全文获取类型
收费全文 | 96篇 |
免费 | 15篇 |
国内免费 | 1篇 |
专业分类
化学 | 93篇 |
晶体学 | 1篇 |
数学 | 6篇 |
物理学 | 12篇 |
出版年
2021年 | 2篇 |
2020年 | 1篇 |
2019年 | 4篇 |
2018年 | 3篇 |
2017年 | 1篇 |
2015年 | 7篇 |
2014年 | 8篇 |
2013年 | 5篇 |
2012年 | 5篇 |
2011年 | 9篇 |
2010年 | 5篇 |
2009年 | 5篇 |
2008年 | 8篇 |
2007年 | 7篇 |
2006年 | 5篇 |
2005年 | 8篇 |
2004年 | 2篇 |
2003年 | 4篇 |
2002年 | 9篇 |
2001年 | 1篇 |
2000年 | 2篇 |
1999年 | 3篇 |
1998年 | 2篇 |
1997年 | 2篇 |
1995年 | 1篇 |
1994年 | 1篇 |
1989年 | 1篇 |
1988年 | 1篇 |
排序方式: 共有112条查询结果,搜索用时 0 毫秒
71.
We have developed a convenient chemoenzymatic method for the preparation of (4aS,5S)-4,4a,5,6,7,8-hexahydro-5-hydroxy-4a-methylnaphthalen-2(3H)-one by taking advantage of the excellent enantioselectivity of alcalase. Four different esters were compared, and the butanoate ester was found to be the best substrate. The stereochemistry of the product is the same as the one predicted from the binding model of alcalase. A simple extraction/partition procedure was used to separate the hydroxyenone product from the remaining ester. This practical procedure would be very useful in a gram-scale operation for securing the title compound in high optical purity. 相似文献
72.
[reaction: see text] A highly regioselective borane-reductive ring opening of the 4,6-O-benzylidene-D-hexopyranosides to the corresponding 6-alcohols in excellent yields at room temperature via various metal trifluoromethanesulfonates as catalysts is described here. Its application in the synthesis of 1,4-dideoxy-1,4-imino-L-xylitol is also highlighted. 相似文献
73.
Szu‐Hsueh Lai Chung‐Jen Hsiao Yu‐Min Huang I‐Chia Chen Wen‐Zhen Wang Shie‐Ming Peng 《Journal of Raman spectroscopy : JRS》2010,41(12):1694-1699
We recorded surface‐enhanced Raman scattering (SERS) spectra of metal‐string complexes Co3(dpa)4 Cl2 [di(2‐pyridyl)amido (dpa)], Ni3(dpa)4 Cl2 and the oxidized form of the Ni3 complex to determine their vibrational wavenumbers and to investigate their structures. For SERS measurements these complexes were adsorbed on silver nanoparticles in aqueous solution to eliminate the constraint of a crystal lattice and the complexes remain in thermal equilibrium. From our analysis of the vibrational normal modes we assigned the SERS lines at 242 and 276 cm−1 to Ni3 and Co3 symmetric‐stretching modes of the symmetric form. For Co3 (dpa)4Cl2 a Raman line at 383 cm−1 was assigned to the Co Co stretching mode of the unsymmetric form. The wavenumber of the Ni3 symmetric‐stretching mode of the oxidized form [Ni3(dpa)4]3+ is 274 cm−1, greater than that for neutral Ni3(dpa)4Cl2, in agreement with a prediction of delocalized molecular‐orbital theory that an electron is removed from an antibonding orbital after oxidation. The experimental data show that the SERS technique serves as an excellent tool to observe the variation of metal–metal bonding during an oxidation or reduction reaction. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
74.
75.
76.
o‐Amino Analogs of Green Fluorescence Protein Chromophore: Photoisomerization,Photodimerization and Aggregation‐induced Emission 下载免费PDF全文
Guan‐Jhih Huang Che‐Jen Lin Yi‐Hung Liu Shie‐Ming Peng Jye‐Shane Yang 《Photochemistry and photobiology》2015,91(3):714-722
The photochemical properties of three o‐amino analogs of the green fluorescence protein chromophore O0, O1 and O8 (o‐ABDIs) have been investigated and compared with those of the m‐ and p‐amino isomers (m‐ABDIs and p‐ABDIs) in solutions, aggregates, and the solid state. In aprotic solvents, the fluorescence competes with the Z → E photoisomerization for all cases, and the o‐ABDIs display a fluorescence quantum efficiency of 1–6%, lying between the m‐ABDIs of 5–48% and the p‐ABDIs of < 0.1%. The fluorescence of both the o‐ and m‐ABDIs is nearly quenched in protic solvents, attributable to the solvent–solute hydrogen bonding (SSHB) interactions. The phenomenon of aggregation‐induced emission observed for O8 in poor solvents resembles the behavior of M8 as a consequence of exclusion of the SSHB interactions and restriction of internal rotation for molecules located inside the aggregates. The occurrence of [2 + 2] photodimerization for O0 in the solid state is unique among the ABDIs, and the X‐ray crystal structures of O0 and the photodimer OD reveal the head‐to‐tail syn‐oriented stereochemistry. Analysis on the X‐ray crystal structures of O0, O1, M0, M1 and P0 shows that not only the pairwise topochemical geometry but also the columnar packing mode is important in determining the photodimerization reactivity. 相似文献
77.
78.
79.
80.
Ishai?Menache Shie?MannorEmail author Nahum?Shimkin 《Annals of Operations Research》2005,134(1):215-238
Reinforcement Learning (RL) is an approach for solving complex multi-stage decision problems that fall under the general framework
of Markov Decision Problems (MDPs), with possibly unknown parameters. Function approximation is essential for problems with
a large state space, as it facilitates compact representation and enables generalization. Linear approximation architectures
(where the adjustable parameters are the weights of pre-fixed basis functions) have recently gained prominence due to efficient
algorithms and convergence guarantees. Nonetheless, an appropriate choice of basis function is important for the success of
the algorithm. In the present paper we examine methods for adapting the basis function during the learning process in the
context of evaluating the value function under a fixed control policy. Using the Bellman approximation error as an optimization
criterion, we optimize the weights of the basis function while simultaneously adapting the (non-linear) basis function parameters.
We present two algorithms for this problem. The first uses a gradient-based approach and the second applies the Cross Entropy
method. The performance of the proposed algorithms is evaluated and compared in simulations.
This research was partially supported by the Fund for Promotion of Research at the Technion. The work of S.M. was partially
supported by the National Science Foundation under grant ECS-0312921. 相似文献