全文获取类型
收费全文 | 11654篇 |
免费 | 1939篇 |
国内免费 | 1232篇 |
专业分类
化学 | 6001篇 |
晶体学 | 86篇 |
力学 | 778篇 |
综合类 | 66篇 |
数学 | 1130篇 |
物理学 | 3584篇 |
无线电 | 3180篇 |
出版年
2024年 | 61篇 |
2023年 | 279篇 |
2022年 | 389篇 |
2021年 | 502篇 |
2020年 | 461篇 |
2019年 | 407篇 |
2018年 | 348篇 |
2017年 | 359篇 |
2016年 | 511篇 |
2015年 | 541篇 |
2014年 | 593篇 |
2013年 | 831篇 |
2012年 | 922篇 |
2011年 | 975篇 |
2010年 | 726篇 |
2009年 | 696篇 |
2008年 | 785篇 |
2007年 | 619篇 |
2006年 | 682篇 |
2005年 | 517篇 |
2004年 | 398篇 |
2003年 | 343篇 |
2002年 | 328篇 |
2001年 | 270篇 |
2000年 | 288篇 |
1999年 | 253篇 |
1998年 | 241篇 |
1997年 | 224篇 |
1996年 | 230篇 |
1995年 | 180篇 |
1994年 | 149篇 |
1993年 | 137篇 |
1992年 | 117篇 |
1991年 | 89篇 |
1990年 | 89篇 |
1989年 | 62篇 |
1988年 | 48篇 |
1987年 | 37篇 |
1986年 | 40篇 |
1985年 | 26篇 |
1984年 | 20篇 |
1983年 | 18篇 |
1982年 | 17篇 |
1981年 | 4篇 |
1980年 | 7篇 |
1979年 | 2篇 |
1978年 | 1篇 |
1975年 | 1篇 |
1957年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
2.
3.
4.
Shi-Jin Ding Hang Hu Lim H.F. Kim S.J. Yu X.F. Chunxiang Zhu Li M.F. Byung Jin Cho Chan D.S.H. Rustagi S.C. Yu M.B. Chin A. Dim-Lee Kwong 《Electron Device Letters, IEEE》2003,24(12):730-732
For the first time, we successfully fabricated and demonstrated high performance metal-insulator-metal (MIM) capacitors with HfO/sub 2/-Al/sub 2/O/sub 3/ laminate dielectric using atomic layer deposition (ALD) technique. Our data indicates that the laminate MIM capacitor can provide high capacitance density of 12.8 fF//spl mu/m/sup 2/ from 10 kHz up to 20 GHz, very low leakage current of 3.2 /spl times/ 10/sup -8/ A/cm/sup 2/ at 3.3 V, small linear voltage coefficient of capacitance of 240 ppm/V together with quadratic one of 1830 ppm/V/sup 2/, temperature coefficient of capacitance of 182 ppm//spl deg/C, and high breakdown field of /spl sim/6 MV/cm as well as promising reliability. As a result, the HfO/sub 2/-Al/sub 2/O/sub 3/ laminate is a very promising candidate for next generation MIM capacitor for radio frequency and mixed signal integrated circuit applications. 相似文献
5.
自由电子激光的预群聚 总被引:1,自引:0,他引:1
研究了自由电子激光预群聚产生的辐射,表明预群聚不仅可以提高效率而且使低增益得到增强,从而在理论上解释了由射频直线加速器驱动的自由电子激光预群聚器(prebuncher)的作用。同时还指出,预群聚有在不增加电子束能量情况下缩短激光波长和降低对电子束质量要求等作用。 相似文献
6.
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
7.
Kameyama H. Miyajima T. Zhi Ding 《IEEE transactions on circuits and systems. I, Regular papers》2008,55(3):851-860
In multicarrier systems, when the order of a channel impulse response is larger than the length of the cyclic prefix (CP), there is a significant performance degradation due to interblock interference (IBI). This paper proposes a blind-channel shortening method in which the equalizer parameter vector is formed by the noise subspace of the received signal correlation matrix so that the output power is maximized. The proposed method can not only shorten the effective channel impulse response to within the CP length but also maximize the output signal-to-interference-and-noise ratio while eliminating the IBI. We point out that the performance depends on the choice of a decision delay and propose a simple method for determining the appropriate delay. We propose both a batch algorithm and an adaptive algorithm and show by simulation that they are superior to the conventional algorithms. 相似文献
8.
Eng Leong Tan Ding Yu Heh 《Microwave and Wireless Components Letters, IEEE》2008,18(5):296-298
This letter presents an unconditionally stable alternating direction implicit finite-difference time-domain (ADI-FDTD) method with fourth order accuracy in time. Analytical proof of unconditional stability and detailed analysis of numerical dispersion are presented. Compared to second order ADI-FDTD and six-steps SS-FDTD, the fourth order ADI-FDTD generally achieves lower phase velocity error for sufficiently fine mesh. Using finer mesh gridding also reduces the phase velocity error floor, which dictates the accuracy limit due to spatial discretization errors when the time step size is reduced further. 相似文献
9.
Bin Xie Shi X.Q. Han Ding 《Components and Packaging Technologies, IEEE Transactions on》2008,31(2):361-369
In an anisotropic conductive adhesive (ACA) assembly, the electrical conduction is usually achieved with the conductive particles between the bumps of integrated circuit (IC) and corresponding conductive tracks on the glass substrate. Fully understanding of the mechanical and electrical characteristics of ACA particles can help to optimize the assembly process and improve the reliability of ACA interconnection. Most conductive particles used in the ACA assembly are with cracks in the metal coating of the particles after the ACA bonding. This paper introduced the fracture analysis by applying the cohesive elements in the numerical model of the nickel-coated polymer particle and further simulating the cracks initiation and propagation in the nickel coating during the ACA bonding. The simulation results showed that the stress distribution on the nickel-coated particle with cracks was significantly different from that on the nickel-coated particle without crack, indicating that the stress analysis by taking the crack into consideration is very important for the reliability assessment of the ACA interconnection. The stress analysis of cohesive elements indicated that the cracks initiated at the central area of the nickel coating and propagated to the polar area. Furthermore, by the introduction of a new parameter of the virtual resistance, a mathematical model was established to describe the electrical characteristics of the nickel-coated particle with cracks. The particle resistance of the nickel-coated particle with cracks was found to be much higher than that of the particle without crack in the optimized bonding pressure range, indicating that it is necessary to take the crack into consideration for the particle conduction analysis as well. Therefore, the fracture analysis on the conductive particle by taking the crack into consideration could accurately evaluate the reliability of ACA interconnection and avoid serious reliability issues. 相似文献
10.