全文获取类型
收费全文 | 17079篇 |
免费 | 1233篇 |
国内免费 | 48篇 |
专业分类
电工技术 | 229篇 |
综合类 | 16篇 |
化学工业 | 3761篇 |
金属工艺 | 604篇 |
机械仪表 | 1237篇 |
建筑科学 | 318篇 |
矿业工程 | 3篇 |
能源动力 | 715篇 |
轻工业 | 1427篇 |
水利工程 | 95篇 |
石油天然气 | 19篇 |
无线电 | 3202篇 |
一般工业技术 | 3772篇 |
冶金工业 | 872篇 |
原子能技术 | 248篇 |
自动化技术 | 1842篇 |
出版年
2024年 | 9篇 |
2023年 | 199篇 |
2022年 | 221篇 |
2021年 | 569篇 |
2020年 | 385篇 |
2019年 | 458篇 |
2018年 | 517篇 |
2017年 | 596篇 |
2016年 | 658篇 |
2015年 | 569篇 |
2014年 | 787篇 |
2013年 | 1154篇 |
2012年 | 1200篇 |
2011年 | 1467篇 |
2010年 | 989篇 |
2009年 | 1063篇 |
2008年 | 940篇 |
2007年 | 760篇 |
2006年 | 653篇 |
2005年 | 585篇 |
2004年 | 535篇 |
2003年 | 513篇 |
2002年 | 507篇 |
2001年 | 408篇 |
2000年 | 360篇 |
1999年 | 329篇 |
1998年 | 431篇 |
1997年 | 281篇 |
1996年 | 227篇 |
1995年 | 163篇 |
1994年 | 145篇 |
1993年 | 107篇 |
1992年 | 85篇 |
1991年 | 75篇 |
1990年 | 65篇 |
1989年 | 80篇 |
1988年 | 42篇 |
1987年 | 52篇 |
1986年 | 34篇 |
1985年 | 40篇 |
1984年 | 27篇 |
1983年 | 11篇 |
1982年 | 10篇 |
1981年 | 12篇 |
1980年 | 7篇 |
1979年 | 4篇 |
1978年 | 6篇 |
1977年 | 6篇 |
1976年 | 8篇 |
1973年 | 4篇 |
排序方式: 共有10000条查询结果,搜索用时 171 毫秒
91.
Yi Kai Zhou Sung Woo Choi Shigeya Kimura Shuichi Emura Shigehiko Hasegawa Hajime Asahi 《Journal of Superconductivity and Novel Magnetism》2007,20(6):429-432
GaGdN layers were grown at temperatures below 300°C by radio-frequency plasma-assisted molecular beam epitaxy on sapphire
substrates. GaGdN samples with high Gd concentration as high as 12.5% were obtained by lowering the growth temperature. X-ray
diffraction results showed no obvious secondary phase, which means that the phase separation can be suppressed by the growth
at low temperatures. All samples, including those grown at room temperature, showed ferromagnetic characteristics. Photoluminescence
emission was observed, though spectra exhibit broad and sharp luminescence bands related to many kinds of defects. It is suggested
that electrons coming from defects, especially, nitrogen vacancy, stabilize ferromagnetism, and that the carrier-induced ferromagnetism
occurs in the low-temperature-growth GaGdN. 相似文献
92.
Novel floating-patch micro-electro-mechanical system (MEMS) antennas are proposed for millimetre-wave applications. The floating-patch MEMS antennas are fabricated on a high resistivity silicon (HRS) substrate using surface micromachining technology. Simulation and experimental results for reflection coefficients and radiation patterns are presented. 相似文献
93.
The distinct advantages of the electromagnetic casting (EMC) process consist in the presence of stirring motions in the melt,
which lead to significant grain size reduction in solidified ingot. Furthermore, surface and subsurface qualities are improved
due to the absence of ingot mold. However, it is impossible to achieve the aforementioned advantages in conventional direct
chill casting (DCC). In order to contrast the before and after heat treatments of the microstructural and mechanical characteristics
of EMC and DCC 2024 aluminium alloys, optical microscopy, scanning electron microscopy, transmission electron microscopy (TEM),
X-ray diffractions (XRD), differential scanning calorimetry (DSC), etc. were carried out. Compared with the DCC ingot, the EMC ingot has better mechanical properties not only in the ascast condition
but also in the as-aged condition. The DSC curves show that the EMC specimens have high enthalpy, i.e., the thermal kinetic
energy to form precipitates during the aging treatment process. Despite heat treatments applied to the DCC ingot, it fails
to attain the same mechanical properties as the EMC ingot. Moreover, considering the expernsive scalping operation for DCC
ingots, the EMC technique, which offers a lower manufacturing cost, is one of the best manufacturing methods used in obtaining
the ingots of wrought aluminum alloys. 相似文献
94.
In this paper, we introduce a transmit multiple-input multiple-output (MIMO) scheme with frequency domain pre-equalization for a multipath or frequency selective channel. In this scheme, MIMO processing in the frequency domain is performed at the transmitter or base station so that the receiver or mobile station only requires limited processing. This scheme provides high data rates and also inherits from the frequency domain equalization the property of relatively low complexity in severe multipath environments. The MIMO transmit processing is derived by minimizing the minimum mean square errors (MMSE), and expressions for the signal-to-interference-plus-noise ratio and error probability based on the Gaussian approximation of the interference term are provided. Some important associated issues, such as channel errors and computational complexity, are also investigated. Numerical simulations are also provided and these demonstrate the improved performance of our proposed scheme compared to other transmit MIMO schemes. In particular, they show that the proposed system can attain multipath or frequency diversity of the channel. 相似文献
95.
Onishi K. Rino Choi Chang Seok Kang Hag-Ju Cho Young Hee Kim Nieh R.E. Jeong Han Krishnan S.A. Akbar M.S. Lee J.C. 《Electron Devices, IEEE Transactions on》2003,50(6):1517-1524
Bias-temperature instabilities (BTI) of HfO/sub 2/ metal oxide semiconductor field effect transistors (MOSFETs) have been systematically studied for the first time. NMOS positive BTI (PBTI) exhibited a more significant V/sub t/ instability than that of PMOS negative BTI (NBTI), and limited the lifetime of HfO/sub 2/ MOSFETs. Although high-temperature forming gas annealing (HT-FGA) improved the interface quality by passivating the interfacial states with hydrogen, BTI behaviors were not strongly affected by the technique. Charge pumping measurements were extensively used to investigate the nature of the BTI degradation, and it was found that V/sub t/ degradation of NMOS PBTI was primarily caused by charge trapping in bulk HfO/sub 2/ rather than interfacial degradation. Deuterium (D/sub 2/) annealing was found to be an excellent technique to improve BTI immunity as well as to enhance the mobility of HfO/sub 2/ MOSFETs. 相似文献
96.
We developed a new type of human-sized biped walking robot (BWR) driven by the closed-chain type of joint actuator. Each leg of the robot is composed of three pitch joints and one roll joint. In all, a 15 degree-of-freedom robot including four arm joints and three joints for the head was developed. The BWR was developed to walk autonomously such that all leg joints are actuated by small 90 W dc motors/drivers and dc batteries and controllers which are boarded. The joint actuator for the BWR is composed of the four-bar-link mechanism driven by the ball screw which has high strength and high gear ratio. A dynamics modeling of the developed BWR for forward walking is presented in which the revolute joint dynamics are transformed into the prismatic joint dynamics of the ball screw. Also, an analysis on the four-bar-link mechanism applied to the joint actuator and on the structure of the BWR is shown. The design specification of the actuating motor for the BWR is analyzed through the torque analysis of the four-bar-link actuator. Through walking experiments of the BWR, the walking performance and trajectory tracking ability is shown. © 2004 Wiley Periodicals, Inc. 相似文献
97.
In this paper, we report on the design, fabrication, and test of a passive pressure transensor. The sensor uses the self-resonant frequency modulation of an integrated coil to detect the pressure variations. This modulation is generated by the relative displacement of a ferrite core attached to a silicone rubber membrane. This scheme simplifies the packaging of the passive transensor by removing the requirement for a separate capacitor to form the resonator. A 30-turn 1.7-/spl mu/H coil having dimensions of 3/spl times/3 mm/sup 2/ is used in a prototype design yielding a sensitivity of 9.6 kHz/kPa with a cylindrical ferrite core of 0.95-mm diameter and 0.5-mm height. We also present a theoretical model of the sensor that shows good agreement with the experimental data. This model can be a useful tool for further optimization of the senors. 相似文献
98.
Jae-Duk Lee Jeong-Hyuk Choi Donggun Park Kinam Kim 《Electron Device Letters, IEEE》2003,24(12):748-750
In contrast to the conventional theories, we have revealed that the most distinguished mechanism in the data retention phenomenon after Fowler-Nordheim (FN) stress in sub-100 nm NAND Flash memory cells is the annihilation of interface states. Interface state generation rate increases rapidly as the channel width of NAND flash cell decreases. Comparison of interface states and stress-induced leakage current (SILC) component during retention mode shows that the annihilation of interface states strongly affects data retention characteristics of the programmed cells. 相似文献
99.
100.
Si-Woong Lee Jae Gark Choi Byoung-Ju Yun 《Electronics letters》2003,39(9):712-714
An adaptive contour smoothing algorithm designed as a preprocessor for shape coders is presented. In the method, the degree of the adaptive smoothing is controlled based on the significance of each contour point, which is quantified according to inter-region contrast in an intensity image. The actual smoothing consists of an expansion operator and a thinning algorithm. 相似文献