全文获取类型
收费全文 | 10784篇 |
免费 | 355篇 |
国内免费 | 32篇 |
专业分类
化学 | 7604篇 |
晶体学 | 25篇 |
力学 | 152篇 |
综合类 | 1篇 |
数学 | 2076篇 |
物理学 | 1313篇 |
出版年
2020年 | 80篇 |
2019年 | 100篇 |
2016年 | 190篇 |
2015年 | 186篇 |
2014年 | 240篇 |
2013年 | 410篇 |
2012年 | 276篇 |
2011年 | 278篇 |
2010年 | 236篇 |
2009年 | 225篇 |
2008年 | 307篇 |
2007年 | 289篇 |
2006年 | 318篇 |
2005年 | 297篇 |
2004年 | 272篇 |
2003年 | 281篇 |
2002年 | 287篇 |
2001年 | 208篇 |
2000年 | 184篇 |
1999年 | 126篇 |
1998年 | 116篇 |
1997年 | 139篇 |
1996年 | 143篇 |
1995年 | 123篇 |
1994年 | 135篇 |
1993年 | 155篇 |
1992年 | 153篇 |
1991年 | 128篇 |
1990年 | 143篇 |
1989年 | 137篇 |
1988年 | 144篇 |
1987年 | 145篇 |
1986年 | 121篇 |
1985年 | 235篇 |
1984年 | 207篇 |
1983年 | 127篇 |
1982年 | 176篇 |
1981年 | 168篇 |
1980年 | 205篇 |
1979年 | 204篇 |
1978年 | 204篇 |
1977年 | 235篇 |
1976年 | 188篇 |
1975年 | 173篇 |
1974年 | 137篇 |
1973年 | 191篇 |
1972年 | 96篇 |
1971年 | 92篇 |
1970年 | 71篇 |
1933年 | 69篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
In CSFeBr3 the Fe2+ ion with effective spin one has locally a singlet ground state (m=0). The antiferromagnetic interactions between neighbouring Fe-ions are too weak as compared with the anisotropy constant to introduce long range order in the absence of an external field. By inelastic neutron scattering we studied the magnetic excitations in an external magnetic field up to 5 Tesla applied along thec-axis. A linear Zeeman splitting was observed with a Landé factorg=2.4. The field renormalizes the dispersion curves in such a way that the exchange interaction has decreasing influence with increasing field. Theoretical calculations according to the excitonic model of Lindgård describe the experimental results very well. At 4.1 Tesla a phase transition appears to a commensurate long range order with a 120° arrangement of the spins in the hexagonal plane. Within the limits of experimental observation this phase transition has no influence on the dynamical behaviour. No critical phenomena could be observed. The dynamical structure factor |G
j()|2 of the lower Zeeman split modes decreases with increasing field. 相似文献
72.
Preservation mechanisms of trehalose in food and biosystems 总被引:15,自引:0,他引:15
The stability or shelf-life of food and biomaterials has always been a critical issue in the food and pharmaceutical industry. Trehalose (alpha-D-glucopyranosyl-alpha-D-glucopyranoside), a non-reducing diglucose sugar found in nature, confers to certain plant and animal cells the ability to survive dehydration for decades and to restore activity soon after rehydration. The interaction between trehalose and cell membranes or proteins, however, remains a debated subject, and a significant amount of work has been done to elucidate the mechanisms resulting in this unique behavior of preservation. This study shows how an interfacial phenomena approach has led to the use of trehalose as an excipient during freeze drying of a variety of products in the pharmaceutical industry. It also suggests opportunities as an ingredient for dried and processed food, as well as a non-toxic cryoprotectant of vaccines and organs for surgical transplants. 相似文献
73.
Five low-lying negative parity states of103Rh up to 1277 keV excitation energy were observed to be Coulomb excited with 2·5–4·5 MeV protons. The de-excitation gamma rays from these levels were identified in the singles spectra recorded with a 57 cc Ge(Li) detector. The level energies, branching ratios, reduced transition probabilitiesB(E2) and the multipole mixing ratios () were obtained. The 880, 1106 and 1277 keV levels have been Coulomb excited with protons for the first time. The ambiguity in theJ
values for 803 and 1106 keV levels have been resolved using 2-fits, the assigned spin values are 1/2– and 5/2–, respectively. The-values for 474·1 and 811·2 keV transitions were obtained for the first time. The results have been discussed in the light of previously reported results.The authors wish to thank Professor I. M. Govil for his active interest at various stages of this work. One of us (DCT) acknowledges the financial support from U.G.C., New Delhi, under Faculty Improvement Programme. 相似文献
74.
B. Dorner D. Visser U. Steigenberger K. Kakurai M. Steiner 《Zeitschrift für Physik B Condensed Matter》1988,72(4):487-496
We have measured the magnetic excitations in CsFeBr3 along the chain direction (z-axis) and perpendicular to it by inelastic neutron scattering. The measured dispersion curves can be reproduced by the formula $$\omega ^2 (q) = A^2 - 8A[J\cos (\pi q_c ) + J'\gamma (2\pi q_ \bot )]R(T)$$ which is very different from dispersion relations for usual 1 D antiferromagnets, because of the singlet groundstate of this system. The large value of the anisotropy energyA/k=29.8±0.5 K, which is independent of temperature, causes the singlet groundstate. The intra-and inter-chain exchange parameters areJ/k=?3.2±0.15K andJ'/k=?0.32±0.02 K determined atT=1.4 K. At 1.4 K the renormalisation factor is taken to beR(T)=1. AtT=30 K the value forR(T) was found to be 0.5±0.1 keepingJ andJ' unchanged. The excitations at (1/3 1/31) show soft mode behaviour but no phase transition. The observed intensities are interpreted by a heuristic model for the eigenvectors in the excited state including antiferro-as well as ferromagnetic configurations of the fluctuations. 相似文献
75.
76.
77.
78.
79.
Two Optically Active Luteochromes: Preparation, Spectra and Chiroptical and Chromatographic Properties Selective rearrangement of (5R,6S,5′ R,6′S)-5,6:5′, 6′ -diepoxy-5,6,5′, 6′ -tetrahydro- β,β -carotene with the aid ofan ethereal solution of malonic acid leads to the mixture of the C(8′)-epimeric luteochromes. HPLC separation gave the pure isomers. This is the first report on th preparation of optically active luteochromes. 相似文献
80.