全文获取类型
收费全文 | 295篇 |
免费 | 13篇 |
国内免费 | 1篇 |
专业分类
化学 | 230篇 |
晶体学 | 2篇 |
力学 | 8篇 |
数学 | 26篇 |
物理学 | 43篇 |
出版年
2023年 | 1篇 |
2022年 | 2篇 |
2021年 | 8篇 |
2020年 | 5篇 |
2019年 | 12篇 |
2018年 | 17篇 |
2017年 | 14篇 |
2016年 | 13篇 |
2015年 | 13篇 |
2014年 | 14篇 |
2013年 | 29篇 |
2012年 | 18篇 |
2011年 | 12篇 |
2010年 | 10篇 |
2009年 | 10篇 |
2008年 | 21篇 |
2007年 | 15篇 |
2006年 | 8篇 |
2005年 | 13篇 |
2004年 | 9篇 |
2003年 | 10篇 |
2002年 | 7篇 |
2001年 | 12篇 |
2000年 | 3篇 |
1999年 | 5篇 |
1998年 | 1篇 |
1996年 | 3篇 |
1995年 | 2篇 |
1994年 | 2篇 |
1993年 | 2篇 |
1991年 | 2篇 |
1987年 | 1篇 |
1985年 | 3篇 |
1984年 | 5篇 |
1981年 | 1篇 |
1980年 | 3篇 |
1979年 | 1篇 |
1969年 | 1篇 |
1966年 | 1篇 |
排序方式: 共有309条查询结果,搜索用时 15 毫秒
111.
Yousef Hashem Zahran 《Applied mathematics and computation》2009,212(1):37-50
In this paper we propose a new WENO scheme, in which we use a central WENO [G. Capdeville, J. Comput. Phys. 227 (2008) 2977-3014] (CWENO) reconstruction combined with the smoothness indicators introduced in [R. Borges, M. Carmona, B. Costa, W. Sun Don, J. Comput. Phys. 227 (2008) 3191-3211] (IWENO). We use the central-upwind flux [A. Kurganov, S. Noelle, G. Petrova, SIAM J. Sci. Comp. 23 (2001) 707-740] which is simple, universal and efficient. For time integration we use the third order TVD Runge-Kutta scheme. The resulting scheme improves the convergence order at critical points of smooth parts of solution as well as decrease the dissipation near discontinuities. Numerical experiments of the new scheme for one and two-dimensional problems are reported. The results demonstrates that the proposed scheme is superior to the original CWENO and IWENO schemes. 相似文献
112.
Ahmed I. Hashem Wael S. I. Abou‐Elmagd Eman A. El‐Bordany Ahmed Abdel Aziz 《Journal of heterocyclic chemistry》2019,56(1):218-225
A 2(5H)‐furanone bearing two furyl rings was synthesized. The behavior of this furanone toward some nitrogen nucleophiles, namely, hydrazine hydrate, benzylamine, and ammonium acetate, was studied. The nitrile group at position‐3 of the furanone was utilized to construct thiazolidine ring by the action of thioglycollic acid. The acid hydrazide synthesized from the previous step was allowed to react with some carbonyl compounds, namely, acetonylacetone, acetylacetone, ethyl acetoacetate, ethyl cinnamate, diethylmalonate, phthalic anhydride, benzil, and 4‐methoxybenzaldehyde, to form pyrrole, pyrazole, and pyrazolopyridazine ring systems bearing two furyl groups. The structures of all the products obtained were illustrated from their analytical and spectral data. 相似文献
113.
A simple and convenient method for the preparation of Schiff bases is developed. In this method, the Schiff base compounds were prepared from the reaction of carbonyl compounds with primary amines. In this reaction, P2O5/SiO2 have catalyzed the Schiff base formation in dry media under solvent‐free conditions. Advantages of this method are use of an inexpensive and efficient catalyst, high yields of products, short reaction times, and simpli‐city of the reaction and workup. © 2008 Wiley Periodicals, Inc. Heteroatom Chem 19:43–47, 2008; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/hc.20383 相似文献
114.
Shaima Hashem Veronica Macaluso Michele Nottoli Filippo Lipparini Lorenzo Cupellini Benedetta Mennucci 《Chemical science》2021,12(40):13331
Photoreceptor proteins bind a chromophore, which, upon light absorption, modifies its geometry or its interactions with the protein, finally inducing the structural change needed to switch the protein from an inactive to an active or signaling state. In the Blue Light-Using Flavin (BLUF) family of photoreceptors, the chromophore is a flavin and the changes have been connected with a rearrangement of the hydrogen bond network around it on the basis of spectroscopic changes measured for the dark-to-light conversion. However, the exact conformational change triggered by the photoexcitation is still elusive mainly because a clear consensus on the identity not only of the light activated state but also of the dark one has not been achieved. Here, we present an integrated investigation that combines microsecond MD simulations starting from the two conflicting crystal structures available for the AppA BLUF domain with calculations of NMR, IR and UV-Vis spectra using a polarizable QM/MM approach. Thanks to such a combined analysis of the three different spectroscopic responses, a robust characterization of the structure of the dark state in solution is given together with the uncovering of important flaws of the most popular molecular mechanisms present in the literature for the dark-to-light activation.With an integrated molecular dynamics and QM/MM strategy we characterize the dark-state structure of a BLUF photoreceptor and ration alize the discrepancy between published crystal structures. 相似文献
115.
Sumera Zaib Rubina Munir Muhammad Tayyab Younas Naghmana Kausar Aliya Ibrar Sehar Aqsa Noorma Shahid Tahira Tasneem Asif Hashem O. Alsaab Imtiaz Khan 《Molecules (Basel, Switzerland)》2021,26(21)
Alzheimer’s disease (AD) is a progressive neurodegenerative disorder and the leading cause of dementia worldwide. The limited pharmacological approaches based on cholinesterase inhibitors only provide symptomatic relief to AD patients. Moreover, the adverse side effects such as nausea, vomiting, loss of appetite, muscle cramps, and headaches associated with these drugs and numerous clinical trial failures present substantial limitations on the use of medications and call for a detailed insight of disease heterogeneity and development of preventive and multifactorial therapeutic strategies on urgent basis. In this context, we herein report a series of quinoline-thiosemicarbazone hybrid therapeutics as selective and potent inhibitors of cholinesterases. A facile multistep synthetic approach was utilized to generate target structures bearing multiple sites for chemical modifications and establishing drug-receptor interactions. The structures of all the synthesized compounds were fully established using readily available spectroscopic techniques (FTIR, 1H- and 13C-NMR). In vitro inhibitory results revealed compound 5b as a promising and lead inhibitor with an IC50 value of 0.12 ± 0.02 μM, a 5-fold higher potency than standard drug (galantamine; IC50 = 0.62 ± 0.01 μM). The synergistic effect of electron-rich (methoxy) group and ethylmorpholine moiety in quinoline-thiosemicarbazone conjugates contributes significantly in improving the inhibition level. Molecular docking analysis revealed various vital interactions of potent compounds with amino acid residues and reinforced the in vitro results. Kinetics experiments revealed the competitive mode of inhibition while ADME properties favored the translation of identified inhibitors into safe and promising drug candidates for pre-clinical testing. Collectively, inhibitory activity data and results from key physicochemical properties merit further research to ensure the design and development of safe and high-quality drug candidates for Alzheimer’s disease. 相似文献
116.
117.
Oxidation of the cyclohxa-1,3-diene-CCl2 bis-adduct 4 with chromium(VI) oxide in acetic acid gives the diketone 10. Subsequent reduction with sodium borohydride, giving 11, fomation of thionocarbonate 12, and elimination with trimethethyl phosphite provides a facile synthesis of the tetrachloro bis-σ-homobenzene 9, which is totally resistant to further attack of CCl2 and epoxidation. Evidently the formation of hexachloro-tris-σ-homobenzene 3 is extremely hindered. Reaction of tetraphenyl allene 6 with CCl2 gives the heptafulvene 13 in low yield. The previously-described1 hexachloro tris-σ-homobenzene derivative 7, however, could not be isolated. 相似文献
118.
The complex equilibria of iron(III) with 1-amino-4-hydroxyanthraquinone (AMHA) were studied spectrophotometrically in 40% (v/v) ethanol and an ionic strength of 0.1M (NaClO(4)). The complexation reactions were demonstrated and characterized using graphical logarithmic analysis of the absorbance-pH graphs. A simple, rapid, selective and sensitive method for the spectrophotometric determination of trace amounts of Fe(III) is developed based on the formation of Fe(AMHA) complex at pH 2.5 (lambda(max) = 640 nm, epsilon approximately = 2.1 x 10(4) L. mol(-1) . cm(-1)) in the presence of a large number of foreign ions. Interferences caused by palladium(II) was masked by the addition of cyanide ions. The method has been applied to the determination of iron in some synthetic samples and polymetallic iron ores. 相似文献
119.
Zinc oxide (ZnO) is a highly efficient catalyst for the acylation of a variety of alcohols, phenols and amines with acid chlorides or acid anhydrides under solvent free conditions. Primary, secondary, tertiary, allylic and benzylic alcohols, diols and phenols with electron donating or withdrawing substituents can be easily acylated in good to excellent yield. 相似文献
120.
The diene reacted with CHCl3/aq. NaOH/PTC in CH2 Cl2 unexpectedly to give a mixture of the chlorination products and . Usual chlorination with Cl2 yielded similarly , , and dependent on the amount of Cl2. The formation of as well as the reaction of to give (besides ) shows an unusual Cl-Cl-interaction. 相似文献