全文获取类型
收费全文 | 620篇 |
免费 | 61篇 |
国内免费 | 33篇 |
专业分类
化学 | 395篇 |
晶体学 | 8篇 |
力学 | 11篇 |
数学 | 61篇 |
物理学 | 239篇 |
出版年
2023年 | 9篇 |
2022年 | 6篇 |
2021年 | 18篇 |
2020年 | 10篇 |
2019年 | 13篇 |
2018年 | 11篇 |
2017年 | 10篇 |
2016年 | 26篇 |
2015年 | 20篇 |
2014年 | 19篇 |
2013年 | 33篇 |
2012年 | 37篇 |
2011年 | 41篇 |
2010年 | 23篇 |
2009年 | 26篇 |
2008年 | 28篇 |
2007年 | 23篇 |
2006年 | 23篇 |
2005年 | 37篇 |
2004年 | 33篇 |
2003年 | 28篇 |
2002年 | 28篇 |
2001年 | 14篇 |
2000年 | 5篇 |
1999年 | 10篇 |
1998年 | 15篇 |
1997年 | 25篇 |
1996年 | 15篇 |
1995年 | 7篇 |
1994年 | 9篇 |
1992年 | 3篇 |
1989年 | 4篇 |
1986年 | 3篇 |
1985年 | 12篇 |
1984年 | 6篇 |
1982年 | 4篇 |
1981年 | 3篇 |
1979年 | 5篇 |
1978年 | 6篇 |
1977年 | 5篇 |
1976年 | 8篇 |
1975年 | 6篇 |
1974年 | 7篇 |
1973年 | 3篇 |
1967年 | 4篇 |
1965年 | 3篇 |
1964年 | 4篇 |
1961年 | 4篇 |
1934年 | 3篇 |
1924年 | 3篇 |
排序方式: 共有714条查询结果,搜索用时 15 毫秒
81.
Transparent aqueous sols of colloidal tetramethylammonium niobate nanocrystals were synthesized by mixing tetramethylammonium hydroxide (TMAOH), niobium ethoxide, and water at TMAOH/Nb≥0.7 at room temperature. The X-ray diffraction patterns of the thin films prepared by evaporating the colloidal solutions on a glass substrate indicated that the colloidal niobate had a layered crystalline structure. Two types of layered structures are known as a layered niobate, i.e. M(4)Nb(6)O(17)·nH(2)O and MNb(3)O(8) (M=H, H(3)O, or alkaline metal). Raman spectra and electron diffraction suggested that the niobate nanocrystals were similar in crystal structure to M(4)Nb(6)O(17)·nH(2)O compounds. Moreover, when niobium oxide thin films were fabricated from the niobate colloidal solutions by the sol-gel method, oriented T-Nb(2)O(5) thin films, whose c-axis was parallel to the substrate surface, were obtained. The orientation of the thin films was probably attributed to the layered structure of the colloidal niobate nanocrystals. 相似文献
82.
A series of novel furan-2-yl(phenyl)methanone derivatives were synthesized, and their structures were established on the basis of 1H-NMR, 13C-NMR and mass spectral data. All the prepared compounds were screened for their in vitro protein tyrosine kinase inhibitory activity and several new derivatives exhibited promising activity, which, in some cases, was identical to, or even better than that of genistein, a positive reference compound. The preliminary structure-activity relationships of these compounds were investigated and are discussed. 相似文献
83.
84.
高频溅射生长ZnS:Tb,F薄膜的结构与发光 总被引:2,自引:1,他引:1
本文采用X射线衍射和阴极射线发光技术对溅射法生长的ZnS:Tb,F薄膜的发光光谱和薄膜的微观结构进行了研究,得出了激晶薄膜的晶粒尺寸与发光强度的关系.讨论了稀土离子的价态对掺杂稀土微晶薄膜的发光性质与晶粒尺寸的关系的影响. 相似文献
85.
By introducing thet-measures of fuzziness we give a method for determination the degree of interference between the elements with different properties of a universe. Finally, we apply this method in geography of population. 相似文献
86.
The influence of temperature on the surface structure of the octadecylsilica (ODS) bonded phase was investigated with a molecular dynamics (MD) simulation. The MD simulation was applied to a molecular model consisting of three parts: amorphous silica base, dimethyloctadecylsilyl ligands and n-hexane as a mobile phase solvent. More detailed information on the effect of temperature was obtained at the low temperature region than that reported in our previous study. The motion of ODS ligands could be estimated by the mean square displacement (MSD) of the terminal carbon atoms of ODS ligands. The gauche fraction in the ODS ligand conformation can also be estimated to obtain the ligand conformation for each simulation condition in detail. It can be seen that an elevated temperature induced the more bent ligand conformation. The trend has a good agreement to that of the results experimentally observed by using various spectroscopic techniques such as nuclear magnetic resonance (NMR), Fourier-transform infrared spectroscopy (FT-IR), and Raman spectroscopy. 相似文献
87.
在文献[1]中荷清泉提出了纳米级铜原子团簇具有红外吸收特性的理论。本文采用磁控溅射低温液氮收集方法制备了纳米级铜原子团簇,并用红外光谱法测定其吸收红外光的性能,结果表明纳米级钢原子团簇确实具有明显的红外吸收特性,验证了文献[1]中提出的理论预言。 相似文献
88.
Mikiko Shima Etsuyo Ogawa Seiko Ban Mari Sato 《Journal of Polymer Science.Polymer Physics》1977,15(11):1999-2011
Dilute solution properties of (styrene-p-chlorostyrene) triblock copolymers in various solvents were studied over a wide range of molecular weight and composition. Viscosity and osmotic pressure results indicate that the conformational behavior of the BmAnBm and AmBnAm copolymers (A = styrene; B = p-chlorostyrene; m and n denote the number of units) are similar in nonselective solvents such as toluene and 2-butanone, but different in selective solvents such as carbon tetrachloride and cumene. Short-range and long-range interaction parameters of the block copolymers were determined by applying the Stockmayer–Fixman method to viscosity data and also by application of the equation relating the osmotic virial coefficient and the excluded volume. The results show that the unperturbed dimensions of the block copolymers vary linearly with composition, and long-range interaction parameters in nonselective solvents can be expressed by those of the parent homopolymers, the chemical composition, and values of the interaction parameter βAB between styrene and p-chlorostyrene monomeric units. 相似文献
89.
90.