全文获取类型
收费全文 | 17378篇 |
免费 | 1848篇 |
国内免费 | 1146篇 |
专业分类
化学 | 8949篇 |
晶体学 | 148篇 |
力学 | 709篇 |
综合类 | 66篇 |
数学 | 1687篇 |
物理学 | 4944篇 |
无线电 | 3869篇 |
出版年
2024年 | 54篇 |
2023年 | 314篇 |
2022年 | 414篇 |
2021年 | 476篇 |
2020年 | 543篇 |
2019年 | 509篇 |
2018年 | 460篇 |
2017年 | 415篇 |
2016年 | 642篇 |
2015年 | 642篇 |
2014年 | 748篇 |
2013年 | 1153篇 |
2012年 | 1180篇 |
2011年 | 1260篇 |
2010年 | 851篇 |
2009年 | 874篇 |
2008年 | 959篇 |
2007年 | 844篇 |
2006年 | 826篇 |
2005年 | 766篇 |
2004年 | 586篇 |
2003年 | 525篇 |
2002年 | 518篇 |
2001年 | 406篇 |
2000年 | 401篇 |
1999年 | 369篇 |
1998年 | 287篇 |
1997年 | 259篇 |
1996年 | 297篇 |
1995年 | 231篇 |
1994年 | 274篇 |
1993年 | 222篇 |
1992年 | 228篇 |
1991年 | 191篇 |
1990年 | 141篇 |
1989年 | 143篇 |
1988年 | 116篇 |
1987年 | 94篇 |
1986年 | 94篇 |
1985年 | 108篇 |
1984年 | 90篇 |
1983年 | 67篇 |
1982年 | 80篇 |
1981年 | 68篇 |
1980年 | 69篇 |
1979年 | 61篇 |
1978年 | 62篇 |
1977年 | 51篇 |
1976年 | 50篇 |
1973年 | 44篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
B. Dagens A. Martinez D. Make O. Le Gouezigou J.-G. Provost V. Sallet K. Merghem J.-C. Harmand A. Ramdane B. Thedrez 《Photonics Technology Letters, IEEE》2005,17(5):971-973
Among the new semiconductor materials for telecom devices, the GaInNAs-GaAs structure presents interesting properties for low-cost applications, like high differential gain and high T/sub 0/. Another key aspect of the performance is the behavior of the GaInNAs-GaAs based lasers under high bit rate direct modulation. Here, we demonstrate the dynamic capabilities of GaInNAs-GaAs three-quantum-well ridge structure through 2.5-Gb/s directly modulated laser emission and transmission on standard fiber, in the temperature range 25/spl deg/C-85/spl deg/C. Besides transmission is demonstrated up to 10 Gb/s at 25/spl deg/C on the same fiber, without penalty and bit-error-rate floor. 相似文献
82.
The effects of partial substitution of Mn for Co on the thermoelectric properties of Ca3MnxCo4−xO9 (x=0, 0.03, 0.9), prepared by sol-gel process, were investigated at the temperatures from 380 K down to 5 K. The results indicate that the substitution of Mn for Co results in increase in thermopower at temperatures >∼80 K, and substantial (23-31% at 300 K) decrease in lattice thermal conductivity in the whole temperature range investigated. The temperature behavior of ZT suggests that Ca3MnxCo4−xO9 with light Mn substitution would be a promising candidate for high-temperature thermoelectric applications. 相似文献
83.
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
84.
The postulate of a linear tensor relation in the measured equation of invariance (MEI) is proposed for three-dimensional (3D) problems. As a result, all three components of the field vector to be solved are coupled in the MEI. Combined with the finite difference method, the present method is applied to the analysis of scattering by 3D conducting objects and results in a significant improvement in the accuracy of numerical results as compared to those obtained with an uncoupled linear relation. 相似文献
85.
86.
通过适当的工艺措施,采用Bridgman法生长了直径为30mm的X射线及γ射线探测器级的Cd.9Zn0.1Te晶锭.测试结果表明:该晶锭结晶质量良好,位错密度低,成分均匀,杂质含量低,红外透过率和电阻率都十分接近本征Cd.9Zn0.1Te的值.并从晶体的生长特性、缺陷和杂质的角度,分析了生长高性能晶体的条件,研究了生长Cdl-xZnxTe晶体的x值与缺陷和杂质浓度之间的关系. 相似文献
87.
The influence of hydrogen bonds on the physical and chemical properties of hydrogen bonding fluid system of A a D d type is investigated from two viewpoints by the principle of statistical mechanics. In detail, we proposed two new ways that can be used to obtain the equilibrium size distribution of the hydrogen bonding clusters, and derived the analytical expression of a relationship between the hydrogen bonding free energy and hydrogen bonding degree. For the nonlinear hydrogen bonding systems, it is shown that the sol-gel phase transition can take place under proper conditions, which is further proven to be a kind of geometrical phase transition rather than a thermodynamic one. Moreover, several problems associated with the geometrical phase transition and liquid-solid phase transition in nonlinear hydrogen bonding systems are discussed. 相似文献
88.
Zukerman M. Wong E.W.M. Rosberg Z. Gyu Myoung Lee Hai Le Vu 《Communications Letters, IEEE》2004,8(2):116-118
We provide teletraffic models for loss probability evaluation of optical burst switching (OBS). We show that the popular Engset formula is not exact for OBS modeling and demonstrate that in certain cases it is not appropriate. A new exact model is provided. The various models are compared using numerical results for various OBS alternatives with and without burst segmentation. 相似文献
89.
Chuxiang Li Jianhua Lu Jun Gu Ming L. Liou 《The Journal of VLSI Signal Processing》2003,33(3):277-285
In this paper, error-resilient schemes are proposed to support robust video transmission for digital terrestrial TV broadcasting (DTTB). In particular, a temporal error concealment incorporated with a low-complexity block-matching is developed, achieving an effective reception of predictive pictures in harsh terrestrial environment. Special algorithms are also designed for isolated I-pictures. Moreover, combined with an intra/inter case prediction, an adaptive error concealment scheme is further contrived to fit for different error conditions. Extensive simulations have been conducted under various DTTB channel conditions, even with a very high packet error rate, to verify the effectiveness of the proposed schemes. 相似文献
90.