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91.
Dr. Marcin A. Majewski Wojciech Stawski Dr. Jeff M. Van Raden Michael Clarke Jack Hart Dr. James N. O'Shea Dr. Alex Saywell Prof. Harry L. Anderson 《Angewandte Chemie (International ed. in English)》2023,62(18):e202302114
Rings of porphyrins mimic natural light-harvesting chlorophyll arrays and offer insights into electronic delocalization, providing a motivation for creating larger nanorings with closely spaced porphyrin units. Here, we demonstrate the first synthesis of a macrocycle consisting entirely of 5,15-linked porphyrins. This porphyrin octadecamer was constructed using a covalent six-armed template, made by cobalt-catalyzed cyclotrimerization of an H-shaped tolan with porphyrin trimer ends. The porphyrins around the circumference of the nanoring were linked together by intramolecular oxidative meso-meso coupling and partial β-β fusion, to give a nanoring consisting of six edge-fused zinc(II) porphyrin dimer units and six un-fused nickel(II) porphyrins. STM imaging on a gold surface confirms the size and shape of the spoked 18-porphyrin nanoring (calculated diameter: 4.7 nm). 相似文献
92.
Raphael Bigler Kyle A. Mack Jeff Shen Paolo Tosatti Chong Han Stephan Bachmann Haiming Zhang Michelangelo Scalone Andreas Pfaltz Scott E. Denmark Stefan Hildbrand Francis Gosselin 《Angewandte Chemie (International ed. in English)》2020,59(7):2844-2849
Asymmetric hydrogenation has evolved as one of the most powerful tools to construct stereocenters. However, the asymmetric hydrogenation of unfunctionalized tetrasubstituted acyclic olefins remains the pinnacle of asymmetric synthesis and an unsolved challenge. We report herein the discovery of an iridium catalyst for the first, generally applicable, highly enantio‐ and diastereoselective hydrogenation of such olefins and the mechanistic insights of the reaction. The power of this chemistry is demonstrated by the successful hydrogenation of a wide variety of electronically and sterically diverse olefins in excellent yield and high enantio‐ and diastereoselectivity. 相似文献
93.
Erin W. Chambers ric Colin de Verdire Jeff Erickson Francis Lazarus Kim Whittlesey 《Computational Geometry》2008,41(1-2):94
Let be an orientable combinatorial surface. A cycle on is splitting if it has no self-intersections and it partitions into two components, neither of which is homeomorphic to a disk. In other words, splitting cycles are simple, separating, and non-contractible. We prove that finding the shortest splitting cycle on a combinatorial surface is NP-hard but fixed-parameter tractable with respect to the surface genus g and the number of boundary components b of the surface. Specifically, we describe an algorithm to compute the shortest splitting cycle in (g+b)O(g+b)nlogn time, where n is the complexity of the combinatorial surface. 相似文献
94.
Giacalone F Segura JL Martín N Ramey J Guldi DM 《Chemistry (Weinheim an der Bergstrasse, Germany)》2005,11(16):4819-4834
A series of donor-acceptor arrays (C60-oligo-PPV-exTTF; 16-20) incorporating pi-conjugated oligo(phenylenevinylene) wires (oligo-PPV) of different length between pi-extended tetrathiafulvalene (exTTF) as electron donor and C60 as electron acceptor has been prepared by multistep convergent synthetic approaches. The electronic interactions between the three electroactive species present in 16-20 were investigated by UV-visible spectroscopy and cyclic voltammetry (CV). Our studies clearly show that, although the C60 units are connected to the exTTF donors through a pi-conjugated oligo-PPV framework, no significant electronic interactions are observed in the ground state. Interestingly, photoinduced electron-transfer processes over distances of up to 50 Angstroms afford highly stabilized radical ion pairs. The measured lifetimes for the photogenerated charge-separated states are in the range of hundreds of nanoseconds (approximately 500 ns) in benzonitrile, regardless of the oligomer length (i.e., from the monomer to the pentamer). A different lifetime (4.35 micros) is observed for the heptamer-containing array. This difference in lifetime has been accounted for by the loss of planarity of the oPPV moiety that increases with the wire length, as established by semi-empirical (PM3) theoretical calculations carried out with 19 and 20. The charge recombination dynamics reveal a very low attenuation factor (beta = 0.01 +/- 0.005 Angstroms(-1)). This beta value, as well as the strong electron coupling (V approximately 5.5 cm(-1)) between the donor and the acceptor units, clearly reveals a nanowire behavior for the pi-conjugated oligomer, which paves the way for applications in nanotechnology. 相似文献
95.
C. Jeff Harlan Simon G. Bott Andrew R. Barron 《Journal of chemical crystallography》1998,28(8):649-651
Reaction of AlH3[N(CH2CH2)3CH] with hexamethyltrisiloxane, (OSiMe2)3, gives rise to the bis-quinuclidine complex AlH3[N(CH2CH2)3CH]2, which has been characterized by 1H and 13C NMR spectroscopy and X-ray crystallography. The molecular structure of AlH3[N(CH2CH2)3CH]2 consists of a trigonal bipyramidal aluminum with axial coordination of the quinuclidine ligands. Crystal data: orthorhombic, space group Pbcn, a = 10.6895(9), b = 12.266(1), c = 12.3794(9) Å, V = 1623.2(2) Å3, and Z = 4. 相似文献
96.
Ratnesh K. Shukla Jeff. D. Eldredge 《Theoretical and Computational Fluid Dynamics》2007,21(5):343-368
An inviscid vortex sheet model is developed in order to study the unsteady separated flow past a two-dimensional deforming
body which moves with a prescribed motion in an otherwise quiescent fluid. Following Jones (J Fluid Mech 496, 405–441, 2003)
the flow is assumed to comprise of a bound vortex sheet attached to the body and two separate vortex sheets originating at
the edges. The complex conjugate velocity potential is expressed explicitly in terms of the bound vortex sheet strength and
the edge circulations through a boundary integral representation. It is shown that Kelvin’s circulation theorem, along with
the conditions of continuity of the normal velocity across the body and the boundedness of the velocity field, yields a coupled
system of equations for the unknown bound vortex sheet strength and the edge circulations. A general numerical treatment is
developed for the singular principal value integrals arising in the solution procedure. The model is validated against the
results of Jones (J Fluid Mech 496, 405–441, 2003) for computations involving a rigid flat plate and is subsequently applied
to the flapping foil experiments of Heathcote et al. (AIAA J, 42, 2196–2204, 2004) in order to predict the thrust coefficient.
The utility of the model in simulating aquatic locomotion is also demonstrated, with vortex shedding suppressed at the leading
edge of the swimming body.
相似文献
97.
Maysa Faisal Suyagh Godwill Iheagwaram Prashant Laxman Kole Jeff Millership Paul Collier Henry Halliday James C. McElnay 《Analytical and bioanalytical chemistry》2010,397(2):687-693
A selective and sensitive high-performance liquid chromatography method with UV detection for the determination of metronidazole in dried blood spots (DBS) has been developed and validated. DBS samples [spiked or patient samples] were prepared by applying blood (30 µL) to Guthrie cards. Discs (6 mm diameter) were punched from the cards and extracted using water containing the internal standard, tinidazole. The extracted sample was chromatographed without further treatment using a reversed phase system involving a Symmetry® C18 (5 µm, 3.9?×?150 mm) preceded by a Symmetry® guard column of matching chemistry and a detection wavelength of 317 nm. The mobile phase comprised acetonitrile/0.01?M phosphate solution (KH2PO4), pH 4.7, 15:85, v/v, with a flow rate of 1 mL/min. The calibration was linear over the range 2.5–50 mg/mL. The limits of detection and quantification were 0.6 and 1.8 µg/mL, respectively. The method has been applied to the determination of 203 DBS samples from neonatal patients for a phamacokinetic/pharmacodynamic study. 相似文献
98.
Jeff Knisley 《Integral Equations and Operator Theory》1990,13(4):576-592
The analytic model of a class of semi-hyponormal operators is derived using three kernal functions. In addition, explicit forms of the kernal functions are given and the Pincus principal functions of the operators are calculated. 相似文献
99.
100.
Chen M Dong C Penfold J Thomas RK Smyth TJ Perfumo A Marchant R Banat IM Stevenson P Parry A Tucker I Campbell RA 《Langmuir : the ACS journal of surfaces and colloids》2011,27(14):8854-8866
The adsorption of the lactonic (LS) and acidic (AS) forms of sophorolipid and their mixtures with the anionic surfactant sodium dodecyl benzene sulfonate (LAS) has been measured at the air/water interface by neutron reflectivity, NR. The AS and LS sophorolipids adsorb with Langmuir-like adsorption isotherms. The more hydrophobic LS is more surface active than the AS, with a lower critical micellar concentration, CMC, and stronger surface adsorption, with an area/molecule ~70 ?(2) compared with 85 ?(2) for the AS. The acidic sophorolipid shows a maximum in its adsorption at the CMC which appears to be associated with a mixture of different isomeric forms. The binary LS/AS and LS/LAS mixtures show a strong surface partitioning in favor of the more surface active and hydrophobic LS component but are nevertheless consistent with ideal mixing at the interface. In contrast, the surface composition of the AS/LAS mixture is much closer to the solution composition, but the surface mixing is nonideal and can be accounted for by regular solution theory, RST. In the AS/LS/LAS ternary mixtures, the surface adsorption is dominated by the sophorolipid, and especially the LS component, in a way that is not consistent with the observations for the binary mixtures. The extreme partitioning in favor of the sophorolipid for the LAS/LS/AS (1:2) mixtures is attributed to a reduction in the packing constraints at the surface due to the AS component. Measurements of the surface structure reveal a compact monolayer for LS and a narrow solvent region for LS, LS/AS, and LS/LAS mixtures, consistent with the more hydrophobic nature of the LS component. The results highlight the importance of the relative packing constraints on the adsorption of multicomponent mixtures, and the impact of the lactonic form of the sophorolipid on the adsorption of the sophorolipid/LAS mixtures. 相似文献