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71.
T Gunnlaugsson D A Mac Dónaill D Parker 《Journal of the American Chemical Society》2001,123(51):12866-12876
The Eu(III) tetraazamacrocyclic complexes [Eu.1] and [Eu.2], and the Tb(III) and Yb(III) complexes [Tb.1] and [Yb.2], have been synthesized as luminescent molecular-level devices. The Eu complexes exhibit unique dual pH switching behavior in water under ambient conditions. The delayed Eu emission is reversibly switched on in acid, with an enhancement factor of several hundred for [Eu.1]. These observations are consistent with the protonation of the quinoline aryl nitrogen moiety (pK(a) approximately equal to 5.9 for [Eu.1]). The fluorescence emission spectra of these complexes are unaffected by acid, but pronounced changes occur in alkaline solution due to the deprotonation of the aryl amide nitrogen (pK(a) approximately 9.4 for [Eu.1]). [Tb.1] shows a more intriguing pH dependence; Tb emission is switched "on" only in the presence of H+ and in the absence of molecular oxygen, whereas the fluorescence emission properties are similar to those observed with [Eu.1]. This behavior can be conveniently described as a molecular-level logic gate, corresponding to a two-input INHIBIT function, A wedge B'. The analogous [Yb.2] complex shows no such pH or O(2) dependence. 相似文献
72.
Substitution of the weakly binding aqua ligand in [Cu(tren)OH2](2+) and [Cu(tpa)OH2](2+) (tren = tris(2-aminoethyl)amine; tpa = tris(2-pyridylmethyl)amine) by a cyano ligand on ferricyanide results in the assembly of heteropolynuclear cations around the cyanometalate core. In water, the reduction of the Fe(III) core to Fe(II) generates complexes that feature heteropolycations in which ferrocyanide is encapsulated by the Cu(II) moieties: [(Cu(tpa)CN)6Fe][ClO4]8-3H2O 1, [(Cu(tren)CN)6Fe][ClO4]8-10H2O 2, [(Cu(tren)CN)6Fe][Fe(CN)6]2[ClO4]2-15.8H2O 3, and [(Cu(tren)CN)6Fe][(Cu(tren)CN)4Fe(CN)2][Fe(CN)6)]4-6DMSO-21H2O 4. The formation of discrete molecules, in preference to extended networks or polymeric structures, has been encouraged through the use of branched tetradentate ligands in conjunction with copper(II), a metal center with the propensity to form five-coordinate complexes. Complex 3 crystallizes in the monoclinic space group P2(1)/c (#14) with a = 14.8674(10), b = 25.9587(10), c = 27.5617(10) A, beta = 100.8300(10) degrees, and Z = 4, and it is comprised of almost spherical heptanuclear cations, [(Cu(tren)CN)6Fe](8+), whose charge is balanced by two ferricyanide and two perchlorate counteranions. Complex 4 crystallizes in the triclinic space group P1 (# 1) with a = 14.8094(8), b = 17.3901(7), c = 21.1565(11) A, alpha = 110.750(3), beta = 90.206(2), gamma = 112.754(3) degrees, and Z = 1, and it is comprised of the heptanuclear [(Cu(tren)CN)6Fe](8+) cation and pentanuclear [(Cu(tren)CN)4Fe(CN)2](4+) cation, whose terminal cyano ligands are oriented trans to each other. The charge is balanced exclusively by ferricyanide counteranions. In both complexes, H-bonding interactions between hydrogens on primary amines of the tren ligand, terminal cyano groups of the ferricyanide counterions, and the solvent of crystallization generate intricate 3D H-bonding networks. 相似文献
73.
Measurements of the equilibrium constants for ligand exchange (MeCN, 295 K) involving the axial donor in a C4-symmetric, mono-capped, square antiprismatic cationic Eu complex, supported by calculations based on an electrostatic perturbation model, have been interpreted in terms of a predominant ligand polarisation interaction defined by observation of the hypersensitive delta J = 2 normalised emission intensity, in association with measurements correlating delta J = 1 band splitting and 1H NMR dipolar shifts that vindicate Bleaney's theory of magnetic anisotropy. 相似文献
74.
Kassandra Cendejas Hope E. Parker Dennis Molina Rajib Choudhury 《Journal of inclusion phenomena and macrocyclic chemistry》2017,89(1-2):199-205
In this study, we have examined supramolecular self-assembly process of a hydrophobic guest with a water-soluble host known by the trivial name octa acid (OA). Two octa acids form a capsular assembly only in presence of a nonpolar guest(s). Size and shape of the guest control the stoichiometry of the capsular complex. Here, all atom molecular dynamics simulation has been utilized to investigate complex formation mechanisms of a nonpolar guest (nonylbenzene) with two OA cavitands. Nonylbenzene was encapsulated into the nonpolar cavity of OA capsule owing to solvophobic interactions. Upon encapsulation it was twisted and bent due to lack of free space within the capsule. These unusual forms obtained from the simulation study were in accord with experimental findings. The post-complexation attributes of the guest were regulated by the available free space within the OA and favorable non-covalent interactions between the guest and the walls of the OA capsule. In the identical simulation condition two OA cavitands did not form a capsule without a guest, thus indicating requirement of a guest during the self-assembly of OA cavitands. 相似文献
75.
Indra K. Varma George M. Fohlen John A. Parker 《Journal of polymer science. Part A, Polymer chemistry》1982,20(2):283-297
Ten structurally different bisimide resins were prepared by reacting maleic anhydride/citraconic anhydride and benzophenone tetracarboxylic dianhydride with aromatic diamines and fused aromatic structures or heterocyclic groups. The amines included were 1,5-diaminonaphthalene, 2,5-bis(p-aminophenyl)1,3,4-oxadiazole, 3,3-bis(p-aminophenyl)phthalide, 9,9-bis(p-aminophenyl)fluorene. and 10,10-bis(p-aminophenyl)anthrone. These monomers were characterized by infrared (IR). 1H-NMR, mass spectroscopy, and elemental analysis. Thermal polymerization of these monomers was investigated by differential scanning calorimetry. Broad exothermic peaks were observed for a temperature range of 225–380°C. Temperature of exothermic peak position was influenced by the presence of substituents at the olefinic bond, and in biscitraconimides it was 40–50°C lower than in the corresponding bismaleimides. Anaerobic char yields of cured bisimide resins ranged from 44 to 64%. Oxadiazole-containing bisimides had low thermal stability. Increase in formula weight between the imide groups did not influence the char yields in a systematic manner. Graphite cloth laminates with two of these bisimide resins were fabricated and tested for a number of physical properties. Their limiting oxygen index was 70–72%. 相似文献
76.
The interaction of q = 0 delta- and lambda-Tb and Eu complexes with poly(dAdT), poly(dGdC) and calf-thymus DNA has been examined by absorption, emission and chiroptical spectroscopy and is sensitive to complex helicity, base-pair type and the nature of the lanthanide excited state. 相似文献
77.
78.
S.G. Parker 《Solid State Communications》1979,31(6):403-408
Factors which influence coercivity, Hc, in (Y,Sm,Lu,Ca)3(FeGe)5O12 films and in (Y,Sm,Tm)3(FeGa)5O12 films grown by LPE have been identified. An anomalous layer at the film-substrate interface exhibits coercivity values different from that of the middle, bulk, portion of the film. The contribution of the transient layer at the substrate interface could be reduced by increasing the rotation rate while immersing the substrate into the melt. Films containing Ga show lower coercivities than films containing CaGe possibly because films with Ga are more uniform in composition. Films with Ga show increased coercivities with increasing growth rates and with increasing Sm content throughout the film. 相似文献
79.
J.C. Selover Marianne Marsi David W. Parker J.A. Gladysz 《Journal of organometallic chemistry》1981,206(3):317-329
A series of kinetically unstable mononuclear anionic formyl complexes have been prepared by the action of Li(C2H5)3BH on neutral metal carbonyl precursors. One of these, Li+[(CO)4Mn(COC6H5)(CHO)]?, is shown to decompose by a hydride transfer disproportionation mechanism involving the by-product (C2H5)3B. 相似文献
80.
Techniques have been developed which permit the direct analysis of optical purity in α-deuterated amines and carboxylic acids. 相似文献