全文获取类型
收费全文 | 1747篇 |
免费 | 41篇 |
国内免费 | 7篇 |
专业分类
化学 | 912篇 |
晶体学 | 25篇 |
力学 | 71篇 |
数学 | 208篇 |
物理学 | 579篇 |
出版年
2023年 | 7篇 |
2022年 | 26篇 |
2021年 | 17篇 |
2020年 | 31篇 |
2019年 | 41篇 |
2018年 | 28篇 |
2017年 | 40篇 |
2016年 | 64篇 |
2015年 | 35篇 |
2014年 | 55篇 |
2013年 | 98篇 |
2012年 | 109篇 |
2011年 | 125篇 |
2010年 | 82篇 |
2009年 | 65篇 |
2008年 | 103篇 |
2007年 | 107篇 |
2006年 | 74篇 |
2005年 | 70篇 |
2004年 | 56篇 |
2003年 | 46篇 |
2002年 | 45篇 |
2001年 | 27篇 |
2000年 | 36篇 |
1999年 | 12篇 |
1998年 | 22篇 |
1997年 | 25篇 |
1996年 | 20篇 |
1995年 | 21篇 |
1994年 | 15篇 |
1993年 | 25篇 |
1992年 | 15篇 |
1991年 | 9篇 |
1990年 | 13篇 |
1989年 | 22篇 |
1988年 | 9篇 |
1987年 | 22篇 |
1986年 | 8篇 |
1985年 | 16篇 |
1984年 | 16篇 |
1983年 | 14篇 |
1982年 | 13篇 |
1981年 | 13篇 |
1980年 | 13篇 |
1979年 | 9篇 |
1978年 | 9篇 |
1977年 | 5篇 |
1975年 | 5篇 |
1974年 | 5篇 |
1954年 | 5篇 |
排序方式: 共有1795条查询结果,搜索用时 31 毫秒
91.
Polymer composite comprising polyvinylidene fluoride (PVDF) and potassium hexatitante (K2Ti6O13) was synthesized by solution casting. The effect of K2Ti6O13 on surface, thermal, and electrical properties of polymer composite were investigated. The addition of K2Ti6O13 with polymer leads to thermal degradation and transition of polymer composite from semi-crystalline to amorphous phase. The optimum results of contact angle for different loading wt% of K2Ti6O13 were directly correlated with the surface morphology. Our experimental results confirmed the incorporation of K2Ti6O13 in polymer by SEM micrographs. The evaluated dielectric properties (ε' = 424; tan δ = 2.14 at 130 °C and 100 Hz frequency for 20 wt% loading of K2Ti6O13) for polymer composite are higher in compared to pure polymer. The enhancement in dielectric constant and changing the surface properties of polymer composite can be used for the development of electrochemical storage device applications. 相似文献
92.
The effect of finite energy of intravalley acoustic phonons on the electric field dependence of the temperature of the non-equilibrium carriers in a quantum surface has been studied here. The calculations have been made, for a rather pure material, at low lattice temperature. Numerical results are obtained for GaAs and Si. The results are interesting being significantly different from what one obtains by neglecting the phonon energy. 相似文献
93.
Yogendra K. Gautam Amit K. ChawlaRajan Walia R.D. AgrawalRamesh Chandra 《Applied Surface Science》2011,257(14):6291-6295
Structural and optical properties of pure Mg thin film coated with Pd have been investigated. Pd-capped Mg thin films had been prepared by DC magnetron sputtering. This work presents an ex situ study on hydrogenation and dehydrogenation kinetics of Pd/Mg films at different conditions using XRD, AFM and optical spectrophotometer. We have succeeded to load thin films of Mg to MgH2 at normal temperature and normal pressure of hydrogen gas. In hydrogenation, α-MgH2 phase of magnesium hydride was observed in hydrogenated films at 200 °C and γ-MgH2 at 250 °C respectively. The desorption kinetics in vacuum also revealed the phase transformation α-MgH2 to γ-MgH2. A reflectance change was observed in hydrogenated films in comparison of as deposited thin film. Hydrogenated (H loaded) samples were observed partially transparent in comparison of as deposited. 相似文献
94.
95.
96.
Gautam Gundiah M Eswaramoorthy S Neeraj Srinivasan Natarajan C N R Rao 《Journal of Chemical Sciences》2001,113(3):227-234
Mesoporous aluminosilicate spheres of 0.3–0.4 Μm diameter, with different Si/Al ratios, have been prepared by surfactant templating.
Surface area of these materials is in the 510–970 m2 g-1 range and pore diameter in the 15–20 ? range. 相似文献
97.
98.
[structure: see text] Crystal engineering of an organic ladder can be achieved with a T-shaped molecule, 4,4-bis(4'-hydroxyphenyl)-1-cyclohexanol, having three hydroxyl functionalities that can form O-H...O hydrogen-bonded helices. The topology of this network structure finds a parallel in three-connected coordination polymers. 相似文献
99.
The total synthesis of the methyl glycoside of GM(1) (1b) has been accomplished. The key step in the synthesis involves the sulfonamidoglycosidation reaction, which is used to create a beta-linkage leading to a GalNAc residue joined to the C4 hydroxyl group of a galactose unit of a C3 sialylated lactosyl moiety. The "proximal hydroxyl" directing effect, which has been postulated before, manifests in this context as well leading to the preponderant formation of the beta-glycoside. Together with asialo GM(1) and other substructures, the GM(1) methyl glycoside has been submitted for biological assays as potential ligands for bacterial and viral infection sites. 相似文献
100.
Under a notion of splitting the existence of a unique invariant probability, and a geometric rate of convergence to it in an appropriate metric, are established for Markov processes on a general state space S generated by iterations of i.i.d. maps on S. As corollaries we derive extensions of earlier results of Dubins and Freedman;(17) Yahav;(30) and Bhattacharya and Lee(6) for monotone maps. The general theorem applies in other contexts as well. It is also shown that the Dubins–Freedman result on the necessity of splitting in the case of increasing maps does not hold for decreasing maps, although the sufficiency part holds for both. In addition, the asymptotic stationarity of the process generated by i.i.d. nondecreasing maps is established without the requirement of continuity. Finally, the theory is applied to the random iteration of two (nonmonotone) quadratic maps each with two repelling fixed points and an attractive period-two orbit. 相似文献