全文获取类型
收费全文 | 397篇 |
免费 | 18篇 |
国内免费 | 44篇 |
专业分类
化学 | 239篇 |
晶体学 | 4篇 |
力学 | 34篇 |
综合类 | 3篇 |
数学 | 65篇 |
物理学 | 114篇 |
出版年
2023年 | 10篇 |
2022年 | 18篇 |
2021年 | 20篇 |
2020年 | 34篇 |
2019年 | 14篇 |
2018年 | 5篇 |
2017年 | 7篇 |
2016年 | 8篇 |
2015年 | 16篇 |
2014年 | 16篇 |
2013年 | 20篇 |
2012年 | 34篇 |
2011年 | 35篇 |
2010年 | 16篇 |
2009年 | 14篇 |
2008年 | 21篇 |
2007年 | 29篇 |
2006年 | 25篇 |
2005年 | 22篇 |
2004年 | 18篇 |
2003年 | 12篇 |
2002年 | 7篇 |
2001年 | 4篇 |
2000年 | 3篇 |
1999年 | 8篇 |
1998年 | 3篇 |
1997年 | 12篇 |
1996年 | 4篇 |
1995年 | 7篇 |
1994年 | 6篇 |
1993年 | 3篇 |
1992年 | 2篇 |
1991年 | 1篇 |
1988年 | 1篇 |
1987年 | 1篇 |
1985年 | 2篇 |
1981年 | 1篇 |
排序方式: 共有459条查询结果,搜索用时 15 毫秒
21.
弱碱性离子交换树脂在柠檬酸提炼中的应用 总被引:4,自引:1,他引:4
本文选用多种弱碱性阴离子交换树脂,去除柠檬酸酸解液中、Cl-等阴离子,比较其交换容量、柠檬酸的回收率、再生性能、机械强度等。实验表明:D315弱碱性树脂的效果明显优于其它几种树脂。 相似文献
22.
Microemulsion-based synthesis of titanium phosphate nanotubes via amine extraction system 总被引:2,自引:0,他引:2
Yin Z Sakamoto Y Yu J Sun S Terasaki O Xu R 《Journal of the American Chemical Society》2004,126(29):8882-8883
The first titanium phosphate nanotubes with alternating interlayer spacings have been successfully prepared and characterized. The synthesis is accomplished in a reverse microemulsion formed in an amine extraction system. TEM data from samples made after different times of reaction suggest a scrolling-formation mechanism. 相似文献
23.
Zhongzhi Zhang Shuigeng Zhou Lichao Chen Jihong Guan Lujun Fang Yichao Zhang 《The European Physical Journal B - Condensed Matter and Complex Systems》2007,59(1):99-107
We propose a geometric growth model for weighted
scale-free networks, which is controlled by two tunable parameters.
We derive exactly the main characteristics of the networks, which
are partially determined by the parameters. Analytical results
indicate that the resulting networks have power-law distributions of
degree, strength, weight and betweenness, a scale-free behavior for
degree correlations, logarithmic small average path length and
diameter with network size. The obtained properties are in agreement
with empirical data observed in many real-life networks, which shows
that the presented model may provide valuable insight into the real
systems. 相似文献
24.
25.
Wen J Zhao H Lv L Yuan B Wang G Wen X 《The Journal of the Acoustical Society of America》2011,130(3):1201-1208
Recently, by introducing locally resonant scatterers with spherical shape proposed in phononic crystals into design of underwater sound absorption materials, the low-frequency underwater sound absorption phenomenon induced by the localized resonances is observed. To reveal this absorption mechanism, the effect of the locally resonant mode on underwater sound absorption should be studied. In this paper, the finite element method, which is testified efficiently by comparing the calculation results with those of the layer multiple scattering method, is introduced to investigate the dynamic modes and the corresponding sound absorption of localized resonance. The relationship between the resonance modes described with the displacement contours of one unit cell and the corresponding absorption spectra is discussed in detail, which shows that the localized resonance leads to the absorption peak, and the mode conversion from longitudinal to transverse waves at the second absorption peak is more efficient than that at the first one. Finally, to show the modeling capability of FEM and investigate shape effects of locally resonant scatterers on underwater sound absorption, the absorption properties of viscoelastic materials containing locally resonant scatterers with ellipsoidal shape are discussed. 相似文献
26.
27.
28.
Yanfeng Wang Li ZhengxianDu Jihong Hua YunfengWang Baoyun 《Applied Surface Science》2011,258(1):456-460
Materials’ surface service property could be enhanced by transition metal nitride hard coatings due to their high hardness, wear and high temperature oxidation resistance, but the higher friction coefficient (0.4-0.9) of which aroused terrible abrasion. In this work, quinternary (Ti,Al,Si,C)N hard coating 3-4 μm was synthesized at 300 °C using plasma enhanced magnetron sputtering system. It was found that the coating's columnar crystals structure was restrained obviously with the increase of C content and a non-columnar crystals growth mode was indicated at the C content of 33.5 at.%. Both the XRD and TEM showed that the (Ti,Al,Si,C)N hard coatings had unique nanocomposite structures composed of nanocrystalline and amorphous nc-(Ti,Al)(C,N)/nc-AlN/a-Si3N4/a-Si/a-C. However, the coatings were still super hard with the highest hardness of 41 GPa in spite of the carbon incorporation. That a-C could facilitate the graphitization process during the friction process which could improve the coating's tribological performance. Therefore, that nanocomposite (Ti,Al,Si,C)N coatings with higher hardness (>36 GPa) and a lower friction coefficient (<0.2) could be synthesized and enhance the tribological performance and surface properties profoundly. 相似文献
29.
We study uniqueness of weak solution for the generalized incompressible magneto-hydrodynamic (GMHD) system with suitable \(\beta \) , and we prove that the weak solutions are unique in the class \(L^{\frac{2\beta }{2\beta -1+r}}(0,T;B^{r}_{\infty ,\infty })\) with \(r\in (1-2\beta ,1]\) . 相似文献
30.
The authors establish a Serrin's regularity criterion for the β-generalized dissipative surface quasi-geostrophic equation.More precisely,it is shown that if the smooth solution θ satisfies ▽θ∈L~q(0,T;L~P(R~2)) with α/q+2/p≤α+β-1,then the solution θcan be smoothly extended after time T.In particular,when α+β≥2,it is shown that if α_yθ∈L~q(0,T;L~P(R~2)) with α/q+2/p≤α+β-1,then the solution θ can also be smoothly extended after time T.This result extends the regularity result of Yamazaki in 2012. 相似文献