全文获取类型
收费全文 | 5888篇 |
免费 | 190篇 |
国内免费 | 16篇 |
专业分类
化学 | 3881篇 |
晶体学 | 47篇 |
力学 | 155篇 |
综合类 | 5篇 |
数学 | 678篇 |
物理学 | 1328篇 |
出版年
2023年 | 43篇 |
2022年 | 120篇 |
2021年 | 184篇 |
2020年 | 141篇 |
2019年 | 151篇 |
2018年 | 158篇 |
2017年 | 119篇 |
2016年 | 224篇 |
2015年 | 181篇 |
2014年 | 204篇 |
2013年 | 368篇 |
2012年 | 381篇 |
2011年 | 436篇 |
2010年 | 298篇 |
2009年 | 301篇 |
2008年 | 374篇 |
2007年 | 327篇 |
2006年 | 269篇 |
2005年 | 214篇 |
2004年 | 190篇 |
2003年 | 135篇 |
2002年 | 149篇 |
2001年 | 104篇 |
2000年 | 92篇 |
1999年 | 67篇 |
1998年 | 66篇 |
1997年 | 63篇 |
1996年 | 47篇 |
1995年 | 44篇 |
1994年 | 61篇 |
1993年 | 49篇 |
1992年 | 60篇 |
1991年 | 34篇 |
1990年 | 27篇 |
1989年 | 20篇 |
1988年 | 35篇 |
1987年 | 20篇 |
1986年 | 21篇 |
1985年 | 28篇 |
1984年 | 26篇 |
1983年 | 22篇 |
1982年 | 37篇 |
1981年 | 27篇 |
1980年 | 26篇 |
1979年 | 23篇 |
1978年 | 20篇 |
1977年 | 17篇 |
1976年 | 13篇 |
1975年 | 11篇 |
1974年 | 12篇 |
排序方式: 共有6094条查询结果,搜索用时 15 毫秒
21.
Humberto César Chaves Fernandes Arthur Rodrigo Barros da Rocha 《International Journal of Infrared and Millimeter Waves》2003,24(7):1171-1176
The use of photonic materials has been used in the theory of optical waves. The PBG (Photonic Band Gap) theory and material, was developed recently for optical frequencies and can be easily applied to millimeter waves, microwaves and planar antenna frequencies. The presence of photonic materials as substrate in antennas has some good characteristics such as, supression of light spontaneous emission and suppression of surface waves, allowing the application in planar antenna array. In this work an elaborate analysis using the full wave Transverse Transmission Line - TTL method, that provides efficient and concise results is applied to the planar antennas array with PBG substrate. 相似文献
22.
字节全加器及其在无线电测控系统中的应用 总被引:1,自引:1,他引:0
对全加器概念进行了推广,并在此基础上给出了使用字节全加器网络的无线电抗干扰算法。通过在实际的无线电测控系统中的应用,结果表明该算法具有良好的无线电抗干扰效果。 相似文献
23.
J. H. de Araújo J. B. M. da Cunha A. Vasquez L. Amaral J. T. Moro F. C. Montenegro S. M. Rezende M. D. Coutinho Filho 《Hyperfine Interactions》1991,67(1-4):507-511
57Fe Mössbauer effect measurements in the diluted Ising antiferromagnet Fe x Zn1?x F2 withx=0.25 andx=0.57 at temperatures between 4.2 and 55 K, are reported. DC suceptibility measurements show a spin-glass (SG) phase at low temperatures forx≤0.31. Our Mössbauer spectra show a phase transition to a SG state with antiferromagnetic order (AFSG) forx=0.25 and only antiferromagnetic order forx=0.57. 相似文献
24.
25.
Ivan Nunes da Silva Wagner Caradori do AmaralLucia Valeria de Arruda 《Applied Mathematical Modelling》2007
This paper presents an efficient approach based on recurrent neural network for solving nonlinear optimization. More specifically, a modified Hopfield network is developed and its internal parameters are computed using the valid subspace technique. These parameters guarantee the convergence of the network to the equilibrium points that represent an optimal feasible solution. The main advantage of the developed network is that it treats optimization and constraint terms in different stages with no interference with each other. Moreover, the proposed approach does not require specification of penalty and weighting parameters for its initialization. A study of the modified Hopfield model is also developed to analyze its stability and convergence. Simulation results are provided to demonstrate the performance of the proposed neural network. 相似文献
26.
Given a rectangular array whose entries represent the pixels of a digitalized image, we consider the problem of reconstructing an image from the number of occurrences of each color in every column and in every row. The complexity of this problem is still open when there are just three colors in the image. We study some special cases where the number of occurrences of each color is limited to small values. Formulations in terms of edge coloring in graphs and as timetabling problems are used; complexity results are derived from the model. 相似文献
27.
M. Alves Da Silva M. Helena Gil A. P. Piedade J. S. Redinha A. M. Oliveira Brett J. M. Caridade Costa 《Journal of polymer science. Part A, Polymer chemistry》1991,29(2):269-274
The immobilization of catalase on grafted membranes of poly(ethylene)-g-co-acrylic acid and poly(tetrafluoroethylene)-g-co-acrylic acid and their application in hydrogen peroxide electrochemical sensors is described. The introduction of carboxylic acid groups onto a hydrophobic support provides a good environment for subsequent enzyme immobilization. This single membrane, hydrogen peroxide sensor showed significant improvement with respect to the double membrane versions. The response is very rapid, the linear range being from 10 μM up to 6 mM, with a detection limit of 4.7 μM, and a lifetime of more than 4 months. 相似文献
28.
L. S. de C. Oliveira M. T. X. Silva A. Vasquez J. A. H. da Jornada 《Hyperfine Interactions》1991,66(1-4):267-270
An exploratory Mössbauer spectroscopy study of the Fe-C system in the C rich region, prepared by high pressure-high temperature treatment near the graphite-diamond stability line, was made. The results obtained for the different processing conditions give no evidence of Fe intercalation in graphite. The presence of some water in the cell produced hydrated Fe complexes, which can explain the deleterious effect of water or hydrogen in the high pressure diamond synthesis. 相似文献
29.
Eggenhffner R. Masini R. Bellingeri E. Cimberle M. R. Ferdeghini C. Costa G. A. Kaiser E. Signorelli E. 《Il Nuovo Cimento D》1994,16(10):1659-1664
Il Nuovo Cimento D - The formation of Hg-based HTSC materials was investigated through the development of non-conventional techniques. The former was based on a singlestep synthesis at temperatures... 相似文献
30.
The fully frustrated planar rotator and fully frustrated XY models in two dimensions have two phase transitions: one of the Berezinskii–Kosterlitz–Thouless type and other in the Ising universality class. We use Monte Carlo simulation to study both models. We fix our attention in the Ising-like transition, which we show can be understood as a percolation transition. We obtain the critical temperature as well as the critical exponents of the mean cluster size, γ, and Fisher's exponent τ. The critical temperature agree very well with other calculations. We found that the critical exponents are smaller than in the pure two-dimensional percolation case. We interpret this as due to the long-range interaction between vortex and antivortex. 相似文献