全文获取类型
收费全文 | 673885篇 |
免费 | 8572篇 |
国内免费 | 2861篇 |
专业分类
电工技术 | 12340篇 |
综合类 | 3214篇 |
化学工业 | 99352篇 |
金属工艺 | 29420篇 |
机械仪表 | 21985篇 |
建筑科学 | 15967篇 |
矿业工程 | 3247篇 |
能源动力 | 17400篇 |
轻工业 | 51469篇 |
水利工程 | 6838篇 |
石油天然气 | 9495篇 |
武器工业 | 94篇 |
无线电 | 81160篇 |
一般工业技术 | 131219篇 |
冶金工业 | 116484篇 |
原子能技术 | 12271篇 |
自动化技术 | 73363篇 |
出版年
2021年 | 5400篇 |
2020年 | 4010篇 |
2019年 | 5047篇 |
2018年 | 21877篇 |
2017年 | 20788篇 |
2016年 | 18275篇 |
2015年 | 6581篇 |
2014年 | 9944篇 |
2013年 | 28713篇 |
2012年 | 18572篇 |
2011年 | 29890篇 |
2010年 | 24588篇 |
2009年 | 24145篇 |
2008年 | 25970篇 |
2007年 | 26677篇 |
2006年 | 17804篇 |
2005年 | 17093篇 |
2004年 | 16138篇 |
2003年 | 16144篇 |
2002年 | 15096篇 |
2001年 | 14551篇 |
2000年 | 13606篇 |
1999年 | 14411篇 |
1998年 | 36442篇 |
1997年 | 25407篇 |
1996年 | 19731篇 |
1995年 | 14668篇 |
1994年 | 12945篇 |
1993年 | 12862篇 |
1992年 | 9283篇 |
1991年 | 8901篇 |
1990年 | 8541篇 |
1989年 | 8142篇 |
1988年 | 7852篇 |
1987年 | 6859篇 |
1986年 | 6711篇 |
1985年 | 7658篇 |
1984年 | 6976篇 |
1983年 | 6289篇 |
1982年 | 5861篇 |
1981年 | 5963篇 |
1980年 | 5561篇 |
1979年 | 5317篇 |
1978年 | 5277篇 |
1977年 | 6236篇 |
1976年 | 8560篇 |
1975年 | 4532篇 |
1974年 | 4285篇 |
1973年 | 4309篇 |
1972年 | 3625篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
Intensive fertilizer use has led to nitrate contamination of groundwater in many areas. This article examines the possibility of removing nitrates through the construction of artificial wetlands. A pilot study conducted in Denmark has found that the method is effective and economical, at least for small waterworks, though further treatment is necessary before an acceptable microbiological water quality is attained. 相似文献
102.
103.
Nagpal R. Zambonelli F. Sirer E.G. Chaouchi H. Smirnov M. 《Intelligent Systems, IEEE》2006,21(2):50-58
No generally accepted principles and guidelines currently exist to help engineers design local interaction mechanisms that result in a desired global behavior. However, several communities have developed ways of approaching this problem in the context of niched application areas. Because the ideas underlying these approaches are often obscured or underemphasized in technical papers, the authors review the role of self-organization in their work. They provide a better picture of the status of the emerging field of self-organizing systems or autonomic computing. 相似文献
104.
105.
L. GbahoueF. Barbeu S. Martemianov 《International Journal of Heat and Mass Transfer》2002,45(18):3865-3873
Electrochemical method is applied to study coherent structures in a complex three-dimensional flow generated by a rotating magnetic rod. In order to detect these structures, the power spectral density (PSD) analysis of the limiting diffusion current fluctuations is provided. This analysis reveals the existence of resonance frequencies when the probe is located in the very vicinity of the stirrer. The main resonance is related to the mechanical excitation frequency. The detailed analysis of the PSD curves points out some mechanisms of development of turbulence as sub-harmonics and non-linear interactions. For different locations of the probe and different angular rates of the stirrer Ω, a similarity of the energy repartition is obtained when the PSD is plotted versus the adimensional frequency f/Ω. Flow visualization by laser tomography is also provided and the local secondary flow past the electrode probe is sketched. The laser Doppler velocimetry (LDV) at a given location in a horizontal z-plane indicates a tornado wise mean flow structure. 相似文献
106.
Hayashi M. Tanaka H. Ohara K. Otani T. Suzuki M. 《Lightwave Technology, Journal of》2002,20(2):236-242
An all-optical multiplexing technique using wavelength division multiplexing (WDM)-time division multiplexing (TDM) conversion with an electroabsorption wavelength converter has been proposed and demonstrated. The effectiveness of this WDM-TDM conversion technique for various pulsewidth settings was experimentally investigated. The fluctuation of the signal performance, which was inevitably caused by the coherent crosstalk between adjacent pulses in the conventional optical time division multiplexing (OTDM) technique, were successfully suppressed, even in the case of wide pulse duration. High Q-factor performance has been maintained for a wide range of duty ration from 36% to 74%. By introducing this technique to the optical time division multiplexer, a highly stable and high-quality 40-Gb/s optical signal can be effectively produced without generating the short pulse or setting two tributaries at orthogonal polarization states, and without introducing high-speed electronics for signal multiplexing. The WDM-TDM conversion with an electroabsorption wavelength converter was extended to 60-Gb/s operation by using three 20-Gb/s tributaries. A clear eye opening was confirmed for a waveform after the WDM-TDM conversion of the 60-Gb/s signal 相似文献
107.
108.
A.S. Fraser 《Journal of Great Lakes research》1980,6(1):83-87
An apparent decrease in total phosphorus concentrations of approximately 4.l μgP/L has been reported recently for the spring values of 1977 and 1978 in Lake Ontario. Investigation of the loading reduction for this period independent of sedimentation factors can account for only 10% of the change. The results indicate that changes in the sedimentation rate of total phosphorus during this period offer an explanation for the majority of the change in concentration. 相似文献
109.
The application of recently developed algorithms to antenna systems design is demonstrated by the worst-case tolerance optimization of linear broadside arrays, using both spacings and excitation coefficients as design parameters. The resulting arrays are optimally immunized against deviations of the design parameters from their nominal values. 相似文献
110.