首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   65篇
  免费   2篇
化学   24篇
力学   6篇
数学   3篇
物理学   34篇
  2023年   2篇
  2021年   2篇
  2018年   1篇
  2017年   2篇
  2016年   2篇
  2015年   2篇
  2013年   4篇
  2012年   3篇
  2011年   3篇
  2010年   1篇
  2009年   1篇
  2008年   3篇
  2007年   5篇
  2006年   4篇
  2005年   3篇
  2004年   2篇
  2003年   3篇
  2002年   4篇
  2001年   2篇
  2000年   4篇
  1999年   1篇
  1997年   1篇
  1996年   1篇
  1995年   1篇
  1994年   2篇
  1993年   1篇
  1991年   1篇
  1986年   2篇
  1982年   2篇
  1981年   1篇
  1979年   1篇
排序方式: 共有67条查询结果,搜索用时 15 毫秒
1.
2.
3.
The kinetics of the C2H5 + Cl2, n‐C3H7 + Cl2, and n‐C4H9 + Cl2 reactions has been studied at temperatures between 190 and 360 K using laser photolysis/photoionization mass spectrometry. Decays of radical concentrations have been monitored in time‐resolved measurements to obtain reaction rate coefficients under pseudo‐first‐order conditions. The bimolecular rate coefficients of all three reactions are independent of the helium bath gas pressure within the experimental range (0.5–5 Torr) and are found to depend on the temperature as follows (ranges are given in parenthesis): k(C2H5 + Cl2) = (1.45 ± 0.04) × 10?11 (T/300 K)?1.73 ± 0.09 cm3 molecule?1 s?1 (190–359 K), k(n‐C3H7 + Cl2) = (1.88 ± 0.06) × 10?11 (T/300 K)?1.57 ± 0.14 cm3 molecule?1 s?1 (204–363 K), and k(n‐C4H9 + Cl2) = (2.21 ± 0.07) × 10?11 (T/300 K)?2.38 ± 0.14 cm3 molecule?1 s?1 (202–359 K), with the uncertainties given as one‐standard deviations. Estimated overall uncertainties in the measured bimolecular reaction rate coefficients are ±20%. Current results are generally in good agreement with previous experiments. However, one former measurement for the bimolecular rate coefficient of C2H5 + Cl2 reaction, derived at 298 K using the very low pressure reactor method, is significantly lower than obtained in this work and in previous determinations. © 2007 Wiley Periodicals, Inc. Int J Chem Kinet 39: 614–619, 2007  相似文献   
4.
The kinetics of the i-C4H5 (buta-1,3-dien-2-yl) radical reaction with molecular oxygen has been measured over a wide temperature range (275–852 K) at low pressures (0.8–3 Torr) in direct, time-resolved experiments. The measurements were performed using a laminar flow reactor coupled to photoionization mass spectrometer (PIMS), and laser photolysis of either chloroprene (2-chlorobuta-1,3-diene) or isoprene was used to produce the resonantly stabilized i-C4H5 radical. Under the experimental conditions, the measured bimolecular rate coefficient of i-C4H5 + O2 reaction is independent of bath gas density and exhibits weak, negative temperature dependency, and can be described by the expression k3 = (1.45 ± 0.05) × 10?12 × (T/298 K)?(0.13±0.05) cm3 s?1. The measured bimolecular rate coefficient is surprisingly fast for a resonantly stabilized radical. Under combustion conditions, the reactions of i-C4H5 radical with ethylene and acetylene are believed to play an important role in forming the first aromatic ring. However, the current measurements show that i-C4H5 + O2 reaction is significantly faster under combustion conditions than previous estimations suggest and, consequently, inhibits the soot forming propensity of i-C4H5 radicals. The bimolecular rate coefficient estimates used for the i-C4H5 + O2 reaction in recent combustion simulations show significant variation and are up to two orders of magnitude slower than the current, measured value. All estimates, in contrast to our measurements, predict a positive temperature dependency. The observed products for the i-C4H5 + O2 reaction were formaldehyde and ketene. This is in agreement with the one theoretical study available for i-C4H5 + O2 reaction, which predicts the main bimolecular product channels to be H2CO + C2H3 + CO and H2CCO + CH2CHO.  相似文献   
5.
The kinetics of four gas-phase reactions involving halogenated methyl radicals (R ? CF3, CF2Cl, CFCI2, and CCI3) with molecular chlorine have been studied using a tubular reactor coupled to a photoionization mass spectrometer. The radicals were homogeneously generated by the pulsed photolysis of precursor molecules at 193 nm. The subsequent decays of the radical concentration were monitored in real-time experiments as a function of Cl2 concentration to obtain the rate constants of these R + Cl2 reactions. Where possible, the rate constants were measured as a function of temperature to determine Arrhenius parameters. Apparent discrepancies between these measured rate constants for CF3 and CCl3 with Cl2 and ones obtained in prior indirect studies are explained. The higher activation energies for these R + Cl2 reactions compared to that of the CH3 + Cl2 reaction are attributed in part to the different polarities of the transition states formed.  相似文献   
6.
It was reported in a previous study that simulated guided wave axial transmission velocities on two-dimensional (2D) numerically reproduced geometry of long bones predicted moderately real in vitro ultrasound data on the same bone samples. It was also shown that fitting of ultrasound velocity with simple analytical model yielded a precise estimate (UTh) for true cortical bone thickness. This current study expands the 2D bone model into three dimensions (3D). To this end, wave velocities and UTh were determined from experiments and from time-domain finite-difference simulations of wave propagation, both performed on a collection of 10 human radii (29 measurement sites). A 3D numerical bone model was developed with tuneable fixed material properties and individualized geometry based on X-ray computed tomography reconstructions of real bones. Simulated UTh data were in good accordance (root-mean-square error was 0.40 mm; r(2)=0.79, p<0.001) with true cortical thickness, and hence the measured phase velocity can be well estimated by using a simple analytical inversion model also in 3D. Prediction of in vitro data was improved significantly (by 10% units) and the upgraded bone model thus explained most of the variability (up to 95% when sites were carefully matched) observed in in vitro ultrasound data.  相似文献   
7.
A series of 7‐(2‐oxoalkoxy)coumarins have been synthesized by conjugating substituted 7‐hydroxycoumarins with different chloroketones. The anti‐inflammatory properties of 7‐(2‐oxoalkoxy)coumarins were studied in LPS‐induced inflammatory response in J774 macrophages. Western blot was used to determine the expression of iNOS and COX‐2, NO was determined by measuring its metabolite nitrite by Griess reaction and IL‐6 was measured by ELISA. Seventeen of the studied compounds inhibited NO and IL‐6 production over 50% at 100 μM concentrations. IC50 values of the best inhibitors were 21 μM/24 μM (NO/IL‐6) for compound 12 and 30 μM/10 μM (NO/IL‐6) for compound 20 . The main result was that the substitution with 7‐(2‐oxoalkoxy) group improved the anti‐inflammatory properties of most of the investigated 7‐hydroxycoumarins.  相似文献   
8.
9.
A model transport system is considered in which a pulse of tracer molecules is advected along a flow channel with porous walls. The advected tracer thus undergoes diffusion, matrix-diffusion, inside the walls, which affects the breakthrough curve of the tracer. Analytical solutions in the form of series expansions are derived for a number of situations which include a finite depth of the porous matrix, varying aperture of the flow channel, and longitudinal diffusion and Taylor dispersion of the tracer in the flow channel. Novel expansions for the Laplace transforms of the concentration in the channel facilitated closed-form expressions for the solutions. A rigorous result is also derived for the asymptotic form of the breakthrough curve for a finite depth of the porous matrix, which is very different from that for an infinite matrix. A specific experimental system was created for validation of matrix-diffusion modeling for a matrix of finite depth. A previously reported fracture-column experiment was also modeled. In both cases model solutions gave excellent fits to the measured breakthrough curves with very consistent values for the diffusion coefficients used as the fitting parameters. The matrix-diffusion modeling performed could thereby be validated.  相似文献   
10.
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号