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121.
The mononuclear iron(III) complexes [Fe(LH2)(H2O)Cl](ClO4)2.2H2O (1) and [Fe(LH2)(H2O)2](ClO4)3.H2O (2) have been prepared by reacting [Pb(LH(2))](ClO4)2 with FeCl3.6H2O and Fe(ClO(4))(3).6H(2)O, respectively. Complex 2 upon treatment with 1 equiv of alkali produces the oxo-bridged dimer [{Fe(LH2)(H2O)}2(mu-O)](ClO4)4.2H2O (3). In these compounds, LH2 refers to the tetraiminodiphenol macrocycle in the zwitterionic form whose two uncoordinated imine nitrogens are protonated and hydrogen-bonded to the metal-bound phenolate oxygens. The aqua ligands of complexes 1-3 get exchanged in acetonitrile. Reaction equilibria involving binding and exchange of the terminal ligands (Cl-/H2O/CH3CN) in these complexes have been studied spectrophotometrically. The equilibrium constant for the aquation reaction (K(aq)) [1]2+ + H2O <==> [2]3+ + Cl- in acetonitrile is 8.65(5) M, and the binding constant (K(Cl)-) for the reaction [1]2+ + Cl- [1Cl]+ + CH3CN is 4.75(5) M. The pK(D) value for the dimerization reaction 2[2]3+ + 2OH- <==> [3]4+ + 3H(2)O in 1:1 acetonitrile-water is 9.38(10). Complexes 1-3 upon reaction with Zn(ClO4)(2).6H(2)O and sodium acetate (OAc), pivalate (OPiv), or bis(4-nitrophenyl)phosphate (BNPP) produce the heterobimetallic complexes [{FeLZn(mu-X)}2(mu-O)](ClO4)2, where X = OAc (4), OPiv (5), and BNPP (6). The pseudo-first-order rate constant (k(obs)) for the formation of 4 at 25 degrees C from either 1 or 3 with an excess of Zn(OAc)2.2H2O in 1:1 acetonitrile-water at pH 6.6 is found to be the same with k(obs) = 1.6(2) x 10(-4) s(-1). The X-ray crystal structures of 3, 4, and 6 have been determined, although the structure determination of 3 was severely affected because of heavy disordering. In 3, the Fe-O-Fe angle is 168.6(6) degrees, while it is exactly 180.0 degrees in 4 and 6. Cyclic and square-wave voltammetric (CV and SWV) measurements have been carried out for complexes 1-4 in acetonitrile. The variation of the solvent composition (acetonitrile-water) has a profound effect on the E(1/2) and DeltaE(p) values. The binding of an additional chloride ion to an iron(III) center in 1-3 is accompanied by a remarkable shift of E(1/2) to more negative values. The observation of quasi-reversible CV for complexes containing a Fe(III)-O-Fe(III) unit (3 and 4) indicates that in the electrochemical time scale unusual Fe(III)-O-Fe(II) is produced. The 1H NMR spectra of complexes 3-6 exhibit hyperfine-shifted signals in the range 0-90 ppm with similar features. The metal-hydrogen distances obtained from T(1) measurements are in good agreement with the crystallographic data. Variable-temperature (2-300 K) magnetic susceptibility measurements carried out for 3 and 4 indicate strong antiferromagnetic exchange interaction (H = -2JS1.S2) between the high-spin iron(III) centers in the Fe-O-Fe unit with J = -114 cm(-1) (3) and -107 cm(-1) (4). 相似文献
122.
Shilpi Agarwal Tapas K. Das Rukmini Dey Sankhasubhra Nag 《General Relativity and Gravitation》2012,44(7):1637-1655
We apply the theory of algebraic polynomials to analytically study the transonic properties of general relativistic hydrodynamic axisymmetric accretion onto non-rotating astrophysical black holes. For such accretion phenomena, the conserved specific energy of the flow, which turns out to be one of the two first integrals of motion in the system studied, can be expressed as a 8th degree polynomial of the critical point of the flow configuration. We then construct the corresponding Sturm’s chain algorithm to calculate the number of real roots lying within the astrophysically relevant domain of \mathbbR{\mathbb{R}}. This allows, for the first time in literature, to analytically find out the maximum number of physically acceptable solution an accretion flow with certain geometric configuration, space-time metric, and equation of state can have, and thus to investigate its multi-critical properties completely analytically, for accretion flow in which the location of the critical points can not be computed without taking recourse to the numerical scheme. This work can further be generalized to analytically calculate the maximal number of equilibrium points certain autonomous dynamical system can have in general. We also demonstrate how the transition from a mono-critical to multi-critical (or vice versa) flow configuration can be realized through the saddle-centre bifurcation phenomena using certain techniques of the catastrophe theory. 相似文献
123.
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124.
Choudhury Dibyasree Lahiri Susanta Nag Taraknath Sodaye Suparna Bombard Aude 《Journal of Radioanalytical and Nuclear Chemistry》2020,323(2):897-902
Journal of Radioanalytical and Nuclear Chemistry - Poly (vinyl alcohol)-ethylene glycol (PVA-EG) composites were geared up using casting method. The PVA-EG composite films have been irradiated at... 相似文献
125.
Using atom probe tomography, the partitioning of alloying elements between α and β in the alloy Ti metal-5553 (Ti–5Al–5Mo–5V–3Cr–0.5Fe) has been investigated as a function of heat-treatment. It has been shown that β-solutionizing followed by step-quenching to a higher temperature (700°C) or slow-cooling leads to substantial partitioning of the alloying elements, including an enrichment of slow-diffusing Mo at the α/β interfaces. In contrast, it was found that the combination of β-solutionizing, quenching to room temperature and aging at 400°C leads to rather limited partitioning of these alloying elements. 相似文献
126.
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128.
Amiya Kumar Panda Phil Wojciechowski Kaushik Nag Fred Possmayer Nils O. Petersen 《Journal of Dispersion Science and Technology》2013,34(9):1255-1261
Studies on the interaction of cholesterol (CHOL) with palmitoyl-oleoyl phosphatidylcholine (POPC) and sphingomyelin (SPM) are considered to be important because of the occurrence of strong interactions between sphingolipids and CHOL, which lead to the formation of microdomains or rafts within biological membranes. In the present investigation, studies on the surface pressure (π)-area ( A ) measurements and fluorescence microscopic studies on monolayers of the above mentioned system have been reported. Ideality/nonideality of mixing, excess area, and free energy changes during the formation of the monolayers at different surface pressures for the mixed lipid systems were evaluated from the π– A data. Interactions were found to be repulsive at lower CHOL content, which became associative at higher CHOL content. Condensing effects of CHOL on the mixed monolayers were found. Fluorescence studies on the systems revealed similar overall results. 相似文献
129.
Terpene esters of fatty acids have potential applications in food, cosmetic, and pharmaceutical industries. The present study
focuses on the synthesis of terpene esters of long chain fatty acids catalyzed by Candida antarctica lipase B. Different parameters like temperature, solvent, and enzyme concentration for the esterification of terpene alcohols
(geraniol and citronellol) with oleic acid were studied. Maximum conversion (98 %) was found for both terpene esters at 60°C
in 2,2,4-trimethylpentane as well as in dry hexane and around 95–97 % in other tested solvents. The reaction was also carried
out using stearic and linoleic acid in hexane to study the effects of unsaturation in the substrate in which stearic acid
showed the maximum conversion. The reaction was monitored by 1H nuclear magnetic resonance spectroscopy. Using the peak integration values of methylene protons of terpene and terpene ester
of δ = 3.6 and 4.0 for citronellol and δ = 4.2 and 4.6 for geraniol, respectively, percentage conversions of each of the esters
were calculated. 相似文献
130.
Habibul Arfin Jagjit Kaur Tariq Sheikh Sudip Chakraborty Angshuman Nag 《Angewandte Chemie (International ed. in English)》2020,59(28):11307-11311
Bi3+ and lanthanide ions have been codoped in metal oxides as optical sensitizers and emitters. But such codoping is not known in typical semiconductors such as Si, GaAs, and CdSe. Metal halide perovskite with coordination number 6 provides an opportunity to codope Bi3+ and lanthanide ions. Codoping of Bi3+ and Ln3+ (Ln=Er and Yb) in Cs2AgInCl6 double perovskite is presented. Bi3+‐Er3+ codoped Cs2AgInCl6 shows Er3+ f‐electron emission at 1540 nm (suitable for low‐loss optical communication). Bi3+ codoping decreases the excitation (absorption) energy, such that the samples can be excited with ca. 370 nm light. At that excitation, Bi3+‐Er3+ codoped Cs2AgInCl6 shows ca. 45 times higher emission intensity compared to the Er3+ doped Cs2AgInCl6. Similar results are also observed in Bi3+‐Yb3+ codoped sample emitting at 994 nm. A combination of temperature‐dependent (5.7 K to 423 K) photoluminescence and calculations is used to understand the optical sensitization and emission processes. 相似文献