全文获取类型
收费全文 | 808篇 |
免费 | 1篇 |
国内免费 | 2篇 |
专业分类
化学 | 556篇 |
晶体学 | 2篇 |
力学 | 5篇 |
数学 | 168篇 |
物理学 | 80篇 |
出版年
2023年 | 5篇 |
2021年 | 6篇 |
2020年 | 7篇 |
2015年 | 9篇 |
2013年 | 14篇 |
2012年 | 35篇 |
2011年 | 34篇 |
2010年 | 22篇 |
2009年 | 11篇 |
2008年 | 32篇 |
2007年 | 39篇 |
2006年 | 37篇 |
2005年 | 31篇 |
2004年 | 23篇 |
2003年 | 20篇 |
2002年 | 23篇 |
2001年 | 9篇 |
2000年 | 8篇 |
1999年 | 13篇 |
1998年 | 18篇 |
1997年 | 11篇 |
1996年 | 15篇 |
1995年 | 18篇 |
1994年 | 16篇 |
1993年 | 17篇 |
1992年 | 15篇 |
1991年 | 12篇 |
1990年 | 9篇 |
1989年 | 19篇 |
1988年 | 11篇 |
1987年 | 12篇 |
1986年 | 13篇 |
1985年 | 13篇 |
1984年 | 21篇 |
1983年 | 8篇 |
1982年 | 14篇 |
1981年 | 15篇 |
1980年 | 12篇 |
1979年 | 17篇 |
1978年 | 15篇 |
1977年 | 17篇 |
1976年 | 14篇 |
1975年 | 6篇 |
1974年 | 9篇 |
1971年 | 7篇 |
1967年 | 4篇 |
1961年 | 7篇 |
1958年 | 8篇 |
1957年 | 4篇 |
1956年 | 5篇 |
排序方式: 共有811条查询结果,搜索用时 15 毫秒
61.
Tan B Vyas SM Lehmler HJ Knutson BL Rankin SE 《The journal of physical chemistry. B》2005,109(49):23225-23232
A series of porous silica particles is prepared with different concentrations of the fluorinated cationic surfactant 1-(3,3,4,4,5,5,6,6,7,7,8,8,9,9,10,10,10)-heptadecafluorodecyl)pyridinium chloride (HFDePC) to trace the changes in pore structure and particle morphology as the surfactant concentration increases. At the lowest concentration studied (1.5 mmol/L), the product consists of small round particles with close-packed cylindrical mesopores. As the HFDePC concentration increases, macroporous voids are introduced to create multi-chambered hollow particles with mesoporous walls. With a still higher concentration of HFDePC the macropore volume decreases, and elongated, tactoid-like nanoparticles are formed with random mesh-phase pores oriented with silica layers perpendicular to the main axis of the particles. Further increasing the concentration of HFDePC eventually leads to the formation of round particles with disordered pores. These changes are consistent with increasing HFDePC concentration favoring increasingly oblate or disklike micelles. The process of forming the elongated particles with random mesh-phase structure is investigated by TEM of chilled and dried samples. The results indicate that the oriented tactoid-like structure forms spontaneously within 2 min by co-assembly of silica and HFDePC rather than by preferred growth perpendicular to the layers. The particle shape and layer orientation are consistent with what would be expected for a liquid-crystal particle with orientation-dependent surface tension. Finally, we compare samples prepared with a high HFDePC and with good or poor mixing. With inadequate mixing, a gel layer forms at the top of the sample which is composed of elongated mesoporous particles with a thick coating of microporous silica. The lower particulate phase contains small disordered particles similar to those obtained in a well-mixed sample. Presumably, the structure of the upper layer results from initial immiscibility of the precursor and slow diffusion of silicates out of the gel. 相似文献
62.
The spatial distribution of single Au atoms on a thin FeO film has been investigated by low-temperature scanning tunneling microscopy and spectroscopy. The adatoms preferentially adsorb on distinct sites of the Moiré cell formed by the oxide layer and the Pt(111) support and arrange into a well-ordered hexagonal superlattice with 25 angstroms lattice constant. The self-organization is the consequence of an inhomogeneous surface potential within the FeO Moiré cell and substantial electrostatic repulsion between the adatoms. 相似文献
63.
64.
65.
it is said that when Pythagoras discovered his famous theorem, in a right-angled triangle the squares of the smaller sides
sum up to the square of the hypoteneuse, he sacrificed a hundred oxen to thank the gods. 相似文献
66.
67.
Small bimetallic Pd-Fe particles supported on a well ordered alumina film grown on NiAl (1 1 0) were studied focusing on the geometric, electronic, adsorption, as well as magnetic properties. The morphology, growth mode and surface composition were investigated by combining scanning tunneling microscopy (STM), temperature-programmed desorption (TPD) and infrared spectroscopy (IRAS) using CO as a probe molecule. Information on the electronic properties of the bimetallic systems was obtained by means of X-ray photoelectron spectroscopy (XPS). These measurements were amended by in situ ferromagnetic resonance spectroscopy to address the magnetic properties of the bimetallic particles. The subsequent deposition of the metals at 300 K varying the order of metal deposition resulted in two distinct bimetallic systems. Pd deposited on existing Fe particles forms a shell, however, FMR and XPS suggest that intermixing of Pd and Fe occurs to some extent. For the reverse order, a larger amount of Fe is required to coat Pd particles, due to the strong tendency of Pd to segregate to the surface of the particles. 相似文献
68.
We introduce the notion of n-fold track extensions of a category C by a natural system D and prove that such extensions represent classes in the cohomology of C with coefficients in D introduced by Baues–Wirsching. This generalizes a result of Huebschmann on the cohomology of groups. 相似文献
69.
70.