全文获取类型
收费全文 | 1730篇 |
免费 | 33篇 |
国内免费 | 88篇 |
专业分类
系统科学 | 47篇 |
丛书文集 | 34篇 |
教育与普及 | 4篇 |
理论与方法论 | 2篇 |
现状及发展 | 8篇 |
综合类 | 1756篇 |
出版年
2024年 | 3篇 |
2023年 | 9篇 |
2022年 | 9篇 |
2021年 | 10篇 |
2020年 | 17篇 |
2019年 | 12篇 |
2018年 | 17篇 |
2017年 | 22篇 |
2016年 | 29篇 |
2015年 | 55篇 |
2014年 | 102篇 |
2013年 | 66篇 |
2012年 | 86篇 |
2011年 | 138篇 |
2010年 | 124篇 |
2009年 | 104篇 |
2008年 | 161篇 |
2007年 | 219篇 |
2006年 | 167篇 |
2005年 | 121篇 |
2004年 | 110篇 |
2003年 | 71篇 |
2002年 | 41篇 |
2001年 | 42篇 |
2000年 | 24篇 |
1999年 | 19篇 |
1998年 | 16篇 |
1997年 | 11篇 |
1996年 | 1篇 |
1995年 | 6篇 |
1994年 | 10篇 |
1993年 | 3篇 |
1992年 | 4篇 |
1991年 | 4篇 |
1990年 | 4篇 |
1989年 | 4篇 |
1988年 | 4篇 |
1987年 | 4篇 |
1955年 | 2篇 |
排序方式: 共有1851条查询结果,搜索用时 312 毫秒
921.
Wavelet transform has attracted attention because it is a very useful tool for signal analyzing. As a fundamental characteristic
of an image, texture traits play an important role in the human vision system for recognition and interpretation of images.
The paper presents an approach to implement texture-based image retrieval usingM-band wavelet transform. Firstly the traditional 2-band wavelet is extended toM-band wavelet transform. Then the wavelet moments are computed byM-band wavelet coefficients in the wavelet domain. The set of wavelet moments forms the feature vector related to the texture
distribution of each wavelet images. The distances between the feature vectors describe the similarities of different images.
The experimental result shows that theM-band wavelet moment features of the images are effective for image indexing. The retrieval method has lower computational
complexity, yet it is capable of giving better retrieval performance for a given medical image database.
Foundation item: Supported by the National Natural Science Foundation of China (69983005)
Biography: Liao Ya-li(1979-), female, Master candidate, research direction: distributed network communication and multimedia information
processing. 相似文献
922.
侯长来 《科技情报开发与经济》2005,15(3):83-84
介绍了一种用于主动信息服务的《SCI)论文收录的检索策略。利用刊物形式的《SCI》以手工检索为基础,借助《中国科技论文与引文数据库),实现了对《SCI》论文收录著者名、址追踪,对检索效果进行了综合评价,并分析了影响检索效果的因素。 相似文献
923.
In an effort to study the severe rainfall event of 4?5th July 2000 in Beijing (with 24h accumulated precipitation of 240 mm), we perform numerical simulations to investigate this event using the MM5v3.6 model. The model is initialized with the MM5/WRF 3DVAR analysis, which incorporates the ground-based GPS precipitable water vapor, automatic and conventional meteorological observations in its assimilation step. For 24 h accumulated precipitation forecast, the threat scores are 0.72, 0.76, 0.67 and 0.63, for thresholds of 1, 5, 10, and 20 mm, respectively. Holding other factors unchanged, sensitivity experiments were conducted with different topographic resolutions of 110, 50 and 3.7 km to investigate the topographic effects on precipitation over the Beijing area. In these sensitivity experiments, we attempt to preserve the realistic orographic distribution in the model topography under the condition of keeping the dynamic-thermodynamic consistency of the initial model atmosphere to the extent possible. Results indicate that the unique topographic distribution and variations in the Beijing area play an important role in determining the location, distribution and intensity of heavy precipitation. 相似文献
924.
In medical research and clinical diagnosis, automated or computer-assisted classification and retrieval methods are highly desirable to offset the high cost of manual classification and manipulation by medical experts. To facilitate the decision-making in the health-care and the related areas, in this paper, a two-step content-based medical image retrieval algorithm is proposed. Firstly, in the preprocessing step, the image segmentation is performed to distinguish image objects, and on the basis of the segmentation results, the boundary of each object is extracted to simplify each object feature space; and then in the second step, the binary vector for each object is generated to record their spatial information; and based on these local binary vectors, the global image vector is obtained. The proposed algorithm provides potential method for large image database retrieval and browsing. 相似文献
925.
图书馆跨平台信息检索系统初探 总被引:9,自引:0,他引:9
徐汝兴 《上海交通大学学报》2003,(Z1)
随着计算机和因特网的飞速发展 ,数字图书馆的电子资源日益丰富 .图书馆数字资源和发布方式的多样性使用户在使用过程中越来越感到不便 .跨平台信息检索系统成为目前数字图书馆建设中一个重要的课题 .本文试图通过对现行各类整合系统的分析 ,提出一个跨平台检索系统的模式 ,并通过实践经验对这个系统进行进一步展望 相似文献
926.
A single-channel (9.5 mm) airborne microwave radiometer with one antenna is developed. The retrieval methods and primary observation results of cloud liquid water and super-cooled cloud liquid water are discussed. The aircraft experiments show that the cloud liquid water and super-cooled liquid water can be sensitively monitored at some level of accuracy by the radiometer. The results of cloud liquid water content are reasonable and correspond well with the surface radar echo intensity. The design of the airborne radiometer and its retrieval methods are feasible, giving it application value. 相似文献
927.
利用SVM和灰度基元共生矩阵进行图像数据库检索 总被引:2,自引:0,他引:2
提出了一种新的基于内容的图像检索方法,其关键技术是:(i)提出一种检索图像内容纹理统计特征的新方法,定义若干规范灰度像素模式基元;计算这些基元沿不同方向和不同跨距成对出现的概率,可以组成灰度一基元共生矩阵;该矩阵可用来描述图像纹理方面的特征。(ii)通过构建分类矩阵进行二叉树判别,扩展了SVM的多类分类功能。实验测试表明该法可行,且具有较好检索性能。 相似文献
928.
网络信息资源的检索技巧和策略 总被引:2,自引:0,他引:2
网络信息资源种类繁多,网络检索工具数量之大,给我们的网上查询带来困难。文章论述了Internet信息资源检索工具的分类,提出了网络信息资源的检索技巧和策略,以使检索结果尽量优化。 相似文献
929.
一种基于LSI的图像语义检索技术 总被引:6,自引:0,他引:6
探讨如何将LSI技术应用于图像检索中,以实现基于语义的图像检索的技术途径,给出了一种新的图像索引方法,它使用灰色模型GM(1,1)对图像的像素值进行模型化处理,并且使用模型参数的概率分布来描述图像,在此基础上,详细讨论了将隐含主义索引应用于图像检索中的具体方法,并给出了相应的算法,最后,给出了实验结果和尚需进一步研究的问题。 相似文献
930.
文章介绍了国际联机系统特别是Dialog近几年的一系列新进展,同时探讨和分析了这些新进展对科技查新的影响和促进作用。 相似文献