 |
1998年 | 7231篇 |
1997年 | 6160篇 |
1996年 | 5855篇 |
1995年 | 4795篇 |
1994年 | 3899篇 |
1993年 | 2632篇 |
1992年 | 2086篇 |
1991年 | 1592篇 |
1990年 | 1233篇 |
1989年 | 996篇 |
1988年 | 841篇 |
1987年 | 526篇 |
1986年 | 410篇 |
1985年 | 258篇 |
1984年 | 206篇 |
1983年 | 164篇 |
1982年 | 128篇 |
1981年 | 76篇 |
1980年 | 96篇 |
1968年 | 46篇 |
1966年 | 45篇 |
1965年 | 45篇 |
1955年 | 63篇 |
1954年 | 68篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
61.
62.
戴力农 《艺术与设计.数码设计》2007,(5)
在上海地铁研究中,我们发现了许多使用者的不满。这些不满来自于设计师对使用者的缺乏了解和缺乏关注。通过对上海地铁真实的使用者、真实的地点和真实的时间的调研,我们分析出25项上海地铁使用者的需求。并提出希望设计师能够从这些使用者的需求出发,去作为使用者带来良好体验的设计。 相似文献
63.
64.
65.
Nabesna Glacier is one of the longest land-terminus mountain glaciers in North America. However, its flow has never been studied. We derived detailed motion patterns of Nabesna Glacier in winter and spring 1994–1996 from the synthetic aperture radar (SAR) images acquired by the European Remote Sensing satellites (ERS-1 and ERS-2) using interferometric SAR (InSAR) techniques. Special effort was made to assess the accuracy of the motion estimates, and remove data points with high uncertainty from the motion profiles, enabling us to obtain reliable glacier flow patterns along the highly curved main course of Nabesna Glacier. The results, covering 80 km of the 87 km main course of the glacier, were used to delineate four distinctive sections in terms of spatial and temporal variability of the glacier speed: (1) the upper section where glacier flow was apparently random both temporally and spatially presumably due to development of crevasses; (2) the upper-middle section with relatively steady flow around 0.27 to 0.4 m/day; (3) the middle section with a stable pattern of acceleration from 0.27–0.3 m/day to the maximum about 0.67–0.73 m/day, followed by a general deceleration to 0.17–0.33 m/day before reaching (4) the lower section where the glacier motion was generally slow yet highly variable although uncertainty in the estimation is high. Occurrence of the flow maximum, as well as many local maxima and minima at consistent locations over different periods suggests that the valley geometry affect the overall flow pattern. On top of this general trend, many small-scale temporal/spatial variations in the glacier flow patterns were observed along the glacier, especially in the lower sections. On average, the flow speeds were in the range of 0.3 to 0.7 m/day; however this lacks any measurements of summer flow speeds which are expected to be significantly higher. 相似文献
66.
67.
68.
69.
70.
M. Del C. Ruiz J. A. González J. B. Rivarola 《Metallurgical and Materials Transactions B》2004,35(3):439-448
The mechanism and kinetics of β-Ta2O5 chlorination, mixed with sucrose carbon, have been studied by a thermogravimetric technique. The investigated temperature
range was 500 °C to 850 °C. The reactants and reaction residues were analyzed by scanning electronic microscopy (SEM), X-ray
diffraction (XRD), and Brunauer-Emmett-Teller method for surface area (BET). The effect of various experimental parameters
was studied, such as carbon percentage, temperature, chlorine partial pressure, and flow, use of the multiple sample method,
and carbon previous oxidation. The carbon percentage and previous treatment have an effect on the system reactivity. The temperature
has a marked effect on the reaction rate. In the 500 °C to 600 °C temperature interval, the apparent activation energy is
144 kJ/mol of oxide, while at higher temperatures, the activation energy decreases. With high chorine partial pressures, the
order of reaction is near zero. The kinetic contractile plate model, X=kt, considering carbon oxidation as the controlling stage, is the one with the best fit to the experimental data. A probable
mechanism for the carbochlorination of β-Ta2O5 is proposed: (1) activation of chlorine on the carbon surface, (2) chlorination of Ta2O5, (3) oxidation of carbon, and (4) recrystallization of β-Ta2O5. 相似文献