全文获取类型
收费全文 | 6144篇 |
免费 | 127篇 |
国内免费 | 22篇 |
专业分类
电工技术 | 347篇 |
综合类 | 14篇 |
化学工业 | 1524篇 |
金属工艺 | 190篇 |
机械仪表 | 217篇 |
建筑科学 | 157篇 |
能源动力 | 200篇 |
轻工业 | 435篇 |
水利工程 | 15篇 |
石油天然气 | 3篇 |
无线电 | 473篇 |
一般工业技术 | 1227篇 |
冶金工业 | 938篇 |
原子能技术 | 184篇 |
自动化技术 | 369篇 |
出版年
2023年 | 26篇 |
2022年 | 72篇 |
2021年 | 91篇 |
2020年 | 33篇 |
2019年 | 56篇 |
2018年 | 85篇 |
2017年 | 67篇 |
2016年 | 84篇 |
2015年 | 78篇 |
2014年 | 128篇 |
2013年 | 275篇 |
2012年 | 185篇 |
2011年 | 315篇 |
2010年 | 213篇 |
2009年 | 267篇 |
2008年 | 271篇 |
2007年 | 212篇 |
2006年 | 225篇 |
2005年 | 208篇 |
2004年 | 161篇 |
2003年 | 204篇 |
2002年 | 158篇 |
2001年 | 136篇 |
2000年 | 121篇 |
1999年 | 154篇 |
1998年 | 414篇 |
1997年 | 292篇 |
1996年 | 222篇 |
1995年 | 132篇 |
1994年 | 123篇 |
1993年 | 113篇 |
1992年 | 64篇 |
1991年 | 77篇 |
1990年 | 79篇 |
1989年 | 85篇 |
1988年 | 74篇 |
1987年 | 66篇 |
1986年 | 89篇 |
1985年 | 84篇 |
1984年 | 79篇 |
1983年 | 66篇 |
1982年 | 54篇 |
1981年 | 45篇 |
1980年 | 38篇 |
1979年 | 39篇 |
1978年 | 36篇 |
1977年 | 37篇 |
1976年 | 50篇 |
1974年 | 26篇 |
1973年 | 15篇 |
排序方式: 共有6293条查询结果,搜索用时 0 毫秒
1.
Akira Yamamoto Kentaro Teramura Saburo Hosokawa Tsunehiro Tanaka 《Science and Technology of Advanced Materials》2015,16(2)
The effect of SO2 gas was investigated on the activity of the photo-assisted selective catalytic reduction of nitrogen monoxide (NO) with ammonia (NH3) over a TiO2 photocatalyst in the presence of excess oxygen (photo-SCR). The introduction of SO2 (300 ppm) greatly decreased the activity of the photo-SCR at 373 K. The increment of the reaction temperature enhanced the resistance to SO2 gas, and at 553 K the conversion of NO was stable for at least 300 min of the reaction. X-ray diffraction, FTIR spectroscopy, thermogravimetry and differential thermal analysis, x-ray photoelectron spectroscopy (XPS), elemental analysis and N2 adsorption measurement revealed that the ammonium sulfate species were generated after the reaction. There was a strong negative correlation between the deposition amount of the ammonium sulfate species and the specific surface area. Based on the above relationship, we concluded that the deposition of the ammonium sulfate species decreased the specific surface area by plugging the pore structure of the catalyst, and the decrease of the specific surface area resulted in the deactivation of the catalyst. 相似文献
2.
H. Sakata A. Katagiri M. Yokoi T. Kato H. Morimoto 《Journal of Low Temperature Physics》2003,131(3-4):275-279
We have measured the tunneling spectra in Bi2Sr2CaCu2O8 with a scanning tunneling microscope(STM) at various tip-sample distances by changing the tunneling conductance in a controlled manner. When the tunneling conductance is increased from 1×10–9 to 1×10–5 S, the spectra do not show changes in particular. However, the gap value decreases steeply and the asymmetric back ground density of states turns inverted V-shaped one above 6×10–4 S. The changes in the tunneling spectra at the high tunneling conductances are explained by the enhancement of the local carrier density induced by the pressure that the STM tip applied to the sample. 相似文献
3.
4.
5.
Yamaoka M. Shinozaki Y. Maeda N. Shimazaki Y. Kato K. Shimada S. Yanagisawa K. Osada K. 《Solid-State Circuits, IEEE Journal of》2005,40(1):186-194
An on-chip 1-Mb SRAM suitable for embedding in the application processor used in mobile cellular phones was developed. This SRAM supports three operating modes - high-speed active mode, low-leakage low-speed active mode, and standby mode - and uses a subdivisional power-line control (SPC) scheme. The combination of three operating modes and the SPC scheme realizes low-power operation under actual usage conditions. It operates at 300 MHz, with leakage of 25 /spl mu/A/Mb in standby mode, and 50 /spl mu/A/Mb at the low-leakage active mode. This SRAM also uses a self-bias write scheme that decreases of minimum operating voltage by about 100 mV. 相似文献
6.
Takeshi Kondo Hiroyuki Ito Kazuhide Kusakabe Kazuhiro Ohkawa Kensuke Honda Yasuaki Einaga Akira Fujishima Takeshi Kawai 《Diamond and Related Materials》2008,17(1):48-54
The effect of CF4 plasma etching on diamond surfaces, with respect to treatment time, was investigated using scanning electron microscopy (SEM), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), and electrochemical measurements. SEM observations and Raman spectra indicated an increase in surface roughening on a scale of 10–20 nm, and an increase in crystal defect density was apparent with treatment time in the range of 10 s to 30 min. In contrast, alteration of the diamond surface terminations from oxygen to fluorine was found to be rather rapid, with saturation of the F/C atomic ratio estimated from XPS analysis after treatment durations of 1 min and more. The redox kinetics of Fe(CN)63−/4− was also found to be significantly modified after 10 s of CF4 plasma treatment. This behavior shows that C–F terminations predominantly affect the redox kinetics compared to the effect on the surface roughness and crystal defects. The double-layer capacitance (Cdl) of the electrolyte/CF4 plasma-treated boron-doped diamond interface was found to show a minimum value at 1 min of treatment. These results indicate that a short-duration CF4 plasma treatment is effective for the fabrication of fluorine-terminated diamond surfaces without undesirable surface damage. 相似文献
7.
Akira Watanabe Yoshimitsu Takeuchi Goji Saeki 《Journal of the American Ceramic Society》1985,68(11):308-C
The length of potassium titanate fibers produced by several conventional methods averages 50 μm, with a maximum of 100 μm. Extremely long fibers (most >1000 μm long) were obtained by calcination in N2 gas flowing at 5.2×10-4 m/s. 相似文献
8.
9.
We succeeded in the fabrication of bonded laser crystals composed of a neodymium-doped YVO4 laser crystal (Nd:YVO4) and its host crystals YVO4 by a newly developed dry etching technique using an argon ion beam. The optical distortion caused by the bonded interface of size 5 mm × 6 mm was estimated to be 0.05λ at 633 nm. From the comparison of laser performance pumped by a laser diode, the bonded crystals could increase the laser output power by nearly twice that of the non-bonded crystals with the same degree of polarization of 99.2%. To analyze the mechanism of the enhanced reduction of the thermal load in the bonded crystals, numerical simulations with a finite-element method were also performed. 相似文献
10.
A new configuration based on the polarization-mismatching scheme with time delay for efficient frequency tripling conversion is proposed in this paper. The calculated results showed that the requirement for the efficient frequency tripling conversion of a 1-ps laser pulse is not only the optimization of peak intensity of the second-harmonic pulse, but also the optimization of the pulse duration ratio and temporal difference between the o-polarization second-harmonic pulse and the e-polarization first-harmonic pulse due to group-velocity mismatch among the interacting pulses. With the proposed scheme the group velocity mismatch can be compensated. Overall energy conversion efficiency increases from 55% to 75% under the optimized conditions at the intensity of 6 GW/cm2. The temporal shape of the third-harmonic pulse with 1 ps pulse duration has no subpulses. The optimization of the efficient frequency tripling conversion for intensities of over 75 GW/cm2 is also described. The results showed that the maximum tripling energy conversion efficiency is close to 80% with the optimized doubler and tripler 相似文献