全文获取类型
收费全文 | 1587篇 |
免费 | 37篇 |
国内免费 | 6篇 |
专业分类
化学 | 949篇 |
晶体学 | 32篇 |
力学 | 18篇 |
数学 | 154篇 |
物理学 | 477篇 |
出版年
2022年 | 10篇 |
2021年 | 14篇 |
2020年 | 13篇 |
2019年 | 18篇 |
2017年 | 8篇 |
2016年 | 33篇 |
2015年 | 30篇 |
2014年 | 41篇 |
2013年 | 39篇 |
2012年 | 60篇 |
2011年 | 76篇 |
2010年 | 43篇 |
2009年 | 59篇 |
2008年 | 50篇 |
2007年 | 62篇 |
2006年 | 80篇 |
2005年 | 75篇 |
2004年 | 45篇 |
2003年 | 44篇 |
2002年 | 31篇 |
2001年 | 46篇 |
2000年 | 48篇 |
1999年 | 27篇 |
1998年 | 25篇 |
1997年 | 28篇 |
1996年 | 45篇 |
1995年 | 48篇 |
1994年 | 35篇 |
1993年 | 31篇 |
1992年 | 28篇 |
1991年 | 21篇 |
1990年 | 20篇 |
1989年 | 15篇 |
1988年 | 19篇 |
1987年 | 21篇 |
1986年 | 15篇 |
1984年 | 10篇 |
1983年 | 18篇 |
1982年 | 20篇 |
1981年 | 15篇 |
1980年 | 17篇 |
1979年 | 12篇 |
1978年 | 15篇 |
1977年 | 21篇 |
1976年 | 19篇 |
1975年 | 13篇 |
1974年 | 19篇 |
1973年 | 12篇 |
1971年 | 9篇 |
1935年 | 7篇 |
排序方式: 共有1630条查询结果,搜索用时 15 毫秒
1.
G. Ullrich D. Herzog R. Liska P. Burtscher N. Moszner 《Journal of polymer science. Part A, Polymer chemistry》2004,42(19):4948-4963
Camphorquinone (CQ), a widely used photoinitiator (PI) in dental applications, was covalently bonded to aromatic amines to enhance the rate of electron and proton transfer effect due to the close vicinity of the diketone and the amine group. 10‐bromocamphorquinone and 10‐bromomethylcamphorquinone were selected as suitable precursors for esterification with the carboxyl group containing aromatic amines based on 4‐dimethylaminobenzoic acid. Properties of the new photoinitiating systems were investigated by UV spectroscopy and differential scanning photocalorimetry in lauryl acrylate. Compared to physical mixtures, in all cases similar or even better performance was obtained. Surprisingly, 10‐acetyl derivatives 7 – 9 and 18 especially, were found to be highly reactive. Compared to CQ/ethyl 4‐dimethylaminobenzoate, the rate of photopolymerization was increased by a factor of up to 2. Intramolecular reaction was confirmed by photo‐differential scanning calorimetry experiments with varying PI concentrations. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 4948–4963, 2004 相似文献
2.
Elon Santos Correa Maria Teresinha A. Steiner Alex A. Freitas Celso Carnieri 《Numerical Algorithms》2004,35(2-4):373-388
Facility-location problems have several applications, such as telecommunications, industrial transportation and distribution. One of the most well-known facility-location problems is the p-median problem. This work addresses an application of the capacitated p-median problem to a real-world problem. We propose a genetic algorithm (GA) to solve the capacitated p-median problem. The proposed GA uses not only conventional genetic operators, but also a new heuristic “hypermutation” operator suggested in this work. The proposed GA is compared with a tabu search algorithm. 相似文献
3.
4.
M. Froese C. Champagne J. R. Crespo López-Urrutia S. Epp G. Gwinner A. Lapierre J. Pfister G. Sikler J. Ullrich J. Dilling 《Hyperfine Interactions》2006,173(1-3):85-92
The precision of atomic mass measurements in a Penning trap is directly proportional to the charge state q of the ion and,
hence, can be increased by using highly charged ions (HCI). For this reason, charge breeding with an electron beam ion trap
(EBIT) is employed at TRIUMF’s Ion Trap for Atomic and Nuclear science (TITAN) on-line facility in Vancouver, Canada. By bombarding
the injected and trapped singly charged ions with an intense beam of electrons, the charge state of the ions is rapidly increased
inside the EBIT. To be compatible with the on-line requirements of short-lived isotopes, very high electron beam current densities
are needed. The TITAN EBIT includes a 6 Tesla superconducting magnet and is designed to have electron beam currents and energies
of up to 5 A and 60 keV, respectively. Once operational at full capacity, most species can be bred into a He-like configuration
within tens of ms. Subsequently, the HCI are extracted, pass a Wien filter to reduce isobaric contamination, are cooled, and
injected into a precision Penning trap for mass measurement. We will present the first results and current status of the TITAN
EBIT, which has recently been moved to TRIUMF after assembly and commissioning at the Max-Planck-Institute (MPI) for Nuclear
Physics in Heidelberg, Germany. 相似文献
5.
6.
7.
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
8.
9.
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