全文获取类型
收费全文 | 126325篇 |
免费 | 10360篇 |
国内免费 | 4950篇 |
专业分类
电工技术 | 7160篇 |
技术理论 | 7篇 |
综合类 | 7605篇 |
化学工业 | 22135篇 |
金属工艺 | 6610篇 |
机械仪表 | 7426篇 |
建筑科学 | 10130篇 |
矿业工程 | 3522篇 |
能源动力 | 3709篇 |
轻工业 | 8500篇 |
水利工程 | 2203篇 |
石油天然气 | 7330篇 |
武器工业 | 877篇 |
无线电 | 13939篇 |
一般工业技术 | 15424篇 |
冶金工业 | 7631篇 |
原子能技术 | 1385篇 |
自动化技术 | 16042篇 |
出版年
2024年 | 557篇 |
2023年 | 2067篇 |
2022年 | 3611篇 |
2021年 | 4980篇 |
2020年 | 3834篇 |
2019年 | 3240篇 |
2018年 | 3496篇 |
2017年 | 4031篇 |
2016年 | 3425篇 |
2015年 | 4798篇 |
2014年 | 5876篇 |
2013年 | 7218篇 |
2012年 | 7700篇 |
2011年 | 8332篇 |
2010年 | 7237篇 |
2009年 | 6940篇 |
2008年 | 6794篇 |
2007年 | 6429篇 |
2006年 | 6652篇 |
2005年 | 5776篇 |
2004年 | 3991篇 |
2003年 | 3524篇 |
2002年 | 3287篇 |
2001年 | 2950篇 |
2000年 | 3091篇 |
1999年 | 3302篇 |
1998年 | 2792篇 |
1997年 | 2393篇 |
1996年 | 2211篇 |
1995年 | 1964篇 |
1994年 | 1604篇 |
1993年 | 1184篇 |
1992年 | 993篇 |
1991年 | 768篇 |
1990年 | 600篇 |
1989年 | 558篇 |
1988年 | 469篇 |
1987年 | 358篇 |
1986年 | 284篇 |
1985年 | 243篇 |
1984年 | 200篇 |
1983年 | 167篇 |
1982年 | 193篇 |
1981年 | 165篇 |
1980年 | 124篇 |
1979年 | 133篇 |
1978年 | 123篇 |
1977年 | 103篇 |
1974年 | 90篇 |
1973年 | 99篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
992.
Nanocomposite powders from polypropylene filled with surface modified and unmodified fumed silica have been prepared from polymer solution to achieve improved mixing and have been forwarded to fiber melt spinning. The surface of the fumed silica was modified with dodecyl alkoxy silanes. Crystallization velocity and viscosity of the PP nanocomposites thereof were determined to ensure good melt spinning processing conditions for all composite compositions. Upon addition of untreated filler particles, a shear thinning and an increased crystallization velocity of the polymer melt was found, while only minor changes were detected in the presence of surface modified fumed silica particles. The composites and the polymer fibers made from these powder composites by melt spinning were mainly characterized by optical microscopy (OM), scanning electron microscopy (SEM), mechanical measurements, differential scanning calorimetry (DSC), and solid‐state NMR. The unmodified fumed silica was found to have a strong influence on the mechanical fiber properties, while the surface modified silica only a small one. Fibers were additionally characterized with respect to the uniformity, the PP crystallinity, moisture absorption, and the water contact angle. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 218–227, 2007 相似文献
993.
山东东华水泥有限公司是隶属于淄博矿业集团有限责任公司的子公司,东华水泥5000t/d新型干法水泥熟料线是淄矿建设“煤、电、材”产业链的建材板块龙头项目,第一条5000t/d水泥熟料生产线已于2005年2月投产,目前生产稳定,产品质量优良。配套200万吨粉磨站于2005年11月顺利投产。东华公司根据本公司的实际情况,结合国家资源综合利用的产业政策,委托天津水泥工业设计院设计,利用5000t/d水泥熟料生产线的余热配套一座纯低温余热电站(同时对2号5000t/d水泥熟料生产线配套余热电站进行规划)。 相似文献
994.
Commutative Encryption and Watermarking (CEW) is a technology combined with encryption and watermarking, which is used for providing comprehensive security protection for multimedia information. This paper presents a novel CEW scheme based on orthogonal decomposition. Different from current CEW, the proposed CEW not only achieves the integration of encryption and watermarking in the final data but also has no specific restrictions in selecting encryption and watermarking algorithms. Therefore, the proposed CEW possesses higher security and applicability. Experimental results demonstrate that the proposed CEW can keep the performances of selected encryption and watermarking algorithm and show more robustness than other current CEW schemes. 相似文献
995.
Automatic detection and precise localization of human eye centers are the essential processes in photo related multimedia applications. Since eye center points are used as reference base points for further intelligent processing, precise eye center localization is very important. In face recognition the accuracy of localization of eye centers directly influences the identification accuracy. A multiple stage approach with multiple cues for detection and precise localization of eye centers is presented in this paper. Multiple scopes searching strategy is used for correctly extracting eye patch images from the background. Dedicated gradient based features and curvelet based features are constructed and used for comprehensively revealing the intensity distribution characteristics and the edge based texture around eye centers. A rebuilt score calculation mechanism is proposed and the rebuilt scores are used as a specific measurement index reflecting the matching accuracy. The final localizations of eye centers are determined with integrating the gradient based scores and curvelet based scores. The experiment results testing on public face datasets show that the localization accuracy of proposed approach outperforms the accuracy with other state of the art methods. 相似文献
996.
Dynamics modeling and analysis of a flexible-base space robot for capturing large flexible spacecraft 总被引:2,自引:0,他引:2
Wenfu Xu Deshan Meng Yongquan Chen Huihuan Qian Yangsheng Xu 《Multibody System Dynamics》2014,32(3):357-401
Space robots are in huge demand due to the rapid growth of their service targets, i.e., spacecraft. There are generally large flexible components on spacecraft, such as antenna reflectors and solar paddles. Due to the vibratility of their structure, it is challenging for a space robot with flexible appendages (the base is then called flexible-base) to capture and repair the large flexible spacecraft. After capturing, the two spacecraft with flexible appendages are connected by a space manipulator, and a compounded system is formed. In this paper, we developed a dynamic model and a closed-loop simulation system, to provide a means to verify path planning and control algorithms. Initially, the dynamic characteristics of different capturing stages (preimpact and post-impact) were analyzed. The topologies of a flexible-base space robot and the compounded system were described based on incidence and channel matrices. Secondly, the recursive dynamics was formulated and resolved by an effective numerical method. The modeling was verified by Adams’ model. Thirdly, we implemented a dynamics calculation block in Matlab/Simulink environment using the S-function package for the C program, and developed a closed-loop simulation system, which was composed of the Planning and Controller, the Multibody Dynamic, and the 3D Display modules. Finally, based on the simulation system, two typical missions—target berthing and on-orbital manipulation of the target along a circle, were simulated and evaluated. Dynamics analysis results presented some useful rules for the path planning and control to suppress the vibration of the flexible structure. 相似文献
997.
Association Link Network (ALN) is a kind of Semantic Link Network built by mining the association relations among multimedia Web resources for effectively supporting Web intelligent application such as Web-based learning, and semantic search. This paper explores the Small-World properties of ALN to provide theoretical support for association learning (i.e., a simple idea of “learning from Web resources”). First, a filtering algorithm of ALN is proposed to generate the filtered status of ALN, aiming to observe the Small-World properties of ALN at given network size and filtering parameter. Comparison of the Small-World properties between ALN and random graph shows that ALN reveals prominent Small-World characteristic. Then, we investigate the evolution of Small-World properties over time at several incremental network sizes. The average path length of ALN scales with the network size, while clustering coefficient of ALN is independent of the network size. And we find that ALN has smaller average path length and higher clustering coefficient than WWW at the same network size and network average degree. After that, based on the Small-World characteristic of ALN, we present an Association Learning Model (ALM), which can efficiently provide association learning of Web resources in breadth or depth for learners. 相似文献
998.
Guofeng Zhao Minchang Yu Chuan Xu Hong Tang 《通讯和计算机》2014,(1):59-65
Generating web traffic is of great importance to analyze performance of new designed network, test new equipment, and verify new protocols, etc.. However, most existing traffic generation systems tend to simulate the overall characteristics of network traffic, while neglecting of the behavior of the individual users. Nevertheless, in principle, the emerged characteristics of overall traffic originate from the aggregation of individual users' access behavior. In this paper, we propose an innovative web traffic generating method based on user browsing behavior. Our method simulates the real users' accessing behavior, and visits the real web servers. Then, we design and develop a web traffic generating system. Because our system accesses the real websites, it can produce almost the real network traffic. The test results show that the traffic generated by our system has characteristics of burstiness and self-similarity, which are widely found and characterized in many real networks. In addition, our system can better reflect real user's web browsing behavior. 相似文献
999.
Sihua Xu Glenn W. Patterson William R. Lusby Kathy M. Schmid Thomas A. Salt 《Lipids》1990,25(1):61-64
Twenty-one species in the Chenopodiaceae were analyzed for sterol composition. In ten of eleven species ofChenopodium, the major desmethylsterols were Δ7-sterols accompanied by lower proportions of Δ5-sterols. InC. fremontii this pattern was reversed. The sterol profiles of five species ofAtriplex were characterized by the coexistence of Δ7- and Δ5-sterols in ratios of 0.3∶1 to 0.4∶1. MaleAtriplex plants contained higher proportions of Δ5-sterols than femaleAtriplex plants. OneCeratoides and twoSalicornia species contained Δ5-sterols as their predominant sterols. 相似文献
1000.