全文获取类型
收费全文 | 206230篇 |
免费 | 42969篇 |
国内免费 | 15911篇 |
专业分类
化学 | 171512篇 |
晶体学 | 2025篇 |
力学 | 12068篇 |
综合类 | 959篇 |
数学 | 21935篇 |
物理学 | 56611篇 |
出版年
2024年 | 423篇 |
2023年 | 5985篇 |
2022年 | 5299篇 |
2021年 | 7259篇 |
2020年 | 10336篇 |
2019年 | 9337篇 |
2018年 | 6679篇 |
2017年 | 5293篇 |
2016年 | 13026篇 |
2015年 | 12915篇 |
2014年 | 13917篇 |
2013年 | 16994篇 |
2012年 | 16890篇 |
2011年 | 15445篇 |
2010年 | 13503篇 |
2009年 | 13233篇 |
2008年 | 11714篇 |
2007年 | 10216篇 |
2006年 | 8917篇 |
2005年 | 7718篇 |
2004年 | 6196篇 |
2003年 | 5047篇 |
2002年 | 5484篇 |
2001年 | 4334篇 |
2000年 | 3831篇 |
1999年 | 3372篇 |
1998年 | 2647篇 |
1997年 | 2470篇 |
1996年 | 2691篇 |
1995年 | 2278篇 |
1994年 | 2116篇 |
1993年 | 1888篇 |
1992年 | 1614篇 |
1991年 | 1421篇 |
1990年 | 1169篇 |
1989年 | 888篇 |
1988年 | 802篇 |
1987年 | 687篇 |
1986年 | 597篇 |
1985年 | 575篇 |
1984年 | 483篇 |
1983年 | 384篇 |
1976年 | 456篇 |
1975年 | 542篇 |
1974年 | 569篇 |
1972年 | 490篇 |
1971年 | 442篇 |
1970年 | 642篇 |
1969年 | 489篇 |
1968年 | 512篇 |
排序方式: 共有10000条查询结果,搜索用时 140 毫秒
991.
四阶方程两点边值问题Hermite有限元解的渐近展式与外推 总被引:1,自引:0,他引:1
1引言有限元解的渐近展式是提高微分方程数值解精度的重要工具,比如亏量校正和外推就是建立在有限元解的渐近展式的基础之上.许多作者对此进行了大量的研究(见[1]-[4]),特别是文[1],提出了在研究有限元解的渐近展式中十分有用的能量嵌入技巧.本文利用能量嵌入定理得到了四阶方程两点边值问题Hermite有限元解及其二阶平均导数的渐近展式,进一步我们还讨论了它们的Richardson外推公式.考虑四阶方程两点边值问题 相似文献
992.
Meihua Lu H. Gong T. Song Jian-Ping Wang Hong-Wei Zhang T.J. Zhou 《Journal of magnetism and magnetic materials》2006
We present a simple way to synthesize FePt and ZnO (wide-band-gap semiconductor) nanoparticle composites. The FePt nanoparticles were fabricated using the method reported by Sun et al. By controlling the heating rate, 3 nm FePt nanoparticles were synthesized. Well-dispersed FePt and ZnO nanoparticle composites were prepared by further adding zinc acetate and oleyl amine into the 3 nm FePt nanoparticle dispersion. By controlling the molar ratio of the FePt and zinc acetate, FePt and ZnO nanoparticle composites with different FePt particle fractions were obtained. The intensity of photo luminescence spectra of the nanoparticle composites increases very much with decreasing FePt particle fraction, whereas the peak position shifts a little. After annealing at 550 °C for half an hour, the nanoparticle composites become magnetically hard or semi-hard with coercivity much dependent on the FePt particle volume fraction. The coercivity of the composites increases with annealing temperature. The composites hold the promise of applications in new generation recording and/or optical devices. 相似文献
993.
994.
Suchada Suntornchashwej Dr. Khanit Suwanborirux Dr. Kazushi Koga Minoru Isobe Prof. Dr. 《化学:亚洲杂志》2007,2(1):114-122
Malyngamide X ( 1 ), the first (7R)‐lyngbic acid connected to a new tripeptide backbone, was isolated from the Thai sea hare Bursatella leachii. The gross structure of 1 was established on the basis of 1D and 2D NMR and mass spectroscopic data. Combination of the NMR spectroscopic experiments with α‐methoxy‐α‐(trifluoromethyl)phenylacetic acid esters, 2,2,2‐trifluoro‐1‐(9‐anthryl)ethanol chiral solvating agent, and molecular mechanics of 1 and the synthetic molecular fragments allowed us to determine the absolute stereochemistry of all six stereogenic centers without hydrolytic degradation of the compound. Compound 1 displayed moderate cytotoxic, antitubercular, and antimalarial properties. 相似文献
995.
In this paper, we discuss the local and global existence ofweak solutions for some hyperbolicparabolic systems modellingchemotaxis. 相似文献
996.
Chenghang Wang 《Applied Surface Science》2006,253(4):2282-2288
In this paper, thin films of titanium oxide imprinted with O,O-dimethyl-(2,4-dichlorophenoxyacetoxyl)(3′-nitrobenyl) methinephosphonate (Phi-NO2) were prepared via liquid phase deposition (LPD) method on a glassy carbon electrode. The imprinted molecular in the films was removed by treatment with immersion in CH2Cl2. X-ray diffraction (XRD) and electrochemical methods were introduced to show the evidence of the molecular imprinting phenomenon. It was also found that the recognition ability of the sensor depended on the substituents associated with tridimensional structures of the nitro-compounds. Under the optimized condition, the sensor showed better sensitivity, selectivity and reproducibility to the imprinted molecule and the linear relationship between the current and the concentration of analyte in the range of 0.1-50 μM was obtained. LPD proved to be a powerful method for imprinting titanium oxide thin sense films. 相似文献
997.
采用溶胶-凝胶工艺与原位生长技术,制备了ZnSe/SiO2复合薄膜.X射线衍射分 析表明薄膜中ZnSe晶体呈立方闪锌矿结构.X射线荧光分析结果显示薄膜中Zn与Se摩尔比为1 ∶1.01—1∶1.19.利用场发射扫描电子显微镜观察了复合薄膜的表面形貌,结果表明复合薄 膜表面既存在尺寸约为400nm的ZnSe晶粒,也存在尺寸小于100nm的ZnSe晶粒.利用椭偏仪测 量了薄膜椭偏角Ψ,Δ与波长λ的关系,采用Maxwell-Garnett有效介质理论对薄膜的光学 常数、厚度、气孔率、ZnS
关键词:
2复合薄膜')" href="#">ZnSe/SiO2复合薄膜
光学性质
椭偏光度法
荧光光谱 相似文献
998.
999.
1000.
In this paper we formulate a theorem on the persistence of elliptic lower-dimensional invariant tori for nearly integrable analytic Hamiltonian systems under the first Melnikov condition and Rüssmann’s non-degeneracy condition, and give the measure estimates of parameters for the non-resonance conditions under Rüssmann’s non-degeneracy condition, which is essential for the proof of our result. 相似文献