全文获取类型
收费全文 | 655篇 |
免费 | 19篇 |
国内免费 | 5篇 |
专业分类
化学 | 414篇 |
晶体学 | 17篇 |
力学 | 27篇 |
数学 | 47篇 |
物理学 | 174篇 |
出版年
2023年 | 6篇 |
2022年 | 23篇 |
2021年 | 31篇 |
2020年 | 23篇 |
2019年 | 25篇 |
2018年 | 21篇 |
2017年 | 22篇 |
2016年 | 27篇 |
2015年 | 18篇 |
2014年 | 32篇 |
2013年 | 56篇 |
2012年 | 30篇 |
2011年 | 53篇 |
2010年 | 29篇 |
2009年 | 20篇 |
2008年 | 23篇 |
2007年 | 16篇 |
2006年 | 17篇 |
2005年 | 11篇 |
2004年 | 11篇 |
2003年 | 11篇 |
2002年 | 8篇 |
2001年 | 6篇 |
2000年 | 6篇 |
1999年 | 7篇 |
1998年 | 4篇 |
1997年 | 6篇 |
1996年 | 5篇 |
1995年 | 4篇 |
1994年 | 11篇 |
1993年 | 4篇 |
1992年 | 5篇 |
1991年 | 5篇 |
1990年 | 12篇 |
1989年 | 15篇 |
1986年 | 4篇 |
1985年 | 6篇 |
1984年 | 8篇 |
1982年 | 5篇 |
1981年 | 9篇 |
1980年 | 6篇 |
1979年 | 2篇 |
1978年 | 2篇 |
1977年 | 5篇 |
1976年 | 2篇 |
1975年 | 3篇 |
1974年 | 4篇 |
1972年 | 3篇 |
1970年 | 2篇 |
1966年 | 2篇 |
排序方式: 共有679条查询结果,搜索用时 250 毫秒
91.
92.
Sylvester I. Omoruyi Abobaker S. Ibrakaw Okobi E. Ekpo James S. Boatwright Christopher N. Cupido Ahmed A. Hussein 《Molecules (Basel, Switzerland)》2021,26(13)
Parkinson’s disease (PD) is one of the most common neurodegenerative diseases and affects approximately 6.3 million people worldwide. To date, the treatment of PD remains a challenge, as available treatment options are known to be associated with serious side effects; hence, the search for new treatment strategies is critical. Extracts from the Amaryllidaceae plant family as well as their alkaloids have been reported to have neuroprotective potentials. This study, therefore, investigated the biological activities of Crossyne flava and its isolated alkaloids in an in vitro MPP+ (1-methyl-4-phenylpyridinium) PD model using SH-SY5Y cells. The effects of the total extract as well as the four compounds isolated from Crossyne flava (i.e., pancratinine B (1), bufanidrine (2), buphanisine (3), and epibuphanisine (4)) were evaluated for cell viability, neuroprotection, levels of reactive oxygen species (ROS), adenosine triphosphate activity (ATP), and caspase 3/7 activity in SH-SY5Y cells. The results obtained showed that pre-treatment with both the extract and the isolated compounds was effective in protecting the SH-SY5Y cells from MPP+-induced neurotoxicity and inhibited ROS generation, ATP depletion as well as apoptosis induction in the SH-SY5Y cells. The results of this study show that the Amaryllidaceae plant family may be a source of novel compounds for the treatment of neurodegenerative diseases, which validates the reported traditional uses. 相似文献
93.
Basel F. Abu-Sharkh Adam M. Giri Ibnelwaleed A. Hussein 《European Polymer Journal》2004,40(6):1177-1182
Microstructure of linear low-density polyethylene (LLDPE) with linear high-density polyethylene (HDPE) is investigated by molecular dynamics (MD) simulation. The branch content of LLDPE was varied from 10 to 60 branches/1000 C. An equimolar mixture of each of the two polymers is simulated in the NVT ensemble at 500 K and at average experimental densities of the two polymer melts. Initially, chains of LLDPE and HDPE were completely mixed and evolution of conformations with time was monitored. The blends were found to microphase separate when the branch content of LLDPE exceeded 30 branches/1000 C. At 40 branches/1000 C, the two polymers displayed partial microphase separation and complete microphase separation was observed at 60 branches/1000 C. Substantial short-range order and mismatch of molecular conformations is observed in the microphase-separated systems. 相似文献
94.
Angular distributions of the48Ti(d, t)47Ti and47Ti(d, t)46Ti reactions have been measured atE d =19.5 MeV and analyzed by DWBA. The data suggest an explanation of the48Ti(d, t)47Ti ground state transition by means of a [f 7 2/5 ·f 5/2]0+ neutron component in the ground state of48Ti. 相似文献
95.
96.
97.
A.H. Dayem T.H. Geballe R.B. Zubeck A.B. Hallak G.W. Hull 《Journal of Physics and Chemistry of Solids》1978,39(5):529-538
This is a report on a cooperative research carried out in Stanford University to investigate the possibility of using epitaxy to prepare the high Tc superconductor Nb3Ge in an A15 crystalline structure at the 3:1 stoichiometry.Nb3Ir polycrystalline films with the A15 structure deposited on sapphire were used as substrates for the epitaxial growth of Nb3Ge because of the favorable lattice parameter match. The experimental results clearly show that epitaxial growth indeed occurs and helps to extend the range of homogeneity of the A15 phase up to 26.3 at.% Ge as compared with the thermodynamic equilibrium boundary at 19 at.% Ge. We also used Nb3Rh films as substrates and found them inferior to Nb3Ir because of the multiphase nature of the films.In addition to extending the A15 phase boundary epitaxy results in a considerable rise in the superconducting transition temperature for Ge-rich samples together with a reduction in the transition width. The work suggests that polycrystalline epitaxy can be an important tool in the synthesis of thin-film intermetallic compounds. 相似文献
98.
Facile syntheses of pyrazole, pyridine, pyrimidine and pyrazolo[3,4-d]pyrimidine derivatives have been achieved by the reaction of β-enamino nitrile 2a with hydrazines, phenyl isothiocyanate, thiourea and active methylene reagents. The β-enamino ketone 2e with the same reagents affords 3,5-dimethyl heterocyclic ring systems. 相似文献
99.
100.
The angular distributions for elastic scattering and breakup of halo nuclei are analysed using a near-side/far-side decomposition within the framework of the dynamical eikonal approximation. This analysis is performed for 11Be impinging on Pb at 69 MeV/nucleon. These distributions exhibit very similar features. In particular they are both near-side dominated, as expected from Coulomb-dominated reactions. The general shape of these distributions is sensitive mostly to the projectile-target interactions, but is also affected by the extension of the halo. This suggests the elastic scattering not to be affected by a loss of flux towards the breakup channel. 相似文献