全文获取类型
收费全文 | 1692篇 |
免费 | 36篇 |
国内免费 | 8篇 |
专业分类
电工技术 | 112篇 |
综合类 | 4篇 |
化学工业 | 481篇 |
金属工艺 | 57篇 |
机械仪表 | 32篇 |
建筑科学 | 29篇 |
能源动力 | 60篇 |
轻工业 | 98篇 |
水利工程 | 4篇 |
石油天然气 | 5篇 |
无线电 | 125篇 |
一般工业技术 | 331篇 |
冶金工业 | 200篇 |
原子能技术 | 70篇 |
自动化技术 | 128篇 |
出版年
2023年 | 9篇 |
2022年 | 12篇 |
2021年 | 23篇 |
2020年 | 16篇 |
2019年 | 7篇 |
2018年 | 21篇 |
2017年 | 20篇 |
2016年 | 20篇 |
2015年 | 18篇 |
2014年 | 35篇 |
2013年 | 80篇 |
2012年 | 42篇 |
2011年 | 84篇 |
2010年 | 62篇 |
2009年 | 59篇 |
2008年 | 83篇 |
2007年 | 64篇 |
2006年 | 63篇 |
2005年 | 74篇 |
2004年 | 47篇 |
2003年 | 47篇 |
2002年 | 42篇 |
2001年 | 42篇 |
2000年 | 37篇 |
1999年 | 34篇 |
1998年 | 93篇 |
1997年 | 59篇 |
1996年 | 46篇 |
1995年 | 48篇 |
1994年 | 35篇 |
1993年 | 36篇 |
1992年 | 21篇 |
1991年 | 24篇 |
1990年 | 26篇 |
1989年 | 28篇 |
1988年 | 26篇 |
1987年 | 16篇 |
1986年 | 27篇 |
1985年 | 18篇 |
1984年 | 28篇 |
1983年 | 31篇 |
1982年 | 18篇 |
1981年 | 18篇 |
1980年 | 18篇 |
1979年 | 23篇 |
1978年 | 13篇 |
1977年 | 10篇 |
1976年 | 6篇 |
1974年 | 4篇 |
1972年 | 4篇 |
排序方式: 共有1736条查询结果,搜索用时 15 毫秒
21.
Masatomo Yamagiwa Takayuki Ogawa Takeo Minamikawa Dahi Ghareab Abdelsalam Kyosuke Okabe Noriaki Tsurumachi Yasuhiro Mizutani Testuo Iwata Hirotsugu Yamamoto Takeshi Yasui 《Journal of Infrared, Millimeter and Terahertz Waves》2018,39(6):561-572
Terahertz digital holography (THz-DH) has the potential to be used for non-destructive inspection of visibly opaque soft materials due to its good immunity to optical scattering and absorption. Although previous research on full-field off-axis THz-DH has usually been performed using Fresnel diffraction reconstruction, its minimum reconstruction distance occasionally prevents a sample from being placed near a THz imager to increase the signal-to-noise ratio in the hologram. In this article, we apply the angular spectrum method (ASM) for wavefront reconstruction in full-filed off-axis THz-DH because ASM is more accurate at short reconstruction distances. We demonstrate real-time phase imaging of a visibly opaque plastic sample with a phase resolution power of λ/49 at a frame rate of 3.5 Hz in addition to real-time amplitude imaging. We also perform digital focusing of the amplitude image for the same object with a depth selectivity of 447 μm. Furthermore, 3D imaging of visibly opaque silicon objects was achieved with a depth precision of 1.7 μm. The demonstrated results indicate the high potential of the proposed method for in-line or in-process non-destructive inspection of soft materials. 相似文献
22.
Hashido R. Suzuki A. Iwata A. Okamoto T. Satoh Y. Inoue M. 《Solid-State Circuits, IEEE Journal of》2003,38(2):274-280
We have developed a capacitive fingerprint sensor chip using low-temperature poly-Si thin film transistors (TFTs). We have obtained good fingerprint images which have sufficient contrast for fingerprint certification. The sensor chip comprises sensor circuits, drive circuits, and a signal processing circuit. The new sensor cell employs only one transistor and one sensor plate within one cell. There is no leakage current to other cells by using a new and unique sensing method. The output of this sensor chip is an analog wave and the designed maximum output level is almost equal to the TFT's threshold voltage, which is 2-3 V for low-temperature poly-Si TFTs. We used a glass substrate and only two metal layers to lower the cost. The size of the trial chip is 30 mm/spl times/20 mm/spl times/1.2 mm and the sensor area is 19.2 mm/spl times/15 mm. The size of the prototype cell is now 60 /spl mu/m/spl times/60 /spl mu/m at 423 dpi, but it will be easy to increase the resolution up to more than 500 dpi. The drive frequency is now 500 kHz and the power consumption is 1.2 mW with a 5-V supply voltage. This new fingerprint sensor is most suitable for mobile use because the sensor chip is low cost and in a thin package with low power consumption. 相似文献
23.
Jungo Kondo Aoki K. Kondo A. Ejiri T. Iwata Y. Hamajima A. Mori T. Mizuno Y. Imaeda M. Kozuka Y. Mitomi O. Minakata M. 《Photonics Technology Letters, IEEE》2005,17(10):2077-2079
We present a novel thin-sheet X-cut LiNbO/sub 3/ optical modulator structure which can be fabricated by precise polishing and lapping to obtain a thinner LiNbO/sub 3/ substrate for a lower driving voltage in addition to velocity matching and impedance matching. We demonstrated that the fabricated modulator had a driving voltage V/spl pi/ of 2 V and zero chirp for 40-Gb/s operation and had a high potential for suppressed dc drift, and long-term reliability. 相似文献
24.
T. Idehara Y. Iwata I. Ogawa 《Journal of Infrared, Millimeter and Terahertz Waves》2003,24(2):119-128
Frequency down-shift in the initial stage of CW or long pulse operation of a submillimeter wave gyrotron, Gyrotron FU IV, is observed. The shift occurs in a few minutes after turning on the operation and the amount of the shift attains even 0.1 GHz. The observation results are analyzed on the basis of a simple model for heat conduction in the region of a resonant cavity. The frequency shift is explained consistently by expansion of the cavity. 相似文献
25.
This paper proposes a hierarchical multilayer QoS routing system with dynamic SLA management for large-scale IP networks. Previously, the promising approach to provide QoS in large-scale IP networks using a mixture of DiffServ-based QoS management and MPLS-based traffic engineering has been actively discussed. However, the introduction of QoS exacerbates the already existing scalability problems of the standard IP routing protocols. In order to address this issue, we propose a new scalable routing framework based on hierarchical QoS-aware path computation. We augment the existing OSPF and CR-LDP protocols to support hierarchical QoS routing, QoS aggregation, and QoS reservation in our MPLS-DiffServ-based hierarchical routing network. In order to provide additional flexibility and cost-efficiency, we augment the network with a policy server which is capable of dynamically handling SLAs between the networks and providing load balancing management within the network. We implement a prototype of the proposed framework and study its performance with a virtual network simulator and specially designed QoS routing algorithm simulator. In our simulations, we evaluate both the implementation complexity and algorithms performance; the results demonstrate the efficiency of the framework and its advantages over the existing proposals 相似文献
26.
Yumiko Kaji Ryoji Mitsuhashi Xuesong Lee Hideki Okamoto Takashi Kambe Naoshi Ikeda Akihiko Fujiwara Minoru Yamaji Kenji Omote Yoshihiro Kubozono 《Organic Electronics》2009,10(3):432-436
C60 and picene thin film field-effect transistors (FETs) in bottom contact structure have been fabricated with poly(3,4-ethylenedioxythiophene): poly(styrenesulfonate) (PEDOT:PSS) electrodes for a realization of mechanical flexible organic FETs. The C60 thin film FETs showed n-channel enhancement-type characteristics with the field-effect mobility μ value of 0.41 cm2 V?1 s?1, while the picene thin film FET showed p-channel enhancement-type characteristics with the μ of 0.61 cm2 V?1 s?1. The μ values recorded for C60 and picene thin film FETs are comparable to those for C60 and picene thin film FETs with Au electrodes. 相似文献
27.
A highly functional circuit for pulse width modulation (PWM) signal processing is proposed as a core of the A-D merged circuit architecture for time-domain information processing. The core circuit employs a switched-current integration technique as its computing architecture and functions as a linear arithmetic operator, a memory, and also a delaying device of PWM signals. A 0.8-μm CMOS test chip includes 110 transistors plus two capacitors and performs parallel additions and multiplications at the accuracy of 1.2 ns. A cumulative property of the technique allows the circuit to serve as a low-power accumulator that consumes 23% of the energy of the full digital 7-b accumulator. A PWM multiply-accumulate unit and a nonlinear operation unit are also proposed to extend functionality of the circuit. Since the PWM signal carries multibit data in a binary amplitude pulse, these circuits can be favorably applicable to low-voltage and low-power designs in the deep submicrometer era 相似文献
28.
Heavy erosion of the electrode is a problem in using ac plasma torches. In a series of our studies, the effects of electrode stem size (diameter and length) and tip shape on the electrode erosion were clarified at a low current of 200 A. In this paper, on the basis of the 200-A data, in order to reduce the electrode erosion with the current increased, the effects of current and electrode size on electrode erosion were clarified experimentally and analytically between 100 and 550 A. The electrode used was of solid type and the material was tungsten containing 2 wt% of lanthanum oxide. The plasma gas was argon. Main results are as follows. (1) As the current increased, the electrode erosion increased linearly. In the case of thin electrodes (8 mm ø), between 450 and 550 A, the electrode tip was molten partially and the electrode erosion increased rapidly over 5 mg/h. However, for thick electrodes (13 mm ø), the electrode erosion did not increase rapidly. (2) The temperature distribution along the electrode axis was calculated. As a result, a good correlation was obtained between the calculated temperature of electrode tip and the measured electrode erosion. As the tip temperature decreased to 3000 K (cf. tungsten melting point: 3660 K), the electrode erosion decreased below 5 mg/h of the linearly increasing range. 相似文献
29.
The unsteady behavior of flow driven by a jet suddenly injected into a cell is numerically studied by solving the axisymmelric two-dimensional compressible Navier-Stokes equations. The system of the calculation is a model of the laser ablation of a certain duration followed by a discharging process through the exit hole at the down- stream end of the cell. In the calculations, the contour of the cell is changed while other parameters such as the Mach number of the jet, its duration, and the diameter of the cell exit are fixed. Monitoring the velocity at the exit hole is used to investigate the influence of the shape on the interaction between the shock wave and the jet. As the result, it was found that the velocity peak value and its arrival time at the downstream end of the cell exit are determined by the diameter of the cell. 相似文献
30.