全文获取类型
收费全文 | 679篇 |
免费 | 64篇 |
国内免费 | 47篇 |
专业分类
化学 | 347篇 |
晶体学 | 1篇 |
力学 | 4篇 |
综合类 | 12篇 |
数学 | 87篇 |
物理学 | 339篇 |
出版年
2024年 | 2篇 |
2023年 | 12篇 |
2022年 | 20篇 |
2021年 | 34篇 |
2020年 | 28篇 |
2019年 | 21篇 |
2018年 | 20篇 |
2017年 | 24篇 |
2016年 | 33篇 |
2015年 | 24篇 |
2014年 | 40篇 |
2013年 | 42篇 |
2012年 | 40篇 |
2011年 | 31篇 |
2010年 | 30篇 |
2009年 | 32篇 |
2008年 | 38篇 |
2007年 | 50篇 |
2006年 | 33篇 |
2005年 | 31篇 |
2004年 | 28篇 |
2003年 | 20篇 |
2002年 | 19篇 |
2001年 | 12篇 |
2000年 | 15篇 |
1999年 | 9篇 |
1998年 | 15篇 |
1997年 | 8篇 |
1996年 | 9篇 |
1995年 | 7篇 |
1994年 | 14篇 |
1993年 | 3篇 |
1992年 | 7篇 |
1991年 | 3篇 |
1990年 | 3篇 |
1989年 | 4篇 |
1988年 | 5篇 |
1987年 | 4篇 |
1986年 | 2篇 |
1985年 | 2篇 |
1984年 | 1篇 |
1983年 | 2篇 |
1982年 | 2篇 |
1981年 | 5篇 |
1979年 | 3篇 |
1978年 | 2篇 |
1936年 | 1篇 |
排序方式: 共有790条查询结果,搜索用时 623 毫秒
781.
We clarify the domain needed for the mixing angles in three flavor neutrino oscillations. By comparing the ranges of the transition probabilities as functions of the domains of the mixing angles, we show that it is necessary and sufficient to let all mixing angles be in
. This holds irrespectively of any assumptions on the neutrino mass squared differences. 相似文献
782.
783.
Andrea Cesari Federica Balzano Gloria Uccello Barretta Alessandra Recchimurzo 《Molecules (Basel, Switzerland)》2021,26(21)
Partially and exhaustively methylated β-cyclodextrins [(2-methyl)-β-CD (MCD), heptakis-(2,6-di-O-methyl)-β-CD (DIMEB), and heptakis-(2,3,6-tri-O-methyl)-β-CD (TRIMEB)] have been compared in the hydrolysis and enantiodiscrimination of benzodiazepine derivative (R)- or (S)-oxazepam hemisuccinate (OXEMIS), using nuclear magnetic resonance (NMR) spectroscopy as an investigation tool. After 6 h, MCD induced an 11% hydrolysis of OXEMIS, remarkably lower in comparison with underivatized β-CD (48%), whereas no hydrolysis was detected in the presence of DIMEB or TRIMEB after 24 h. DIMEB showed greater ability to differentiate OXEMIS enantiomers in comparison to TRIMEB, by contrast MCD did not produce any splitting of racemic OXEMIS resonances. Both enantiomers of OXEMIS underwent deep inclusion of their phenyl pendant into cyclodextrins cavities from their wider rims, but tighter complexes were formed by DIMEB with respect to TRIMEB. 相似文献
784.
A. L. Burke T. A. Duever A. Penlidis 《Journal of polymer science. Part A, Polymer chemistry》1996,34(13):2665-2678
In this article, the modified Buzzi–Ferraris model discrimination method was used to design experiments to discriminate between the terminal and penultimate models for styrene methyl methacrylate (STY/MMA) copolymerization. The measured variables were 13C-NMR peak areas. The peak area assignments of Aerdts8 were used. After nine experiments, the terminal model was picked over the penultimate model at 99.99% confidence. More importantly, the experimental data showed that computer simulated data used in previous studies were realistic, and the conclusions drawn from the simulation studies were valid. This experimental verification continues to show that the use of statistical model discrimination techniques can improve our ability to discriminate between competing copolymerization models. © 1996 John Wiley & Sons, Inc. 相似文献
785.
786.
Jin-Hua Zhang Fu-Lin Zhang Zhi-Xi Wang Hui Yang Shao-Ming Fei 《Entropy (Basel, Switzerland)》2022,24(1)
We investigate the discrimination of pure-mixed (quantum filtering) and mixed-mixed states and compare their optimal success probability with the one for discriminating other pairs of pure states superposed by the vectors included in the mixed states. We prove that under the equal-fidelity condition, the pure-pure state discrimination scheme is superior to the pure-mixed (mixed-mixed) one. With respect to quantum filtering, the coherence exists only in one pure state and is detrimental to the state discrimination for lower dimensional systems; while it is the opposite for the mixed-mixed case with symmetrically distributed coherence. Making an extension to infinite-dimensional systems, we find that the coherence which is detrimental to state discrimination may become helpful and vice versa. 相似文献
787.
788.
By solving two body Dirac equations with potentials at finite temperature, we calculate the dissociation temperature \begin{document}$ T_d $\end{document} ![]()
![]()
of \begin{document}$ B_c $\end{document} ![]()
![]()
mesons in quark-gluon plasma. It is found that \begin{document}$ T_d $\end{document} ![]()
![]()
becomes higher with the relativistic correction than the \begin{document}$ T_d $\end{document} ![]()
![]()
from the Schr?dinger equation. Both the short range interaction and the constant term of the potential at the long-range scale have a contribution to the shift of \begin{document}$ T_d $\end{document} ![]()
![]()
, while the spin interaction is negligible. 相似文献
789.
Gan Chen Hong Zhang Jiaming Jiang Simin Chen Hongmei Zhang Gongmin Zhang Changwu Zheng Hongxi Xu 《Journal of separation science》2023,46(22):2300445
Mountain-cultivated ginseng is typically harvested after 10 years, while ginseng aged over 15 years is considered wild ginseng. This study aims to differentiate mountain-cultivated ginseng by age, as the fraudulent practice of selling low-aged cultivated ginseng disguised as high-aged one is damaging the market. In this study, LC-MS analyzed 98 ginseng samples, and multivariate statistical analysis identified patterns between samples to select influential components. Machine learning models were developed to identify ginseng samples of different ages. The untargeted metabolomic analysis clearly divided samples aged 4-20 years into three age groups. Twenty-two potential age-dependent biomarkers were discovered to differentiate the three sample groups. Three machine learning models were used to predict new samples, and the optimal model was selected. Some biomarkers could determine age phases according to the differentiation of mountain-cultivated ginseng samples. These biomarkers were thoroughly analyzed for variation trends. The machine learning models established using the screened biomarkers successfully predicted the age group of new samples. 相似文献
790.
A study of the generalized global flavor symmetries of the Standard Model is initiated. The presence of nonzero triangle diagrams between the U(3)5 flavor currents and the hypercharge current intertwines them in the form of a higher-group which mixes the zero-form flavor symmetries with the one-form magnetic hypercharge symmetry. This higher symmetry structure greatly restricts the possible flavor symmetries that may remain unbroken in any ultraviolet completion that includes magnetic monopoles. In the context of unification, this implies tight constraints on the combinations of fermion species which may be joined into multiplets. Three of four elementary possibilities are reflected in the classic unification models of Georgi–Glashow, , and Pati–Salam. The final pattern is realized non-trivially in trinification, which exhibits the sense in which Standard Model Yukawa couplings which violate these flavor symmetries may be thought of as spurions of the higher-group. Such modifications of the ultraviolet flavor symmetries are possible only if new vector-like matter is introduced with masses suppressed from the unification scale by the Yukawa couplings. 相似文献