全文获取类型
收费全文 | 56880篇 |
免费 | 13820篇 |
国内免费 | 3707篇 |
专业分类
化学 | 48554篇 |
晶体学 | 476篇 |
力学 | 1103篇 |
综合类 | 164篇 |
数学 | 3433篇 |
物理学 | 6549篇 |
无线电 | 14128篇 |
出版年
2024年 | 31篇 |
2023年 | 263篇 |
2022年 | 355篇 |
2021年 | 624篇 |
2020年 | 2192篇 |
2019年 | 3559篇 |
2018年 | 1828篇 |
2017年 | 1433篇 |
2016年 | 4478篇 |
2015年 | 4663篇 |
2014年 | 4775篇 |
2013年 | 5531篇 |
2012年 | 4615篇 |
2011年 | 3939篇 |
2010年 | 4223篇 |
2009年 | 4243篇 |
2008年 | 3877篇 |
2007年 | 3276篇 |
2006年 | 2796篇 |
2005年 | 2772篇 |
2004年 | 2416篇 |
2003年 | 2146篇 |
2002年 | 2940篇 |
2001年 | 2104篇 |
2000年 | 1945篇 |
1999年 | 770篇 |
1998年 | 349篇 |
1997年 | 280篇 |
1996年 | 259篇 |
1995年 | 214篇 |
1994年 | 191篇 |
1993年 | 193篇 |
1992年 | 136篇 |
1991年 | 107篇 |
1990年 | 91篇 |
1989年 | 69篇 |
1988年 | 70篇 |
1987年 | 64篇 |
1986年 | 46篇 |
1985年 | 51篇 |
1984年 | 47篇 |
1983年 | 29篇 |
1982年 | 35篇 |
1981年 | 44篇 |
1980年 | 31篇 |
1979年 | 50篇 |
1978年 | 40篇 |
1977年 | 37篇 |
1976年 | 29篇 |
1974年 | 29篇 |
排序方式: 共有10000条查询结果,搜索用时 625 毫秒
91.
基于充放电原理实现的微电容测量电路 总被引:1,自引:0,他引:1
具有抗分布电容以及简单实用等特性的充放电电路是目前微电容测量中广泛采用的一种测量电路。本文对基于充放电原理的微电容测量电路进行了深入研究,并介绍一种基于充放电原理的实用电路。 相似文献
92.
93.
Effect of misalignment on electrical characteristics of ACF joints for flip chip on flex applications 总被引:1,自引:0,他引:1
The effect of misalignment on the electrical properties of anisotropic conductive film (ACF) joints is investigated in this work. It is found that along with the increase of misalignment, the connection resistance of ACF joints increases. When the misalignment in x-direction is less than 5 μm, the increase rate of connection resistance is quite large. Then, along with the severity of misalignment, the increase rate becomes smaller. Finally, when the misalignment is close to 20 μm, the increase rate rises again. The Holm's electric contact theory is used for understanding the connection resistance variation. On the other hand, with the increase of misalignment in x-direction, the insulation resistance between ACF joints decreases. If the misalignment exceeded 10 μm, the decrease is prominent for the Ni particle ACF joints. This phenomenon can be explained by the effect of dielectric damage of the epoxy.Computer programs are also developed to calculate the variation of the probability of open and shorting after misalignment and predicate the maximum misalignment tolerance. The results show that the open and shorting probability increase abruptly after misalignment. On the view of pad parameters, the open probability is mainly related to the pad area, while the pads gap is critical to the shorting probability. Large pads gap (small pad width) can reduce the shorting probability obviously. On the other hand, enlarging the pad area by increasing pad length decreases the open probability significantly. So comparing to square shape pad, rectangle shape pad can reduce the failure probability greatly. 相似文献
94.
95.
Proton conductivity of phosphoric acid derivative of fullerene 总被引:1,自引:0,他引:1
The proton conductive property of methano [60] fullerene diphosphoric acid has been investigated under various humidity conditions at the temperature range between 15 and 45 °C. It shows proton conductivity as high as 10−2 S cm−1 at 25 °C under relative humidity of 95%. Thermal analyses including TG–DTA and thermal desorption mass spectroscopy (TDS) confirm that the compound is thermally stable up to 200 °C. Proton conduction of the compound depends very much on humidity or water content. The logarithmic conductivity at 25 °C is increased linearly with increasing relative humidity. The activation energy (Ea) estimated from the slope of log(σT) vs. 1/T is decreased from 1.08 to 0.52 eV, as the relative humidity is increased from 40% to 75%. The humidity dependence of conductivity is discussed in the light of the observed hydration isotherm. 相似文献
96.
We report on the Langmuir-Blodgett film deposition and plasma etching of cadmium distearate on n-Gao.47Ino.53As to form a high-barrier-height Schottky barrier. Using this technique to form the gate electrode, we fabricated a 1?m-gate-length inverted InP-GalnAs modulation-doped field-effect transistor (MODFET) with an extrinsic transconductance of 170mS/mm and a cutoff frequencyfT of 19 GHz. 相似文献
97.
98.
Wen Zhang Hui Huang Yu Ding Margherita Gavagnin Ernesto Mollo Guido Cimino Yue‐Wei Guo 《Helvetica chimica acta》2006,89(4):813-820
Three new polyoxygenated steroids, muricesteroid ( 1 ), and menellsteroids A ( 2 ) and B ( 3 ), were isolated from two species of the South China Sea gorgonian Muricella flexuosa and Menella verrucosa Brundin , respectively. The structures of these new compounds were elucidated on the basis of extensive spectroscopic analysis, chemical methods and comparison with known related compounds. 相似文献
99.
It is proved that the variety of relevant disjunction lattices has the finite embeddability property. It follows that Avron's relevance logic RMI min has a strong form of the finite model property, so it has a solvable deducibility problem. This strengthens Avron's result that RMI min is decidable. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
100.