全文获取类型
收费全文 | 42519篇 |
免费 | 5021篇 |
国内免费 | 2644篇 |
专业分类
电工技术 | 3284篇 |
技术理论 | 4篇 |
综合类 | 3712篇 |
化学工业 | 6646篇 |
金属工艺 | 2509篇 |
机械仪表 | 2548篇 |
建筑科学 | 3397篇 |
矿业工程 | 1292篇 |
能源动力 | 1290篇 |
轻工业 | 4002篇 |
水利工程 | 970篇 |
石油天然气 | 1798篇 |
武器工业 | 544篇 |
无线电 | 5123篇 |
一般工业技术 | 4708篇 |
冶金工业 | 1503篇 |
原子能技术 | 682篇 |
自动化技术 | 6172篇 |
出版年
2024年 | 285篇 |
2023年 | 920篇 |
2022年 | 1863篇 |
2021年 | 2552篇 |
2020年 | 1772篇 |
2019年 | 1450篇 |
2018年 | 1513篇 |
2017年 | 1616篇 |
2016年 | 1391篇 |
2015年 | 2136篇 |
2014年 | 2417篇 |
2013年 | 2773篇 |
2012年 | 3108篇 |
2011年 | 3268篇 |
2010年 | 2898篇 |
2009年 | 2824篇 |
2008年 | 2579篇 |
2007年 | 2276篇 |
2006年 | 2087篇 |
2005年 | 1662篇 |
2004年 | 1324篇 |
2003年 | 1215篇 |
2002年 | 1489篇 |
2001年 | 1305篇 |
2000年 | 787篇 |
1999年 | 598篇 |
1998年 | 374篇 |
1997年 | 335篇 |
1996年 | 287篇 |
1995年 | 212篇 |
1994年 | 198篇 |
1993年 | 173篇 |
1992年 | 96篇 |
1991年 | 77篇 |
1990年 | 73篇 |
1989年 | 49篇 |
1988年 | 42篇 |
1987年 | 40篇 |
1986年 | 25篇 |
1985年 | 16篇 |
1984年 | 10篇 |
1983年 | 10篇 |
1982年 | 9篇 |
1981年 | 8篇 |
1980年 | 14篇 |
1979年 | 7篇 |
1972年 | 1篇 |
1969年 | 1篇 |
1959年 | 7篇 |
1951年 | 10篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
51.
论述了参数设计法在铝电解电容器设计开发阶段的应用。文中阐明了铝电解电容器的主要质量特性(损耗因子、电容量)及芯包外径的参数设计原理,并建立了归一化函数作为优选设计方案的判据。实例证明在铝电解电容器的设计过程中应用参数设计法以减小产品质量特性变异是有效的。 相似文献
52.
The Role of Network Topologies in the Optical Core of IP-over-WDM Networks with Static Wavelength Routing 总被引:3,自引:0,他引:3
Freire Mário M. Rodrigues Joel J.P.C. Coelho Rui M.F. 《Telecommunication Systems》2003,24(2-4):111-122
In this paper, we present a performance analysis of network topologies for the optical core of IP-over-WDM networks with static wavelength routing. The performance analysis is focused on regular degree four topologies, and, for comparison purposes, degree three topologies are also considered. It is shown that the increase of the nodal degree from three (degree three topology with smallest diameter) to four (degree four topology with smallest diameter) improves the network performance if a larger number of wavelengths per link is available. However, the influence of wavelength interchange on the nodal degree gain is small. The performance of regular degree four topologies with smallest diameter is also compared with the performance of mesh–torus topologies (which are also degree four topologies), and it is shown that the blocking probability of degree four topologies with smallest diameter is about two orders of magnitude lower than the blocking probability of mesh–torus topologies. It is also presented a performance comparison of WDM-based networks with nodal degrees ranging from two to five and it is shown that the increase of the nodal degree from two to three leads to high nodal degree gains, while de increase of the nodal degree from four to five leads to low nodal degree gains. These results show that degree three and degree four topologies are very attractive for use in the optical core of IP-over-WDM networks. 相似文献
53.
54.
55.
关于Ada95变体部分等语法的修正意见 总被引:1,自引:0,他引:1
徐宝文 《计算机研究与发展》1997,34(1):78-80
本文指出了Ada95 参考手册中记录变体部分、记录聚集、分情形语句与异常处理段等语法描述中存在的问题,并分别给出了它们的修正方案。 相似文献
56.
57.
包行方 《石油化工设备技术》1996,17(1):5-8
充分利用了带主焊缝的役后试板,在国内首次开展回火脆化、氢介质下断裂韧性与疲劳扩展的研究,结果表明,加氢反应器焊缝有明显的脆化表现。同时,核查了反应器开停车升温速度和降温速度规定,以及确定了裂纹允许尺寸的参考数据,为今后安全运行提供了充分的依据。 相似文献
58.
Eroding poly(DL-lactide-co-glycolide)(PDLLG) washers were observed chronically in vitro and in vivo following loading in a bone chamber tibial implant (BCI). Images were recorded using intravital microscopy of the implanted rabbit and direct pH measurements were obtained of the tissue in the bone chamber using a combination probe-reference microelectrode. While statistically significant pH differences were found between the control (unloaded) and experimental (PDLLG-bearing) BCIs, they were only of the order of 0.2 pH units. This value proved to be physiologically insignificant as no statistically significant difference in bone defect healing, as indicated by angiogenesis, was detected. It was shown that the measured small pH changes during PDLLG washers erosion would result whether the buffer was phosphate-buffered saline replaced weekly or interstitial fluid subject to vascular exchanges. 相似文献
59.
60.
Gang Bao 《Wireless Networks》1996,2(3):229-237
Due to the high frame error rate in wireless communication channels, an additional link layer protocol, Radio Link Protocol (RLP), has been introduced in the newly approvedData Services Option Standard for Wideband Spread Spectrum Digital Cellular System. In this paper, we investigate performance issues of a typical Cod Division Multiple Access (CDMA) wireless link using the protocol stack given in the standard. In particular, we focus on the dynamics of the TCP and RLP layers of the protocol stack since the fluctuation of system performance is largely caused by Automatic Repeat Request (ARQ) mechanisms implemented at these two layers. We compare the network performance of default parameter setting to those of other possible parameter settings. Analytical and simulation results presented in this paper can provide guidance to those attempting to further improve performance of interest. 相似文献