全文获取类型
收费全文 | 72267篇 |
免费 | 6766篇 |
国内免费 | 3808篇 |
专业分类
电工技术 | 5046篇 |
技术理论 | 6篇 |
综合类 | 5271篇 |
化学工业 | 11371篇 |
金属工艺 | 4130篇 |
机械仪表 | 4277篇 |
建筑科学 | 6215篇 |
矿业工程 | 1786篇 |
能源动力 | 2085篇 |
轻工业 | 5136篇 |
水利工程 | 1339篇 |
石油天然气 | 3900篇 |
武器工业 | 610篇 |
无线电 | 8620篇 |
一般工业技术 | 8662篇 |
冶金工业 | 3063篇 |
原子能技术 | 968篇 |
自动化技术 | 10356篇 |
出版年
2024年 | 396篇 |
2023年 | 1325篇 |
2022年 | 2247篇 |
2021年 | 3219篇 |
2020年 | 2304篇 |
2019年 | 1866篇 |
2018年 | 2139篇 |
2017年 | 2401篇 |
2016年 | 2129篇 |
2015年 | 2945篇 |
2014年 | 3529篇 |
2013年 | 4345篇 |
2012年 | 4706篇 |
2011年 | 4917篇 |
2010年 | 4432篇 |
2009年 | 4132篇 |
2008年 | 4242篇 |
2007年 | 3995篇 |
2006年 | 3994篇 |
2005年 | 3404篇 |
2004年 | 2383篇 |
2003年 | 2178篇 |
2002年 | 2300篇 |
2001年 | 2044篇 |
2000年 | 1750篇 |
1999年 | 1815篇 |
1998年 | 1330篇 |
1997年 | 1185篇 |
1996年 | 1135篇 |
1995年 | 903篇 |
1994年 | 746篇 |
1993年 | 538篇 |
1992年 | 477篇 |
1991年 | 347篇 |
1990年 | 244篇 |
1989年 | 206篇 |
1988年 | 178篇 |
1987年 | 114篇 |
1986年 | 75篇 |
1985年 | 60篇 |
1984年 | 37篇 |
1983年 | 24篇 |
1982年 | 35篇 |
1981年 | 21篇 |
1980年 | 20篇 |
1979年 | 10篇 |
1978年 | 5篇 |
1974年 | 3篇 |
1959年 | 2篇 |
1951年 | 6篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
31.
32.
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
33.
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
34.
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
35.
化学还原法制备纳米铜粉的研究 总被引:18,自引:1,他引:17
本文采用KBH4在液相中化学还原CuSO4,并加入KOH和络合剂EDTA ,制得了纳米级的纯净的铜粉 ,通过调整反应物的浓度 ,可以消除Cu2 O等杂质。制备的纳米铜粉还存在一定程度的团聚 ,需试验加入分散剂来改善。 相似文献
36.
石蜡微胶囊中脲醛树脂壁材渗透性的研究 总被引:7,自引:0,他引:7
利用差示扫描量热法研究了石蜡微胶囊中脲醛树脂壁材对水及甲苯的渗透性 ,结果表明 ,水不能透过脲醛树脂壁材 ,而甲苯则易透过脲醛树脂壁材。因此 ,该石蜡微胶囊不能用于芳香族溶剂存在的场合。 相似文献
37.
J Shan 《Canadian Metallurgical Quarterly》1997,32(6):323-325
Between 1990 and 1992, external sphincter repair was performed in 20 patients rendered faecally incontinent after earlier fistula surgery. All were improved, 13 (65%) achieving Grade 1 or 2 continence. Postoperative ultrasound was useful in explaining the sub-optimal outcome of 3 patients who still had defects. Clinical outcome in female patients was better than in male patients. Clinical outcome was not related to the results of preoperative manometry, the site of external sphincter damage, the use of a stoma, or the occurrence of wound complications. External sphincter repair for faecal incontinence after fistula surgery achieves good results in the majority of patients. 相似文献
38.
In this article, a new algorithm based on an artificial potential field and hierarchical cell decomposition technique is developed to solve the find-path problem for a mobile robot. The complete map of the workspace including obstacle locations is assumed to be known a priori. The basic cell structure used for decomposition is a hexagon. The artificial potential field is based on an attractive force from the goal position and repelling forces from the obstacles. Computer simulations of the algorithm for various obstacle scenarios are also presented. © 1994 John Wiley & Sons, Inc. 相似文献
39.
在各糖厂现用连续离心机原有生产实践基础上,对其机械吸震、加温、布温、机索结构、物料密封、机座等部件做了进一步改进,并取得可观的实效。 相似文献
40.
利用挤压铸造制备氧化铝/锌合金复合材料,在扫描电镜(SEM)上观察复合材料的界面。结果表明,在复合材料中纤维与基体间存在致密界面层,合金元素通过适当的化学反应可改善纤维与基体间的结合;在凝固过程中,纤维/基体界面上的硅在共晶体的共生生长过程中起了领先相作用,导致复合材料的共晶转变是由铝硅共晶转变和锌铝共晶转变两者组成。 相似文献