全文获取类型
收费全文 | 82654篇 |
免费 | 6840篇 |
国内免费 | 3385篇 |
专业分类
电工技术 | 4665篇 |
技术理论 | 6篇 |
综合类 | 5183篇 |
化学工业 | 14103篇 |
金属工艺 | 4391篇 |
机械仪表 | 5346篇 |
建筑科学 | 6059篇 |
矿业工程 | 2678篇 |
能源动力 | 2508篇 |
轻工业 | 5799篇 |
水利工程 | 1260篇 |
石油天然气 | 5647篇 |
武器工业 | 565篇 |
无线电 | 8759篇 |
一般工业技术 | 10449篇 |
冶金工业 | 4250篇 |
原子能技术 | 857篇 |
自动化技术 | 10354篇 |
出版年
2024年 | 399篇 |
2023年 | 1514篇 |
2022年 | 2607篇 |
2021年 | 3556篇 |
2020年 | 2653篇 |
2019年 | 2347篇 |
2018年 | 2702篇 |
2017年 | 2907篇 |
2016年 | 2464篇 |
2015年 | 3208篇 |
2014年 | 4073篇 |
2013年 | 4830篇 |
2012年 | 5029篇 |
2011年 | 5589篇 |
2010年 | 4819篇 |
2009年 | 4562篇 |
2008年 | 4394篇 |
2007年 | 4186篇 |
2006年 | 4228篇 |
2005年 | 3762篇 |
2004年 | 2550篇 |
2003年 | 2286篇 |
2002年 | 2081篇 |
2001年 | 1834篇 |
2000年 | 1898篇 |
1999年 | 2176篇 |
1998年 | 1832篇 |
1997年 | 1488篇 |
1996年 | 1467篇 |
1995年 | 1226篇 |
1994年 | 975篇 |
1993年 | 741篇 |
1992年 | 560篇 |
1991年 | 437篇 |
1990年 | 340篇 |
1989年 | 261篇 |
1988年 | 236篇 |
1987年 | 144篇 |
1986年 | 128篇 |
1985年 | 98篇 |
1984年 | 68篇 |
1983年 | 43篇 |
1982年 | 45篇 |
1981年 | 32篇 |
1980年 | 28篇 |
1979年 | 15篇 |
1977年 | 7篇 |
1976年 | 9篇 |
1975年 | 5篇 |
1945年 | 4篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
82.
Effect of deformation route on microstructural development in aluminum processed by equal channel angular extrusion 总被引:3,自引:0,他引:3
Pei-Ling Sun Po-We Kao Chih-Pu Chang 《Metallurgical and Materials Transactions A》2004,35(4):1359-1368
Aluminum has been deformed by equal channel angular extrusion (ECAE) to obtain submicron-grained structures under different
deformation routes. The deformation routes were varied by rotating billets through 0, 90, and 180 deg between each extrusion
pass, and were designated as route A, BC, and C, respectively. Based on quantitative microstructural analysis, the effectiveness of the deformation route is shown
to depend upon the different definition used. The order of effectiveness is (a) A > BC > C for both 90 and 120 deg dies, in terms of the generation of high-angle grain boundaries (HAGBs); (b) BC > C > A for both 90 and 120 deg dies, in terms of the formation of equiaxed shape of grains; and (c) BC > A > C for 90 deg die and BC ∼ A > C for 120 die, in terms of reducing grain size. It is suggested that the generation of HAGBs can be related to the
accumulation of nonredundant strain, while the shape and orientation of grains may be linked to the shearing patterns of the
deformation route. 相似文献
83.
Perturbation analysis and control of two-class stochastic fluid models for communication networks 总被引:2,自引:0,他引:2
Cassandras C.G. Gang Sun Panayiotou C.G. Wardi Y. 《Automatic Control, IEEE Transactions on》2003,48(5):770-782
This paper uses stochastic fluid models (SFMs) for the control and optimization (rather than performance analysis) of communication network nodes processing two classes of traffic: one is uncontrolled and the other is subject to threshold-based buffer control. We derive gradient estimators for packet loss and workload related performance metrics with respect to threshold parameters. These estimators are shown to be unbiased and directly observable from a sample path without any knowledge of underlying stochastic characteristics of the traffic processes. This renders them computable in online environments and easily implementable for network management and control. We further demonstrate their use in buffer control problems where our SFM-based estimators are evaluated based on data from an actual system. 相似文献
84.
Zhishou Zhang Qibin Sun Wai-Choong Wong John Apostolopoulos Susie Wee 《Multimedia, IEEE Transactions on》2007,9(2):320-331
This paper proposes an optimized content-aware authentication scheme for JPEG-2000 streams over lossy networks, where a received packet is consumed only when it is both decodable and authenticated. In a JPEG-2000 codestream, some packets are more important than others in terms of coding dependency and image quality. This naturally motivates allocating more redundant authentication information for the more important packets in order to maximize their probability of authentication and thereby minimize the distortion at the receiver. Towards this goal, with the awareness of its corresponding image content, we formulate an optimization framework to compute an authentication graph to maximize the expected media quality at the receiver, given specific authentication overhead and knowledge of network loss rate. System analysis and experimental results demonstrate that the proposed scheme achieves our design goal in that the rate-distortion (R-D) curve of the authenticated image is very close to the R-D curve when no authentication is required 相似文献
85.
86.
87.
The strengths of two graphite/epoxy notched laminate systems with a softening strip were investigated. The softening strip was created by replacing the 0°-graphite/epoxy plies by a glass/epoxy composite. Experimental results indicated that the use of softening strips could significantly increase the laminate strength. Analysis was performed with finite elements developed using the classical laminated plate theory and was shown to be adequate. A simple point-stress failure criterion was used to predict the strength of notched laminates with softening strips and the result was found to be satisfactory. 相似文献
88.
本文介绍了笔者设计并实现的一种新型的面向对象的程序设计语言,着重讨论了在设计过程中采用的新的概念,并和其它类似语言作了比较. 相似文献
89.
用单透镜变换由多模光纤出射的大功率Nd:YAG激光束的特性 总被引:1,自引:0,他引:1
根据理论假设,通过选取单透镜的参数和位置,计算说明了单透镜使经由多模光纤出射的大功率Nd:YAG激光束的发射角压缩,光束聚焦效率提高,光束截面场为高斯分布;文中的计算结果符合已知规律,从而说明了理论假设的正确性。 相似文献
90.