全文获取类型
收费全文 | 17779篇 |
免费 | 2622篇 |
国内免费 | 1870篇 |
专业分类
电工技术 | 1486篇 |
综合类 | 2225篇 |
化学工业 | 848篇 |
金属工艺 | 250篇 |
机械仪表 | 748篇 |
建筑科学 | 653篇 |
矿业工程 | 277篇 |
能源动力 | 267篇 |
轻工业 | 445篇 |
水利工程 | 348篇 |
石油天然气 | 494篇 |
武器工业 | 248篇 |
无线电 | 5092篇 |
一般工业技术 | 1280篇 |
冶金工业 | 470篇 |
原子能技术 | 83篇 |
自动化技术 | 7057篇 |
出版年
2024年 | 80篇 |
2023年 | 261篇 |
2022年 | 484篇 |
2021年 | 632篇 |
2020年 | 611篇 |
2019年 | 587篇 |
2018年 | 534篇 |
2017年 | 633篇 |
2016年 | 733篇 |
2015年 | 897篇 |
2014年 | 1216篇 |
2013年 | 1206篇 |
2012年 | 1365篇 |
2011年 | 1481篇 |
2010年 | 1100篇 |
2009年 | 1125篇 |
2008年 | 1257篇 |
2007年 | 1352篇 |
2006年 | 1085篇 |
2005年 | 1027篇 |
2004年 | 830篇 |
2003年 | 772篇 |
2002年 | 600篇 |
2001年 | 532篇 |
2000年 | 415篇 |
1999年 | 313篇 |
1998年 | 209篇 |
1997年 | 177篇 |
1996年 | 140篇 |
1995年 | 136篇 |
1994年 | 85篇 |
1993年 | 74篇 |
1992年 | 50篇 |
1991年 | 43篇 |
1990年 | 38篇 |
1989年 | 35篇 |
1988年 | 23篇 |
1987年 | 17篇 |
1986年 | 10篇 |
1985年 | 15篇 |
1984年 | 13篇 |
1983年 | 11篇 |
1982年 | 8篇 |
1981年 | 11篇 |
1980年 | 7篇 |
1979年 | 3篇 |
1976年 | 6篇 |
1973年 | 3篇 |
1963年 | 3篇 |
1959年 | 5篇 |
排序方式: 共有10000条查询结果,搜索用时 437 毫秒
51.
This investigation proposes a fixed collision rate (FCR) back-off algorithm for wireless networks. The proposed scheme takes advantage of the central unit (CU) in a wireless network to broadcast a common back-off window size to all the users, significantly alleviating the unfairness of bandwidth utilization in conventional binary exponential back-off (BEB) algorithms. It is shown that, when maximum throughput is achieved, collision rate is almost a constant for any traffic load. In the operation of the FCR, the CU dynamically adjusts the back-off window size to keep the collision rate at a constant level for maximum throughput. Simulation results demonstrate that the unfairness of bandwidth utilization in the BEB is significantly lessened and the throughput can be maintained at e-1≈0.368 when the number of users approaches infinity. The capture effect even further improves system performance. 相似文献
52.
应用数学理论知识和CAD技术对施工图进行建模,从而获得准确的放样参数指导施工,并结合工程实例对计算机辅助施工放样过程进行了具体的介绍。 相似文献
53.
54.
It is necessary to determine the accurate reflectance of painted surfaces for the review of paint finishes by computer graphics (CG) before actual painting of the exterior color of automobiles, and for quality control during production and inspection processes. We have optimized a method for measuring reflectance by using a statistical technique. We have found that the reflectance of a painted surface is best measured at an incident angle of 60° and at five aspecular angles of 10°, 18°, 28°, 40°, and 90°. Our method makes it possible to accurately reproduce reflection characteristics of paint finishes containing special flake pigments, such as pearl mica. Also it was proved that our method can apply not only to solid and metallic coatings but to all painted surfaces. © 2005 Wiley Periodicals, Inc. Col Res Appl, 30, 275–282, 2005; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/col.20125 相似文献
55.
Memory loss in retrograde amnesia has long been held to be larger for recent periods than for remote periods, a pattern usually referred to as the Ribot gradient. One explanation for this gradient is consolidation of long-term memories. Several computational models of such a process have shown how consolidation can explain characteristics of amnesia, but they have not elucidated how consolidation must be envisaged. Here findings are reviewed that shed light on how consolidation may be implemented in the brain. Moreover, consolidation is contrasted with alternative theories of the Ribot gradient. Consolidation theory, multiple trace theory, and semantization can all handle some findings well but not others. Conclusive evidence for or against consolidation thus remains to be found. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
56.
57.
介绍了第3代移动通信3种主流技术的市场应用、设备成熟度,以及国际和国内标准化发展状况,我国第3代移动通信技术试验的总体情况。 相似文献
58.
本地多点分配业务(LMDS)是近年来在国际上兴起的固定式宽带无线接入技术,具有传输容量大、起始费用低的优点,受到了国内外电信业务经营者的普遍关注.文章介绍了LMDS提供的业务类型、工作频率、系统结构和标准化情况,并将LMDS与有线电视网络、ADSL、MMDS等现有的接入技术进行了比较.文章认为LMDS的商业推广尚需解决信号质量、服务区尺寸、费用等制约因素. 相似文献
59.
60.
R. Meyer Hilde Hardtdegen R. Carius D. Grützmacher M. Stollenwerk P. Balk A. Kux B. Meyer 《Journal of Electronic Materials》1992,21(3):293-298
This paper presents a study of the structural and optical properties of strained GaInAs/ InP multiple quantum well (MQW) structures
fabricated by LP-MOVPE. The composition of the Ga
x
In1−x
As films ranged fromx = 0.17 tox = 1.0 and was determined by sputtered neutral mass spectrometry (SNMS) on thick layers. The structures of the MQW samples
with well widths from 1.5 to 5 nm were investigated by high resolution x-ray diffraction (HR-XRD). Simulations of the diffraction
patterns showed that transition layers of approximately 2 monolayer (ML) thickness with high lattice mismatch exist at the
interfaces. Photoluminescence (PL) measurements indicate well widths of a multiple of a monolayer with local variations of
one monolayer. The PL peak energies vary smoothly with the Ga concentration. These results were confirmed by optical absorption
measurements. 相似文献