全文获取类型
收费全文 | 105667篇 |
免费 | 15045篇 |
国内免费 | 9514篇 |
专业分类
电工技术 | 9730篇 |
技术理论 | 9篇 |
综合类 | 10527篇 |
化学工业 | 10872篇 |
金属工艺 | 3091篇 |
机械仪表 | 7700篇 |
建筑科学 | 6140篇 |
矿业工程 | 2547篇 |
能源动力 | 5481篇 |
轻工业 | 5443篇 |
水利工程 | 5643篇 |
石油天然气 | 4935篇 |
武器工业 | 1375篇 |
无线电 | 14224篇 |
一般工业技术 | 7797篇 |
冶金工业 | 3687篇 |
原子能技术 | 1833篇 |
自动化技术 | 29192篇 |
出版年
2024年 | 811篇 |
2023年 | 2315篇 |
2022年 | 3929篇 |
2021年 | 4419篇 |
2020年 | 4493篇 |
2019年 | 3627篇 |
2018年 | 3206篇 |
2017年 | 4124篇 |
2016年 | 4454篇 |
2015年 | 4893篇 |
2014年 | 7292篇 |
2013年 | 7200篇 |
2012年 | 8066篇 |
2011年 | 8815篇 |
2010年 | 6446篇 |
2009年 | 6641篇 |
2008年 | 6474篇 |
2007年 | 7323篇 |
2006年 | 6304篇 |
2005年 | 5455篇 |
2004年 | 4309篇 |
2003年 | 3707篇 |
2002年 | 2904篇 |
2001年 | 2289篇 |
2000年 | 1888篇 |
1999年 | 1535篇 |
1998年 | 1296篇 |
1997年 | 1049篇 |
1996年 | 971篇 |
1995年 | 816篇 |
1994年 | 654篇 |
1993年 | 510篇 |
1992年 | 448篇 |
1991年 | 307篇 |
1990年 | 296篇 |
1989年 | 197篇 |
1988年 | 160篇 |
1987年 | 108篇 |
1986年 | 90篇 |
1985年 | 58篇 |
1984年 | 70篇 |
1983年 | 59篇 |
1982年 | 35篇 |
1981年 | 29篇 |
1980年 | 24篇 |
1979年 | 21篇 |
1978年 | 10篇 |
1977年 | 9篇 |
1959年 | 24篇 |
1951年 | 27篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
21.
短模型上的明渠非恒定流试验 总被引:1,自引:0,他引:1
水工整体模型试验中,明渠非恒定流至今大多被简化为恒定流,而效果有时并不理想。本文指出,只要设置固定式曲线尾门,并有必要的动态量测设备,便可模拟原型非恒定流;即使模型偏短,也能得出比恒定流试验更接近原型的成果。在同一模型上,既做恒定流试验,又进行必要的非恒定流试验,二者相辅相成,必将有助于试验水平的提高。作为例证,本文介绍了泄洪调度导致航道水面波动的一项试验成果,并以岩基冲刷、通航水流条件、围堰过水、河床冲淤等研究课题为例,讨论了采用“短模型非恒定流试验方式”的必要性与可行性。 相似文献
22.
Michael E. G. Ferguson Peter L. Spedding 《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》1995,63(3):262-278
Experimental data for air–water two-phase co-current flow in two different pipe diameters were used to test the prediction of pressure drop by a number of existing theories and correlations. Several models are shown to be useful for prediction, particularly with the stratified regimes which have proved difficult to handle in the past. The model suggested by Olujic proved to be of particular value. 相似文献
23.
R. Tao 《Chemical engineering science》2006,61(7):2186-2190
Molecular dynamical simulation has been carried out to investigate the structure and dynamics of a dipolar fluid under strong shear. Dipolar fluid consists of polarizable particles, which have an induced dipole moment in the applied field direction. Shear stress is perpendicular to the field direction. When shear stress is small, the flow has a flowing-chain structure. If shear stress increases to pass a critical value, flowing-chain structure changes to flowing layer structure. Each layer is parallel to the flow direction and shear direction. Within one layer, particles form strings in the flow direction. 相似文献
24.
25.
R. GRAY† M. HILARY STEVENSON‡ 《International Journal of Food Science & Technology》1991,26(6):669-672
One hundred and twenty-five pairs of chicken drumsticks were randomly allocated to one of five dose rates: 5, 10, 15, 20 or 600 kGyh-. The highest dose rate was obtained using a linear accelerator whilst the remaining dose rates were provided using a 60 Co gamma source. Each batch of 25 pairs was further divided into groups five of which were stored at 4°C for 0, 7, 14, 21 or 28 days. ESR spectroscopy was used to measure the intensity of the radiation-induced signal. There was a quadratic relationship between ESR signal strength and dose rate, which although statistically significant is unlikely to be of practical importance. The magnitude of the ESR signal declined by about 20% over the first 14 days of storage at 4°C and thereafter the decrease was minimal. 相似文献
26.
J. Balakrishnan W. A. Sethares C. R. Johnson 《International Journal of Adaptive Control and Signal Processing》2002,16(4):309-323
A method of approximate channel identification is proposed that is based on a simplification of the correlation estimator. Despite the numerical simplification (no multiplications or additions are required, only comparisons and an accumulator), the performance of the proposed estimator is not significantly worse than that of the standard correlation estimator. A free (user selectable) parameter moves ‘smoothly’ from a situation with small sum‐squared channel estimation error but hard‐to‐identify channel peaks, to one with a larger sum‐squared estimation error but easy‐to‐identify channel peaks. The proposed estimator is shown to be biased and its behaviour is analysed in a number of situations. Applications of the proposed estimator to sparsity detection, symbol timing recovery and to the initialization of blind equalizers are suggested. Copyright © 2002 John Wiley & Sons, Ltd. 相似文献
27.
A new definition of the flooding point in a two-phase counter-current trickle bed column has been proposed. Based on this point a versatile correlation of liquid hold-up has been formulated. The coefficients of this correlation are invariant to the change of physical properties of liquid, type and size of the packing forming the bed and gas velocity. This conclusion has been reached from the analysis of experiments with four different liquids irrigating the bed and three types of packing of various size. The versatile correlation can be used also re-currently to calculate flooding hold-up and flooding liquid rate from two known values of liquid hold-up for a given gas rate. 相似文献
28.
In various medium‐to‐large‐scale fire test equipments like the ISO room corner test (RC), and more recently, the single burning item test (SBI) the mass flow rate measurement of the combustion gases plays a key role in the determination of the heat‐release rate and smoke‐production rate. With the knowledge of the velocity profile and the temperature of the flow, the mass flow rate is obtained by measuring the velocity on the axis of the duct. This is done by means of a bi‐directional probe based on the pitot principle. However, due to the variation of the mean temperature and the temperature gradient in any cross section of the duct, introduced by ever changing combustion gas temperatures, the velocity nor the density profile are constant in time. This paper examines the resulting uncertainty on the mass flow rate. Copyright © 2006 John Wiley & Sons, Ltd. 相似文献
29.
The mirror effect for word frequency refers to the finding that low-frequency words have higher hit rates and lower false alarm rates than high-frequency words. This result is typically interpreted in terms of conventional signal detection theory (SDT), in which case it indicates that the order of the underlying old item distributions mirrors the order of the new item distributions. However, when viewed in terms of a mixture version of SDT, the order of hits and false alarms does not necessarily imply the same order in the underlying distributions because of possible effects of mixing. A reversal in underlying distributions did not appear for fits of mixture SDT models to data from 4 experiments. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
30.
Identification of gaps in mangrove forests with airborne LIDAR 总被引:2,自引:0,他引:2
Mangrove forests change frequently due to disturbances from tropical storms, frost, lightning, and insects. It has been suggested that the death and regeneration of trees in small gaps due to lightning may play a critical role in mangrove forest turnover; however, the large-scale quantification of spatial pattern and areas of gaps is lacking for investigating this issue. Airborne light detection and ranging (LIDAR) technology provides an effective way for identifying gaps by remotely obtaining direct measurements of ground and canopy elevations. A method based on an alternative sequential filter and black top-hat mathematical morphological transformation was developed to extract gap features. Comparison of identified gap polygons with raw LIDAR measurements and field surveys shows that the proposed method successfully extracted gap features in mangrove forests in Everglades National Park. There are 400–500 lightning gaps per square kilometer in mangrove forests at the study sites. The distribution of gap sizes follows an exponential form and the area of gaps with sizes larger than 100 m2 account for 55–61% of the total area of gaps. The area of gaps in the mangrove forest in Everglades National Park is about 4–5% of the total forest area and the average gap formation rate is about 0.3% of the total forest area per year, indicating that lightning gaps play an important role in mangrove forest dynamics. 相似文献