全文获取类型
收费全文 | 113篇 |
免费 | 3篇 |
专业分类
化学 | 37篇 |
晶体学 | 1篇 |
力学 | 5篇 |
数学 | 27篇 |
物理学 | 46篇 |
出版年
2024年 | 1篇 |
2021年 | 2篇 |
2020年 | 1篇 |
2018年 | 3篇 |
2017年 | 1篇 |
2016年 | 3篇 |
2015年 | 5篇 |
2014年 | 3篇 |
2013年 | 7篇 |
2012年 | 5篇 |
2011年 | 6篇 |
2010年 | 6篇 |
2009年 | 3篇 |
2008年 | 2篇 |
2007年 | 4篇 |
2006年 | 8篇 |
2005年 | 5篇 |
2004年 | 4篇 |
2003年 | 1篇 |
2002年 | 1篇 |
2001年 | 2篇 |
2000年 | 1篇 |
1999年 | 10篇 |
1998年 | 1篇 |
1997年 | 2篇 |
1996年 | 3篇 |
1995年 | 2篇 |
1994年 | 3篇 |
1993年 | 2篇 |
1991年 | 1篇 |
1990年 | 1篇 |
1987年 | 1篇 |
1986年 | 2篇 |
1985年 | 1篇 |
1982年 | 1篇 |
1981年 | 2篇 |
1979年 | 2篇 |
1978年 | 3篇 |
1975年 | 1篇 |
1973年 | 1篇 |
1971年 | 1篇 |
1937年 | 2篇 |
排序方式: 共有116条查询结果,搜索用时 46 毫秒
101.
102.
103.
The synthesis and analysis of new polymeric materials based on 1,2,4,5-tetrazine are discussed in this study. Tetrazine was mixed with thermoplastic polyurethane in dimethylformamide (DMF) as solvent and dibutyl tin dilaurate as catalyst at 50°C for 24 h to create brush polyurethane-urea, which was then reacted with an unsaturated center in dimethyl sulfoxide as solvent at 60°C for 48 h made of either polyenol or thermoplastic polyurethane through π–π interaction. Because 1,2,4,5-tetrazine (red color) is known to act as an electron-deficient dine in inverse electron demand Diels–Alder reactions and can be easily converted to pyridazine (peach color) via [4 + 2] cycloaddition with suitable followed by expulsion of molecular nitrogen (cycloreversion), we observed a highly colored red shift to peach and this monitor for this reaction. Additionally, polyamide was prepared via reaction of 3,6-diamino-1,2,4,5-tetrazine with terephthaloyl chloride in DMF as a suitable solvent and triethylamine as basic catalyst at 0°C for 3 h and then 36 h at room temperature. The new polymers that were produced were elucidated by spectral data. 相似文献
104.
Angelone LM Vasios CE Wiggins G Purdon PL Bonmassar G 《Magnetic resonance imaging》2006,24(6):801-812
The purpose of the study was to assess the effects of electrodes and leads on electromagnetic field and specific absorption rate (SAR) distributions during simultaneous electroencephalography (EEG) and 7-T MRI. Two different approaches were evaluated and compared to the case without electrodes: (a) the use of different EEG lead resistivity and (b) the use of a radiofrequency (RF) resistor on the lead near the EEG electrode. These configurations are commonly used in research and clinical settings. Electromagnetic field and SAR distributions generated by the transmit RF coil were evaluated using finite difference time domain simulations on an anatomically accurate head model. The spatiotemporal changes of temperature were estimated with the heat equation. Temperature changes during turbo spin echo sequences were also measured using a custom-made phantom: the conductive head mannequin anthropomorphic (CHEMA). The results of this study showed that the SAR and temperature distributions in CHEMA (a) increased when using low resistive leads, with respect to the no-electrode case; (b) were affected by the resistivity of the EEG leads, with carbon fiber leads performing better than standard copper leads; and (c) were not affected by the use of an RF resistor between the EEG electrode and the lead. 相似文献
105.
Krysl P Cranford TW Wiggins SM Hildebrand JA 《The Journal of the Acoustical Society of America》2006,120(4):2328-2339
A finite element model is formulated to study the steady-state vibration response of the anatomy of a whale (Cetacea) submerged in seawater. The anatomy was reconstructed from a combination of two-dimensional (2D) computed tomography (CT) scan images, identification of Hounsfield units with tissue types, and mapping of mechanical properties. A partial differential equation model describes the motion of the tissues within a Lagrangean framework. The computational model was applied to the study of the response of the tissues within the head of a neonate Cuvier's beaked whale Ziphius cavirostris. The characteristics of the sound stimulus was a continuous wave excitation at 3500 Hz and 180 dB re: 1 microPa received level, incident as a plane wave. We model the beaked whale tissues embedded within a volume of seawater. To account for the finite dimensions of the computational volume, we increased the damping for viscous shear stresses within the water volume, in an attempt to reduce the contribution of waves reflected from the boundaries of the computational box. The mechanical response of the tissues was simulated including: strain amplitude; dissipated power; and pressure. The tissues are not likely to suffer direct mechanical or thermal damage, within the range of parameters tested. 相似文献
106.
Simonis AE Baumann-Pickering S Oleson E Melcón ML Gassmann M Wiggins SM Hildebrand JA 《The Journal of the Acoustical Society of America》2012,131(4):EL295-EL301
Killer whales in the North Pacific, similar to Atlantic populations, produce high-frequency modulated signals, based on acoustic recordings from ship-based hydrophone arrays and autonomous recorders at multiple locations. The median peak frequency of these signals ranged from 19.6-36.1 kHz and median duration ranged from 50-163 ms. Source levels were 185-193 dB peak-to-peak re: 1 μPa at 1 m. These uniform, repetitive, down-swept signals are similar to bat echolocation signals and possibly could have echolocation functionality. A large geographic range of occurrence suggests that different killer whale ecotypes may utilize these signals. 相似文献
107.
Barry K. Carpenter Gregory S. Ezra Stavros C. Farantos Zeb C. Kramer Stephen Wiggins 《Regular and Chaotic Dynamics》2018,23(1):60-79
In this paper we analyze a two-degree-of-freedom Hamiltonian system constructed from two planar Morse potentials. The resulting potential energy surface has two potential wells surrounded by an unbounded flat region containing no critical points. In addition, the model has an index one saddle between the potential wells. We study the dynamical mechanisms underlying transport between the two potential wells, with emphasis on the role of the flat region surrounding the wells. The model allows us to probe many of the features of the “roaming mechanism” whose reaction dynamics are of current interest in the chemistry community. 相似文献
108.
Summary. In this paper we develop the mathematical framework for studying transport in two-dimensional flows with aperiodic time dependence
from the geometrical point of view of dynamical systems theory. We show how the notion of a hyperbolic fixed point, or periodic
trajectory, and its stable and unstable manifolds generalize to the aperiodically time-dependent setting. We show how these
stable and unstable manifolds act as mediators of transport, and we extend the technique of lobe dynamics to this context.
We discuss Melnikov's method for two classes of systems having aperiodic time dependence. We develop a numerical method for
computing the stable and unstable manifolds of hyperbolic trajectories in two-dimensional flows with aperiodic time dependence.
The theory and the numerical techniques are applied to study the transport in a kinematic model of Rossby wave flow studied
earlier by Pierrehumbert [1991a]. He considered flows with periodic time dependence, and we continue his study by considering
flows having quasi-periodic, wave-packet, and purely aperiodic time dependencies. These numerical simulations exhibit a variety
of new transport phenomena mediated by the stable and unstable manifolds of hyperbolic trajectories that are unique to the
case of aperiodic time dependence.
Received April 10, 1997; revision received August 1, 1997 and accepted October 7, 1997 相似文献
109.
A systematic approach for the identification and quantification of organic volatile impurities (OVIs) in pharmaceutical excipients is described. Analytical procedures utilizing static headspace capillary gas chromatography coupled with flame-ionization and MS detection techniques were developed for the analysis of toxic ICH class 1 solvents and US Pharmacopeia OVIs at sub-ppm levels, and commonly used organic solvents in a wide range of concentrations. Chromatographic conditions and headspace parameters for the methods were optimized for separation, sensitivity, and speed. The proposed methodologies were demonstrated to be selective, accurate, and reproducible, and were successfully applied to the rapid screening of OVIs in typical excipients. 相似文献
110.