全文获取类型
收费全文 | 507篇 |
免费 | 17篇 |
国内免费 | 1篇 |
专业分类
化学 | 397篇 |
晶体学 | 1篇 |
力学 | 5篇 |
数学 | 36篇 |
物理学 | 86篇 |
出版年
2023年 | 2篇 |
2022年 | 6篇 |
2021年 | 8篇 |
2020年 | 9篇 |
2019年 | 18篇 |
2018年 | 6篇 |
2017年 | 7篇 |
2016年 | 21篇 |
2015年 | 15篇 |
2014年 | 18篇 |
2013年 | 31篇 |
2012年 | 39篇 |
2011年 | 36篇 |
2010年 | 10篇 |
2009年 | 23篇 |
2008年 | 30篇 |
2007年 | 38篇 |
2006年 | 19篇 |
2005年 | 27篇 |
2004年 | 21篇 |
2003年 | 15篇 |
2002年 | 18篇 |
2001年 | 6篇 |
2000年 | 7篇 |
1999年 | 11篇 |
1998年 | 3篇 |
1997年 | 10篇 |
1996年 | 5篇 |
1995年 | 9篇 |
1994年 | 9篇 |
1993年 | 5篇 |
1992年 | 2篇 |
1991年 | 2篇 |
1990年 | 3篇 |
1989年 | 3篇 |
1987年 | 2篇 |
1985年 | 2篇 |
1984年 | 4篇 |
1981年 | 2篇 |
1980年 | 2篇 |
1978年 | 2篇 |
1977年 | 6篇 |
1976年 | 3篇 |
1975年 | 1篇 |
1974年 | 1篇 |
1973年 | 2篇 |
1972年 | 1篇 |
1971年 | 1篇 |
1933年 | 1篇 |
1910年 | 1篇 |
排序方式: 共有525条查询结果,搜索用时 15 毫秒
71.
72.
73.
Arijit Ghorai Arun Kumar Mandal Susanta Banerjee 《Journal of polymer science. Part A, Polymer chemistry》2020,58(2):263-279
Sulfonated polytriazoles have drawn a great attention as high performance polymers and their good film forming ability. In the present study, a phosphorus containing new diazide monomer namely, bis-[4-(4′-aminophenoxy)phenyl]phenylphosphine was synthesized and accordingly, a series of phosphorus containing sulfonated polytriazoles (PTPBSH-XX) was synthesized by reacting equimolar amount of this diazide monomer (PAZ) in combination with another sulfonated diazide monomer (DSAZ) and a terminal bis-alkyne (BPALK) by the Cu (I) catalyzed azide–alkyne click polymerization. The polymers were characterized by nuclear magnetic resonance (1H, 13C, 31P NMR) and Fourier transform infrared spectroscopic techniques. The sulfonic acid content of the copolymers also determined from the different integral values obtained from the 1H NMR signals. The small-angle X-ray scattering results unfolded the well-separated dispersion of the hydrophilic and hydrophobic domains of the polymers. As a whole, the copolymer membranes displayed sufficient thermal, mechanical, and oxidative stabilities high with high proton conductivity and low water uptake that are essential for proton exchange membrane applications. The copolymers exhibited oxidative stability in the range of 15–24 h and had proton conductivity values were found as high as 38–110 mS cm−1 at 80 °C in completely hydrated condition. Among the all copolytriazoles, PTPBSH-90 (BPALK:DSAZ:PAZ = 100:90:10) having IECW = 2.44 mequiv g−1, showed proton conductivity as high as 119 mS cm−1 at 90 °C with an activation energy of 10.40 kJ mol−1 for the proton conduction. © 2020 Wiley Periodicals, Inc. J. Polym. Sci. 2020 , 58, 263–279 相似文献
74.
Pranab Kumar Tarafder Susanta Kumar Pradhan Shaswati Roychowdhury 《Journal of Radioanalytical and Nuclear Chemistry》2018,316(2):527-534
An extractive pellet fluorimetry determination of trace uranium in thorium rich samples has been developed. This is based upon a solvent extraction system which completely separates both the elements uranium and thorium from each other. Thorium as a neutral complex with 2,3-dihydroxynaphthalene at pH 4–6 is extracted into ethylacetate and then uranium-2,3-dihydroxynaphthalene anionic complex is extracted into another batch of ethylacetate at pH 11–12 under the influence of a counter cation, cetyltrimethylammonium ion. This method has been applied for the determination of trace uranium in synthetic nuclear grade thorium oxide and thorium rich mineralized rock with high degree of accuracy and precision. 相似文献
75.
Solvent‐Mediated Functionalization of Benzofuroxan on Electron‐Rich Ruthenium Complex Platform
下载免费PDF全文
![点击此处可从《化学:亚洲杂志》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Dr. Prabir Ghosh Sanchaita Dey Sanjib Panda Prof. Goutam Kumar Lahiri 《化学:亚洲杂志》2018,13(12):1582-1593
An unprecedented reactivity profile of biochemically relevant R‐benzofuroxan (R=H, Me, Cl), with high structural diversity and molecular complexity on a selective {Ru(acac)2} (acac=acetylacetonate) platform, in conjugation with EtOH solvent mediation, is revealed. This led to the development of monomeric [RuIII(acac)2(L1R)] ( 1 a – 1 c ; L1R=2‐nitrosoanilido derivatives) and dimeric [{RuII(acac)2}2(L2R)] ( 2 a – 2 b ; L2R=(1E,2E)‐N1,N2‐bis(2‐nitrosophenyl)ethane‐1,2‐diimine derivatives) complexes in one pot with a change in the metal redox conditions. The functionalization of benzofuroxan in 1 and 2 implied in situ reduction of N=O to NH? in the former and solvent‐assisted multiple N?C coupling in the latter. The aforesaid transformation processes were authenticated through structural elucidation of representative complexes, and evaluated by their spectroscopic/electrochemical features, along with C2D5OD labeling and monitoring of the impact of substituents (R) in the benzofuroxan framework on the product distribution process. The noninnocent potential of newly developed L1 and L2 in 1 and 2 , respectively, was also probed by spectroelectrochemistry in combination with DFT calculations. 相似文献
76.
No-carrier-added (nca) 199–201Tl has been separated from nca 199–201Pb using an environmentally friendly biocompatible polymer, poly(N-vinylpyrrolidone). The method uses no harmful chemicals
and is based on the process of dialysis of PVP-Pb and PVP-Tl complexes against triple-distilled water. It has been observed
after one hour of dialysis that 75–85% Tl (in both +3 and +1 oxidation states) comes out of dialysis sack without any contamination
from lead. 相似文献
77.
Somnath Roy Tarak Nath Mandal Anil Kumar Barik Samik Gupta Ray J. Butcher Mohamed Salah El Fallah Javier Tercero Susanta Kumar Kar 《Polyhedron》2008
The synthesis and structure of a pyrazole-based orthogonal ferromagnetically coupled tetracopper(II) 2 × 2 homoleptic grid complex [Cu4(PzOAPyz)4(ClO4)2](ClO4)2 · 6H2O (1), formed by the reaction between the ditopic ligand PzOAPyz and Cu(ClO4)2 · 6H2O, are described. The ligand contains terminal pyrazole and pyrazine residues bound to a central flexible diazine subunit (N–N) as well as one potentially bridging alkoxo group. The two adjacent metal centers are linked by an alkoxo oxygen forming essentially a square Cu4(μ-O4) cluster. In the Cu4(μ-O4) core, out of the four copper centers, two copper centers are penta-coordinated and the remaining two are hexa-coordinated. In each case of hexa-coordination, the sixth position is occupied by one of the oxygen atoms of a coordinated perchlorate ion. Complex 1 has been characterized structurally and magnetically. Although the large Cu–O–Cu bridge angles (137–138°) and short Cu–Cu distances (3.964–3.970 Å) are suitable for the transmission of the expected antiferromagnetic coupling, the square-based Cu4(μ-O4) cluster exhibits an intramolecular ferromagnetic exchange (J = 7.47 cm−1) between the metal centers with an S = 2 magnetic ground state associated with the quasi orthogonal arrangement of the magnetic orbitals (dx2-y2). The exchange pathway parameters have been evaluated from density functional calculations. 相似文献
78.
Eight poly(imide‐siloxane)s co‐polymers have been prepared by one pot solution imidization method. The polymers are synthesized by the reaction of bisphenol‐A‐dianhydride (BPADA) with fluorinated diamine 4,4′‐bis(3″‐trifluoromethyl‐p‐aminobiphenyl ether) biphenyl, and aminopropyl‐terminated polydimethylsiloxane (APPS). The polymers are synthesized by varying the siloxane loading to 5, 10, 15, 20, 25, 30, 35, and 40 wt%, respectively. Thermal, mechanical, rheological, and dielectric properties of these polymers have been evaluated with respect to siloxane loading. The polymers showed glass transition temperature of 107–203°C and tensile strength at break of 24–75 MPa depending on siloxane loading. The elongation break of the polymers ranges from 24 to 144% depending on siloxane loading. The amounts of char residue in the polymers have been correlated with incorporated siloxane in the polymer by NMR techniques. The polymers showed very low water absorption and dielectric constant as low as 2.43 when the siloxane loading is 40 wt%. Copyright © 2008 John Wiley & Sons, Ltd. 相似文献
79.
Saha SK Jha M Ali M Chakraborty A Bit G Das SK 《The journal of physical chemistry. B》2008,112(15):4642-4647
Effect of 1 and 2-naphthols on the shape transition of cetyl trimethylammonium bromide (CTAB) and cetylpyridinium bromide (CPB) micelles are studied. Stimuli-responsive viscoelastic gels of long wormlike micelles are formed at low surfactant concentrations in the presence of neutral naphthols, where H-bonding plays a key role in micellar shape transition in the absence of any charge screening. Micelle-embedded naphthols also act as novel self-fluorescence probes for monitoring viscoelasticity of the system as a function of applied shear. 1H NMR study shows that the solubilization sites of naphthols in the micelle are located near the surface. While UV absorption and Fourier transform infrared studies confirm the presence of intermolecular H-bonds in micelle embedded naphthols, transmission electron micrographs of vacuum-dried samples at room temperature demonstrate the transition in shape from sphere to rodlike micelles. 相似文献
80.
Ghumaan S Sarkar B Maji S Puranik VG Fiedler J Urbanos FA Jimenez-Aparicio R Kaim W Lahiri GK 《Chemistry (Weinheim an der Bergstrasse, Germany)》2008,14(34):10816-10828
The quinonoid ligand-bridged diruthenium compounds [(acac)(2)Ru(mu-L(2-))Ru(acac)(2)] (acac(-)=acetylacetonato=2,4-pentanedionato; L(2-)=2,5-dioxido-1,4-benzoquinone, 1; 3,6-dichloro-2,5-dioxido-1,4-benzoquinone, 2; 5,8-dioxido-1,4-naphthoquinone, 3; 2,3-dichloro-5,8-dioxido-1,4-naphthoquinone, 4; 1,5-dioxido-9,10-anthraquinone, 5; and 1,5-diimido-9,10-anthraquinone, 6) were prepared and characterized analytically. The crystal structure analysis of 5 in the rac configuration reveals two tris(2,4-pentanedionato)ruthenium moieties with an extended anthracenedione-derived bis(ketoenolate) pi-conjugated bridging ligand. The weakly antiferromagnetically coupled {Ru(III)(mu-L(2-))Ru(III)} configuration in 1-6 exhibits complicated overall magnetic and EPR responses. The simultaneous presence of highly redox-active quinonoid-bridging ligands and of two ruthenium centers capable of adopting the oxidation states +2, +3, and +4 creates a large variety of possible oxidation state combinations. Accordingly, the complexes 1-6 exhibit two reversible one-electron oxidation steps and at least two reversible reduction processes. Shifts to positive potentials were observed on introduction of Cl substituents (1-->2, 3-->4) or through replacement of NH by O (6-->5). The ligand-to-metal charge transfer (LMCT) absorptions in the visible region of the neutral molecules become more intense and shifted to lower energies on stepwise reduction with two electrons. On oxidation, the para-substituted systems 1-4 exhibit monocation intermediates with intervalence charge transfer (IVCT) transitions of Ru(III)Ru(IV) mixed-valent species. In contrast, the differently substituted systems 5 and 6 show no such near infrared (NIR) absorption. While the first reduction steps are thus assigned to largely ligand-centered processes, the oxidation appears to involve metal-ligand delocalized molecular orbitals with variable degrees of mixing. 相似文献