全文获取类型
收费全文 | 1612篇 |
免费 | 89篇 |
国内免费 | 16篇 |
专业分类
化学 | 1093篇 |
晶体学 | 13篇 |
力学 | 34篇 |
数学 | 269篇 |
物理学 | 308篇 |
出版年
2023年 | 3篇 |
2022年 | 4篇 |
2021年 | 26篇 |
2020年 | 17篇 |
2019年 | 33篇 |
2018年 | 26篇 |
2017年 | 16篇 |
2016年 | 58篇 |
2015年 | 51篇 |
2014年 | 76篇 |
2013年 | 92篇 |
2012年 | 121篇 |
2011年 | 104篇 |
2010年 | 71篇 |
2009年 | 71篇 |
2008年 | 98篇 |
2007年 | 105篇 |
2006年 | 80篇 |
2005年 | 91篇 |
2004年 | 76篇 |
2003年 | 79篇 |
2002年 | 67篇 |
2001年 | 44篇 |
2000年 | 39篇 |
1999年 | 25篇 |
1998年 | 23篇 |
1997年 | 16篇 |
1996年 | 21篇 |
1995年 | 16篇 |
1994年 | 13篇 |
1993年 | 25篇 |
1992年 | 19篇 |
1991年 | 19篇 |
1990年 | 15篇 |
1989年 | 9篇 |
1988年 | 4篇 |
1987年 | 10篇 |
1986年 | 7篇 |
1985年 | 9篇 |
1984年 | 11篇 |
1983年 | 6篇 |
1982年 | 3篇 |
1981年 | 3篇 |
1980年 | 3篇 |
1979年 | 2篇 |
1976年 | 2篇 |
1974年 | 3篇 |
1957年 | 1篇 |
1955年 | 1篇 |
1936年 | 2篇 |
排序方式: 共有1717条查询结果,搜索用时 236 毫秒
991.
José F. Fernando Jesú s M. Ruiz Claus Scheiderer 《Transactions of the American Mathematical Society》2004,356(7):2663-2684
Let be an excellent ring. We show that if the real dimension of is at least three then has infinite Pythagoras number, and there exists a positive semidefinite element in which is not a sum of squares in .
992.
993.
Valenzuela MT Núñez MI Guerrero MR Villalobos M Ruiz de Almodóvar JM 《Journal of chromatography. A》2000,871(1-2):321-330
Apoptosis is a type of cellular death but also directly regulates tumorigenesis through different gene expression. This phenomenon is often used as end-point in studies of radio- and chemosensitivity of cancer cells. Restriction DNA fragments have been separated quickly, efficiently and successfully by capillary gel electrophoresis (CGE). In this study CGE has been applied to distinguish between the discrete pattern of degraded DNA produced by apoptosis and randomized DNA breaks produced by ionizing radiation. The influence of different variables has been discussed and an example of fast separation by CGE of the apoptotic fragments produced by UV light treatment is shown. 相似文献
994.
995.
Some works have studied the light scattering from a rough surface immersed in a liquid, where the light scattered from the immersed rough surface was assumed to be equivalent to that scattered from a fictitious rough surface with a different texture. This work deals with this kind of problems analyzing the light scattered by a reflecting strong scatterer and the light scattered by a rough surface immersed in a transparent liquid. The general Kirchhoff solution for scattering from a rough surface has been used.It is shown that under certain conditions, the mean scattered intensity (MSI) from a surface immersed in a liquid can be quasi-indistinguishable from that scattered from a non-immersed surface with an “equivalent texture”. An expression relating the equivalent texture and the immersed surface texture was obtained.The results of this work allow to evaluate the characteristics of any surface immersed in a liquid with a known refractive index. 相似文献
996.
997.
Surface acoustic wave (SAW) velocity spectroscopy has been long considered to be one of the leading candidates for nondestructive characterization of surface-treated metals because of its ability to probe the material properties at different penetration depths depending on the inspection frequency. We developed a high-precision laser-ultrasonic technique to study the feasibility of SAW dispersion spectroscopy for residual stress assessment on shot-peened metals. This technique is capable of measuring SAW dispersion with a relative error of 0.1% over a frequency range from 2 to 15 MHz. Our experimental results obtained from shot-peened aluminum 2024-T351 samples indicate that the dispersion of the surface wave is a superposition of different effects of surface treatment in the material, including surface roughness, compressive residual stress, and cold work. Although the surface roughness induced component is often the dominating part of the overall dispersion, the experimental results also indicate that it is feasible to observe a perceivable change in the dispersion of the SAW when the specimen is heat-treated at different temperatures, which has no perceivable effect on the surface roughness. The part of the dispersion, which changes during annealing via thermal relaxation, is due to near-surface residual stresses and the decay of texture, although at high frequencies nonuniform grain coarsening could also play a significant role. 相似文献
998.
Dario A. Donatti Alberto Ibañez Ruiz Fabrício Gambardella De Moraes Dimas R. Vollet 《Journal of Sol-Gel Science and Technology》2003,28(1):31-35
Cr-doped xerogels were obtained by sol-gel process from the acid-catalyzed and ultrasound-stimulated hydrolysis of tetraethoxysilane (TEOS) with addition of CrCl36H2O in water solution during the liquid step of the process. The gels were aged immersed in different pH solutions for about 30 days, after that they were allowed to dry. The samples were annealed at temperatures ranging from 40 to 600°C and analyzed by UV-visible absorption spectroscopy. Cr3+ is the preferable oxidation state of the chromium ion in the gels annealed up to 250–300°C, in the case of aging in solutions of pH = 5 and 11. A high UV absorption below 320 nm, due to the host gel, and different absorption bands, depending on the temperature, due to the chromium ion were observed in the xerogels at temperatures below 250°C, in the case of aging in solutions of pH = 1 and 2. These absorption bands have not been assigned. Above 300°C up to 600°C, Cr5+, and possibly Cr6+, are the preferable oxidation states of the chromium ion independent of the pH of the aging solution, so the xerogels turn to a yellowish appearance in all cases. 相似文献
999.
Aramendía MA Borau V Jiménez C Marinas JM Ruiz JR Urbano FJ 《Solid state nuclear magnetic resonance》2000,16(4):3129-224
1H, 27Al and 31P MAS, and 13C and 29Si CP/MAS NMR spectroscopies, were used to characterize catalysts of Pd supported on various solids including SiO2, AlPO4 and Mg3(PO4)2 that were activated with the chiral hydrogen-donor limonene. The above-mentioned techniques were used to check for the formation of an organopalladium complex between Pd2+ atoms and the olefin bonds in the limonene molecule on the catalyst surface. The results are compared with those obtained for catalysts activated in a hydrogen stream. 相似文献
1000.
Using the analysis of ChPT to two loops, we perform an error analysis of the threshold and low-energy parameters, based on
the uncertainties for the one-loop low-energy parameters and the resonance saturation mechanism. Different sets of one-loop
low-energy constants have been considered. Thus, the predictive power of the effective field theory, is quantified on the
basis of the present experimental uncertainties.
Communicated by W. Weise 相似文献