全文获取类型
收费全文 | 267篇 |
免费 | 5篇 |
专业分类
化学 | 153篇 |
晶体学 | 1篇 |
力学 | 9篇 |
数学 | 46篇 |
物理学 | 63篇 |
出版年
2022年 | 2篇 |
2021年 | 5篇 |
2020年 | 4篇 |
2019年 | 4篇 |
2018年 | 2篇 |
2017年 | 2篇 |
2016年 | 7篇 |
2015年 | 6篇 |
2014年 | 6篇 |
2013年 | 12篇 |
2012年 | 16篇 |
2011年 | 24篇 |
2010年 | 9篇 |
2009年 | 12篇 |
2008年 | 8篇 |
2007年 | 9篇 |
2006年 | 14篇 |
2005年 | 16篇 |
2004年 | 14篇 |
2003年 | 9篇 |
2002年 | 8篇 |
2000年 | 7篇 |
1999年 | 4篇 |
1997年 | 1篇 |
1996年 | 4篇 |
1995年 | 2篇 |
1994年 | 4篇 |
1993年 | 2篇 |
1992年 | 4篇 |
1991年 | 2篇 |
1990年 | 2篇 |
1989年 | 2篇 |
1988年 | 3篇 |
1987年 | 2篇 |
1986年 | 3篇 |
1985年 | 6篇 |
1984年 | 3篇 |
1982年 | 2篇 |
1981年 | 3篇 |
1980年 | 7篇 |
1979年 | 3篇 |
1978年 | 3篇 |
1976年 | 3篇 |
1974年 | 1篇 |
1973年 | 2篇 |
1972年 | 1篇 |
1971年 | 1篇 |
1968年 | 2篇 |
1919年 | 2篇 |
1890年 | 1篇 |
排序方式: 共有272条查询结果,搜索用时 15 毫秒
71.
Dynamic Monte Carlo (DMC) simulations of the adsorption of simple protein-like chains are used to more clearly define the molecular basis for the dependence of adsorption thermodynamics on the stability of the unique lowest-energy "native state" conformation of the chain. Arai and Norde were among the first to show that proteins of low native-state stability strongly denature upon adsorption to weakly attractive sorbent surfaces, while relatively modest changes in conformation are observed in stable proteins under identical adsorption conditions. When the protein has a low native-state stability, favorable adsorption entropies are typically observed in such systems, leading to the general belief that the chain gains conformational entropy during adsorption through a net reduction in intramolecular interactions specific to the native-state structure. Analysis of energy landscapes generated from our DMC simulation results show that a net loss in specific intramolecular interactions can lead to a positive delta(ads)S under certain adsorption conditions. However, the influence of chain conformation on delta(ads)S is found to correlate more directly with the manner in which the unique states of the system are distributed among the energy levels available to the adsorbed chain. Delta(ads)S is found to tend toward a maximum for adsorption processes described by thermally averaged energy landscapes in which the energy levels carrying the highest Boltzmann weights have a high degree of conformational degeneracy. This condition is met when the average interaction energy between the chain and the sorbent equals that between two hydrophobic segments of the chain. 相似文献
72.
Duygu Avci Camille Haynes Lon J. Mathias 《Journal of polymer science. Part A, Polymer chemistry》1997,35(10):2111-2121
New diacrylate monomers for cyclopolymerization were synthesized from the reaction of ethyl α-chloromethylacrylate (ECMA) and t-butyl α-bromomethyl acrylate (TBBr) with aniline, adamantyl amine, t-butyl amine, cyanamide, and 4-tetradecyl aniline in yields of ca. 50–70%. Bulk and solution polymerizations with azobisisobutyronitrile (AIBN) at 60–85°C gave soluble cyclopolymers with Mn and Mw ranging from 10,000–30,000 and 12,000–40,000, respectively. The ECMA–cyanamide derivative only gave crosslinked polymers. 1H and 13C solution NMR indicated high cyclization efficiency (>93%). A prototype NLO polymer was synthesized from the reaction of the TBBr–aniline cyclopolymer with tetracyanoethylene. The p-hydroxyaniline derivative of ECMA was synthesized and used for further derivatizations; for example, the benzoate ester was made and polymerized (Mn = 21,260 and Mw = 40,317). The ester groups of the TBBrndash;aniline polymer were hydrolyzed completely to give a polymer with both acid and base moieties. DSC thermograms showed glass transitions of 132°C for the ECMA–aniline derivative, 192°C for the ECMA–adamantyl derivative, 53°C for the TBBr–tetradecylaniline derivative, and 120° for the ECMA–p-benzoylaniline derivative. The ECMA–t-butyl amine polymer showed no obvious Tg. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35 : 2111–2121, 1997 相似文献
73.
Richard K. Haynes Burkhard Fugmann Jrg Stetter Karl Rieckmann Hans‐Dietrich Heilmann Ho‐Wai Chan Man‐Ki Cheung Wai‐Lun Lam Ho‐Ning Wong Simon L. Croft Livia Vivas Lauren Rattray Lindsay Stewart Wallace Peters Brian L. Robinson Michael D. Edstein Barbara Kotecka Dennis E. Kyle Bernhard Beckermann Michael Gerisch Martin Radtke Gabriele Schmuck Wolfram Steinke Ute Wollborn Karl Schmeer Axel Rmer 《Angewandte Chemie (International ed. in English)》2006,45(13):1989-1989
74.
[reaction: see text] Diverse Lewis acids and Bronsted acids were examined in the two-step, one-flask synthesis of meso-tetraphenylporphyrin, N-confused tetraphenylporphyrin, and tetraphenylsapphyrin. The scope of acid catalysis was found to be very broad, with 35 of 45 acids providing TPP in yields ranging from 5% to 58%. NC-TPP was also widely observed in yields of 1-40%, and TPS was infrequently observed in yields of <1%. Additionally, conditions were found for direct preparation of magnesium TPP and copper TPP. 相似文献
75.
76.
Coan TE Gao YS Liu F Stroynowski R Artuso M Boulahouache C Blusk S Butt J Dambasuren E Dorjkhaidav O Haynes J Menaa N Mountain R Muramatsu H Nandakumar R Redjimi R Sia R Skwarnicki T Stone S Wang JC Zhang K Mahmood AH Csorna SE Bonvicini G Cinabro D Dubrovin M Bornheim A Lipeles E Pappas SP Shapiro A Weinstein AJ Briere RA Chen GP Ferguson T Tatishvili G Vogel H Watkins ME Adam NE Alexander JP Berkelman K Boisvert V Cassel DG Duboscq JE Ecklund KM Ehrlich R Galik RS Gibbons L Gittelman B 《Physical review letters》2004,92(23):232001
We present the first study of the vector (Wess-Zumino) current in tau(-)-->K-pi-K+nu(tau) decay using data collected with the CLEO III detector at the Cornell Electron Storage Ring. We determine the quantitative contributions to the decay width from the vector and axial vector currents. Within the framework of a model by Kühn and Mirkes, we identify the quantitative contributions to the total decay rate from the intermediate states omegapi, rho(')pi, and K*K. 相似文献
77.
Regan SP Delettrez JA Goncharov VN Marshall FJ Soures JM Smalyuk VA Radha PB Yaakobi B Epstein R Glebov VY Jaanimagi PA Meyerhofer DD Sangster TC Seka W Skupsky S Stoeckl C Haynes DA Frenje JA Li CK Petrasso RD Séguin FH 《Physical review letters》2004,92(18):185002
The mixing of cold, high-density shell plasma with the low-density, hot spot plasma by the Rayleigh-Taylor instability in inertial confinement fusion is experimentally shown to correlate with the calculated perturbation feedthrough from the ablation surface to the inner shell surface. A fourfold decrease in the density of shell material in the mix region of direct drive implosions of gas filled spherical plastic shells having predicted convergence ratios approximately 15 was observed when laser imprint levels were reduced and the initial shell was thicker, corresponding to a reduction in the feedthrough rms level by a factor of 6. Shell mix is also shown to limit the spherical compression of the implosion. 相似文献
78.
We study the evolution of a localized perturbation in a chemical system with multiple homogeneous steady states, in the presence of stirring by a fluid flow. Two distinct regimes are found as the rate of stirring is varied relative to the rate of the chemical reaction. When the stirring is fast localized perturbations decay towards a spatially homogeneous state. When the stirring is slow (or fast reaction) localized perturbations propagate by advection in form of a filament with a roughly constant width and exponentially increasing length. The width of the filament depends on the stirring rate and reaction rate but is independent of the initial perturbation. We investigate this problem numerically in both closed and open flow systems and explain the results using a one-dimensional "mean-strain" model for the transverse profile of the filament that captures the interplay between the propagation of the reaction-diffusion front and the stretching due to chaotic advection. (c) 2002 American Institute of Physics. 相似文献
79.
AbstractHerein, we describe an improved method to synthesise mono-, di- and tetra-cyanocalix[4]arene and report their crystal structure determinations. We also report our attempts to further functionalise the cyanocalix[4]arenes into dithiadiazolyl-calix[4]arenes, and propose a hypothesis as to why the cyano group on a calix[4]arene is an extremely challenging group to modify. 相似文献
80.
Teresa W. Haynes Michael A. Henning Lucas C. van der Merwe Anders Yeo 《Central European Journal of Mathematics》2014,12(12):1882-1889
A graph is diameter-2-critical if its diameter is two and the deletion of any edge increases the diameter. Let G be a diameter-2-critical graph of order n. Murty and Simon conjectured that the number of edges in G is at most ?n 2/4? and that the extremal graphs are the complete bipartite graphs K ?n/2?,?n/2?. Fan [Discrete Math. 67 (1987), 235–240] proved the conjecture for n ≤ 24 and for n = 26, while Füredi [J. Graph Theory 16 (1992), 81–98] proved the conjecture for n > n 0 where n 0 is a tower of 2’s of height about 1014. The conjecture has yet to be proven for other values of n. Let Δ denote the maximum degree of G. We prove the following maximum degree theorems for diameter-2-critical graphs. If Δ ≥ 0.7 n, then the Murty-Simon Conjecture is true. If n ≥ 2000 and Δ ≥ 0.6789 n, then the Murty-Simon Conjecture is true. 相似文献