全文获取类型
收费全文 | 106785篇 |
免费 | 14666篇 |
国内免费 | 9163篇 |
专业分类
电工技术 | 12461篇 |
技术理论 | 4篇 |
综合类 | 9775篇 |
化学工业 | 6047篇 |
金属工艺 | 4902篇 |
机械仪表 | 8447篇 |
建筑科学 | 5464篇 |
矿业工程 | 3829篇 |
能源动力 | 2668篇 |
轻工业 | 6031篇 |
水利工程 | 2010篇 |
石油天然气 | 6940篇 |
武器工业 | 1832篇 |
无线电 | 19443篇 |
一般工业技术 | 9038篇 |
冶金工业 | 2942篇 |
原子能技术 | 1427篇 |
自动化技术 | 27354篇 |
出版年
2024年 | 809篇 |
2023年 | 2277篇 |
2022年 | 3856篇 |
2021年 | 4337篇 |
2020年 | 4371篇 |
2019年 | 3460篇 |
2018年 | 2987篇 |
2017年 | 4098篇 |
2016年 | 4390篇 |
2015年 | 4897篇 |
2014年 | 7544篇 |
2013年 | 6681篇 |
2012年 | 8531篇 |
2011年 | 8900篇 |
2010年 | 6638篇 |
2009年 | 6606篇 |
2008年 | 6222篇 |
2007年 | 7389篇 |
2006年 | 6385篇 |
2005年 | 5465篇 |
2004年 | 4355篇 |
2003年 | 3868篇 |
2002年 | 3007篇 |
2001年 | 2363篇 |
2000年 | 2132篇 |
1999年 | 1748篇 |
1998年 | 1374篇 |
1997年 | 1125篇 |
1996年 | 1017篇 |
1995年 | 785篇 |
1994年 | 645篇 |
1993年 | 466篇 |
1992年 | 396篇 |
1991年 | 319篇 |
1990年 | 274篇 |
1989年 | 233篇 |
1988年 | 171篇 |
1987年 | 75篇 |
1986年 | 68篇 |
1985年 | 53篇 |
1984年 | 57篇 |
1983年 | 39篇 |
1982年 | 35篇 |
1981年 | 31篇 |
1980年 | 28篇 |
1979年 | 15篇 |
1978年 | 10篇 |
1975年 | 8篇 |
1959年 | 14篇 |
1951年 | 11篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
81.
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
82.
83.
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
84.
从理论计算分离器处理能力和现场开展试验两方面入手,对靖边气田目前在用的不同规格分离器的分离效果进行了对比分析,通过对现场数据统计和整理,得到了靖边气田不同规格分离器合理的处理气量,给气田开发建设中分离器的选型和维护改造中分离器的调整提供了依据。 相似文献
85.
86.
The present work is devoted to measure the absolute magnetic field produced by different coils in the EGYPTOR tokamak using a calibrated pickup coil. Scaling these measurements in different equations connected with the discharge currents from each supply system are performed. The pickup coil used in the present study is well calibrated with Helmholz coils at the IPP in Prague, Czech Republic. A 0.2% deviation has been found between an evaluation done in the present study and the calibration using Helmholz coils. Experimental measurements of the toroidal magnetic field are in good agreement with calculations to within 2%. Very low values of stray magnetic field components arising from TF and OH coils are recorded which proves that the compensation coils for these components are sufficient. 相似文献
87.
Kotaro Matsuuchi Tadashi Fukami Nobuyuki Naoe Ryoichi Hanaoka Shinzo Takata Toshio Miyamoto 《Electrical Engineering in Japan》2005,150(2):43-49
This paper presents a method of predicting the steady‐state performance of a new hybrid‐excitation synchronous machine (HESM) theoretically. The field pole of this HESM is axially divided into two parts; one is an excitation part and the other a permanent‐magnet (PM) part. A nonlinear equivalent circuit, which can include the saliency of the rotor and the magnetic saturation due to the iron core, is derived. Based on this equivalent circuit, the steady‐state performance of the HESM is calculated, and the results are confirmed through experiments. © 2004 Wiley Periodicals, Inc. Electr Eng Jpn, 150(2): 43–49, 2005; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20033 相似文献
88.
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
89.
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
90.
NUMERICAL ANALYSIS AND EXPERI- MENT OF UNSTEADY THERMAL FIELD OF ROTOR PLATE FOR EDDY CURRENT RETARDER 总被引:3,自引:0,他引:3
LIU Chengye HE Ren 《机械工程学报(英文版)》2008,21(4):71-75
The physical model based on heat transfer theory and virtual boundary method for analyzing unsteady thermal field of rotor plate for eddy current retarder used in automobile is established and boundary conditions are also defined. The finite element governing equation is derived by Galerkin method. The time differential item is discrete based on Galerkin format that is stable at any condition. And a new style of varying time step method is used in iteration process. The thermal field on the rotor plate at the radial and axle directions is analyzed and varying temperature at appointed points on two side-surfaces is measured. The testing and analytical data are uniform approximately. Finite element method can be used for estimating thermal field of the rotor plate at initial design stage of eddy current retarder. 相似文献