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排序方式: 共有197条查询结果,搜索用时 15 毫秒
51.
Tahir Ali Khan Sultana Naseem Yasser Azim Shama Parveen Mohammad Shakir 《Transition Metal Chemistry》2007,32(6):706-710
A novel series of 16-membered binuclear complexes of octaazatetraimine ligand,
[M = MnII, CoII, NiII, CuII and ZnII; X = Cl or NO3] have been synthesized by metal template condensation reactions of o-phenylenediamine with N,N′-diacetylhydrazine in 1:1:1 molar ratio in methanol. The proposed stoichiometry and the bonding of the macrocyclic moiety
to metal ions along with the overall stereochemistry have been derived from the results of elemental analyses, magnetic susceptibility,
conductivity data and the spectral data revealed from FT-IR,
, ESI mass, UV–visible studies. An octahedral geometry has been envisaged for MnII, CoII, and NiII complexes while a slight distortion in octahedral geometry has been noticed for CuII complexes. The low conductivity data of all the complexes suggest their non-ionic nature. 相似文献
52.
MdNurnobi Rashed Abeda Sultana Touchy Chandan Chaudhari Jaewan Jeon S.M.A.Hakim Siddiki Takashi Toyao Ken-ichi Shimizu 《催化学报》2020,(6):970-976
本文报道了将市售CeO2作为一种高活性和可重复使用的催化剂用于无溶剂条件下氧化吲哚与醛的C3选择性烷基化反应.这种催化方法一般适用于不同的芳香族和脂肪族醛,得到3-烷基二烯-辛醇,产率高(87%–99%),立体选择性高(79%–93%为E-异构体).这是从氧化吲哚与各种脂肪族醛催化合成3-烯基氧化吲哚的首例.采用原位红外光谱研究了CeO2上Lewis酸位点与苯甲醛之间的Lewis酸-碱相互作用.不同粒径CeO2催化剂的构效关系研究表明,无缺陷CeO2表面是该反应的活性中心. 相似文献
53.
A theoretical study on heavier group‐14 substituting effect on the essential property of formamide, strong hydrogen bond with water and internal rotational barrier was performed within the framework of natural bond orbital (NBO) analysis and based on the density functional theory calculation. For heavier group‐14 analogues of formamide (YHONH2, Y = Si, Ge and Sn), the nN–πY=O conjugation strength does not always reduce as Y becomes heavier, for example, silaformamide and germaformamide have similar strength of delocalization. Heavier formamides prefer being H‐bond donors to form FYO–H2O complexes to being H‐bond acceptors to form FYH–H2O complexes. The NEDA analysis indicates that H‐bond energies of FYO–H2O complexes increase as moving down group 14 due to concurrently stronger charge transfer (CT) and electrostatic attraction and for the FYH–H2O complexes H‐bond strengths are similar. The model of CTs from FYO to H2O differs from that at FYH–H2O complexes, which are contributed not only by aligning lone‐pair orbital of O but also by another lone‐pair orbital. At two lowest lying excited states (the triplet and S1 excited states), formamide and its heavier analogues form double H‐bonds with H2O molecule at the same time. The barrier heights of internal rotation become gradually low from C to Sn, formamide (15.73 kcal/mol) > silaformamide (11.73 kcal/mol) > germaformamide (9.45 kcal/mol) > stannaformamide (7.50 kcal/mol) at the CCSD(T)/aug‐cc‐pVTZ//B3LYP/cc‐pVTZ level. NBO analysis indicates that the barrier does not only come from the nN→π*YO conjugation, and for heavier analogues of formamide, the nN→σ*YO hyperconjugation effect and steric effect considerably contribute to the overall rotational barrier. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
54.
Muhammad Mufakkar Anvarhusein A. Isab Tobias Rüffer Heinrich Lang Saeed Ahmad Najma Arshad Abdul Waheed 《Transition Metal Chemistry》2011,36(5):505-512
Copper(I) complexes of thioureas having the general formulae [CuLnBr] and [CuLn]Br [where, n = 1 − 4 and L = thiourea (Tu), N-methylthiourea (Metu), N-ethylthiourea (Ettu), N,N′-dipropylthiourea (Dprtu), N,N′-dibutylthiourea (Dbtu) or N,N′-diphenylthiourea (Dphtu)] were prepared and characterized by elemental analysis, IR, and NMR (1H and 13C) spectroscopy. The crystal structure of one of them, [Cu(Metu)4]Br (1), was determined by X-ray crystallography. The X-ray structure of 1 describes a tetrahedral geometry around copper(I) with all Metu ligands binding through sulfur atoms. An upfield shift in
the 13C NMR and downfield shift in the 1H NMR spectra are consistent with the thione coordination to copper(I). Antimicrobial activities of the complexes were evaluated
by the minimum inhibitory concentration method. The results showed that only [Cu(Ettu)3Br] was effective in inhibiting the growth of all the tested organisms (gram-positive, gram-negative bacteria, and Candida sp.), while the other complexes were not effective against all the organisms. 相似文献
55.
Tasnádi G Winkler CK Clay D Sultana N Fabian WM Hall M Ditrich K Faber K 《Chemistry (Weinheim an der Bergstrasse, Germany)》2012,18(33):10362-10367
The degree of C?C bond activation in the asymmetric bioreduction of α,β-unsaturated carboxylic esters by ene-reductases was studied, and general recommendations to render these "borderline-substrates" more reactive towards enzymatic reduction are proposed. The concept of "supported substrate activation" was developed. In general, an additional α-halogenated substituent proved to be beneficial for enzymatic activity, whereas β-alkyl or β-aryl substituents were detrimental for the reactivity of nonhalogenated substrates, and α-cyano groups showed little effect. The alcohol moiety of the ester functionality was found to have a strong influence on the reaction rate. Overall, activities were determined by both steric and electronic effects. 相似文献
56.
ABSTRACT: A rapid and reproducible stability indicating TLC method was developed for the determination of prednisolone acetate and chloramphenicol in presence of their degraded products. Uniform degradation conditions were maintained by refluxing sixteen reaction mixtures for two hours at 80°C using parallel synthesizer including acidic, alkaline and neutral hydrolysis, oxidation and wet heating degradation. Oxidation at room temperature, photochemical and dry heating degradation studies were also carried out. Separation was done on TLC glass plates, pre-coated with silica gel 60F-254 using chloroform: methanol (14:1 v/v). Spots at Rf 0.21 ± 0.02 and Rf 0.41 ± 0.03 were recognized as chloramphenicol and prednisolone acetate, respectively. Quantitative analysis was done through densitometric measurements at multiwavelength (243 nm, λmax of prednisolone acetate and 278 nm, λmax of chloramphenicol), simultaneously. The developed method was optimized and validated as per ICH guidelines. Method was found linear over the concentration range of 200-6000 ng/spot with the correlation coefficient (r2 ± S.D.) of 0.9976 ± 3.5 and 0.9920 ± 2.5 for prednisolone acetate and chloramphenicol, respectively. The developed TLC method can be applied for routine analysis of prednisolone acetate and chloramphenicol in presence of their degraded products in their individual and combined pharmaceutical formulations. 相似文献
57.
58.
S. Sultana I. Kourakis 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2012,66(4):100
The propagation of electron-acoustic solitary waves and shock structures is investigated in a plasma characterized by a superthermal
electron population. A three-component plasma model configuration is employed, consisting of inertial (“cold”) electrons,
inertialess κ (kappa) distributed superthermal (“hot”) electrons and stationary ions. A multiscale method is employed, leading to a Korteweg-de
Vries (KdV) equation for the electrostatic potential (in the absence of dissipation). Taking into account dissipation, a hybrid
Korteweg-de Vries-Burgers (KdVB) equation is derived. Exact negative-potential pulse- and kink-shaped solutions (shocks) are
obtained. The relative strength among dispersion, nonlinearity and damping coefficients is discussed. Excitations formed in
superthermal plasma (finite κ) are narrower and steeper, compared to the Maxwellian case (infinite κ). A series of numerical simulations confirms that energy initially stored in a solitary pulse which propagates in a stable
manner for large κ (Maxwellian plasma) may break down to smaller structures or/and to random oscillations, when it encounters a small-κ (nonthermal) region. On the other hand, shock structures used as initial conditions for numerical simulations were shown
to be robust, essentially responding to changed in the environment by a simple profile change (in width). 相似文献
59.
Using the unified method, the inverse processes of photoionization and electron–ion recombination are studied in detail for neutral chromium, (), for the ground and excited states. The unified method based on close-coupling approximation and R-matrix method (i) subsumes both the radiative recombination (RR) and dielectronic recombination (DR) for the total rate and (ii) provides self-consistent sets of photoionization cross sections σPI and recombination rates αRC. The present results show in total photoionization of the ground and excited states an enhancement in the background at the first excited threshold, state of the core. One prominent phot-excitation-of-core (PEC) resonance due to one dipole allowed transition (6S-6Po) in the core is found in the photoionization cross sections of most of the valence electron excited states. Structures in the total and partial photoionization, for ionization into various excited core states and ground state only, respectively, are demonstrated. Results are presented for the septet and quintet states with n≤10 and l≤9 of Cr I. These states couple to the core ground state 6S and contribute to the recombination rates. State-specific recombination rates are also presented for these states and their features are illustrated. The total recombination rate shows two DR peaks, one at a relatively low temperature, at 630 K, and the other around 40,000 K. This can explain existence of neutral Cr in interstellar medium. Calculations were carried out in LS coupling using a close-coupling wave function expansion of 40 core states. The results illustrate the features in the radiative processes of Cr I and provide photoionization cross sections and recombination rates with good approximation for this astrophysically important ion. 相似文献
60.
Victor Alexandru Angel Popescu Elena Liliana Popescu Sobia Sultana 《Monatshefte für Mathematik》2009,38(3):223-233
Let (K, v) be a perfect rank one valued field and let ([`(Kv)],[`(v)]){(\overline{K_{v}},\overline{v})} be the canonical valued field obtained from (K, v) by the unique extension of the valuation [(v)\tilde]{\widetilde{v}} of K
v
, the completion of K relative to v, to a fixed algebraic closure [`(Kv)]{\overline{K_{v}}} of K
v
. Let [`(K)]{\overline{K}} be the algebraic closure of K in [`(Kv)]{\overline {K_{v}}}. An algebraic extension L of K, L ì [`(K)]{L\subset\overline{K}}, is said to be a v-adic maximal extension, if [`(v)] | L{\overline{v}\mid_{L}} is the only extension of v to L and L is maximal with this property. In this paper we describe some basic properties of such extensions and we consider them in
connection with the v-adic spectral norm on [`(K)]{\overline{K}} and with the absolute Galois groups Gal([`(K)]/K){(\overline{K}/K)} and Gal([`(Kv)] /Kv){(\overline{K_{v}} /K_{v})}. Some other auxiliary results are given, which may be useful for other purposes. 相似文献