全文获取类型
收费全文 | 76521篇 |
免费 | 5878篇 |
国内免费 | 3349篇 |
专业分类
电工技术 | 3869篇 |
技术理论 | 2篇 |
综合类 | 4134篇 |
化学工业 | 12208篇 |
金属工艺 | 4937篇 |
机械仪表 | 4556篇 |
建筑科学 | 5132篇 |
矿业工程 | 2157篇 |
能源动力 | 2206篇 |
轻工业 | 4610篇 |
水利工程 | 1165篇 |
石油天然气 | 4056篇 |
武器工业 | 525篇 |
无线电 | 9445篇 |
一般工业技术 | 11365篇 |
冶金工业 | 4719篇 |
原子能技术 | 800篇 |
自动化技术 | 9862篇 |
出版年
2024年 | 358篇 |
2023年 | 1176篇 |
2022年 | 1912篇 |
2021年 | 2730篇 |
2020年 | 2066篇 |
2019年 | 1906篇 |
2018年 | 2162篇 |
2017年 | 2347篇 |
2016年 | 2199篇 |
2015年 | 2690篇 |
2014年 | 3331篇 |
2013年 | 4484篇 |
2012年 | 4581篇 |
2011年 | 5222篇 |
2010年 | 4266篇 |
2009年 | 4314篇 |
2008年 | 4088篇 |
2007年 | 3999篇 |
2006年 | 4304篇 |
2005年 | 3519篇 |
2004年 | 2639篇 |
2003年 | 2186篇 |
2002年 | 1970篇 |
2001年 | 1852篇 |
2000年 | 1947篇 |
1999年 | 2079篇 |
1998年 | 2183篇 |
1997年 | 1732篇 |
1996年 | 1555篇 |
1995年 | 1235篇 |
1994年 | 1055篇 |
1993年 | 742篇 |
1992年 | 564篇 |
1991年 | 502篇 |
1990年 | 371篇 |
1989年 | 307篇 |
1988年 | 258篇 |
1987年 | 171篇 |
1986年 | 150篇 |
1985年 | 99篇 |
1984年 | 75篇 |
1983年 | 57篇 |
1982年 | 55篇 |
1981年 | 34篇 |
1980年 | 41篇 |
1979年 | 28篇 |
1978年 | 27篇 |
1977年 | 22篇 |
1976年 | 22篇 |
1975年 | 18篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
82.
AC hot-carrier effects in n-MOSFETs with thin (~85 Å) N2O-nitrided gate oxides have been studied and compared with control devices with gate oxides grown in O2. Results show that furnace N2O-nitrided oxide devices exhibit significantly reduced AC-stress-induced degradation. In addition, they show weaker dependences of device degradation on applied gate pulse frequency and pulse width. Results suggest that the improved AC-hot-carrier immunity of the N2O-nitrided oxide device may be due to the significantly suppressed interface state generation and neutral electron trap generation during stressing 相似文献
83.
84.
A general approach toE,E-diene hydroperoxides is described based upon photoisomerization of readily availableZ,E-diene monoperoxyketals. Protection of aZ,E-diene hydroperoxide as the 2-methoxypropyl peroxyketal is followed by iodine-mediated photoisomerization to produce a mixture
enriched in theE,E isomer. After chromatographic purification, deprotection of the peroxyketal with mild acid furnishes theE,E-diene hydroperoxide. 相似文献
85.
Puente C. Claret J. Sagues F. Romeu J. Lopez-Salvans M.Q. Pous R. 《Electronics letters》1996,32(25):2298-2299
Experimental results on a fractal tree-like antenna are reported. The fractal structure is generated by electrochemical deposition. The antenna presents a multiband behaviour with a denser band distribution than the previously reported Sierpinski fractal antenna. The matched frequencies are related to the length distribution over the fractal shape 相似文献
86.
The probabilistic distribution properties of a set of medical images are studied. It is shown that the generalized Gaussian function provides a good approximation to the distribution of AP chest radiographs. Based on this result and a goodness-of-fit test, a generalized Gaussian autoregressive model (GGAR) is proposed. Its properties and limitations are also discussed. It is expected that the GGAR model will be useful in describing the stochastic characteristics of some classes of medical images and in image data compression and other applications. 相似文献
87.
M. Alghane Y. Q. Fu B. X. Chen Y. Li M. P. Y. Desmulliez A. J. Walton 《Microfluidics and nanofluidics》2012,13(6):919-927
This paper reports an experimental and numerical investigation on the scaling effects in the flow hydrodynamics for confined microdroplets induced by a surface acoustic wave (SAW). The characteristic parameters of the flow hydrodynamics were studied as a function of the separation height, H, between the LiNbO3 substrate and a top glass plate, for various droplets volumes and radio-frequency powers. The ratio of the gap height to attenuation length of the SAW, H/l SAW, is shown to be an important parameter affecting the streaming flow induced in this confined regime. The reported numerical and experimental results are in good agreement over the range examined in this study and demonstrate that, at a lower gap heights of H?≤?100?μm, a significant decrease in streaming velocity or Reynolds number is induced, with the velocity approaching zero when the gap height is decreased to ~50?μm. An increase in the gap height results in an increased streaming velocity; however, if the gap height exceeds 70?% of the SAW attenuation length, any further increase in the gap height induces a drop in the streaming velocity. 相似文献
88.
Observations of fatigue-induced slip patterns on the surface of polycrystalline gold (+99.9%) using the scanning tunnelling microscope (STM) are presented. The samples were cycled in four-point bending between zero and 0.0025 strain for 250 and 2500 cycles. STM observations of the sample fatigued for 250 cycles revealed broad slip bands 0.38–0.69 m wide containing narrow slip bands 0.015–0.123 m wide and fine slip lines 0.006 m wide. The depth of these features are 20–57 nm for broad slip bands, 3–7 nm for narrow slip bands, and approximately 2–4 nm for fine slip lines. The sample fatigued for 2500 cycles showed similar values for the width of the slip bands and slip lines except that their depth was increased by a factor of between 2 and 4 times for the narrow slip bands and the fine slip lines. Apparent persistent slip bands (PSBs) spaced 2.4 m, 300–500 nm deep were also observed. These results demonstrate that STM is a significant new tool for observing and distinguishing various types of fatigue-induced surface slip patterns on suitably prepared samples. The vertical resolution obtained with STM is vastly superior to current SEM and TEM methods. 相似文献
89.
90.