全文获取类型
收费全文 | 106332篇 |
免费 | 7826篇 |
国内免费 | 3207篇 |
专业分类
电工技术 | 4575篇 |
技术理论 | 4篇 |
综合类 | 4380篇 |
化学工业 | 19594篇 |
金属工艺 | 5427篇 |
机械仪表 | 7044篇 |
建筑科学 | 5608篇 |
矿业工程 | 1337篇 |
能源动力 | 3677篇 |
轻工业 | 7929篇 |
水利工程 | 1455篇 |
石油天然气 | 2728篇 |
武器工业 | 486篇 |
无线电 | 14927篇 |
一般工业技术 | 17582篇 |
冶金工业 | 6257篇 |
原子能技术 | 1384篇 |
自动化技术 | 12971篇 |
出版年
2024年 | 283篇 |
2023年 | 1375篇 |
2022年 | 2477篇 |
2021年 | 3691篇 |
2020年 | 2680篇 |
2019年 | 2564篇 |
2018年 | 2918篇 |
2017年 | 3087篇 |
2016年 | 3427篇 |
2015年 | 3603篇 |
2014年 | 4885篇 |
2013年 | 6411篇 |
2012年 | 6898篇 |
2011年 | 7922篇 |
2010年 | 6491篇 |
2009年 | 6324篇 |
2008年 | 6199篇 |
2007年 | 5375篇 |
2006年 | 5225篇 |
2005年 | 4494篇 |
2004年 | 3598篇 |
2003年 | 3454篇 |
2002年 | 3552篇 |
2001年 | 2981篇 |
2000年 | 2488篇 |
1999年 | 2211篇 |
1998年 | 2600篇 |
1997年 | 1852篇 |
1996年 | 1595篇 |
1995年 | 1244篇 |
1994年 | 1045篇 |
1993年 | 850篇 |
1992年 | 614篇 |
1991年 | 537篇 |
1990年 | 449篇 |
1989年 | 387篇 |
1988年 | 333篇 |
1987年 | 244篇 |
1986年 | 177篇 |
1985年 | 152篇 |
1984年 | 121篇 |
1983年 | 77篇 |
1982年 | 62篇 |
1981年 | 60篇 |
1980年 | 46篇 |
1979年 | 39篇 |
1978年 | 31篇 |
1977年 | 38篇 |
1976年 | 69篇 |
1975年 | 26篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
We propose a face detection method based on skin color likelihood via a boosting algorithm which emphasizes skin color information while deemphasizing non-skin color information. A stochastic model is adapted to compute the similarity between a color region and the skin color. Both Haar-like features and Local Binary Pattern (LBP) features are utilized to build a cascaded classifier. The boosted classifier is implemented based on skin color emphasis to localize the face region from a color image. Based on our experiments, the proposed method shows good tolerance to face pose variation and complex background with significant improvements over classical boosting-based classifiers in terms of total error rate performance. 相似文献
992.
Pt-V2O5-WO3/TiO2 catalysts supported on SiC filter for NO reduction at low temperature 总被引:1,自引:0,他引:1
Joo-Hong Choi Jin-Hyun Kim Young-Cheoul Bak Rose Amal Jason Scott 《Korean Journal of Chemical Engineering》2005,22(6):844-851
The catalytic filter, V2O5-WO3-TiO2 supported on a ceramic filter, is known as a promising material for treating particulates and NO
x
simultaneously at optimum temperatures around 320°C. In order to improve its catalytic activity at low temperatures, the
effect of Pt addition on the catalytic filter has been investigated. Catalytic filters, Pt-V2O5-WO3-TiO2/SiC, were prepared by co-impregnation of Pt, V, and W precursors on TiO2 coated-SiC filter by vacuum aided-dip coating. The Pt-added catalytic filter shifted the optimum working temperature from
280–330°C (for the non Pt-impregnated filter) to 180–230°C, providing N
x
slip concentration less than 20 ppm for the treatment of 700 ppm NO at a face velocity of 2 cm/s with the same value over
the non Pt-added catalytic filters. The promotional effect following the addition of Pt is believed to result from electrical
modification of the catalyst maintaining a high electron transfer state. Ammonia oxidation was also observed to be dominant
above the optimal temperature for SCR. 相似文献
993.
Self-Organizing Networks (SONs) are attractive for applications where flexibility, resilience, and a large network service area are required. In order to meet the requirements of those applications, the principal issue is to guarantee efficient routing in SONs. Hence, the design and selection of appropriate routing metrics is important. A mass of metrics have been proposed in the past several decades. Among all the metrics, Expected Transmission Count (ETX) has drawn the most attention. Since the proposal of ETX, many ETX-based or extended metrics have been proposed. ETX and its descendants compose the ETX family. This paper is an attempt to analyze, compare and summarize traffic-based routing metrics in the ETX family. Details of each routing metric are presented and analyzed. Some of our viewpoints on the principal for designing metrics in SONs are presented. 相似文献
994.
Spaceborne microwave synthetic aperture radar (SAR), with its high spatial resolution (10–100 m), large area coverage, and day/night imaging capability, has been used as an important tool for typhoon monitoring. Since the microwave signal can penetrate through clouds, SAR images reveal typhoon morphology at the sea surface. Within the region of a typhoon eye, wind speed and the associated sea surface roughness are usually low. Therefore, the typhoon eye can be well distinguished as dark areas in SAR images. However, automatic typhoon eye extraction from SAR images is hampered by SAR image speckle noise and other false-alarm dark features contained in an image. In this study, we propose an image processing approach to extract typhoon eyes from SAR images. The three-step image processing includes: (1) applying an extended non-local means image denoizing algorithm to reduce image speckle noise; (2) applying a top-hat transform to denoized imagery to enhance the contrast; and (3) using a labelled watershed to segment the typhoon eye. Experimental results from analysing three Environmental Satellite SAR typhoon images show that our approach provides fast and efficient SAR image segmentation for typhoon eye extraction. Typhoon eyes are segmented correctly, and their edges are well detected. Our experimental results are comparable to manually extracted typhoon eye information. Fine-tuning of this approach will provide an automatic tool for typhoon eye information extraction from SAR images. 相似文献
995.
Zhenzhan Wang Dehai Zhang Yun Li Jin Zhao 《International journal of remote sensing》2014,35(11-12):4496-4514
The atmospheric correction microwave radiometer (ACMR) is one of the main payloads for correcting atmospheric path delay in the radar altimeter on the Haiyang-2A (HY-2A) satellite. The ACMR is a three-band microwave radiometer operating at 18.7, 23.8, and 37.0 GHz. Calibration of the ACMR is important for applying its measurements to correct for atmospheric effects on the HY-2A altimeter signal transmission in the air. Therefore, a detailed introduction to the principles and specifications of the ACMR system is given first. The thermal vacuum calibration method of the ACMR is discussed and analysed, and the microwave transfer functions and related coefficients are given, especially the nonlinear coefficients derived from a test for correcting nonlinear responses between the input of antenna temperature and the output of voltage at each channel of the ACMR. Furthermore, antenna pattern correction algorithms for removing the effects of side lobe and cross-polarization are derived and their coefficients are used for in-orbit data processing. Primary calibration results are given by comparing with the similar spaceborne Jason microwave radiometer (JMR) on the Jason-1 satellite and with the advanced microwave radiometer (AMR) on Jason-2. The results of this comparison show that the data from the ACMR match well to those from the JMR and AMR. 相似文献
996.
Unsaturated polyester (UP)/montmorillonite (MMT) nanocomposite was prepared by using hydroxypropylacrylate (HPA) as a reactive diluent instead of conventional styrene monomer and the effect of polarity of reactive diluent on properties of nanocomposite was investigated. X‐ray and mechanical test data indicated that mixing for an extended period of time is essential to enhance the physical properties of nanocomposites in the UP/Cloisite 6A system. This was attributed to the high polarity of HPA that may disturb the preintercalation of UP resin into the galleries of MMT. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 238–242, 2004 相似文献
997.
998.
Natural objects often contain vivid color distribution with wide variety of colors. Conventional colorization techniques, on the other hand, produce colors that are relatively flat with little color variation. In this paper, we introduce a randomized algorithm which considers not only the value of target color but also the distribution of target color. In essence, our algorithm paints a color distribution to a region which synthesizes color distribution of a natural object. Our approach models the correlation between intensity and color in HSV color space in terms of H – S, H – V and S – V joint histogram. During the colorization process, we randomly swap and reassign color of a pixel to minimize a cost function that measures color consistency to its neighborhood and intensity‐to‐color correlation captured in the joint histogram. We tested our algorithm extensively on many natural objects and our user study confirms that our results are more vivid and natural compared to results from previous techniques. 相似文献
999.
This paper proposes a new approach for color transfer between two images. Our method is unique in its consideration of the scene illumination and the constraint that the mapped image must be within the color gamut of the target image. Specifically, our approach first performs a white‐balance step on both images to remove color casts caused by different illuminations in the source and target image. We then align each image to share the same ‘white axis’ and perform a gradient preserving histogram matching technique along this axis to match the tone distribution between the two images. We show that this illuminant‐aware strategy gives a better result than directly working with the original source and target image's luminance channel as done by many previous methods. Afterwards, our method performs a full gamut‐based mapping technique rather than processing each channel separately. This guarantees that the colors of our transferred image lie within the target gamut. Our experimental results show that this combined illuminant‐aware and gamut‐based strategy produces more compelling results than previous methods. We detail our approach and demonstrate its effectiveness on a number of examples. 相似文献
1000.