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排序方式: 共有166条查询结果,搜索用时 15 毫秒
31.
J. Naga Siva RaoR. Raghunathan 《Tetrahedron letters》2012,53(7):854-858
Synthesis of pyrrolidinyl-spirooxindoles fused to sugar lactone has been achieved by a one pot three component 1,3-dipolar cycloaddition (1,3-DC) reaction. A unique dipolarophile (α,β-unsaturated lactone) derived from d-glucose/d-galactose reacted with azomethine ylide generated in situ from isatin/N-substituted isatin and secondary amino acids (sarcosine/proline/piperidine-2-carboxylic acid) to give the corresponding cycloadducts in good yield. The cycloaddition was found to be highly regio- and diastereoselective. 相似文献
32.
Alexander Lubotzky Shahar Mozes M. S. Raghunathan 《Publications Mathématiques de L'IHéS》2000,91(1):5-53
Let G be a semisimple Lie group of rank ⩾2 and Γ an irreducible lattice. Γ has two natural metrics: a metric inherited from
a Riemannian metric on the ambient Lie group and a word metric defined with respect to some finite set of generators. Confirming
a conjecture of D. Kazhdan (cf. Gromov [Gr2]) we show that these metrics are Lipschitz equivalent. It is shown that a cyclic
subgroup of Γ is virtually unipotent if and only if it has exponential growth with respect to the generators of Γ. 相似文献
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35.
Krishnaswamy R Ghosh SK Lakshmanan S Raghunathan VA Sood AK 《Langmuir : the ACS journal of surfaces and colloids》2005,21(23):10439-10443
We have characterized the phase behavior of mixtures of the cationic surfactant cetyltrimethylammonium bromide (CTAB) and the organic salt 3-sodium-2-hydroxy naphthoate (SHN) over a wide range of surfactant concentrations using polarizing optical microscopy and X-ray diffraction. A variety of liquid crystalline phases, such as hexagonal, lamellar with and without curvature defects, and nematic, are observed in these mixtures. At high temperatures the curvature defects in the lamellar phase are annealed gradually on decreasing the water content. However, at lower temperatures these two lamellar structures are separated by an intermediate phase, where the bilayer defects appear to order into a lattice. The ternary phase diagram shows a high degree of symmetry about the line corresponding to equimolar CTAB/SHN composition, as in the case of mixtures of cationic and anionic surfactants. 相似文献
36.
The far-uv photolysis of phosphine sorbed in cancrinite matrix at 77 K has been studied by epr spectroscopy. Cancrinite is
demonstrated to stabilise the photolytically generated radicals ·PH2, ·P and ·H. Computer simulation of the entire lineshapes has been employed to assess the spin Hamiltonian parameters for
both ·PH2 and ·P. The intensity distribution pattern of the ·PH2 spectrum at 77 K is indicative of a thermally-equilibrated population of rotational states of this radical in its matrix
environment. The similarity of the epr data of ·PH2 trapped in cancrinite to that isolated in rare gas matrices, as well as theisotropic nature of the31P and1H hyperfine couplings in the former situation, suggest that ·PH2 is trapped in pseudospherical cavities of cancrinite with minimal matrix perturbations. Marked departures are observed for
theg- andA- values of cancrinite-trapped P atoms as compared with the gasphase counterparts. 相似文献
37.
Dr. Elango Kumarasamy Sunil Kumar Kandappa Dr. Ramya Raghunathan Dr. Steffen Jockusch Prof. Jayaraman Sivaguru 《Angewandte Chemie (International ed. in English)》2017,56(25):7056-7061
Intramolecular atropselective aza Paternò–Büchi reaction involving atropisomeric enamide and imine functionalities under sensitized irradiation leads to azetidine products in good yield and selectivity (ee >96 %). A mechanistic model based on detailed photophysical and isomerization kinetic studies is provided that shed light into the reactivity of enamides leading to aza Paternò–Büchi reaction. 相似文献
38.
NL Asfandiarov AI Fokin VG Lukin EP Nafikova GS Lomakin VS Fal'ko YV Chizhov 《Rapid communications in mass spectrometry : RCM》1999,13(12):1116-1123
A series of anthraquinone (C(14)O(2)H(8)) derivatives has been studied by means of electron capture negative ion mass spectrometry (ECNI-MS), photoelectron spectroscopy (PES), and AM1 quantum chemical calculations. Mean lifetimes of molecular negative ions M(-.) (MNI) have been measured. The mechanism of long-lived MNI formation in the epithermal energy region of incident electrons has been investigated. A simple model of a molecule (a spherical potential well with the repulsive centrifugal term) has been applied for the analysis of the energy dependence of cross sections at the first stage of the electron capture process. It has been shown that a temporary resonance of MNI at the energy approximately 0.5 eV corresponds to a shape resonance with lifetime 1-2.10(-13) s in the f-partial wave (l = 3) of the incident electron. The next resonant state of MNI at the energy approximately 1.7 eV has been associated with the electron excited Feshbach resonance (whose parent state is a triplet npi* transition). In all cases the initial electron state of the MNI relaxes into the ground state by means of a radiationless transition, and the final state of the MNI is a nuclear excited resonance with a lifetime measurable on the mass spectrometry timescale. Copyright 1999 John Wiley & Sons, Ltd. 相似文献
39.
A. K. Mitra Struther Arnott R. P. Millane S. Raghunathan J. K. Sheehan 《Journal of Macromolecular Science: Physics》2013,52(1-4):21-38
Glycosaminoglycans are prominent components of mammalian connective tissue and possess important ion-binding properties. X-ray fiber diffraction studies have demonstrated that glycosaminoglycans show different conformational responses to mono-and divalent cations. 相似文献
40.
Mukherjee A Raghunathan R Saha MK Nethaji M Ramasesha S Chakravarty AR 《Chemistry (Weinheim an der Bergstrasse, Germany)》2005,11(10):3087-3096
Three cubane copper(II) clusters, namely [Cu(4)(HL')4] (1), [Cu4L2(OH)2] (2), and [Cu4L2(OMe)2] (3), of two pentadentate Schiff-base ligands N,N'-(2-hydroxypropane-1,3-diyl)bis(acetylacetoneimine) (H3L') and N,N'-(2-hydroxypropane-1,3-diyl)bis(salicylaldimine) (H3L), are prepared, structurally characterized by X-ray crystallography, and their variable-temperature magnetic properties studied. Complex 1 has a metal-to-ligand stoichiometry of 1:1 and it crystallizes in the cubic space group P43n with a structure that consists of a tetranuclear core with metal centers linked by a mu(3)-alkoxo oxygen atom to form a cubic arrangement of the metal and oxygen atoms. Each ligand displays a tridentate binding mode which means that a total of eight pendant binding sites remain per cubane molecule. Complexes [Cu4L2(OH)2] (2) and [Cu4L2(OMe)2] (3) crystallize in the orthorhombic space group Pccn and have a cubane structure that is formed by the self-assembly of two {Cu2L}+ units. The variable-temperature magnetic susceptibility data in the range 300-18 K show ferromagnetic exchange interactions in the complexes. Along with the ferromagnetic exchange pathway, there is also a weak antiferromagnetic exchange between the copper centers. The theoretical fitting of the magnetic data gives the following parameters: J1 = 38.5 and J2 = -18 cm(-1) for 1 with a triplet (S = 1) ground state and quintet (S = 2) lowest excited state; J1 = 14.7 and J2 = -18.4 cm(-1) for 2 with a triplet ground state and singlet (S = 0) lowest excited state; and J1 = 33.3 and J2 = -15.6 cm(-1) for 3 with a triplet ground state and quintet lowest excited state, where J1 and J2 are two different exchange pathways in the cubane {Cu4O4} core. The crystal structures of 2 * 6 H2O and 3 * 2 H2O * THF show the presence of channels containing the lattice solvent molecules. 相似文献