全文获取类型
收费全文 | 288972篇 |
免费 | 3104篇 |
国内免费 | 819篇 |
专业分类
电工技术 | 5040篇 |
综合类 | 162篇 |
化学工业 | 45669篇 |
金属工艺 | 11924篇 |
机械仪表 | 8619篇 |
建筑科学 | 6890篇 |
矿业工程 | 1838篇 |
能源动力 | 6756篇 |
轻工业 | 26028篇 |
水利工程 | 3231篇 |
石油天然气 | 7113篇 |
武器工业 | 16篇 |
无线电 | 31548篇 |
一般工业技术 | 57141篇 |
冶金工业 | 51721篇 |
原子能技术 | 7546篇 |
自动化技术 | 21653篇 |
出版年
2021年 | 2115篇 |
2018年 | 3693篇 |
2017年 | 3647篇 |
2016年 | 3927篇 |
2015年 | 2481篇 |
2014年 | 4255篇 |
2013年 | 12113篇 |
2012年 | 6871篇 |
2011年 | 9287篇 |
2010年 | 7620篇 |
2009年 | 8689篇 |
2008年 | 8984篇 |
2007年 | 8864篇 |
2006年 | 7877篇 |
2005年 | 7349篇 |
2004年 | 6847篇 |
2003年 | 6599篇 |
2002年 | 6661篇 |
2001年 | 6521篇 |
2000年 | 6202篇 |
1999年 | 6240篇 |
1998年 | 14780篇 |
1997年 | 11077篇 |
1996年 | 8600篇 |
1995年 | 6545篇 |
1994年 | 5938篇 |
1993年 | 5810篇 |
1992年 | 4509篇 |
1991年 | 4460篇 |
1990年 | 4306篇 |
1989年 | 4325篇 |
1988年 | 4282篇 |
1987年 | 3613篇 |
1986年 | 3612篇 |
1985年 | 4172篇 |
1984年 | 3982篇 |
1983年 | 3645篇 |
1982年 | 3442篇 |
1981年 | 3577篇 |
1980年 | 3440篇 |
1979年 | 3376篇 |
1978年 | 3454篇 |
1977年 | 3934篇 |
1976年 | 5048篇 |
1975年 | 3172篇 |
1974年 | 3014篇 |
1973年 | 3037篇 |
1972年 | 2656篇 |
1971年 | 2477篇 |
1970年 | 2112篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
901.
Kerber A. Cartier E. Pantisano L. Degraeve R. Kauerauf T. Kim Y. Hou A. Groeseneken G. Maes H.E. Schwalke U. 《Electron Device Letters, IEEE》2003,24(2):87-89
The magnitude of the V/sub T/ instability in conventional MOSFETs and MOS capacitors with SiO/sub 2//HfO/sub 2/ dual-layer gate dielectrics is shown to depend strongly on the details of the measurement sequence used. By applying time-resolved measurements (capacitance-time traces and charge-pumping measurements), it is demonstrated that this behavior is caused by the fast charging and discharging of preexisting defects near the SiO/sub 2//HfO/sub 2/ interface and in the bulk of the HfO/sub 2/ layer. Based on these results, a simple defect model is proposed that can explain the complex behavior of the V/sub T/ instability in terms of structural defects as follows. 1) A defect band in the HfO/sub 2/ layer is located in energy above the Si conduction band edge. 2) The defect band shifts rapidly in energy with respect to the Fermi level in the Si substrate as the gate bias is varied. 3) The rapid energy shifts allows for efficient charging and discharging of the defects near the SiO/sub 2//HfO/sub 2/ interface by tunneling. 相似文献
902.
M. Blaho D. Pogany E. Gornik M. Denison G. Groos M. Stecher 《Microelectronics Reliability》2003,43(4):545-548
Current distribution in vertical double-diffused MOS (DMOS) transistors of a Smart Power Technology are investigated under high current, short duration operation conditions by means of a backside laser interferometric thermal mapping technique. DMOS devices of different areas are studied under pulsed gate forward operation mode and under electrostatic discharge (ESD)-like stress with floating and grounded gate. The internal behavior of the devices observed by thermal mapping under these stress conditions is correlated with the electrical characteristics. 相似文献
903.
Weight-loss kinetics were studied for 10 industrial extruded samples of poly(vinyl chloride) (PVC) plasticized by 20–30% by weight of didecylphtalate at 85, 95, 105, 110, and 120deg;C. For the most unstable samples, which contained a light coplasticizer, the weight-loss rate obeyed Fick's law. In the other cases, it was constant in the early period of exposure. The apparent Arrhenius parameters (i.e., preexponential factor and activation energy) were intercorrelated and varied strongly from one sample to another. This was explained by the existence of two distinct kinetic regimes corresponding, respectively, to diffusion or evaporation, the whole process being controlled by the slowest step, and a transition between both regimes occurring in the temperature range of exposure. In the proposed model, small changes of the preexponential factor of diffusion from one sample to another are sufficient to take into account the observed behavior. 相似文献
904.
Arjavalingam G. Pastol Y. Halbout J.-M. Robertson W.M. 《Antennas and Propagation Magazine, IEEE》1991,33(1):7-11
A brief tutorial on the picosecond photoconductive effect is given. The use of picosecond optoelectronics for the characterization of broadband antennas is described. In particular, the transient radiation properties of equiangular-spiral and exponentially tapered coplanar-strip antennas are discussed. The transient radiation behavior and the polarization and radiation patterns of these antennas are easily determined with this measurement technique, without the need for anechoic chambers. Applications of picosecond-duration transient electromagnetic radiation to filter measurements, materials measurements, and scattering studies are discussed 相似文献
905.
906.
Some flaws in a recent article by S.B. Alexander et al. (ibid., vol.7, no.1, p.11-23, Jan. 1989) on the theory of equalization of FM response of a laser diode using passive filters are noted. An error has occurred as a result of assuming a constant C as a positive instead of negative. When C is negative and large, the equalization network cannot be realized with passive networks. Also the simulated time waveform shown in the article for the optical frequency of an equalized laser does not show some spikes which are expected theoretically. The spikes occur as a result of an imperfect equalization provided by the proposed passive filters that were realized assuming C as positive. In replying the original author feels that the comments and observations result simply from attempting to extend the simple FM transfer-function model far beyond its limits while trying to introduce unnecessary theoretical rigor 相似文献
907.
908.
The crystal structure of CaMgGeO4 is described. CaMgGeO4, Mr = 200.9, orthorhombic, Pnam, A = 11.285(5) Å, B = 5.016(2) Å, C = 6.435(2) Å, V = 364.36 Å3, Dx = 3.664 Mg/m3.λ(MoKa = 0.71069 Å, F(000) = 384, room temperature, final R = 0.045 for 1752 observed reflections. The structure is isomorphous with CaMgSiO4 (monticellite). 相似文献
909.
Voltage switching induced by long-wavelength infrared light from a CO2 laser was observed using a double-barrier resonant tunneling diode (RTD) biased in the bistable region and the intersubband transition (IT) between the quantum confined states. Possible optoelectronic and all-optical switching applications involving hysteresis are proposed and discussed 相似文献
910.
A rotative quadrature phase-shift keying (RQPSK) modulation scheme is proposed. By rotating the QPSK signal constellation by pi /2 either clockwise or anticlockwise during a symbol duration, the conventional QPSK scheme can be modified to transmit 3 bits per symbol to achieve both power and bandwidth efficiency.<> 相似文献