全文获取类型
收费全文 | 376篇 |
免费 | 13篇 |
国内免费 | 2篇 |
专业分类
化学 | 242篇 |
力学 | 13篇 |
数学 | 27篇 |
物理学 | 109篇 |
出版年
2023年 | 5篇 |
2022年 | 7篇 |
2021年 | 9篇 |
2020年 | 8篇 |
2019年 | 15篇 |
2018年 | 9篇 |
2017年 | 15篇 |
2016年 | 23篇 |
2015年 | 11篇 |
2014年 | 16篇 |
2013年 | 26篇 |
2012年 | 36篇 |
2011年 | 38篇 |
2010年 | 20篇 |
2009年 | 17篇 |
2008年 | 16篇 |
2007年 | 25篇 |
2006年 | 18篇 |
2005年 | 20篇 |
2004年 | 14篇 |
2003年 | 12篇 |
2002年 | 6篇 |
2001年 | 3篇 |
2000年 | 2篇 |
1999年 | 3篇 |
1998年 | 1篇 |
1996年 | 2篇 |
1995年 | 1篇 |
1994年 | 1篇 |
1993年 | 2篇 |
1984年 | 3篇 |
1980年 | 1篇 |
1979年 | 2篇 |
1978年 | 2篇 |
1976年 | 1篇 |
1975年 | 1篇 |
排序方式: 共有391条查询结果,搜索用时 15 毫秒
81.
82.
83.
84.
Manoj K. Yadav Abhijit Mookerjee Biplab Sanyal 《Journal of magnetism and magnetic materials》2010,322(2):253-256
We show that the antiferromagnetic coupling between Mn atoms in MnO can be tuned to a ferromagnetic one by doping it with a small concentration of 2p elements like boron, carbon and nitrogen. Our ab initio density functional calculations in the Hubbard U framework show that the coupling between Mn atoms turns ferromagnetic for 3 at% B doping. B is found to be the most effective one in stabilizing ferromagnetism. We discuss the role of 2p states of the dopant atoms to explain the trend of ferromagnetism in MnO. 相似文献
85.
Abhijit Pramanick Anderson D. Prewitt Michelle A. Cottrell Wayne Lee Andrew J. Studer Ke An Camden R. Hubbard Jacob L. Jones 《Applied Physics A: Materials Science & Processing》2010,99(3):557-564
Structural changes in commercial lead zirconate titanate (PZT) ceramics (EC-65) under the application of electric fields and
mechanical stress were measured using neutron diffraction instruments at the Australian Nuclear Science and Technology Organisation
(ANSTO) and the Oak Ridge National Laboratory (ORNL). The structural changes during electric-field application were measured
on the WOMBAT beamline at ANSTO and include non-180° domain switching, lattice strains and field-induced phase transformations.
Using time-resolved data acquisition capabilities, lattice strains were measured under cyclic electric fields at times as
short as 30 μs. Structural changes including the (002) and (200) lattice strains and non-180° domain switching were measured
during uniaxial mechanical compression on the NRSF2 instrument at ORNL. Contraction of the crystallographic polarization axis,
(002), and reorientation of non-180° domains occur at lowest stresses, followed by (200) elastic strains at higher stresses. 相似文献
86.
A new approach to carbasugars in enantiomerically pure form is reported. The key step involves ring-closing metathesis of dienols 6 derived from a (R)-(+)-glyceraldehyde derivative 4 to form the substituted cyclopentenol 9 and cyclohexenol 34a. Stereocontrolled addition of hydroxyl groups followed by conversion of the ketal unit to hydroxymethyl group in these intermediates led to carbapentoses and -hexoses. Stereoselectivity during introduction of hydroxyl groups arises through the steric hindrance posed by the allylic substituents. A remarkable feature of the present approach is the accessibility of both d- and l-series of carbapentoses as illustrated by the synthesis of beta-D- and beta-L-carbaribofuranoses 17 and 20, respectively. Carba-alpha-D-ribofuranose 25, the biosynthetic intermediate to the antibiotic aristeromycin, has also been synthesized from the same cyclopentenol 9. Functional group manipulation in the cyclopentenol 9a also enabled access to carbaarabinofuranose 32. The present synthetic strategy can be extended for the synthesis of carbahexopyranose, as illustrated by the synthesis of carba-alpha-L-gulopyranose 40b. 相似文献
87.
We propose a new approach for estimating the phase in the presence of a nonlinear response of a phase-shifting device: a piezoelectric transducer (PZT). The method is complemented well by the high resolution and the maximum likelihood estimation techniques in the estimation of the phase step and the nonlinear coefficient. The advantage of the proposed method is that it can be extended to the extraction of multiple phases in configurations involving multiple PZTs in the presence of nonlinearity. Symmetricity in the phase steps is not required in this method. Hence hysteresis of the PZT does not have any influence on the accuracy of the phase estimation. The effectiveness of the method is shown by experimental results. 相似文献
88.
A phase-shifting piezo device commonly employed in phase-shifting interferometry exhibits a nonlinear response to applied voltage. Hence, a method for estimation of phase distribution in the presence of nonlinear phase steps is presented. The proposed method compensates for the harmonics present in the intensity fringe, allows the use of arbitrary phase-step values between 0 and tau rad, and does not impose constraints on the selection of particular phase-step values for minimizing nonlinearity and compensating for the harmonics. The comparison of the proposed method with other well-known benchmarking algorithms shows that our method is highly efficient and also works well in the presence of noise. 相似文献
89.
A new phase-shifting interferometric technique that uses an unknown phase step is described in which the phase step is determined by use of an algorithm called Probabilistic Global Search Lausanne (PGSL). One of the main sources of error in phase stepping is piezoelectric device (PZT) nonlinearity. The PGSL algorithm identifies the characteristics of the response of the PZT to the applied voltage through matching predicted and measured responses. The unknown phase step is also calculated with 0.097% error. This approach overcomes the limitations of existing techniques to determine unknown phase steps. Linear regression is subsequently applied for interference phase determination. 相似文献
90.
Meccanica - Structures such as turbomachinery blades, industrial fans, propellers, etc. can be modeled as twisted beams. The study of dynamics of these structures is vital as operational failure of... 相似文献