全文获取类型
收费全文 | 169篇 |
免费 | 18篇 |
国内免费 | 24篇 |
专业分类
化学 | 109篇 |
晶体学 | 1篇 |
力学 | 3篇 |
数学 | 26篇 |
物理学 | 72篇 |
出版年
2023年 | 1篇 |
2022年 | 1篇 |
2021年 | 8篇 |
2020年 | 4篇 |
2019年 | 7篇 |
2018年 | 9篇 |
2017年 | 8篇 |
2016年 | 7篇 |
2015年 | 2篇 |
2014年 | 11篇 |
2013年 | 9篇 |
2012年 | 13篇 |
2011年 | 10篇 |
2010年 | 10篇 |
2009年 | 9篇 |
2008年 | 5篇 |
2007年 | 12篇 |
2006年 | 7篇 |
2005年 | 6篇 |
2004年 | 7篇 |
2003年 | 10篇 |
2002年 | 12篇 |
2001年 | 7篇 |
2000年 | 10篇 |
1999年 | 2篇 |
1998年 | 1篇 |
1997年 | 2篇 |
1996年 | 1篇 |
1993年 | 1篇 |
1992年 | 1篇 |
1991年 | 3篇 |
1990年 | 2篇 |
1989年 | 4篇 |
1988年 | 3篇 |
1986年 | 1篇 |
1985年 | 1篇 |
1983年 | 1篇 |
1982年 | 3篇 |
排序方式: 共有211条查询结果,搜索用时 898 毫秒
91.
Idris O. Sule Shohel Mahmud Animesh Dutta Syeda Humaira Tasnim 《Heat and Mass Transfer》2016,52(3):421-428
Torrefaction, a thermal treatment process of biomass, has been proved to improve biomass combustible properties. Torrefaction is defined as a thermochemical process in reduced oxygen condition and at temperature range from 200 to 300 °C for shorter residence time whereby energy yield is maximized, can be a bridging technology that can lead the conventional system (e.g. coal-fired plants) towards a sustainable energy system. In efforts to develop a commercial operable torrefaction reactor, the present study examines the minimum input condition at which biomass is torrefied and explores the heat transfer mechanisms during torrefaction in poplar wood samples. The heat transfer through the wood sample is numerically modeled and analyzed. Each poplar wood is torrefied at temperature of 250, 270, and 300 °C. The experimental study shows that the 270 °C-treatment can be deduced as the optimal input condition for torrefaction of poplar wood. A good understanding of heat transfer mechanisms can facilitate the upscaling and downscaling of torrefaction process equipment to fit the feedstock input criteria and can help to develop treatment input specifications that can maximize process efficiency. 相似文献
92.
Abubakr M Idris 《Chemistry Central journal》2011,5(1):9
Background
Despite its potential benefits over univariate, chemometrics is rarely utilized for optimizing sequential injection analysis (SIA) methods. Specifically, in previous vis-spectrophotometric SIA methods, chemometrically optimized conditions were confined within flow rate and reagent concentrations while other conditions were ignored. 相似文献93.
In this paper, we study probabilistic numerical methods based on optimal quantization algorithms for computing the solution to optimal multiple switching problems with regime-dependent state process. We first consider a discrete-time approximation of the optimal switching problem, and analyse its rate of convergence. Given a time step h, the error is in general of order (hlog(1/h))1/2, and of order h1/2 when the switching costs do not depend on the state process. We next propose quantization numerical schemes for the space discretization of the discrete-time Euler state process. A Markovian quantization approach relying on the optimal quantization of the normal distribution arising in the Euler scheme is analysed. In the particular case of uncontrolled state process, we describe an alternative marginal quantization method, which extends the recursive algorithm for optimal stopping problems as in Bally (2003) [1]. A priori Lp-error estimates are stated in terms of quantization errors. Finally, some numerical tests are performed for an optimal switching problem with two regimes. 相似文献
94.
使用LUCIAE3.0模型模拟了SPS能区Pb+Pb和C+C在不同能量(Elab=20—200A GeV)和不同中心度下的重离子碰撞.并通过逐个事件的粒子温度涨落提取出了相应粒子的热容,发现对于同一碰撞系统,单位发射粒子的热容随碰撞能量的升高而下降直至饱和,随着碰撞参数b的增大而减小,而且发现单位发射粒子的热容具有随粒子质量的变大而变大的关系.同时还发现不同碰撞系统中同一种粒子具有相同的单位发射粒子热容,并给出了相应的解释. 相似文献
95.
Idris Olasupo Nathan R. Rose Rosalyn Klein Luqman A. Adams Oluwole B. Familoni 《合成通讯》2014,44(2):251-258
The relative merits of two different Baylis–Hillman approaches toward the preparation of coumarin derivatives, containing peptide-like side chains, have been explored. In one approach, use of methyl acrylate as the activated alkene requires a protecting group strategy, an approach that is not necessary when using tert-butyl acrylate.
[Supplementary materials are available for this article. Go to the publisher's online edition of Synthetic Communications® for the following free supplemental resource(s): Full experimental and spectral details.] 相似文献
96.
Five novel 4-phenylquinazolinols were synthesised in three steps. Their application as ligands in the titanium tetraisopropoxide promoted catalytic enantioselective addition of phenylacetylene to a variety of aldehydes gave propargylic alcohols. Under the optimised reaction conditions, the best enantioselectivity was obtained using l-lactic acid derived 4-phenylquinazolinol and apart from the cyclohexylcarbaldehyde derivative, 16 propargylic alcohols were then synthesised in moderate to excellent enantiomeric excess from 53% to 97%. 相似文献
97.
98.
高能重离子碰撞中正负荷电粒子比单事例起伏研究 总被引:2,自引:0,他引:2
用强子和弦级联模型,JPCIAE及相应的Monte Carlo事例产生器,研究相对论性核–核碰撞中有限快度区间内正负荷电粒子比单事例起伏与能量、中心度、共振态衰变及快度间隔的关系.JPCIAE模型能够较好地符合CERN/SPS能区Pb+Pb碰撞的实验结果.本文还用此模型预言了RHIC能区Au+Au碰撞和ALICE能区Pb+Pb碰撞中的正负荷电粒子比单事例起伏.可以看出碰撞能量、中心度、共振态衰变及快度间隔对正负荷电粒子比单事例起伏的影响都不大. 相似文献
99.
Theoretical study was performed to investigate how the hydration of cadmium ca-tion influences the structure and properties of guanine.The aqueous environment was simulated by both explicit solvent(1-5 water molecules) model and implicit solvent model.For complexes in which Cd2+ attached to the N(7) and O(6) sites of guanine,energy analysis together with the Natural Bonding Orbital(NBO) analysis were performed to elucidate the bonding characteristics in detail.The most stable structures are penta-coordinate complexes without aqua ligand located at the guanine site.Higher number of water ligands corresponds to higher stabilization energies.Average bonding energies of G-Cd increase with the number of water molecules.Bonding energies of water ligands depend on its position in the complexes.The charge distribution of guanine changed with increasing the number of water ligands,which may also influence the base-pairing pattern of guanine.There is positive charge transfer from guanine to aqua ligand as the number of the hydration waters increases.IEFPCM optimization has results comparable to the [CdG(H2O)5]2+ structure 5a. 相似文献
100.
Transition Metal Chemistry - The kinetics of electron transfer between N,N′-phenylenebis-(salicylideneiminato)iron(III), hereafter referred to as [Fe(Salphen)]+, and oxalic acid was studied... 相似文献