全文获取类型
收费全文 | 26598篇 |
免费 | 3743篇 |
国内免费 | 2486篇 |
专业分类
化学 | 13961篇 |
晶体学 | 190篇 |
力学 | 1197篇 |
综合类 | 159篇 |
数学 | 2394篇 |
物理学 | 7654篇 |
无线电 | 7272篇 |
出版年
2024年 | 54篇 |
2023年 | 622篇 |
2022年 | 617篇 |
2021年 | 929篇 |
2020年 | 895篇 |
2019年 | 800篇 |
2018年 | 757篇 |
2017年 | 678篇 |
2016年 | 1008篇 |
2015年 | 1088篇 |
2014年 | 1312篇 |
2013年 | 1725篇 |
2012年 | 2070篇 |
2011年 | 2211篇 |
2010年 | 1535篇 |
2009年 | 1507篇 |
2008年 | 1654篇 |
2007年 | 1569篇 |
2006年 | 1452篇 |
2005年 | 1228篇 |
2004年 | 908篇 |
2003年 | 748篇 |
2002年 | 727篇 |
2001年 | 650篇 |
2000年 | 590篇 |
1999年 | 619篇 |
1998年 | 567篇 |
1997年 | 493篇 |
1996年 | 496篇 |
1995年 | 456篇 |
1994年 | 399篇 |
1993年 | 340篇 |
1992年 | 278篇 |
1991年 | 300篇 |
1990年 | 271篇 |
1989年 | 191篇 |
1988年 | 158篇 |
1987年 | 125篇 |
1986年 | 99篇 |
1985年 | 117篇 |
1984年 | 85篇 |
1983年 | 74篇 |
1982年 | 69篇 |
1981年 | 53篇 |
1980年 | 28篇 |
1979年 | 28篇 |
1978年 | 29篇 |
1977年 | 33篇 |
1976年 | 32篇 |
1974年 | 27篇 |
排序方式: 共有10000条查询结果,搜索用时 375 毫秒
91.
The distortion theorem for biholomorphic convex mappings in bounded symmetric domains are considered. Especially the distortion theorem for biholomorphic convex mappings in classical domain of type IV and two exceptional domains are given. 相似文献
92.
Gong S.S. Burnham M.E. Theodore N.D. Schroder D.K. 《Electron Devices, IEEE Transactions on》1993,40(7):1251-1257
Electrical time-to-breakdown (TTB) measurements have shown the charge to breakdown Q bd of gate oxide capacitors fabricated on n-type well (n-well) substrates always to be higher than that of capacitors on p-type well (p-well) substrates on the same wafer when both are biased into accumulation under normal test conditions. Here the authors correlate the higher n-well Q bd to smooth capacitor oxide/substrate interfaces and minimized grain boundary cusps at the poly-Si gate/oxide interfaces, confirming that Fowler-Nordheim tunneling is the dominant current conduction mechanisms through the oxide. They correlate higher Q bd to higher barrier height for a given substrate type and observe that the slope of the barrier height versus temperature plot is lower for both p-well and n-well cases with electrons tunneling from the silicon substrate. This is attributed to surface roughness at the poly-Si gate/SiO2 interface. A poly-Si gate deposition and annealing process with clean, smooth oxide/substrate interfaces will improve the p-well breakdown characteristics and allow higher Q bd to be achieved 相似文献
93.
A structured genetic algorithm (SGA) approach is developed for robust controller design based on the concept of an H∞ loop-shaping technique and the method of inequalities. Such an SGA is capable of simultaneously searching the orders and coefficients of the precompensator and postcompensator for the weighted plant. It is, therefore, not necessary to predefine the order of compensators as in usual practice. A multiple objective ranking approach is also incorporated so that the design criteria of extreme plants can be easily achieved. The effectiveness of such a technique is illustrated by a high-purity distillation column design example 相似文献
94.
This paper introduces genetic algorithms (GA) as a complete entity, in which knowledge of this emerging technology can be integrated together to form the framework of a design tool for industrial engineers. An attempt has also been made to explain “why” and “when” GA should be used as an optimization tool 相似文献
95.
MOS控制晶闸管的三重扩散工艺研究 总被引:1,自引:0,他引:1
本文对MCT的核心工艺-三重扩散工艺进行了详细研究。通过SUPREM-Ⅲ计算机工艺仿真,获得了三重扩散的工艺条件。 相似文献
96.
本文报道了Pancharatnam位相非线性变化的实验研究,实验结果与理论预言符合得很好。Pancharatnam位相的这种非线性可能在光开关中得到应用。 相似文献
97.
Kwok Kee Chan Rao S.K. Morin G.A. Tang M.Q. 《Antennas and Propagation, IEEE Transactions on》1997,45(8):1277-1285
A new method of analysis for the radiation characteristics of dielectric lens antennas with arbitrary inner and outer surfaces is presented. The analysis is based on representing the feed illumination by a contiguous set of ray tubes and including the effects of surface reflections and ray divergence. Radiation patterns and the antenna gain are then computed by evaluating the closed-form expressions developed for the Kirchhoff's integral of the aperture fields. The validity of the analysis method has been demonstrated by comparing the computations with measured results of two different spherical lenses and a shaped lens configurations. The analysis method presented takes into account some of the practical aspects associated with lens design such as surface zoning to reduce the mass and surface matching to minimize the reflection loss 相似文献
98.
结构振动控制中压电阻尼技术研究:(三)机敏约束层阻尼技术 总被引:9,自引:1,他引:8
给出了机敏约束阻尼概念,阐述了机敏约束层阻尼系统特征,分析了结构设计和系统建模方法。以典型梁系统为例,比较了被动约束阻尼技术和机敏约束层阻尼技术减振效果。结果表明;机敏约束层阻尼控制技术是一种更为有效的振动控制方法。最后,提出了今后重点研究问题。 相似文献
99.
Ming-Jer Jeng Jenn-Gwo Hwu 《Electron Device Letters, IEEE》1996,17(12):575-577
Anodic oxidation at room temperature with pure deionized water as electrolyte and then followed by high-temperature rapid thermal densification was used to prepare high breakdown endurance thin-gate oxides with thicknesses of about 50 Å. It was observed that the oxides prepared by anodic oxidation followed by rapid thermal densification (AOD) show better electrical characteristics than those grown by rapid thermal oxidation (RTO) only. The AOD oxides have a very low midgap interface trap density, Ditm, of smaller than 1×1010 eV-1 cm-2 and negative effective oxide trapped charge. From the smaller leakage currents observed during staircase ramp voltage time-zero dielectric breakdown (TZDB) and constant field time-dependent dielectric breakdown (TDDB) testings, it is supposed that the uniform interfacial property and the pretrapped negative charges in AOD oxides are responsible for the improved characteristics 相似文献
100.