全文获取类型
收费全文 | 689篇 |
免费 | 41篇 |
国内免费 | 17篇 |
专业分类
化学 | 513篇 |
晶体学 | 3篇 |
力学 | 40篇 |
数学 | 92篇 |
物理学 | 99篇 |
出版年
2023年 | 1篇 |
2022年 | 15篇 |
2021年 | 25篇 |
2020年 | 30篇 |
2019年 | 42篇 |
2018年 | 39篇 |
2017年 | 35篇 |
2016年 | 72篇 |
2015年 | 38篇 |
2014年 | 47篇 |
2013年 | 101篇 |
2012年 | 56篇 |
2011年 | 47篇 |
2010年 | 44篇 |
2009年 | 28篇 |
2008年 | 25篇 |
2007年 | 33篇 |
2006年 | 8篇 |
2005年 | 16篇 |
2004年 | 8篇 |
2003年 | 8篇 |
2002年 | 7篇 |
2001年 | 3篇 |
2000年 | 1篇 |
1998年 | 1篇 |
1997年 | 1篇 |
1996年 | 1篇 |
1995年 | 2篇 |
1994年 | 1篇 |
1993年 | 2篇 |
1989年 | 1篇 |
1988年 | 1篇 |
1987年 | 1篇 |
1986年 | 1篇 |
1985年 | 1篇 |
1984年 | 2篇 |
1983年 | 1篇 |
1980年 | 1篇 |
1970年 | 1篇 |
排序方式: 共有747条查询结果,搜索用时 546 毫秒
661.
Javad Safari Soheila Gandomi-Ravandi Saeedeh Shariat 《Journal of the Iranian Chemical Society》2016,13(8):1499-1507
In the present investigation, we have developed a novel technique to prepare azines using nano-WCl6 loaded on Montmorillonite K10 clay as a highly active catalyst. A variety of aldehydes and ketones were efficiently converted to the corresponding azines using catalytic amounts of nanosized WCl6/Mont. K10 under mild conditions. The nanostructures of WCl6 loaded on Mont. K10 as solid acid catalyst have been prepared by solid dispersion method. The advantages of this catalyst are rapid completion of the reactions, simplicity of performance, lack of pollution and mild and green reaction conditions. The morphologies, structure, and chemical components of parent and modified clay were successfully characterized using SEM, FT-IR, CV, XRD and EDX measurements. 相似文献
662.
Javad Safari Azade Enayati Najafabadi Zohre Zarnegar Shabnam Farkhonde Masoule 《Green Chemistry Letters and Reviews》2016,9(1):20-26
Biodegradable copolymers have received much more attention in the last decades due their potential applications in the fields related to environmental protection, medicine, agriculture, and the chemical processes. Silver nanoparticles (Ag NPs) were prepared via reduction of silver nitrate (AgNO3) using biodegradable amphiphilic copolymers in aqueous solution. The micelles were constructed from the amphiphilic copolymer composed of poly(2-ethyl-2-oxazoline) and poly(ε-caprolactone). The Ag NPs with a diameter of 10–15?nm were found to show a comparable high catalytic activity toward the reduction of 4-nitrophenol (4-NP) in the presence of an excess amount of NaBH4. The synthesized Ag NPs-loaded copolymer exhibits high catalytic activity for the reduction of 4-NP to 4-aminophenol. 相似文献
663.
664.
Davide?SpinelloEmail authorView authors OrcID profile Javad?S.?Fattahi 《Journal of Nonlinear Science》2017,27(4):1093-1119
We present the mechanical model of a bio-inspired deformable system, modeled as a Timoshenko beam, which is coupled to a substrate by a system of distributed elements. The locomotion action is inspired by the coordinated motion of coupling elements that mimic the legs of millipedes and centipedes, whose leg-to-ground contact can be described as a peristaltic displacement wave. The multi-legged structure is crucial in providing redundancy and robustness in the interaction with unstructured environments and terrains. A Lagrangian approach is used to derive the governing equations of the system that couple locomotion and shape morphing. Features and limitations of the model are illustrated with numerical simulations. 相似文献
665.
Jürgen?Berndt José?Carlos?Díaz-RamosEmail author Mohammad?Javad?Vanaei 《Monatshefte für Mathematik》2017,184(2):185-200
We study isometric cohomogeneity one actions on the \((n+1)\)-dimensional Minkowski space \(\mathbb {L}^{n+1}\) up to orbit-equivalence. We give examples of isometric cohomogeneity one actions on \(\mathbb {L}^{n+1}\) whose orbit spaces are non-Hausdorff. We show that there exist isometric cohomogeneity one actions on \(\mathbb {L}^{n+1}\), \(n \ge 3\), which are orbit-equivalent on the complement of an n-dimensional degenerate subspace \(\mathbb {W}^n\) of \(\mathbb {L}^{n+1}\) and not orbit-equivalent on \(\mathbb {W}^n\). We classify isometric cohomogeneity one actions on \(\mathbb {L}^2\) and \(\mathbb {L}^3\) up to orbit-equivalence. 相似文献
666.
Parvin Safari Simon Gückel Dr. Josef B. G. Gluyas Prof. Stephen A. Moggach Prof. Martin Kaupp Prof. Paul J. Low 《Chemistry (Weinheim an der Bergstrasse, Germany)》2022,28(44):e202200926
The electronic structure and associated spectroscopic properties of ligand-bridged, bimetallic ‘mixed-valence’ complexes of the general form {M}(μ-B){M+} are dictated by the electronic couplings, and hence orbital overlaps, between the metal centers mediated by the bridge. In the case of complexes such as [{Cp*(dppe)Ru}(μ-C≡CC6H4C≡C){Ru(dppe)Cp*}]+, the low barrier to rotation of the half-sandwich metal fragments and the arylene bridge around the acetylene moieties results in population of many energy minima across the conformational energy landscape. Since orbital overlap is also sensitive to the particular mutual orientations of the metal fragment(s) and arylene bridge through a Karplus-like relationship, the different members of the population range exemplify electronic structures ranging from strongly localized (weakly coupled Robin-Day Class II) to completely delocalized (Robin-Day Class III). Here, we use electronic structure calculations with the hybrid density functional BLYP35-D3 and a continuum solvent model in combination with UV-vis-NIR and IR spectroelectrochemical studies to show that the conformational population in complexes [{Cp*(dppe)Ru}(μ-C≡CArC≡C){Ru(dppe)Cp*]+, and hence the dominant electronic structure, can be biased through the steric and electronic properties of the diethynylarylene (Ar) moiety (Ar=1,4-C6H4, 1,4-C6F4, 1,4-C6H2-2,5-Me2, 1,4-C6H2-2,5-(CF3)2, 1,4-C6H2-2,5-iPr2). 相似文献
667.
Hassan?KeypourEmail author Mohammad?Hasan?Zebarjadian Seyyed?Javad?Sabounchei 《Journal of the Iranian Chemical Society》2015,12(1):121-126
The reaction of phosphorus ylide, acetylmethylenetriparatolylphosphorane (L) with HgX2 (X = Cl, Br, I and NO3) in equimolar ratios using acetone and dimethylformamide as solvents leads to binuclear products. 31P NMR spectroscopy was used to investigate the stoichiometry and stability of a HgX2 complex with CH3COCHP(p-tolyl)3 (L) in binary acetone–dimethylformamide mixtures of varying composition. In all cases studied, the variation of 31P NMR chemical shift with the [HgX2]/[L] mole ratio indicated the formation of 1:1 complexes. The formation constants of the resulting complexes were evaluated from computer fitting of the mole ratio data to an equation that relates the observed chemical shifts to the formation constant. In all mercuric salts used, the stabilities of the resulting 1:1 complexes varied in the order Hg(NO3)2 > HgCl2 > HgBr2 > HgI2. It was found that, in the case of all complexes, an increase in the percentage of dimethylformamide in the solvent mixtures significantly decreases the stability of the complexes. 相似文献
668.
MnO2/TiO2-ZrO2, which was synthesized by the adsorption method, demonstrated very high catalytic activity in the selective oxidation of benzyl alcohols to benzaldehydes with excellent yields and selectivity in short reaction times. The physical and chemical properties of MnO2/TiO2-ZrO2 were investigated by XRD, XRF, BET, FT-IR and SEM techniques. The influence of the catalyst support (SBA-15, ZSM-5, TiO2-ZrO2 and Y), type of metal oxide supported, method of loading and amount of manganese nitrate loading have been thoroughly investigated. Moreover, the catalyst has shown excellent reusability in the process. 相似文献
669.
670.
Javad Safari Sayed Hossein Banitaba Shiva Dehghan Khalili 《Arabian Journal of Chemistry》2011,4(1):11-15
Silica sulfuric acid was found to be an efficient, reusable and environment-friendly catalyst for fast hydrolysis of various isobenzofuranone to corresponding 2-ketomethylquinoline derivatives in a high yield under solvent-free using microwave irradiation. As the activator of silica sulfuric acid the wet SiO2 was chosen. The reactions in conventional conditions were compared with the microwave assisted reactions. This approach can prove beneficial since the recovery of solvents from conventional reaction systems always results in some losses. 相似文献