全文获取类型
收费全文 | 3262篇 |
免费 | 252篇 |
国内免费 | 127篇 |
专业分类
电工技术 | 173篇 |
综合类 | 180篇 |
化学工业 | 555篇 |
金属工艺 | 157篇 |
机械仪表 | 166篇 |
建筑科学 | 231篇 |
矿业工程 | 61篇 |
能源动力 | 109篇 |
轻工业 | 177篇 |
水利工程 | 75篇 |
石油天然气 | 209篇 |
武器工业 | 25篇 |
无线电 | 371篇 |
一般工业技术 | 430篇 |
冶金工业 | 214篇 |
原子能技术 | 64篇 |
自动化技术 | 444篇 |
出版年
2024年 | 12篇 |
2023年 | 50篇 |
2022年 | 91篇 |
2021年 | 166篇 |
2020年 | 127篇 |
2019年 | 94篇 |
2018年 | 114篇 |
2017年 | 106篇 |
2016年 | 129篇 |
2015年 | 152篇 |
2014年 | 144篇 |
2013年 | 208篇 |
2012年 | 219篇 |
2011年 | 208篇 |
2010年 | 193篇 |
2009年 | 174篇 |
2008年 | 154篇 |
2007年 | 138篇 |
2006年 | 131篇 |
2005年 | 120篇 |
2004年 | 96篇 |
2003年 | 88篇 |
2002年 | 67篇 |
2001年 | 61篇 |
2000年 | 61篇 |
1999年 | 68篇 |
1998年 | 71篇 |
1997年 | 60篇 |
1996年 | 58篇 |
1995年 | 49篇 |
1994年 | 42篇 |
1993年 | 29篇 |
1992年 | 25篇 |
1991年 | 26篇 |
1990年 | 17篇 |
1989年 | 13篇 |
1988年 | 10篇 |
1987年 | 7篇 |
1986年 | 4篇 |
1985年 | 7篇 |
1984年 | 10篇 |
1983年 | 6篇 |
1982年 | 7篇 |
1980年 | 8篇 |
1978年 | 8篇 |
1977年 | 5篇 |
1974年 | 2篇 |
1972年 | 1篇 |
1971年 | 1篇 |
1966年 | 1篇 |
排序方式: 共有3641条查询结果,搜索用时 15 毫秒
11.
12.
病险水工建筑物可靠性评估方法初探 总被引:4,自引:0,他引:4
水工建筑物可靠性评估是水利工程管理中急需解决的问题,将水工建筑物分解为由分部工程组成的层次结构,引入子系统概率重要性系数,用层次分析法导出水工建筑物系统可靠度指标的实用计算方法。 相似文献
13.
14.
For a PC-mobile download system which is embedded with streaming download protocol, there are problems that the data cannot be transmitted correctly from the PC to the mobile, or the transmission is unacceptably slow. To solve these problems, we carry out a formal analysis for the protocol with some timing parameters and a given probability of message loss and unordered data using a probabilistic model checking tool PRISM. We introduce a technique to reduce the state space of the system modeling the protocol which is a network of probabilistic timed automata. The experimental results in PRISM give us a clear explanation to the problems, and are helpful in identifying the optimal parameter settings to meet industrial requirements. 相似文献
15.
16.
17.
Fabrication and characteristics of high-speed implant-confined index-guided lateral-current 850-nm vertical cavity surface-emitting lasers 总被引:2,自引:0,他引:2
Dang G.T. Mehandru R. Luo B. Ren F. Hobson W.S. Lopata J. Tayahi M. Chu S.N.G. Pearton S.J. Chang W. Shen H. 《Lightwave Technology, Journal of》2003,21(4):1020-1031
Process technology of high-speed implant-apertured index-guide lateral-current-injection top dielectric-mirror quantum-well 850-nm vertical cavity surface-emitting lasers (VCSELs) has been developed. Oxygen and helium implantation for aperture definition and extrinsic capacitance reduction, dielectric mirror formation, p- and n-ohmic contact formation, VCSEL resistance, and thermal analysis were investigated. Employing this technology, GaAs/AlGaAs-based 850-nm VCSELs with small signal modulation bandwidths up to 11.5 Gb/s and an eye diagram generated at 12 Gb/s by a pseudorandom bit sequence of 2/sup 31/-1 were achieved. The bit-error rates were below 10/sup -13/. The threshold current is as low as 0.8 mA for 7-/spl mu/m-diameter current apertures and typical slope efficiencies of 0.45-0.5 mA/mW were obtained. 相似文献
18.
19.
20.
In this study, nitrogen removal was investigated in pilot-scale subsurface flow (SSF) and in free water surface flow (FWS) constructed wetlands installed in the campus of TUBITAK-Marmara Research Center, Gebze, near Istanbul, Turkey. The main purposes of this study are to apply constructed wetlands for the protection of water reservoirs and to reuse wastewater. Experiments were carried out at continuous flow reactors. The effects of the type of plants on the removal were investigated by using emergent (Canna, Cyperus, Typhia spp., Phragmites spp., Juncus, Poaceae, Paspalum and Iris.), submerged (Elodea, Egeria) and floating (Pistia, Salvina and Lemna) marsh plants at different conditions. During the study period HLRs were 30, 50, 70, 80 and 120 L m(2)d(-1) respectively. The average annual NH4-N, NO(3)-N, organic N and TN treatment efficiencies in SSF and FWS wetlands are 81% and 68%, 37% and 49%, 75% and 68%, 47% and 53%, respectively. Nitrification, denitrification and ammonification rate constant (k20) values in SSF and FNS systems have been found as 0.898 d(-1) and 0.541 d(-1), 0.488 d(-1) and 0.502 d(-1), 0.986 d(-1) and 0.908 respectively. Two types of the models (first-order plug flow and multiple regression) were tried to estimate the system performances. 相似文献