全文获取类型
收费全文 | 45154篇 |
免费 | 6541篇 |
国内免费 | 4513篇 |
专业分类
化学 | 31603篇 |
晶体学 | 458篇 |
力学 | 3036篇 |
综合类 | 407篇 |
数学 | 5247篇 |
物理学 | 15457篇 |
出版年
2024年 | 110篇 |
2023年 | 846篇 |
2022年 | 1097篇 |
2021年 | 1363篇 |
2020年 | 1665篇 |
2019年 | 1633篇 |
2018年 | 1332篇 |
2017年 | 1267篇 |
2016年 | 1889篇 |
2015年 | 1834篇 |
2014年 | 2316篇 |
2013年 | 3054篇 |
2012年 | 3951篇 |
2011年 | 4094篇 |
2010年 | 2637篇 |
2009年 | 2501篇 |
2008年 | 2751篇 |
2007年 | 2571篇 |
2006年 | 2408篇 |
2005年 | 1982篇 |
2004年 | 1512篇 |
2003年 | 1300篇 |
2002年 | 1263篇 |
2001年 | 1002篇 |
2000年 | 881篇 |
1999年 | 991篇 |
1998年 | 849篇 |
1997年 | 829篇 |
1996年 | 944篇 |
1995年 | 726篇 |
1994年 | 655篇 |
1993年 | 541篇 |
1992年 | 532篇 |
1991年 | 487篇 |
1990年 | 378篇 |
1989年 | 322篇 |
1988年 | 238篇 |
1987年 | 204篇 |
1986年 | 203篇 |
1985年 | 177篇 |
1984年 | 140篇 |
1983年 | 104篇 |
1982年 | 72篇 |
1981年 | 67篇 |
1980年 | 46篇 |
1978年 | 43篇 |
1977年 | 48篇 |
1976年 | 42篇 |
1975年 | 46篇 |
1974年 | 44篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
181.
将心磁信号从干扰噪声中加以提取并有效地消除噪声干扰是心磁信号处理中尤为重要的环节 .从改进算法的角度出发,提出互补型自适应滤波器结构以实现心磁信号的消噪处理.该滤波器针对心磁这类非平稳信号进行设计,有效地解决了常规自适应滤波器应用于心磁信号处理时收敛速度和稳态误差的矛盾.通过仿真实验和心磁实验结果表明,该算法能有效地消除心磁信号的背景噪声和工频干扰噪声.同时该算法也可用于其他非平稳信号的消噪处理.
关键词:
自适应滤波
心磁图
最小均方误差 相似文献
182.
With the advances in pulsed laser systems, microscopic imaging techniques such as multiphoton and pump-probe fluorescence microscopy have developed into effective tools for investigating intensity and time-resolved phenomena inside biological systems. However, pulsed lasers used in these techniques usually are commercial systems with repetition frequencies of around 80 MHz. While these systems have proven to be adequate for multiphoton and pump-probe microscopic imaging applications, the temporal separation of the laser pulse train (around 12.5 ns) is long compared to the fluorescence lifetimes of many common fluorescence species. In this work, we present the designs of repetition rate multipliers based on passive optical components that can be used to increase the efficiency in multiphoton and pump-probe fluorescence microscopy. Depending on the lifetime of fluorescence molecules under investigation, the passive repetition rate multiplier can increase the duty cycle of multiphoton or pump-probe microscopy up to fourfold. 相似文献
183.
A new fluorescent chemosensor with imidazole as ionophore was synthesized by the selective derivation of calixarene, which can effectively recognize Cu2+ and Zn2+ leading to different fluoroscopic behaviors in CH3OH-H2O. This system could be considered as a molecular switch. By modulating the pH of the solution, on-off-on fluorescent switching is carried out upon combinatory addition of acid, base and Cu2+. 相似文献
184.
Jin Cheng Ching-Lung Lin Gen Nakamura 《Proceedings of the American Mathematical Society》2005,133(8):2359-2367
In this paper we prove the following kind of unique continuation property. That is, the zero on each geodesic of the solution in a real analytic hypersurface for second order anisotropic hyperbolic systems with real analytic coefficients can be continued along this curve.
185.
In this paper, we present some counterexamples which show that there is no theory on the spectrum of homogeneous compact operators which parallels the Riesz-Schauder theory on the spectrum of linear compact operators. These counterexamples also illustrate that it is impossible to study in a unified setting the Fucik spectrum of the Laplacian: -△w = au+ - bu- inΩand u = 0 on (?)Ω, as well as the spectrum of the p-Laplacian: -div(|(?)u| p-2(?)u) = λ|u|p-2u and u = 0 on (?)Ω. 相似文献
186.
187.
Optical characterization of bromo-alkoxyl-substituted copper phthalocyanine derivative thin films 总被引:2,自引:0,他引:2
A series of thin films of copper phthalocyanine derivatives with bromine and alkoxyl substituents [CuPc(OC8H17)4Brm, m=0,1,2,4] were prepared on single-crystal silicon substrates by spin coating. The ellipsometric spectra of the films have been studied on a rotating analyzer–polarizer type of scanning ellipsometer. The optical, dielectric constants and absorption coefficients of the films in 500–800 nm wavelength region were obtained. The results show that the complex refractive index, dielectric constants and absorption coefficient of these thin films are influenced regularly by bromine substituent on conjugated macrocycle. It was found that there are approximately linear relationships between the resonance absorption wavelengths of the films and the average number of bromine atoms substituted on the phthalocyanine ring. 相似文献
188.
189.
The SmF_(2.01)was synthesized by reducing SmF_3 in H_2 stream.As it was doped inKM_gF_3 and KCaF_3.there was emission of Sm~(2+) in KMgF_3 but no emission of Sm~(2+) inKCaF_3 was observed. 相似文献
190.