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51.
52.
Brothers PJ 《Inorganic chemistry》2011,50(24):12374-12386
Complexes of boron with ligands containing pyrrolyl motifs are surveyed. The ligands range from simple pyrrolyl groups to dipyrroles and linear terpyrroles. Macrocyclic ligands include tripyrroles, which encompass subphthalocyanines, subporphyrins, subtriazaporphyrins, and subtribenzoporphyins, the familiar tetrapyrroles porphyrin and corrole but also N-confused and -fused porphyrins, and expanded porphyrins containing up to eight pyrroles. The role of boron in these compounds depends on the nature of the ligand. Boron acts as a Lewis acid center in simple boron pyrrolyl compounds, and as a structure-directing and templating agent in the cyclic terpyrroles and some of the expanded porphyrins. The difluorboron dipyrrins are well-known as fluorescent dyes. Boron porphyrins and corroles are unusual in containing two coordinated boron atoms rather than the single coordinated atom usually occurring in these ligands, and the proximity of two boron atoms at close quarters in the ligand cavities gives rise to some unusual reaction and redox chemistry. The survey is organized by the number of pyrrole moieties occurring in the ligand and focuses on new and unique chemistry observed for the complexes. 相似文献
53.
Lemon CM Brothers PJ Boitrel B 《Dalton transactions (Cambridge, England : 2003)》2011,40(25):6591-6609
Metalloporphyrin complexes of the period six metals gold, mercury, thallium, lead and bismuth are often overlooked in favour of their lighter congeners. These complexes exhibit unusual coordination geometries, prominently featuring the metal centre residing out the porphyrin plane. Not only are these compounds chemically interesting, but several applications for these complexes are beginning to emerge. Gold and bismuth porphyrins have medicinal applications including novel chemotherapeutics and sensitizers for α-radiotherapy, while gold porphyrins have applications in materials chemistry and catalysis. This perspective serves to highlight trends in the synthesis and structure of these heavy metal complexes as well as illustrate the considerations necessary for rationally designing elaborate porphyrin architectures. 相似文献
54.
Readily available C-acylated cycloalkanones undergo efficient Pd catalyzed ring closure/cross-coupling providing 7-substituted tetrahydroxanthones in a single operation. One of the synthesized derivatives (depicted) is shown to selectively kill pancreatic cancer (PANC-1) cells under conditions of nutrient deprivation indicating that the tetrahydroxanthone is responsible, in part, for the "antiausterity" effects of the naturally occurring kigamicins. 相似文献
55.
Let B be a fiber bundle with compact fiber F over a compact Riemannian n-manifold M
n. There is a natural Riemannian metric on the total space B consistent with the metric on M. With respect to that metric, the volume of a rectifiable section σ: M → B is the mass of the image σ(M) as a rectifiable n-current in B.
Theorem 1. For any homology class of sections of B, there is a mass-minimizing rectifiable current T representing that homology class which is the graph of a C1 section on an open dense subset of M.
Mathematics Subject Classifications (2000): 49F20, 49F22, 49F10, 58A25, 53C42, 53C65. 相似文献
56.
Penelope Smith 《Journal of Mathematical Analysis and Applications》2006,316(2):483-494
In part I (P. Smith, Perron's method for quasilinear hyperbolic systems, part I, J. Math. Anal., in press) of this paper we defined a notion of viscosity solution (sub- (super-)solution) for these systems, proved a comparison principle for viscosity sub- and supersolutions. Here, in part II, we prove existence of viscosity solutions to the Cauchy problem, using a Perron-like method, for long time, and for all time. 相似文献
57.
Eleonora Del Federico Silvia A. Centeno Cindie Kehlet Penelope Currier Denise Stockman Alexej Jerschow 《Analytical and bioanalytical chemistry》2010,396(1):213-220
In conventional NMR, samples from works of art in sizes above those considered acceptable in the field of art conservation would have to be removed to place them into the bore of large superconducting magnets. The portable permanent-magnet-based systems, by contrast, can be used in situ to study works of art, in a noninvasive manner. One of these portable NMR systems, NMR-MOUSE®, measures the information contained in one pixel in an NMR image from a region of about 1 cm2, which can be as thin as 2–3 µm. With such a high depth resolution, profiles through the structures of art objects can be measured to characterize the materials, the artists’ techniques, and the deterioration processes. A novel application of the technique to study a deterioration process and to follow up a conservation treatment is presented in which micrometer-thick oil stains on paper are differentiated and characterized. In this example, the spin–spin relaxation T 2 of the stain is correlated to the iodine number and to the degree of cross-linking of the oil, parameters that are crucial in choosing an appropriate conservation treatment to remove them. It is also shown that the variation of T 2 over the course of treatments with organic solvents can be used to monitor the progress of the conservation interventions. It is expected that unilateral NMR in combination with multivariate data analysis will fill a gap within the set of high-spatial-resolution techniques currently available for the noninvasive analysis of materials in works of art, where procedures to study the inorganic components are currently far more developed than those suitable for the study of the organic components. 相似文献
58.
J.K. Yakinthos Ch. Routsi Penelope Schobinger-Papamantellos 《Journal of Physics and Chemistry of Solids》1984,45(6):689-693
Neutron diffraction studies of polycrystalline PrCo2Si2 and TbCo2Si2 compounds were carried out at 4.2 and 293 K. Both samples have collinear antiferromagnetic order below TN(31(1) and 46(1) K for Pr and Tb compound respectively), with their magnetic moments parallel to the c axis. The ordered magnetic moment values of Pr and Tb at 4.2 K (3.19 and 9.12 μB respectively), are close to the saturation value of the free ions. The corresponding magnetic space group Pl4/mnc (Sh410128) is body-anticentered ( refering to Pl cell). 相似文献
59.
γ-Irradiation of solid ammonium compounds at low temperatures nay lead to the formation and trapping of radicals generated from the parent ammonium ions. Thus, NH3+ was observed in NH4PF6 1 and N(CH3)3,+ was found in tetramethyl ammonium halides2. Recently it has been shown that γ-irradiation of tetraalkylammonium iodides at 77 °K leads to the breaking of a C-C bond next to the nitrogen atom3 in agreement with the mass spectrometrlc studies of amines which show the fission of the α, β-C-C bond as the primary process upon electron impact4. 相似文献
60.
Penelope J. Lundmark Gregory J. Kubas Ray J. Butcher 《Journal of chemical crystallography》1997,27(6):377-379
The structure of the title compound,syn-[Cp*MoO(μ?S)]2,1, has been determined.1 crystallized in the monoclinic space groupC2/c with dimensionsa=11.758(2),b=12.243(2), c = 15.585(3)Å, β=104.63(3)°. The reaction of Cp* 2Mo2(S2)(S)(S2O3) with Me2PhP producessyn-[Cp*MoO(μ?S)]2 and Me2PhPO. The compounds [Cp′MoO(μ?S)]2 [Cp′=Cp, CpMe, Cp*] can exist as either thesyn- oranti-isomers. The present structure,syn-[Cp*MoO(μ?S)]2 is compared with the structure of theanti-isomer and with the previously determined structure ofsyn-[Cp*MoO(μ?S)]2 in a different space group. 相似文献