全文获取类型
收费全文 | 35688篇 |
免费 | 4118篇 |
国内免费 | 2531篇 |
专业分类
电工技术 | 2833篇 |
技术理论 | 1篇 |
综合类 | 3686篇 |
化学工业 | 5221篇 |
金属工艺 | 2318篇 |
机械仪表 | 2311篇 |
建筑科学 | 2869篇 |
矿业工程 | 1350篇 |
能源动力 | 937篇 |
轻工业 | 4061篇 |
水利工程 | 1070篇 |
石油天然气 | 1571篇 |
武器工业 | 550篇 |
无线电 | 3574篇 |
一般工业技术 | 3048篇 |
冶金工业 | 1529篇 |
原子能技术 | 590篇 |
自动化技术 | 4818篇 |
出版年
2024年 | 159篇 |
2023年 | 660篇 |
2022年 | 1475篇 |
2021年 | 1936篇 |
2020年 | 1349篇 |
2019年 | 934篇 |
2018年 | 1069篇 |
2017年 | 1183篇 |
2016年 | 1037篇 |
2015年 | 1654篇 |
2014年 | 2049篇 |
2013年 | 2509篇 |
2012年 | 2979篇 |
2011年 | 2954篇 |
2010年 | 2802篇 |
2009年 | 2669篇 |
2008年 | 2650篇 |
2007年 | 2486篇 |
2006年 | 2112篇 |
2005年 | 1657篇 |
2004年 | 1154篇 |
2003年 | 931篇 |
2002年 | 909篇 |
2001年 | 834篇 |
2000年 | 689篇 |
1999年 | 393篇 |
1998年 | 214篇 |
1997年 | 191篇 |
1996年 | 167篇 |
1995年 | 109篇 |
1994年 | 91篇 |
1993年 | 59篇 |
1992年 | 46篇 |
1991年 | 33篇 |
1990年 | 37篇 |
1989年 | 28篇 |
1988年 | 23篇 |
1987年 | 18篇 |
1986年 | 18篇 |
1985年 | 7篇 |
1984年 | 7篇 |
1983年 | 4篇 |
1982年 | 5篇 |
1981年 | 9篇 |
1980年 | 6篇 |
1979年 | 4篇 |
1974年 | 3篇 |
1965年 | 3篇 |
1959年 | 4篇 |
1951年 | 12篇 |
排序方式: 共有10000条查询结果,搜索用时 375 毫秒
61.
62.
63.
64.
65.
Effect of process parameters on impact strength of Al-7% Si alloy castings produced by VAEPC process 总被引:2,自引:2,他引:0
Sudhir Kumar Pradeep Kumar H. S. Shan 《The International Journal of Advanced Manufacturing Technology》2008,38(5-6):586-593
The castings produced by the evaporative pattern casting (EPC) process have blow holes. The blow holes in EPC castings are because of the non-escape of the gas produced as a result of burning of polystyrene pattern in the sand mold. To overcome the problem of blow holes, the EPC process is combined with the vacuum (V)- process. The vacuum applied to EPC mold draws the decomposed gases and improves the casting quality produced by the EPC process. The developed hybrid process has been termed as the vacuum assisted evaporative pattern casting (VAEPC) process. The objective of this paper to investigates the effect of process parameters, i.e, degree of vacuum, pouring temperature, grainfineness number, amplitude of vibration and time of vibration on the impact strength of Al-7% Si alloy castings in VAEPC process. In order to evaluate the effect of selected process parameters, the response surface methodology (RSM) is used to formulate a mathematical model which correlates the independent process parameters with the desired impact strength. The central composite rotatable design has been used to conduct the experiments. The results indicate that the impact strength decreases with increases in the grainfineness number and pouring temperature. Whereas, it has an inverse relationship with amplitude of vibration, time of vibration and degree of vacuum. The best value of impact strength (2.34 N/mm2) has been obtained at 400 mm Hg degree of vacuum imposed, 650°C as pouring temperature, 60 as sand grainfineness number, 460 μm as amplitude of vibration, and 70 s as time of vibration. 相似文献
66.
67.
苏里格低渗强非均质性气田开发技术对策探讨 总被引:29,自引:2,他引:27
鄂尔多斯盆地苏里格气田储集层具有低渗、强非均质性、中强压敏的特点,气井产能低,稳产期短。根据单井模拟及生产动态分析,气井低产量生产可以降低压敏效应的影响,加强气井低产量生产阶段的管理,有利于合理利用地层能量,提高井控外围低渗区储量动用程度;分层压裂、多层合采可以在纵向上充分动用气井控制储量,增加气井最终累计产气量和稳产时间;地质研究与地震相结合,是提高储集层预测精度和钻井成功率的技术关键;降低成本,争取优惠政策也是提高经济效益的有效途径。 相似文献
68.
69.
Similarity retrieval of iconic image database 总被引:3,自引:0,他引:3
The perception of spatial relationships among objects in a picture is one of the important selection criteria to discriminate and retrieve the images in an iconic image database system. The data structure called 2D string, proposed by Chang et al., is adopted to represent symbolic pictures. The 2D string preserves the objects' spatial knowledge embedded in images. Since spatial relationship is a fuzzy concept, the capability of similarity retrieval for the retrieval by subpicture is essential. In this paper, similarity measure based on 2D string longest common subsequence is defined. The algorithm for similarity retrieval is also proposed. Similarity retrieval provides the iconic image database with the distinguishing function different from a conventional database. 相似文献
70.
MRI fuzzy segmentation of brain tissue using neighborhood attraction with neural-network optimization. 总被引:11,自引:0,他引:11
Shan Shen William Sandham Malcolm Granat Annette Sterr 《IEEE transactions on information technology in biomedicine》2005,9(3):459-467
Image segmentation is an indispensable process in the visualization of human tissues, particularly during clinical analysis of magnetic resonance (MR) images. Unfortunately, MR images always contain a significant amount of noise caused by operator performance, equipment, and the environment, which can lead to serious inaccuracies with segmentation. A robust segmentation technique based on an extension to the traditional fuzzy c-means (FCM) clustering algorithm is proposed in this paper. A neighborhood attraction, which is dependent on the relative location and features of neighboring pixels, is shown to improve the segmentation performance dramatically. The degree of attraction is optimized by a neural-network model. Simulated and real brain MR images with different noise levels are segmented to demonstrate the superiority of the proposed technique compared to other FCM-based methods. This segmentation method is a key component of an MR image-based classification system for brain tumors, currently being developed. Index Terms-Improved fuzzy c-means clustering (IFCM), magnetic resonance imaging (MRI), neighborhood attraction, segmentation. 相似文献