全文获取类型
收费全文 | 12341篇 |
免费 | 463篇 |
国内免费 | 362篇 |
专业分类
电工技术 | 201篇 |
综合类 | 911篇 |
化学工业 | 329篇 |
金属工艺 | 2489篇 |
机械仪表 | 4451篇 |
建筑科学 | 202篇 |
矿业工程 | 530篇 |
能源动力 | 124篇 |
轻工业 | 185篇 |
水利工程 | 33篇 |
石油天然气 | 1063篇 |
武器工业 | 66篇 |
无线电 | 271篇 |
一般工业技术 | 688篇 |
冶金工业 | 368篇 |
原子能技术 | 28篇 |
自动化技术 | 1227篇 |
出版年
2024年 | 33篇 |
2023年 | 123篇 |
2022年 | 235篇 |
2021年 | 247篇 |
2020年 | 320篇 |
2019年 | 206篇 |
2018年 | 226篇 |
2017年 | 338篇 |
2016年 | 350篇 |
2015年 | 414篇 |
2014年 | 600篇 |
2013年 | 634篇 |
2012年 | 766篇 |
2011年 | 790篇 |
2010年 | 542篇 |
2009年 | 584篇 |
2008年 | 567篇 |
2007年 | 816篇 |
2006年 | 790篇 |
2005年 | 729篇 |
2004年 | 637篇 |
2003年 | 583篇 |
2002年 | 487篇 |
2001年 | 430篇 |
2000年 | 330篇 |
1999年 | 290篇 |
1998年 | 224篇 |
1997年 | 204篇 |
1996年 | 165篇 |
1995年 | 135篇 |
1994年 | 108篇 |
1993年 | 76篇 |
1992年 | 45篇 |
1991年 | 41篇 |
1990年 | 27篇 |
1989年 | 20篇 |
1988年 | 18篇 |
1987年 | 10篇 |
1986年 | 4篇 |
1985年 | 5篇 |
1984年 | 4篇 |
1983年 | 2篇 |
1982年 | 4篇 |
1981年 | 2篇 |
1979年 | 2篇 |
1975年 | 1篇 |
1958年 | 1篇 |
1955年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
21.
在川渝地区,钻定向井、水平井必然要面对地层岩性变化大、硬度高等复杂地质情况,常常会遇到因井下复杂、事故、修改地质目标等原因需要填井侧钻。侧钻的方法不同,侧钻的成功率和效率差异很大。文中分析了川渝地区近几年硬地层定向井、水平井侧钻效率不高、有时甚至失败的原因,归纳总结了近几年常用的几种侧钻方法的施工效果,提出要根据具体条件灵活应用这几种侧钻方法。 相似文献
22.
23.
In conformity with the principle of Design for Manufacture,feature-based design strate-(?)es have been developed.As the“feature”is relevant to the“macro process plan”and“macro NCprograms”,obviously,“feature”is beyond the power of conventional solid modellers.Neverthe-less,substantial breakthrough has not been made in the solid modeling field,except“feature at-taching”or“feature recognizing”methods have been taken on.In this paper,the theory,concepts,system architecture,and algorithm principles of solid modeling tool system have beenrepresented.The practice of Feature Solid Modeling Tool System (FSMTS) developed atHuazhong University has proved that the tool may be a new foundation of Feature-Based Design. 相似文献
25.
酒泉盆地青西油田快速钻井技术 总被引:3,自引:1,他引:2
酒泉盆地青西地区油层储藏深 ,地层可钻性差 ,钻井过程中存在机械钻速低、井斜不易控制、刺断钻具频繁等问题。为此 ,在近年的钻井实践中 ,采取了优化钻具组合、优选钻头、应用 PDC钻头、强化钻具管理等措施 ,使该区块的钻井速度不断提高 ,钻井周期缩短 ,钻头用量减少 ,从而形成了一套适合该区块的快速钻井技术。 相似文献
26.
对发动机连杆螺纹孔在攻丝过程中出现烂牙、粗糙度差等加工质量问题进行了分析,提出了解决问题的方法,使连杆的合格率行到显著的提高。 相似文献
27.
In this paper we develop and compare several heuristic methods for solving the general two-dimensional cutting stock problem.
We follow the Gilmore-Gomory column generation scheme in which at each iteration a new cutting pattern is obtained as the
solution of a subproblem on one stock sheet. For solving this subproblem, in addition to classical dynamic programming, we
have developed three heuristic procedures of increasing complexity, based on GRASP and Tabu Search techniques, producing solutions
differing in quality and in time requirements. In order to obtain integer solutions from the fractional solutions of the Gilmore-Gomory
process, we compare three rounding procedures, rounding up, truncated branch and bound and the solution of a residual problem.
We have coded and tested all the combinations of algorithms and rounding procedures. The computational results obtained on
a set of randomly generated test problems show their relative efficiency and allow the potential user to choose from among
them, according to the available computing time.
Rceived: January 9, 2001 / Accepted: December 10, 2001 相似文献
28.
29.
The forces, chip thickness, and natural tool–chip contact length in machining with a double-rake-angled tool are predicted in Part II of the present study. It is revealed that in comparison with a single-rake-angled tool, a double-rake-angled tool increases the forces, especially the thrust force. However, the increase in chip thickness and tool–chip contact length is not significant under the input conditions specified in the present study. The effect of seven input variables of the proposed model is quantitatively investigated. The predicted variations of forces, chip thickness, and natural tool–chip contact length are in good agreement with theoretical and experimental results obtained by other researchers. The interrelationships among the resultant force, the chip thickness, and the natural tool–chip contact length are established, which provides a new and promising method to estimate the tool–chip contact length by employing the resultant force. It is demonstrated that the model can also be extended to study the problem of machining with a groove-type chip breaker tool. 相似文献
30.
《Materials and Manufacturing Processes》2006,21(8):819-823
Linear elastic fracture mechanics was used to optimize the vacuum heat-treatment procedures for conventional hot-work AISI H11 tool steel. The fracture toughness was determined with non-standard, circumferentially notched and fatigue-precracked tensile-test specimens. The fracture-testing method is sensitive to changes caused by variations in the microstructure resulting from the austenitizing and tempering temperatures as well as the homogeneity of the material itself. The combined tempering diagram- Rockwell-C hardness, Fracture toughness KIc, Tempering temperature was used for the choice of the vacuum heat-treatment parameters necessary to obtain the best properties for a given application with respect to the investigated steel. 相似文献