全文获取类型
收费全文 | 315篇 |
免费 | 20篇 |
国内免费 | 1篇 |
专业分类
化学 | 199篇 |
晶体学 | 11篇 |
力学 | 4篇 |
数学 | 19篇 |
物理学 | 55篇 |
无线电 | 48篇 |
出版年
2024年 | 2篇 |
2023年 | 9篇 |
2022年 | 18篇 |
2021年 | 13篇 |
2020年 | 18篇 |
2019年 | 19篇 |
2018年 | 13篇 |
2017年 | 23篇 |
2016年 | 21篇 |
2015年 | 12篇 |
2014年 | 16篇 |
2013年 | 32篇 |
2012年 | 16篇 |
2011年 | 24篇 |
2010年 | 8篇 |
2009年 | 11篇 |
2008年 | 14篇 |
2007年 | 15篇 |
2006年 | 10篇 |
2005年 | 9篇 |
2004年 | 11篇 |
2002年 | 5篇 |
2001年 | 1篇 |
2000年 | 2篇 |
1999年 | 1篇 |
1998年 | 2篇 |
1997年 | 3篇 |
1996年 | 1篇 |
1995年 | 1篇 |
1992年 | 1篇 |
1990年 | 1篇 |
1970年 | 4篇 |
排序方式: 共有336条查询结果,搜索用时 15 毫秒
331.
Abstract Anthracene diaryl bromide was prepared via the acid catalyzed condensation of veratrole with p-bromobenzaldehyde. Mixing of toluene solutions of anthracene diaryl bromide and C60 fullerene led to the formation of a 1:1 solid state complex. Evidence for the complex is based on microanalysis and FTIR. A crystal structure of the anthracene diaryl bromide is presented and a dimeric butterfly structure has been proposed for the supramolecular species in solution. 相似文献
332.
H. R. Manjunath S. Naveen C. S. Ananda Kumar S. B. Benaka Prasad M. V. Deepa Naveen M. A. Sridhar J. Shashidhara Prasad K. S. Rangappa 《Journal of Structural Chemistry》2011,52(5):959-963
The title compound 1′-Benzyl-8-(4-fluorobenzyl)-8-azaspiro[bicyclo[3.2.1] octane-3,4′-imidazolidine]-2′,5′-dione, C23H23FN3O2 is synthesized and the structure is investigated by X-ray diffraction studies. The compound crystallizes in the triclinic
crystal class in the P1 space group. The hydantoin ring adopts a planar conformation and is affected by the π conjugation. The pyrrolidine and piperidine
rings in the bicyclo octane moiety adopt envelope and chair conformations respectively. The structure exhibits both inter-
and intramolecular hydrogen bonds of the type N-H...O, C-H...O, and C-H...N. The oxygen atom in the hydantoin ring simultaneously
accepts two hydrogen bonds to form a three-centered hydrogen bonding pattern. 相似文献
333.
The influence of surface plasma waves on high-order harmonic generation from the interaction of intense lasers with overdense plasma is analyzed. It is shown that the surface waves lead to the emission of harmonics away from the optical axis, whereas the high-order on-axis harmonics are lowered in intensity. Our simulation results indicate that surface plasma wave generation plays a crucial role in surface high-order harmonic generation experiments. Furthermore, a novel surface plasma wave generation process different from the well-known two-surface wave decay is observed in the highly relativistic regime. 相似文献
334.
D. Naveen Kumar 《Tetrahedron letters》2004,45(41):7713-7714
A chiron approach to a synthesis of (1R,2R,5S,7R)-2-hydroxy-exo-brevicomin 1, a component of the volatiles obtained from male mountain pine beetles, Dendroctonus ponderosae has been achieved. Our synthesis started with commercially available d-mannitol and involved Wittig olefination, acid catalysed one-pot hydrogenation and internal acetalization as key steps. 相似文献
335.
Aebisher D Azar NS Zamadar M Gandra N Gafney HD Gao R Greer A 《The journal of physical chemistry. B》2008,112(7):1913-1917
Singlet molecular oxygen [1O2 (1Deltag)] is generated cleanly in aqueous solution upon irradiation of a heterogeneous complex, meso-tetra(N-methyl-4-pyridyl)porphine (1) adsorbed onto porous Vycor glass (PVG). The cationic photosensitizer 1 tightly binds onto PVG and gives a stable material, which does not dissociate 1 into the surrounding aqueous phase. The production of 1O2 was measured by monitoring the time-resolved 1O2 (1Deltag) phosphorescence at 1270 nm. Indirect analysis of 1O2 generation was also carried out with the photooxidation of trans-2-methyl-2-pentenoate anion, which afforded the corresponding hydroperoxide. Sensitizer-1-impregnated PVG gives rise to a new singlet oxygen generator but more importantly provides a heterogeneous system for use in water. 相似文献
336.
The boxicity of a graph H, denoted by , is the minimum integer k such that H is an intersection graph of axis-parallel k-dimensional boxes in Rk. In this paper we show that for a line graph G of a multigraph, , where Δ(G) denotes the maximum degree of G. Since G is a line graph, Δ(G)≤2(χ(G)−1), where χ(G) denotes the chromatic number of G, and therefore, . For the d-dimensional hypercube Qd, we prove that . The question of finding a nontrivial lower bound for was left open by Chandran and Sivadasan in [L. Sunil Chandran, Naveen Sivadasan, The cubicity of Hypercube Graphs. Discrete Mathematics 308 (23) (2008) 5795–5800].The above results are consequences of bounds that we obtain for the boxicity of a fully subdivided graph (a graph that can be obtained by subdividing every edge of a graph exactly once). 相似文献