全文获取类型
收费全文 | 111329篇 |
免费 | 10251篇 |
国内免费 | 6183篇 |
专业分类
电工技术 | 7603篇 |
技术理论 | 9篇 |
综合类 | 10328篇 |
化学工业 | 16916篇 |
金属工艺 | 6522篇 |
机械仪表 | 7137篇 |
建筑科学 | 8679篇 |
矿业工程 | 3113篇 |
能源动力 | 3238篇 |
轻工业 | 10979篇 |
水利工程 | 2290篇 |
石油天然气 | 5453篇 |
武器工业 | 1076篇 |
无线电 | 11837篇 |
一般工业技术 | 11467篇 |
冶金工业 | 4292篇 |
原子能技术 | 1184篇 |
自动化技术 | 15640篇 |
出版年
2024年 | 506篇 |
2023年 | 1782篇 |
2022年 | 3544篇 |
2021年 | 4551篇 |
2020年 | 3495篇 |
2019年 | 2797篇 |
2018年 | 3025篇 |
2017年 | 3528篇 |
2016年 | 3128篇 |
2015年 | 4585篇 |
2014年 | 5785篇 |
2013年 | 6632篇 |
2012年 | 7765篇 |
2011年 | 8468篇 |
2010年 | 7675篇 |
2009年 | 7261篇 |
2008年 | 7286篇 |
2007年 | 6835篇 |
2006年 | 6508篇 |
2005年 | 5143篇 |
2004年 | 3960篇 |
2003年 | 3954篇 |
2002年 | 4618篇 |
2001年 | 3887篇 |
2000年 | 2619篇 |
1999年 | 2079篇 |
1998年 | 1366篇 |
1997年 | 1054篇 |
1996年 | 930篇 |
1995年 | 705篇 |
1994年 | 581篇 |
1993年 | 396篇 |
1992年 | 332篇 |
1991年 | 251篇 |
1990年 | 168篇 |
1989年 | 146篇 |
1988年 | 90篇 |
1987年 | 80篇 |
1986年 | 59篇 |
1985年 | 32篇 |
1984年 | 19篇 |
1983年 | 24篇 |
1982年 | 24篇 |
1981年 | 24篇 |
1980年 | 33篇 |
1979年 | 9篇 |
1965年 | 2篇 |
1960年 | 2篇 |
1959年 | 8篇 |
1951年 | 3篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
Pingkun Yan Wuxia Zhang Baris Turkbey Peter L. Choyke Xuelong Li 《Computer Vision and Image Understanding》2013,117(9):1017-1026
Organ shape plays an important role in clinical diagnosis, surgical planning and treatment evaluation. Shape modeling is a critical factor affecting the performance of deformable model based segmentation methods for organ shape extraction. In most existing works, shape modeling is completed in the original shape space, with the presence of outliers. In addition, the specificity of the patient was not taken into account. This paper proposes a novel target-oriented shape prior model to deal with these two problems in a unified framework. The proposed method measures the intrinsic similarity between the target shape and the training shapes on an embedded manifold by manifold learning techniques. With this approach, shapes in the training set can be selected according to their intrinsic similarity to the target image. With more accurate shape guidance, an optimized search is performed by a deformable model to minimize an energy functional for image segmentation, which is efficiently achieved by using dynamic programming. Our method has been validated on 2D prostate localization and 3D prostate segmentation in MRI scans. Compared to other existing methods, our proposed method exhibits better performance in both studies. 相似文献
992.
This paper proposes an improved semi-fragile speech watermarking scheme by quantization of linear prediction (LP) parameters, i.e., the inverse sine (IS) parameters. The spectral distortion due to watermark embedding is controlled to meet the ‘transparency’ criterion in speech coding. A modified bit allocation algorithm combined with watermarking is developed to determine the quantization step so that the ‘transparency’ requirement is satisfied. Due to the statistical nature, the LP coefficients estimated from the watermarked speech signal are different from the watermarked LP coefficients even in the absence of attacks. This effect is the cause of increase in decoding error and minimum authentication length. To tackle this problem, an Analysis by Synthesis (AbS) scheme is developed to reduce the difference between the estimated LP coefficients and the watermarked ones. The watermark detection threshold and minimum authentication length are then derived according to the probability of error and the signal to noise ratio (SNR) requirements. Experimental results show that the proposed AbS based method can effectively reduce the difference between the watermarked IS parameter and the extracted IS parameter when there is no attacks. In addition, the modified bit allocation algorithm can automatically find the appropriate quantization step used in the odd-even modulation so that the transparency requirement is satisfied. 相似文献
993.
Guanhua Yan 《Computer Networks》2013,57(2):540-555
In order to evade detection of ever-improving defense techniques, modern botnet masters are constantly looking for new communication platforms for delivering C&C (Command and Control) information. Attracting their attention is the emergence of online social networks such as Twitter, as the information dissemination mechanism provided by these networks can naturally be exploited for spreading botnet C&C information, and the enormous amount of normal communications co-existing in these networks makes it a daunting task to tease out botnet C&C messages.Against this backdrop, we explore graph-theoretic techniques that aid effective monitoring of potential botnet activities in large open online social networks. Our work is based on extensive analysis of a Twitter dataset that contains more than 40 million users and 1.4 billion following relationships, and mine patterns from the Twitter network structure that can be leveraged for improving efficiency of botnet monitoring. Our analysis reveals that the static Twitter topology contains a small-sized core sugraph, after removing which, the Twitter network breaks down into small connected components, each of which can be handily monitored for potential botnet activities. Based on this observation, we propose a method called Peri-Watchdog, which computes the core of a large online social network and derives the set of nodes that are likely to pass botnet C&C information in the periphery of online social network. We analyze the time complexity of Peri-Watchdog under its normal operations. We further apply Peri-Watchdog on the Twitter graph injected with synthetic botnet structures and investigate the effectiveness of Peri-Watchdog in detecting potential C&C information from these botnets.To verify whether patterns observed from the static Twitter graph are common to other online social networks, we analyze another online social network dataset, BrightKite, which contains evolution of social graphs formed by its users in half a year. We show not only that there exists a similarly relatively small core in the BrightKite network, but also this core remains stable over the course of BrightKite evolution. We also find that to accommodate the dynamic growth of BrightKite, the core has to be updated about every 18 days under a constrained monitoring capacity. 相似文献
994.
Data interoperability between computer-aided design (CAD) systems remains a major obstacle in the information integration and exchange in a collaborative engineering environment. The use of CAD data exchange standards causes the loss of design intent such as construction history, features, parameters, and constraints, whereas existing research on feature-based data exchange only focuses on class-level feature definitions and does not support instance-level verification, which causes ambiguity in data exchange. In this paper, a hybrid ontology approach is proposed to allow for the full exchange of both feature definition semantics and geometric construction data. A shared base ontology is used to convey the most fundamental elements of CAD systems for geometry and topology, which is to both maximize flexibility and minimize information loss. A three-branch hybrid CAD feature model that includes feature operation information at the boundary representation level is constructed. Instance-level feature information in the form of the base ontology is then translated to local ontologies of individual CAD systems during the rule-based mapping and verification process. A combination of the Ontology Web Language (OWL) and Semantic Web Rule Language (SWRL) is used to represent feature classes and properties and automatically classify them by a reasoner in the target system, which requires no knowledge about the source system. 相似文献
995.
淮河流域水质污染时空变异特征分析 总被引:15,自引:0,他引:15
选取淮河流域的82个水质监测站,对各站点的1986—2005年水质监测数据进行统计分析,探讨了全流域内水体污染物浓度变化的时空变异特征,为淮河流域水污染治理、水环境保护以及生态修复提供依据。采用时间序列法分析水体污染物浓度的时间变化规律,应用Mann-Kendall检验法对流域范围内水体污染物浓度变化趋势进行了分析。研究结果表明,淮河流域水质变化主要受到入河排污量、上游来水量、闸坝调控方式以及气候条件等方面因素的影响。蚌埠站的水体污染物浓度多年变化规律表明,1995年是水体污染物浓度变化的转折点,1995年前水体污染物浓度不断恶化,1995年后水体污染物浓度逐渐好转。DO浓度的年内变化主要受到水温的影响,表现为冬季浓度高于夏季浓度;CODMn浓度同时受到闸坝调控方式以及区域来水量的影响,汛期浓度低于非汛期。从全流域的水体污染物浓度变化规律看,有机污染物浓度呈显著上升趋势的河段主要分布在淮北支流上,说明在20世纪90年代后期,虽然流域进入相对丰水期以及进行了大规模的水污染联防工作,淮河流域水质污染得到了一定程度的改善。但在2000年后,随着流域内入河污水量和污染物排放量的增加,淮河流域的水质污染依然严重。 相似文献
996.
997.
998.
Drag reduction experiment of the traveling wavy wall at high Reynolds number is conducted.A suit of traveling wavy wall device is developed.The drag forces of the traveling wavy wall with various wave speeds(c)are measured under different water speeds(U)in the K15 cavitation water tunnel and are compared with that of the flat plate.The results show that the mean drag force of the traveling wavy wall have decreased and then increased with oscillation frequency increasing at the same flow speed.Under different flow speeds,when traveling wave wall reached to the minimum of drag force,the corresponding the ratio of the wall motion phase speed c to flow speed U,c /U is slightly different.Within the parameters of the experiment,whenc /U reaches a certain value,the drag force of the traveling wavy wall can be less than that of the flat plate.The drag reduction can be up to 42%.Furthermore,as the value ofc /U increases,the traveling wavy wall can restrain the separation and improve the quality of flow field. 相似文献
999.
以我国现行典型城市污水处理厂实际运行情况为依托,结合国内外经验成果,在筛选影响城市污水处理厂节能水平重要因子的前提下,初步提出采用打分形式对城市污水处理厂节能水平进行评估的设想,从而建立城市污水处理厂节能水平等级划分标准。 相似文献
1000.