全文获取类型
收费全文 | 115523篇 |
免费 | 14684篇 |
国内免费 | 10285篇 |
专业分类
化学 | 71697篇 |
晶体学 | 1167篇 |
力学 | 6679篇 |
综合类 | 519篇 |
数学 | 18450篇 |
物理学 | 41980篇 |
出版年
2024年 | 316篇 |
2023年 | 1833篇 |
2022年 | 3229篇 |
2021年 | 3405篇 |
2020年 | 3652篇 |
2019年 | 3470篇 |
2018年 | 4171篇 |
2017年 | 4278篇 |
2016年 | 4945篇 |
2015年 | 4774篇 |
2014年 | 5495篇 |
2013年 | 7115篇 |
2012年 | 11193篇 |
2011年 | 10412篇 |
2010年 | 7327篇 |
2009年 | 6749篇 |
2008年 | 6185篇 |
2007年 | 5671篇 |
2006年 | 5242篇 |
2005年 | 8112篇 |
2004年 | 6727篇 |
2003年 | 4526篇 |
2002年 | 2647篇 |
2001年 | 2142篇 |
2000年 | 1714篇 |
1999年 | 1959篇 |
1998年 | 1548篇 |
1997年 | 1474篇 |
1996年 | 1418篇 |
1995年 | 1175篇 |
1994年 | 1028篇 |
1993年 | 859篇 |
1992年 | 894篇 |
1991年 | 773篇 |
1990年 | 658篇 |
1989年 | 525篇 |
1988年 | 451篇 |
1987年 | 348篇 |
1986年 | 309篇 |
1985年 | 252篇 |
1984年 | 176篇 |
1983年 | 131篇 |
1982年 | 101篇 |
1981年 | 88篇 |
1980年 | 79篇 |
1979年 | 63篇 |
1977年 | 58篇 |
1976年 | 110篇 |
1975年 | 60篇 |
1973年 | 76篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
71.
采用固源Si分子束外延,在较高的生长温度于Si(100)衬底上制备出Si1-xGex/Si量子阱发光材料。发光样品的质量和特性通过卢瑟福背散射、X射线双晶衍射及光致发光评估。背散射实验中观察到应变超晶格的反常沟道效应;X射线分析表明材料的生长是共度的、无应力释放的,结晶完整性好。低温光致发光主要是外延合金量子阱中带边激子的无声发射和横光学声子参与的激子复合。并讨论了生长温度对量于阱发光的影响。 相似文献
72.
In theory, both polarity and steric hindrance are basic factors which affect molecular interactions. To investigate the optical properties and steric structures of chiral compounds having different chiral moieties which affect the wavelength of light reflection in liquid crystal (LC) cells, a series of novel chiral compounds and azobenzene derivatives were synthesized. The liquid crystalline phases of the compounds were identified using small angle X-ray diffraction, differential scanning calorimetry and polarizing optical microscopy. Cholesteric LC cells with various synthesized chiral dopants which selectively reflect visible light were first prepared, the photochemical switching behaviour of colours was then investigated, with special reference to the change in transmittance in cholesteric LC cells containing an azobenzene derivative as a photoisomerizable guest molecule. Reversible isomerization of azobenzene molecules occurred in the cholesteric systems, resulting in a depression of TChI and a shift of the selectively reflected wavelength. We discuss the photochemically driven change in the helical pitch of the cholesteric LCs with respect to structural effects involving the chiral moieties. Molecular interactions caused by the added dopants, reliability and stability of the photoisomerization, and UV irradiation effects on the cholesteric LC cells were also investigated. A real image was recorded through a mask on a cholesteric LC cell fabricated in this investigation. 相似文献
73.
Jing Zhang Dan Shan Shaolin Mu 《Journal of polymer science. Part A, Polymer chemistry》2007,45(23):5573-5582
A copolymer, poly(aniline‐co‐o‐aminophenol), was prepared chemically by using ammonium peroxydisulfate as an oxidant. The monomer concentration ratio of o‐aminophenol to aniline strongly influences the copolymerization rate and properties of the copolymer. The optimum composition of a mixture for the chemical copolymerization consisted of 0.3 M aniline, 0.021 M o‐aminophenol, 0.42 M ammonium peroxydisulfate, and 2 M H2SO4. The result of cyclic voltammograms in a potential region of ?0.20 to 0.80 V (vs.SCE) indicates that the electrochemical activity of the copolymer prepared under the optimum condition is similar to that of polyaniline in more acid solutions. However, the copolymer still holds the good electrochemical activity until pH 11.0. Therefore, the pH dependence of the electrochemical property of the copolymer is improved, compared with poly(aniline‐co‐o‐aminophenol) prepared electrochemically, and is much better than that of polyaniline. The spectra of IR and 1H NMR confirm that o‐aminophenol units are included in the copolymer chain, which play a key role in extending the usable pH region of the copolymer. The visible spectra of the copolymers show that a high concentration ratio of o‐aminophenol to aniline in a mixture inhibits the chain growth. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 5573–5582, 2007 相似文献
74.
75.
The microstructure evolution of decagonal quasicrystals in Al72Ni12Co16 alloy was investigated by the electromagnetic melting and cyclic superheating method. Single-phase decagonal quasicrystals have been obtained when the undercoolings were larger than 60 K. The decagonal quasicrystals formed at various undercoolings show different microstructural morphologies. Furthermore, grain refinement was found near the undercooling of 120 K. Based on current thermodynamic and dendrite growth theories, a dimensionless superheating parameter was adopted to explain the effect of processing conditions on the microstructure of Al72Ni12Co16 alloy. The result indicate that the fine equiaxied microstructure of decagonal quasicrystal (D-phase) formed near on undercooling of 120 K originates from the break-up of dendrites. 相似文献
76.
77.
Jiguo Yu Qiuju Bian Guizhen Liu Na Wang 《Journal of Applied Mathematics and Computing》2007,25(1-2):283-291
A simple graphG is said to be fractionaln-factor-critical if after deleting anyn vertices the remaining subgraph still has a fractional perfect matching. For fractionaln-factor-criticality, in this paper, one necessary and sufficient condition, and three sufficient conditions related to maximum matching, complete closure are given. 相似文献
78.
Daniel Pa?ca 《Journal of Mathematical Analysis and Applications》2007,325(1):90-100
Some existence results are obtained for periodic solutions of nonautonomous second-order differential inclusions systems with p-Laplacian. 相似文献
79.
The universal condition for the formation of omnidirectional band gaps (OBG) in photonic crystal (PC) was derived with consideration
of permeability of the materials. And it was found that there are four kinds of PCs: one of them has no OBG, and one always
possesses OBG. For the other two kinds of PCs, there are OBG for only TM or TE waves respectively. Moreover, in all PCs, the
OBG can be broadened by decreasing the refractive index of the ambient medium or/and increasing the contrast between the wave
impedances of the component materials of the PC.
PACS 42.70.Qs; 71.20.Tx 相似文献
80.