全文获取类型
收费全文 | 7874篇 |
免费 | 1120篇 |
国内免费 | 697篇 |
专业分类
电工技术 | 565篇 |
技术理论 | 1篇 |
综合类 | 1217篇 |
化学工业 | 519篇 |
金属工艺 | 324篇 |
机械仪表 | 400篇 |
建筑科学 | 816篇 |
矿业工程 | 319篇 |
能源动力 | 209篇 |
轻工业 | 169篇 |
水利工程 | 351篇 |
石油天然气 | 169篇 |
武器工业 | 125篇 |
无线电 | 881篇 |
一般工业技术 | 1013篇 |
冶金工业 | 148篇 |
原子能技术 | 134篇 |
自动化技术 | 2331篇 |
出版年
2024年 | 40篇 |
2023年 | 174篇 |
2022年 | 217篇 |
2021年 | 272篇 |
2020年 | 308篇 |
2019年 | 274篇 |
2018年 | 228篇 |
2017年 | 278篇 |
2016年 | 342篇 |
2015年 | 370篇 |
2014年 | 530篇 |
2013年 | 609篇 |
2012年 | 597篇 |
2011年 | 597篇 |
2010年 | 452篇 |
2009年 | 521篇 |
2008年 | 515篇 |
2007年 | 521篇 |
2006年 | 504篇 |
2005年 | 369篇 |
2004年 | 317篇 |
2003年 | 231篇 |
2002年 | 239篇 |
2001年 | 172篇 |
2000年 | 164篇 |
1999年 | 121篇 |
1998年 | 112篇 |
1997年 | 91篇 |
1996年 | 72篇 |
1995年 | 64篇 |
1994年 | 78篇 |
1993年 | 53篇 |
1992年 | 41篇 |
1991年 | 38篇 |
1990年 | 34篇 |
1989年 | 30篇 |
1988年 | 19篇 |
1987年 | 9篇 |
1986年 | 15篇 |
1985年 | 7篇 |
1984年 | 16篇 |
1983年 | 9篇 |
1982年 | 9篇 |
1981年 | 6篇 |
1980年 | 3篇 |
1979年 | 2篇 |
1978年 | 4篇 |
1977年 | 4篇 |
1975年 | 3篇 |
1959年 | 4篇 |
排序方式: 共有9691条查询结果,搜索用时 31 毫秒
971.
N. Nordell A. Schöner K. Rottner P. O. Å. Persson Q. Wahab L. Hultman M. K. Linnarsson E. Olsson 《Journal of Electronic Materials》1998,27(7):833-837
Implantation of B has been performed into an epitaxially grown layer of 6H SiC, at two different B concentrations, 2×1016 cm−3 and 2×1018 cm−3. Subsequently, an epitaxial layer was regrown on the B implanted layer. The samples were investigated by transmission electron
microscopy (TEM) and secondary ion mass spectrometry (SIMS). In the highly B-doped layers plate-like defects were found, associated
with large strain fields, and an increased B concentration. These defects were stable at the originally implanted region during
regrowth and at anneal temperatures up to 1700°C. In the samples implanted with the lower B concentration, no crystal defects
could be detected by TEM. No threading dislocations or other defects were observed in the regrown epitaxial layer, which shows
the possibility to grow a layer with high crystalline quality on B implanted 6H SiC. By SIMS, it was found that B piles up
at the interface to the regrown layer, which could be explained by enhanced diffusion from an increased concentration of point
defects created by implantation damage in the region. B is also spread out into the original crystal and in the regrown layer
at a concentration of below 2×1016 cm−3, with a diffusion constant estimated to 1.3×10−12 cm2s−1. This diffusion is most probably not driven by implantation damage, but by intrinsic defects in the grown crystal. Our investigation
shows that the combination of implantation and subsequent regrowth techniques could be used in SiC for building advanced device
structures, with the crystal quality in the regrown layer not being deteriorated by crystal defects in the implanted region.
A device process using B implantation and subsequent regrowth could on the other hand be limited by the diffusion of B. 相似文献
972.
V. V. Gudkov A. T. Lonchakov A. V. Tkach I. V. Zhevstovskikh V. I. Sokolov N. B. Gruzdev 《Journal of Electronic Materials》2004,33(7):815-818
Ultrasonic experiments, done on ZnSe:Ni crystal with the dopant concentration 5.5×1019 cm−3, revealed precursor phenomenon in the form of lattice softening at temperatures significantly exceeding the temperature of
structural transition (Tc=14.5 K). It proved to be that the order parameter of the transition was associated with the shear deformation ε4. Investigation of thermal conductivity (κ) in the same temperature region pointed out that the Jahn-Teller (JT) effect could
be responsible for the anomalous behavior of κ(T) and lattice instability. 相似文献
973.
By using an approach based on the Taylor/Volterra series, nonlinear amplifier characteristics can be introduced into the Barkhausen criterion in order to estimate the amplitude for near‐sinusoidal oscillators. The characteristic equation is similar to the 1st‐order determining equation obtained by Chua. This new method includes all desirable features of Chua's equation and lets us generalize the linear approach directly to a nonlinear one without losing the mathematical simplicity of the Barkhausen criterion. It also allows us to determine the oscillation amplitude with a desired accuracy. Moreover, this method investigates the influence of the feedback factor and the voltage supply on the oscillation amplitude. Employing only the 3rd‐order nonlinearity of the amplifying element, the amplitude of the oscillation predicted by the modified Barkhausen criterion was compared to the one estimated using the transient analysis of SPICE, the harmonic balance analysis of Serenade, and by measurements. The amplitudes obtained by these four approaches for several feedback factors and supply voltages are in good agreement. © 2005 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2005. 相似文献
974.
The iteration space of a loop nest is the set of all loop iterations bounded by the loop limits. Tiling the iteration space
can effectively exploit the available parallelism, which is essential to multiprocessor compiling and pipelined architecture
design. Another improvement brought by tiling is the better data locality that can dramatically reduce memory access and,
consequently, the relevant memory access energy consumptions. However, previous studies on tiling were based on the data dependence,
thus arrays without dependencies such as input arrays (data streams) were not considered. In this paper, we extend the tiling
exploration to also accommodate those dependence-free arrays, and propose a stream-conscious tiling scheme for off-chip memory
access optimization. We show that input arrays are as important, if not more, as the arrays with data dependencies when the
focus is on memory access optimization instead of parallelism extraction. Our approach is verified on TI’s low power C55X
DSP with popular multimedia applications, exhibiting off-chip memory access reduction by 67% on average over the traditional
iteration space tiling. 相似文献
975.
Using the nonlinear Volterra series representation, analytical expressions for the third-order intermodulation distortion power and intercept point for a MESFET small-signal amplifier are derived when its equivalent circuit is bilateral and includes the gate-to-drain capacitance (Cgd) explicitly as a nonlinear element. Previously developed analytical expressions treated Cgd as a linear element or incorporated it as a part of gate-to-source and drain-to-source capacitances (Cgs and Cds). These new analytical expressions are then compared with experimental data and good agreement is obtained. The analytical expressions are also used to study the variation of intermodulation distortion with input power and frequency, and the effect of the individual nonlinear elements in the MESFET’s equivalent circuit. 相似文献
976.
977.
Particle methods such as the meso-particle method or the method of movable cellular automata provide new possibilities for the simulation of wear, mass-transfer, plastic deformation and melting processes. One crucial point, however, is to ensure that in the continuum limit macroscopic isotropy is guaranteed. We show how this can be done in two- and three-dimensional lattices. 相似文献
978.
基于层次分析法的空调冷热源方案优选 总被引:1,自引:0,他引:1
介绍了层次分析法的基本原理和计算步骤,将其应用于空调冷热源方案优选,得出了最优方案。 相似文献
979.
WEI Shuyi YAN Yuli XIA Congxin LIU Guangsheng 《武汉理工大学学报(材料科学英文版)》2006,21(3):123-125
Lattice constants and electronic structures of diluted magnetic semiconductors ( In, Mn ) As were investigated using the first principles LMTO-ASA band calculation by assuming supercell structures. Three concentrations of the 3 d impurities were studied ( x = 1/2, 1/4, 1/8). The effect of varying Mn coucentrations on the lattice constants and the electronic structures are shown. 相似文献
980.
用改进的Nwarmann方法制备出高聚乙炔膜,作碘和四氯化铁重掺杂。用扫描电镜观察到样品纤维间的接触,在链间产生接触垫垒,形成隧穿结,反式聚乙炔在重掺杂时会出现孤子晶格,在能隙中央形成孤子能带。在热激活下,带电弧子中的电子即会跳入附近的中性孤子。这有利于孤子能带中的电子,通过能带中接力式的跳跃,进入导带,成为自由电子。 相似文献