全文获取类型
收费全文 | 929篇 |
免费 | 37篇 |
国内免费 | 8篇 |
专业分类
化学 | 427篇 |
晶体学 | 14篇 |
力学 | 55篇 |
数学 | 166篇 |
物理学 | 312篇 |
出版年
2021年 | 6篇 |
2020年 | 9篇 |
2019年 | 10篇 |
2018年 | 7篇 |
2016年 | 22篇 |
2015年 | 16篇 |
2014年 | 17篇 |
2013年 | 51篇 |
2012年 | 48篇 |
2011年 | 49篇 |
2010年 | 25篇 |
2009年 | 32篇 |
2008年 | 39篇 |
2007年 | 47篇 |
2006年 | 39篇 |
2005年 | 41篇 |
2004年 | 27篇 |
2003年 | 35篇 |
2002年 | 21篇 |
2001年 | 13篇 |
2000年 | 17篇 |
1999年 | 23篇 |
1998年 | 12篇 |
1997年 | 24篇 |
1996年 | 19篇 |
1995年 | 14篇 |
1994年 | 28篇 |
1993年 | 19篇 |
1992年 | 27篇 |
1991年 | 12篇 |
1990年 | 8篇 |
1989年 | 9篇 |
1988年 | 5篇 |
1987年 | 10篇 |
1986年 | 12篇 |
1985年 | 21篇 |
1984年 | 15篇 |
1983年 | 9篇 |
1982年 | 6篇 |
1981年 | 9篇 |
1980年 | 9篇 |
1979年 | 6篇 |
1978年 | 16篇 |
1977年 | 11篇 |
1976年 | 9篇 |
1975年 | 12篇 |
1974年 | 7篇 |
1973年 | 9篇 |
1972年 | 5篇 |
1967年 | 5篇 |
排序方式: 共有974条查询结果,搜索用时 15 毫秒
941.
942.
Nicholas J. Turro Kou-Chang Lru Ming-Fea Chow Plato Lee 《Photochemistry and photobiology》1978,27(5):523-529
Abstract— Phosphorescence of organic molecules in fluid solutions may be conveniently and readily observed under certain conditions. If k p (radiative phosphorescence rate constant) is 10s-1 , then (in the absence of photoreaction) phosphorescence is observable upon N2 purging. For example, nitrogen purged, acetonitrile solutions of bromo and dibromonaphthalene display readily observable phosphorescence as a result of internal heavy atom enhancement of πS , and k p . External heavy atom enhancement of k, (CH2 BrCH2 Br solvent) of aromatic hydrocarbons even allows observation of phosphorescence from these compounds in N2 purged fluid solutions. Although bromonaphthalenes are not significantly phosphorescent in N2 purged aqueous solution, phosphorescence is readily observed in N2 purged detergent (HDTBr, HDTCl, and SDS) solutions above the critical micelle concentration. The general factors which determine whether phosphorescence is "readily" obervable in fluid solution are briefly discussed and the results are interpreted in light of these factors. 相似文献
943.
944.
The instability properties of weakly nonlinear wave packets show a strong directional dependence. The presence of shear is found to enhance the importance of three dimensional effects. 相似文献
945.
Min Xin Lue-Yung Chow Chiu Du Li Yuh-Kang Pan 《Journal of Electron Spectroscopy and Related Phenomena》1984,33(2):93-105
The SCF-Xα-SW method is applied to calculate the ionization energies of the trihalides of all of the Group V elements. The calculated orbital energies agree very well with reported experimental ionization energies. The molecular-orbital orderings obtained coincide with recent experimental orbital assignments. The results are also compared with previous ab initio, semiempirical and Xα calculations for NF3, PF3, PCl3 and PBr3. The comparison indicates that the present results show improved agreement with experiment and clarify certain ambiguities in the earlier molecular-orbital assignments. 相似文献
946.
947.
A new microcavity design is proposed and structures are realized with a two-dimensional photonic-crystal slab. The cavity consists of seven defect holes that encompass a hexagon and is designed to reduce vertical light leakage. From a direct transmission measurement, a Q value of 816+/-30 is achieved at lambda =1.55 mum . This high- Q cavity will permit the realistic realization of spontaneous-emission modification and on-off optical switches. 相似文献
948.
Chow YL Liu ZL Johansson CI Ishiyama J 《Chemistry (Weinheim an der Bergstrasse, Germany)》2000,6(16):2942-2947
Dibenzomethanatoboron difluoride (DBMBF2) interacted with alkylbenzenes from its singlet excited state to form exciplexes ranging from weak polarity up to contact radical ion pairs (CRIP); this exciplex series shows the characteristics in the Marcus "normal" region. In cyclohexane these exciplexes gave intense fluorescence spectra and high quantum yields (phi(infinity)ex). The dipole moment of these exciplexes calculated from the solvatochromic shift of the fluorescence maximums (vmax) was used to estimate the coefficient ("a" and "c") of the CT and LE terms in the exciplex wavefunction. On the basis of the measured lifetimes and phi(infinity)ex of these exciplexes, the radiative (k(ex)f) and nonradiative (k(ex)NR) rate constants were calculated. The former k(ex)f were also computed from a semi-empirical approach based on the assumption that the exciplex wavefunction could be adequately described by CT and LE states, and that *DBMBF2 primarily contributes to the probability of exciplex emission. Two results agree with each other with small systematic deviations for those less polar exciplexes. The plots of k(ex)r and k(ex)NR (or their logarithmic value) against the LE contribution (c2) and transition energy gaps (hvmax) afford better correlation than those against -deltaG(-et). This indicates the role played by the LE contribution in generating the stabilization energy (U(s)) in these exciplexes through the A-D+)<==> *AD) resonance interaction; U(s), in turn, modifies -deltaG(-et) to afford the decay driving force hvmax. Also, those plots from k(ex)f values (being determined directly from experiments) show better correlation than those from k(ex)NR. In contrast to the CRIP type exciplexes in the Marcus "inverted" region, these k(ex)f and k(ex)NR increase in the common trend with increasing transition energy gaps. The k(ex)NR plots show less steep slopes and attains more quickly a minimum toward the CRIP region; the latter is identified as the turning point from the "normal" to "inverted" region. Both the attenuation and reversal of the k(ex)NR value with increasing polarity are believed to be generated by the emerging contribution of the intersystem crossing process as an additional nonradiative process, which is induced by the increased spin-orbit coupling in highly polar exciplexes. 相似文献
949.
Shui-Nee Chow Weishi Liu Yingfei Yi 《Transactions of the American Mathematical Society》2000,352(11):5179-5211
We study dynamics of flows generated by smooth vector fields in in the vicinity of an invariant and closed smooth manifold . By applying the Hadamard graph transform technique, we show that there exists an invariant manifold (called a center manifold of ) based on the information of the linearization along , which contains every locally bounded solution and is persistent under small perturbations.
950.
R. H. Pink Archana Dubey Dip N. Mahato S. R. Badu R. H. Scheicher Mahendra K. Mahanti M. B. Huang H. P. Saha Lee Chow T. P. Das 《Hyperfine Interactions》2007,176(1-3):39-44
Magnetic Hyperfine and Nuclear Quadrupole Interactions (HFI and NQI) are now important tools for characterization of systems of interest in materials research and industry. Boron-Trifluoride is an inorganic compound that is very important in this respect as a catalyst in chemical physics research and industry, forming complexes in the process with compounds like ammonia, water and methyl alcohol. The present paper deals with the BF3–NH3 complex and methyl derivatives BF3NHx(CH3)3?x for which we have studied the electronic structures, binding energies, and 19F* (I?=?5/2) nuclear quadrupole interactions using the first-principles Hartree–Fock–Roothaan procedure combined with electron correlation effects. Our results for the 19F* nuclear quadrupole coupling constant (e 2 qQ/h) in units of MHz compare well with experiment. Trends in the binding energies and NQI parameters between the complexes are discussed. 相似文献