全文获取类型
收费全文 | 20296篇 |
免费 | 3501篇 |
国内免费 | 3268篇 |
专业分类
化学 | 15862篇 |
晶体学 | 432篇 |
力学 | 1035篇 |
综合类 | 305篇 |
数学 | 2159篇 |
物理学 | 7272篇 |
出版年
2024年 | 44篇 |
2023年 | 375篇 |
2022年 | 507篇 |
2021年 | 678篇 |
2020年 | 874篇 |
2019年 | 853篇 |
2018年 | 755篇 |
2017年 | 757篇 |
2016年 | 999篇 |
2015年 | 1087篇 |
2014年 | 1321篇 |
2013年 | 1627篇 |
2012年 | 1783篇 |
2011年 | 1916篇 |
2010年 | 1481篇 |
2009年 | 1319篇 |
2008年 | 1522篇 |
2007年 | 1368篇 |
2006年 | 1160篇 |
2005年 | 996篇 |
2004年 | 746篇 |
2003年 | 665篇 |
2002年 | 666篇 |
2001年 | 559篇 |
2000年 | 483篇 |
1999年 | 378篇 |
1998年 | 283篇 |
1997年 | 236篇 |
1996年 | 273篇 |
1995年 | 198篇 |
1994年 | 195篇 |
1993年 | 137篇 |
1992年 | 122篇 |
1991年 | 110篇 |
1990年 | 97篇 |
1989年 | 70篇 |
1988年 | 67篇 |
1987年 | 58篇 |
1986年 | 44篇 |
1985年 | 43篇 |
1984年 | 31篇 |
1983年 | 25篇 |
1982年 | 28篇 |
1981年 | 18篇 |
1980年 | 14篇 |
1979年 | 14篇 |
1976年 | 7篇 |
1975年 | 8篇 |
1974年 | 7篇 |
1970年 | 13篇 |
排序方式: 共有10000条查询结果,搜索用时 62 毫秒
131.
Lisa A. Liotta Irene Medina Jennifer L. Robinson Po-Shen Pan Jennifer V.C. Johnston Fiona A. Curtis Shelli R. McAlpine 《Tetrahedron letters》2004,45(46):8447-8450
Described are the syntheses of 15 macrocyclic peptides designed to trap Holliday junctions (HJs) in bacteria during site-specific and homologous recombination. This leads to inhibiting bacterial growth. These second generation macrocycles were based on the C-2 symmetrical HJ. They were synthesized using a strategy that permits elucidation of the amino acid role in binding HJs. The syntheses of these macrocycles are an important step in the development of a new class of antibiotics. 相似文献
132.
We propose a minimum mean absolute error linear interpolator (MMAELI), based on theL
1 approach. A linear functional of the observed time series due to non-normal innovations is derived. The solution equation
for the coefficients of this linear functional is established in terms of the innovation series. It is found that information
implied in the innovation series is useful for the interpolation of missing values. The MMAELIs of the AR(1) model with innovations
following mixed normal andt distributions are studied in detail. The MMAELI also approximates the minimum mean squared error linear interpolator (MMSELI)
well in mean squared error but outperforms the MMSELI in mean absolute error. An application to a real series is presented.
Extensions to the general ARMA model and other time series models are discussed.
This research was supported by a CityU Research Grant and Natural Science Foundation of China. 相似文献
133.
Ziqing Duan Xiaofeng Wang Danfeng Yang Xiaoming Pan Pingchu Wang 《Solid State Communications》2005,134(8):559-563
0.65Pb(In1/2Nb1/2)O3-0.35PbTiO3 (PINT65/35) (starting composition) single crystals were grown successfully through the solution Bridgman technique using PbO flux and PMNT67/33 seed crystals. Because of the composition variation, the final composition of achievable crystals is in a range of 0.32-0.34 with the corresponding Tc range of 265-269 °C. The (001) plates of as-grown PINT66/34 single crystals show high Curie temperature (Tc=269 °C) and rhombohedral-tetragonal phase transition temperature (Trt=134 °C). Besides, good electrical properties with high dielectric constant (ε>3000), low dielectric loss (tan δ∼1.2%), high piezoelectric constant (d33∼2000 pC/N) and large electromechanical coupling factor (kt≈59%) at room temperature have been obtained on the (001) plates. The sound velocity, acoustic impedance and other piezoelectric parameters were also measured on the (001) plates in this study, which provide us more detailed information about PINT66/34 single crystals. 相似文献
134.
135.
Gwang Hui Kim 《Journal of Mathematical Analysis and Applications》2004,299(2):375-391
In this paper we investigate a generalization of the Hyers-Ulam-Rassias stability for a functional equation of the form f(φ(X))=?(X)f(X)+ψ(X) and the stability in the sense of Ger for the functional equation of the form f(φ(X))=?(X)f(X), where X lie in n-variables. As a consequence, we obtain a stability result in the sense of Hyers-Ulam-Rassias, Gǎvruta, and Ger for some well-known equations such as the gamma, beta, and G-function type's equations. 相似文献
136.
LI Na ZHAO Degang & YANG Hui State Key Laboratory on Integrated Optoelectronics Institute of Semiconductors Chinese Academy of Sciences Beijing China 《中国科学G辑(英文版)》2004,47(6):694-701
Because of their large band-gap, large high-field electron velocity, large breakdownfield, and large thermal conductivity, GaN and its heterojunction with AlGaN and InGaNhave foreseeable potential in the applications of high-power/temperature electronics, andoptoelectronic devices operative in UV and visible wavelength. Polarization inducedelectric field can reach the magnitude of ~MV/cm[1,2]. For AlGaN/GaN based FETs theconcentration of sheet carrier induced by polarization in the cha… 相似文献
137.
138.
Spirals generated from the excitable media within the Barkley model is investigated under the gradient electric fields by a numerical simulation. The spiral drift and spiral break up are observed when the amplitude of the electric fields is modulated by a constant signal or a chaotic signal. It is also verified that, even in the presence of the white noise, the whole system can reach homogeneous states after the spiral breakup, by using an adaptive strategy. 相似文献
139.
140.