全文获取类型
收费全文 | 88926篇 |
免费 | 8082篇 |
国内免费 | 5424篇 |
专业分类
电工技术 | 6738篇 |
技术理论 | 3篇 |
综合类 | 7671篇 |
化学工业 | 13691篇 |
金属工艺 | 9805篇 |
机械仪表 | 5180篇 |
建筑科学 | 7429篇 |
矿业工程 | 2648篇 |
能源动力 | 4755篇 |
轻工业 | 5055篇 |
水利工程 | 2000篇 |
石油天然气 | 4001篇 |
武器工业 | 818篇 |
无线电 | 7764篇 |
一般工业技术 | 9968篇 |
冶金工业 | 6359篇 |
原子能技术 | 1433篇 |
自动化技术 | 7114篇 |
出版年
2024年 | 361篇 |
2023年 | 1249篇 |
2022年 | 2348篇 |
2021年 | 2861篇 |
2020年 | 3019篇 |
2019年 | 2411篇 |
2018年 | 2258篇 |
2017年 | 2958篇 |
2016年 | 3153篇 |
2015年 | 3403篇 |
2014年 | 5397篇 |
2013年 | 5503篇 |
2012年 | 6530篇 |
2011年 | 7040篇 |
2010年 | 4982篇 |
2009年 | 5131篇 |
2008年 | 4554篇 |
2007年 | 5880篇 |
2006年 | 5378篇 |
2005年 | 4388篇 |
2004年 | 3809篇 |
2003年 | 3279篇 |
2002年 | 2711篇 |
2001年 | 2393篇 |
2000年 | 2021篇 |
1999年 | 1612篇 |
1998年 | 1309篇 |
1997年 | 1182篇 |
1996年 | 1013篇 |
1995年 | 816篇 |
1994年 | 745篇 |
1993年 | 490篇 |
1992年 | 481篇 |
1991年 | 424篇 |
1990年 | 334篇 |
1989年 | 246篇 |
1988年 | 187篇 |
1987年 | 102篇 |
1986年 | 95篇 |
1985年 | 81篇 |
1984年 | 70篇 |
1983年 | 52篇 |
1982年 | 39篇 |
1981年 | 26篇 |
1980年 | 32篇 |
1979年 | 23篇 |
1977年 | 8篇 |
1976年 | 5篇 |
1959年 | 14篇 |
1951年 | 8篇 |
排序方式: 共有10000条查询结果,搜索用时 8 毫秒
21.
Aboubakar Sako Kenneth G. MacLeod Catherine M. O’Reilly 《Journal of Great Lakes research》2007,33(4):806-815
In this study, we measured growth trends in oxygen and carbon isotopic ratios in whole sagittal otoliths from three adult centropomid fish (Lates stappersii) from each of three sub-basins of Lake Tanganyika, East Africa. Sampling density was 20 to 50 samples per otolith. Both δ18O and δ13C values increase with age. The δ18O data suggest that otoliths were precipitated near the expected equilibrium with the ambient environment (ca. +3.5‰) and support a migration pattern from surface waters during larval stages to deeper waters (40 to 80 m) for mature fish. Relatively high δ18O values in the southern sub-basin are consistent with cooler temperatures in the region during seasonal upwelling. The δ13C increase from otolith core to edge is large (up to 4‰) and is interpreted as due to ontogenetic changes in diet and contributions from a decrease in the proportion of respired CO2 incorporated into otolith carbonate as metabolic rates of the fish dropped with maturity. The data seem to successfully reveal life strategy and migration patterns of L. stappersii, document regional differences in lake conditions, and provide a record of temperature within the water column during which the fish lived. Higher resolution studies and analyses of historical samples could be used to constrain modern and past growth patterns, and to reconstruct past temperature gradients and productivity patterns in the lake. 相似文献
22.
Shunsuke Ohashi 《Electrical Engineering in Japan》2005,150(1):71-77
Magnetic bearing using pinning force of a permanent magnet and a high‐temperature superconductor has been developed. Additional permanent magnet is introduced to increase the levitation force of the magnetic bearing. In this hybrid magnetic bearing system, levitation force is mainly given by the repulsive force of the permanent magnets, and stability for the lateral direction is given by pinning force of the superconductor. The experimental device is developed. A ring‐type superconductor and a bulk one are examined. Levitation characteristics of the hybrid magnetic bearing are measured. The bulk superconductor shows better characteristics of both levitation and lateral stability than the ring one. Levitation force of the hybrid system becomes about twice as large as that of the nonhybrid one. Although, the repulsive force of the permanent magnet decreases the lateral stability of the system, its influence becomes small by choosing an adequate position of the permanent magnets and the superconductor. © 2004 Wiley Periodicals, Inc. Electr Eng Jpn, 150(1): 71–77, 2005; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.10350 相似文献
23.
This paper presents a highly stable steady-state torque control system with a feedback of a secondary current signal. The torque control system is constructed with a feedback of the secondary current (I2) signal using a quick response magnetic-field sensor constructed with an amorphous core multivibrator bridge, which can solve the secondary resistance change problem for temperature variation in the IM. Moreover, we added a state feedback to the system to improve the response speed for the unit step function of a torque order. The I2 sensor method has advantages especially at a low-speed range, in which conventional method using an integrator shows control errors. 相似文献
24.
We present a method that is useful in the estimate and assessment of heat capacity data. The approach is based on an analysis of the logarithmic average of the phonon frequencies. In this quantity, that may be easily derived from experimental data on the vibrational entropy, the influence of atomic masses can be exactly accounted for even in polyatomic solids. Our method is applied to Li2O, Na2O, K2O, Rb2O, and Cs2O. In particular, literature data for K2O are critically examined. 相似文献
25.
26.
攀钢转炉炼钢用碳化硅提温的试验研究 总被引:1,自引:1,他引:0
低品位碳化硅是转炉炼钢的有效提高温剂。工业性试验结果表明,碳化硅加入8.0kg/t钢水提温40.3-70.3℃(平均48.4℃);渣中TFe降低1.3%;加提温剂有利于转炉内造渣脱硫和碱少炉渣对耐火砖的侵蚀。文中还给出了攀钢转炉半钢冶炼铸用钢不水时加与不加碳化硅的tλ,[C]λ区域。 相似文献
27.
28.
SKYPE在远程英语教学方面的实时应用 总被引:2,自引:0,他引:2
SKYPE系统是目前世界上最流行的互联网远程视频、音频、文字实时交互平台,其音频、视频传播实时非常清晰,这对将远程教育拓展到家庭,特别是对推动远程英语教育的广泛性和普遍性能够起到很大的作用,本文就该平台的基本功能和性能做了介绍,并在远程英语教育方面的应用提出了实践的方法。 相似文献
29.
在气敏温度区域内研究了α-Fe_2O_3(SO_4~(2-),Sn)材料的电阻-温度特性,认为表面结构的变化导致温度特性出现峰值并呈现气敏性。可利用空气中电阻温度特性提供的信息改性或发现新的气敏材料。 相似文献
30.