全文获取类型
收费全文 | 175969篇 |
免费 | 21575篇 |
国内免费 | 14721篇 |
专业分类
电工技术 | 17739篇 |
技术理论 | 1篇 |
综合类 | 17773篇 |
化学工业 | 22059篇 |
金属工艺 | 12142篇 |
机械仪表 | 12046篇 |
建筑科学 | 14315篇 |
矿业工程 | 6689篇 |
能源动力 | 4888篇 |
轻工业 | 17717篇 |
水利工程 | 6247篇 |
石油天然气 | 5957篇 |
武器工业 | 2574篇 |
无线电 | 19745篇 |
一般工业技术 | 15868篇 |
冶金工业 | 6501篇 |
原子能技术 | 2782篇 |
自动化技术 | 27222篇 |
出版年
2024年 | 1034篇 |
2023年 | 3206篇 |
2022年 | 7331篇 |
2021年 | 9631篇 |
2020年 | 6738篇 |
2019年 | 4946篇 |
2018年 | 5065篇 |
2017年 | 5688篇 |
2016年 | 4976篇 |
2015年 | 7857篇 |
2014年 | 9743篇 |
2013年 | 11434篇 |
2012年 | 14369篇 |
2011年 | 15180篇 |
2010年 | 14046篇 |
2009年 | 13840篇 |
2008年 | 13923篇 |
2007年 | 13534篇 |
2006年 | 11886篇 |
2005年 | 9774篇 |
2004年 | 7025篇 |
2003年 | 4641篇 |
2002年 | 4257篇 |
2001年 | 3978篇 |
2000年 | 3181篇 |
1999年 | 1460篇 |
1998年 | 650篇 |
1997年 | 501篇 |
1996年 | 440篇 |
1995年 | 354篇 |
1994年 | 293篇 |
1993年 | 237篇 |
1992年 | 200篇 |
1991年 | 158篇 |
1990年 | 115篇 |
1989年 | 123篇 |
1988年 | 87篇 |
1987年 | 60篇 |
1986年 | 63篇 |
1985年 | 25篇 |
1984年 | 19篇 |
1983年 | 11篇 |
1982年 | 21篇 |
1981年 | 17篇 |
1980年 | 43篇 |
1979年 | 44篇 |
1973年 | 1篇 |
1959年 | 28篇 |
1958年 | 2篇 |
1951年 | 28篇 |
排序方式: 共有10000条查询结果,搜索用时 296 毫秒
91.
92.
93.
姜浩 《信息安全与通信保密》2006,(10):49-50
论文详细描述并分析了从RC5到RC6的演化设计过程,在详细研究了RC6性能的同时,指出了应该如何从一个旧的密码设计出好的新密码。最后对RC6和Rijndael作了一些比较,指出各自在性能上的优缺点。 相似文献
94.
95.
96.
97.
Hui Luo Wei Hao David H Foos Craig W Cornelius 《IEEE transactions on information technology in biomedicine》2006,10(2):302-311
Chest radiography is one of the most widely used techniques in diagnostic imaging. It comprises at least one-third of all diagnostic radiographic procedures in hospitals. However, in the picture archive and communication system, images are often stored with the projection and orientation unknown or mislabeled, which causes inefficiency for radiologists' interpretation. To address this problem, an automatic hanging protocol for chest radiographs is presented. The method targets the most effective region in a chest radiograph, and extracts a set of size-, rotation-, and translation-invariant features from it. Then, a well-trained classifier is used to recognize the projection. The orientation of the radiograph is later identified by locating the neck, heart, and abdomen positions in the radiographs. Initial experiments are performed on the radiographs collected from daily routine chest exams in hospitals and show promising results. Using the presented protocol, 98.2% of all cases could be hung correctly on projection view (without protocol, 62%), and 96.1% had correct orientation (without protocol, 75%). A workflow study on the protocol also demonstrates a significant improvement in efficiency for image display. 相似文献
98.
为了进一步提高渤海油田J3井区缔合聚合物驱的技术经济效果,在渤海油田室内配方和先导性矿场试验研究基础上,利用化学驱油藏数值模拟软件FAPMS,分析和研究了高浓度缔合聚合物前置段塞、主段塞的大小和浓度以及段塞组合方式对驱油效果的影响,优化设计了渤海绥中油田J3井区块矿场试验的最佳注入程序及段塞大小。结果表明,通过对不同浓度的疏水缔合聚合物注入的前置段塞及主段塞和梯度式后续段塞的优化后,原油采收率比未优化时提高了约10个百分点。研究表明,渤海油田应该高度重视聚合物驱的注入方式和段塞优化设计,进一步提高聚合物的技术经济效果。 相似文献
99.
Jinman Kim Weidong Cai Dagan Feng Hao Wu 《IEEE transactions on information technology in biomedicine》2006,10(3):598-607
The advances in digital medical imaging and storage in integrated databases are resulting in growing demands for efficient image retrieval and management. Content-based image retrieval (CBIR) refers to the retrieval of images from a database, using the visual features derived from the information in the image, and has become an attractive approach to managing large medical image archives. In conventional CBIR systems for medical images, images are often segmented into regions which are used to derive two-dimensional visual features for region-based queries. Although such approach has the advantage of including only relevant regions in the formulation of a query, medical images that are inherently multidimensional can potentially benefit from the multidimensional feature extraction which could open up new opportunities in visual feature extraction and retrieval. In this study, we present a volume of interest (VOI) based content-based retrieval of four-dimensional (three spatial and one temporal) dynamic PET images. By segmenting the images into VOIs consisting of functionally similar voxels (e.g., a tumor structure), multidimensional visual and functional features were extracted and used as region-based query features. A prototype VOI-based functional image retrieval system (VOI-FIRS) has been designed to demonstrate the proposed multidimensional feature extraction and retrieval. Experimental results show that the proposed system allows for the retrieval of related images that constitute similar visual and functional VOI features, and can find potential applications in medical data management, such as to aid in education, diagnosis, and statistical analysis. 相似文献
100.