全文获取类型
收费全文 | 501篇 |
免费 | 21篇 |
国内免费 | 2篇 |
专业分类
化学 | 394篇 |
晶体学 | 12篇 |
力学 | 13篇 |
数学 | 13篇 |
物理学 | 92篇 |
出版年
2024年 | 1篇 |
2023年 | 5篇 |
2022年 | 17篇 |
2021年 | 17篇 |
2020年 | 9篇 |
2019年 | 19篇 |
2018年 | 15篇 |
2017年 | 23篇 |
2016年 | 26篇 |
2015年 | 13篇 |
2014年 | 31篇 |
2013年 | 50篇 |
2012年 | 50篇 |
2011年 | 42篇 |
2010年 | 25篇 |
2009年 | 17篇 |
2008年 | 37篇 |
2007年 | 25篇 |
2006年 | 35篇 |
2005年 | 21篇 |
2004年 | 17篇 |
2003年 | 6篇 |
2002年 | 11篇 |
2001年 | 2篇 |
2000年 | 4篇 |
1995年 | 1篇 |
1994年 | 1篇 |
1993年 | 2篇 |
1984年 | 1篇 |
1982年 | 1篇 |
排序方式: 共有524条查询结果,搜索用时 15 毫秒
101.
P. Lakshmi Praveen 《Liquid crystals》2013,40(6):872-882
The substituent- and solvent-induced shifts in UV-visible absorption bands of naphthyl-ester nematic liquid crystals, viz., 4-octylphenyl-6-octyloxy-2-naphthoate (NAPHE1) and 6-octyloxy-2-naphthylyl-4-octyloxybenzoate (NAPHE2), have been investigated using the DFT, CNDO/S and INDO/S methods. A correlation has been made between molecular charge distribution and phase stability based on Mulliken, Loewdin, AM1, PM3, MNDO, CNDO/S and INDO/S methods. The observed π→π* and n→π* electronic transitions have been reported. The substituent- and solvent-induced shifts in absorption bands, transition energies and energy gaps have been discussed. The photosensitivity of the molecules has been analysed based on these shifts. It has been observed that the substituent has a dominant role on both absorption maxima and energy band gap, whereas the solvent has a dominant role only on absorption maxima, and no effect has been observed on the energy gap. These shifts may provide beneficial consequences in determining the end use of compounds. 相似文献
102.
An efficient, green, and facile method has been developed for the synthesis of benzazole and thiourea analogues from naturally occurring erucin in moderate to good yields. The reaction was carried out in water without using any metal catalyst or base. The present method tolerated the various functional groups on aromatic rings and also applicable for other isothiocyanates. 相似文献
103.
Jinesh M. Kuthanapillil A. Nijamudheen Nayana Joseph Praveen Prakash E. Suresh Ayan Datta K.V. Radhakrishnan 《Tetrahedron》2013
A detailed investigation on the effect of solvent polarity, temperature, and microwave irradiation on periselectivity in cycloaddition reactions of pentafulvenes with 3-oxidopyrylium betaine is described. The base catalyzed generation of 3-oxidopyrylium betaine in CHCl3 resulted in the exclusive formation of [6+3] adducts. With increase in solvent polarity and temperature, mixtures of [6+3] and [3+2] adducts were formed, where as under microwave irradiation, [3+2] adducts were formed exclusively. The experimental results have been rationalized on the basis of theoretical calculations. 相似文献
104.
105.
K. V. P. Pa Van Kumar K. Praveen Kumar M. Vijjulatha K. C. Kumara Swamy 《Journal of Chemical Sciences》2004,116(6):311-317
The compounds S(6-t-Bu-4-Me-C6H2O)2P(O)Cl (1), CH2(6-t-Bu-4-Me-C6H2O)2P(O)Cl (2) and (2,2′-C20H12O2)P(O)Cl (3) react with diazabicycloundecene (DBU) to give rise to, predominantly, the phosphonate compounds [S(6-t-Bu-4-Me-C6H6O)2P(O)(DBU)]+[Cl]− (4), [CH2(6-t-Bu-4-Me-C6H2O)2P(O) (DBU)]+[Cl]− (5) and [(2,2′-C20Hi2O2)P(0)(DBU)]+[Cl]- (6). The first two compounds could be isolated in the pure state. In analogous reactions of 1 and 2 with diazabicyclononene
(DBN) or N-methyl imidazole, only the pyrophosphates [S(6-t-Bu-4-Me-C6H2O)2P(O)]2O (7) and [CH2(6-t-Bu-4-Me-C6H2O)2P(O)]2O (8) could be isolated, although the reaction mixture showed several other compounds in the phosphorus NMR. A possible pathway
for the formation of phosphonate salts is proposed. The X-ray crystal structures of4,7 and8 are also discussed. 相似文献
106.
The reaction between KI and [Fe(CN)6]3– ion, catalysed by hydrogen ions, was found to be catalysed further by PdCl2. Separate reactions under similar conditions, studied in the absence as well as in the presence of PdCl2 catalyst, were found to follow first order kinetics w.r. to [Fe(CN)6]3– and [H+], while the order was two w.r. to [I–]. [Fe(CN)6]4– ions were found to have a negative effect while changes in ionic strength of the medium do not effect the reaction velocity. Reaction in the presence of PdCl2 showed direct proportionality w.r. to [PdCl2]. The rate and extent of the reaction, which takes place even at zero [PdCl2] in the co-catalysed reaction, was calculated and was found to be in accordance with the rate values of the separately studied reaction at similar concentrations without adding PdCl2. 相似文献
107.
Summary Cobalt(II) soaps of general formula, Co(O2CR)2 (where R= C11H23 and C17H33) have been analysed by elemental analysis and i.r. spectra. Nonisothermal decomposition of these soaps has been studied by t.g.a. The activation energy, E, frequency factor, Z, entropy, S, and free energy, G, are calculated and a probable mechanism for decomposition is proposed. 相似文献
108.
109.
Controlling molecular energetics using laser pulses is exemplified for nuclear motion in two different diatomic systems. The
problem of finding the optimized field for maximizing a desired quantum dynamical target is formulated using an iterative
method. The method is applied for two diatomic systems, HF and OH. The power spectra of the fields and evolution of populations
of different vibrational states during transitions are obtained. 相似文献
110.
Rahul D. Jawarkar Praveen Sharma Neetesh Jain Ajaykumar Gandhi Nobendu Mukerjee Aamal A. Al-Mutairi Magdi E. A. Zaki Sami A. Al-Hussain Abdul Samad Vijay H. Masand Arabinda Ghosh Ravindra L. Bakal 《Molecules (Basel, Switzerland)》2022,27(15)
ALK tyrosine kinase ALK TK is an important target in the development of anticancer drugs. In the present work, we have performed a QSAR analysis on a dataset of 224 molecules in order to quickly predict anticancer activity on query compounds. Double cross validation assigns an upward plunge to the genetic algorithm–multi linear regression (GA-MLR) based on robust univariate and multivariate QSAR models with high statistical performance reflected in various parameters like, fitting parameters; R2 = 0.69–0.87, F = 403.46–292.11, etc., internal validation parameters; Q2LOO = 0.69–0.86, Q2LMO = 0.69–0.86, CCCcv = 0.82–0.93, etc., or external validation parameters Q2F1 = 0.64–0.82, Q2F2 = 0.63–0.82, Q2F3 = 0.65–0.81, R2ext = 0.65–0.83 including RMSEtr < RMSEcv. The present QSAR evaluation successfully identified certain distinct structural features responsible for ALK TK inhibitory potency, such as planar Nitrogen within four bonds from the Nitrogen atom, Fluorine atom within five bonds beside the non-ring Oxygen atom, lipophilic atoms within two bonds from the ring Carbon atoms. Molecular docking, MD simulation, and MMGBSA computation results are in consensus with and complementary to the QSAR evaluations. As a result, the current study assists medicinal chemists in prioritizing compounds for experimental detection of anticancer activity, as well as their optimization towards more potent ALK tyrosine kinase inhibitor. 相似文献