全文获取类型
收费全文 | 4602篇 |
免费 | 359篇 |
国内免费 | 307篇 |
专业分类
电工技术 | 134篇 |
综合类 | 437篇 |
化学工业 | 163篇 |
金属工艺 | 175篇 |
机械仪表 | 277篇 |
建筑科学 | 1345篇 |
矿业工程 | 1479篇 |
能源动力 | 110篇 |
轻工业 | 64篇 |
水利工程 | 145篇 |
石油天然气 | 265篇 |
武器工业 | 21篇 |
无线电 | 22篇 |
一般工业技术 | 353篇 |
冶金工业 | 178篇 |
原子能技术 | 25篇 |
自动化技术 | 75篇 |
出版年
2024年 | 8篇 |
2023年 | 44篇 |
2022年 | 155篇 |
2021年 | 160篇 |
2020年 | 140篇 |
2019年 | 111篇 |
2018年 | 103篇 |
2017年 | 92篇 |
2016年 | 133篇 |
2015年 | 147篇 |
2014年 | 298篇 |
2013年 | 218篇 |
2012年 | 296篇 |
2011年 | 330篇 |
2010年 | 260篇 |
2009年 | 301篇 |
2008年 | 285篇 |
2007年 | 293篇 |
2006年 | 274篇 |
2005年 | 223篇 |
2004年 | 215篇 |
2003年 | 198篇 |
2002年 | 159篇 |
2001年 | 128篇 |
2000年 | 110篇 |
1999年 | 102篇 |
1998年 | 93篇 |
1997年 | 89篇 |
1996年 | 63篇 |
1995年 | 55篇 |
1994年 | 43篇 |
1993年 | 36篇 |
1992年 | 33篇 |
1991年 | 14篇 |
1990年 | 14篇 |
1989年 | 6篇 |
1988年 | 10篇 |
1987年 | 12篇 |
1986年 | 4篇 |
1985年 | 3篇 |
1984年 | 1篇 |
1983年 | 2篇 |
1981年 | 4篇 |
1980年 | 2篇 |
1978年 | 1篇 |
排序方式: 共有5268条查询结果,搜索用时 0 毫秒
51.
Once segmentation of 3D surface data of a rock pile has been performed, the next task is to determine the visibility of the surface rocks. A region boundary-following algorithm that accommodates irregularly spaced 3D coordinate data is presented for determining this visibility. We examine 3D surface segmentations of laboratory rock piles and determine which regions in the segmentation correspond to entirely visible rocks, and which correspond to overlapped or partially visible rocks. This is a significant distinction as it allows accurate size determination of entirely visible rocks, separate handling of partially visible rocks, and prevents erroneous bias resulting from mishandling partially visible rocks as smaller entirely visible rocks. Literature review indicates that other rock pile sizing techniques fail to make this distinction. The rock visibility results are quantified by comparison to manual surface classifications of the laboratory piles and the size results are quantified by comparison to the sieve size. 相似文献
52.
Mechanical model of anchorage surrounding rock considering tray effect was established based on elastic theory, in order to study the mechanism of bolt supporting. Elastic solutions of normal force at point in the interior of a semi-infinite solid were obtained by means of classical displacement function method in elasticity. The factors which influence stress of bolted surrounding rock, such as the length of bolt and tray effect, were analyzed. The absolute value of stress along bolt axes decreased rapidly with an increase in radical distance and the maximum appeared near ends of bolt. With increasing radical distance, the value of radical stress changed from positive to negative roughly and then increased to zero, with maximum at the middle of bolt. The evolution of hoop stress as radical distance increasing was similar with stress along bolt axes. With an increase in depth, the radical effect ranges of all normal stress components were reduced. These suggest that the effect from tray on stress along bolt axes of bolted surrounding rock could be neglected, except near surface of surrounding rock. 相似文献
53.
Amin Manouchehrian Mostafa Sharifzadeh Rasoul Hamidzadeh Moghadam Tohid Nouri 《矿业科学技术学报(英文版)》2013,23(4):495-501
Recently, many regression models have been presented for prediction of mechanical parameters of rocks regarding to rock index properties. Although statistical analysis is a common method for developing regression models, but still selection of suitable transformation of the independent variables in a regression model is difficult. In this paper, a genetic algorithm (GA) has been employed as a heuristic search method for selection of best transformation of the independent variables (some index properties of rocks) in regression models for prediction of uniaxial compressive strength (UCS) and modulus of elasticity (E). Firstly, multiple linear regression (MLR) analysis was performed on a data set to establish predictive models. Then, two GA models were developed in which root mean squared error (RMSE) was defined as fitness function. Results have shown that GA models are more precise than MLR models and are able to explain the relation between the intrinsic strength/elasticity properties and index properties of rocks by simple formulation and accepted accuracy. 相似文献
54.
55.
To predict joint development characteristics of coal seams, joint characteristics of rock seams from 88 field stations were observed and comparisons were made between joint characteristics of coal and rock seams at 10 coal outcrops. Additionally, detailed joint measurements of underground coal seams were taken at two coal mines. This study investigated the effects of seam thickness, lithology, and structure on joint development and established the relationship between joint development of coal and rock seams, which allowed predictions of predominant joint densities for the No.5 coal seam in the southeastern margin of the Ordos basin. The results show that outcrop and underground coal seams exhibit the same joint systems as rock seams. The joints are mainly upright. Predominant joints strike 55° on average, followed by joints striking 320°. The joint density of the coal seam is 18.7–22.5 times that of the sandstone seam at the same thickness. The predominant joint density of the No.5 coal seam, controlled by the structure, is ∼4–20 joints per meter. Joint densities exhibit high values at intersecting areas of faults and folds and decrease values in structurally stable areas. The permeability increases exponentially with increasing density of the predominant joints. 相似文献
56.
Yarahmadi Reza Bagherpour Raheb Kakaie Reza Mirzaie N. Hossein Yari Mojtaba 《矿业科学技术学报(英文版)》2014,24(2):191-194
Due to various geological processes such as tectonic activities fractures might be created in rock mass body which causes creation of blocks with different shapes and sizes in the rock body. Exact understanding of these blocks geometry is an essential issue concerned in different domains of rock engineering such as support system of underground spaces built in jointed rock masses, design of blasting pattern, optimization of fragmentation, determination of cube blocks in quarry mines, blocks stability, etc. The aim of this paper is to develop a computer program to determine geometry of rock mass blocks in two dimensional spaces. In this article, the geometry of jointed rock mass is programmed in MATLAB™. 相似文献
57.
玻璃纤维和玄武岩纤维杆体材料具有耐腐蚀性、轻质、高强等优良特性,比钢筋或钢绞线更适于用作锚杆材料。测试玻璃纤维和玄武岩纤维杆体的物理力学性质,结合现行规范对两种材料作为锚杆的设计进行探讨。结果表明:玻璃纤维和玄武岩纤维杆体比普通钢筋等杆体材料的抗拉强度高,质量更轻,参考相关规范设计,适于作为锚杆应用于岩土工程锚固。 相似文献
58.
为简化40SiMnCrNiMo钢钎具的热处理工艺,试验了880℃30min油冷+600℃60min空冷的调质处理,860℃30min空冷的正火和780℃30min空冷的两相区亚临界热处理后钢的组织和性能。结果表明,亚临界热处理后钢中贝氏体区HV显微硬度值低于正火钢,钢的V-型冲击功为30J,高于正火后钢V-型冲击功(12J),接近调质后的V-型冲击功(40J)。钎杆寿命试验得出,正火钢钎具平均钻孔进尺10.78m,亚临界热处理钢钎具平均钻孔进尺108.30m,可满足使用要求和替代调质处理钎杆。 相似文献
59.
ZHAO Yun-sheng WU Tai-xia LIU Bao LUO Yang-jie College of Urban Environmental Sciences Northeast Normal University Changchun Jilin China Foreign Languages Institute Northeast Normal University Changchun Jilin China 《中国矿业大学学报(英文版)》2005,15(3):192-196
1 IntroductionWhile the multi-spectral, multi-temporal andhyper-spectral remote sensing data are applied toenhance the ability to recognize the targets onground, more and more investigators have realizedthe influence and contribution of the angle informa-tion, namely the 3D spectrum characteristics of thetargets in 2π space, for recognizing and classifyingimages in remote sensing. The traditional unidirec-tional remote sensing can only obtain one directionprojection of targets; therefore it l… 相似文献
60.
Theory of Three-Dimensional Discontinuous Deformation Analysis and Its Application to a Slope Toppling at Amatoribashi, Japan 总被引:1,自引:0,他引:1
Jian-Hong Wu Yuzo Ohnishi Gen-Hua Shi Satoshi Nishiyama 《Canadian Metallurgical Quarterly》2005,5(3):179-195
A three-dimensional (3D) rock slope toppling occurred in a discontinuous rock mass. To simulate the failure process and study the mechanism of this rock failure with contact and large displacement in 3D, a new discrete numerical method has been developed called the 3D discontinuous deformation analysis (DDA). This article first introduces the basic principles and then derives the formulas in detail. Finally, the slope failure simulation is applied as an example to investigate the applicability of this new method to rock slope failure research. The simulation results indicate the advantages of using this new method to study the mechanism of a rock slope failure with 3D behavior. 相似文献