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81.
Fatkhulla K. Tadjimukhamedov John A. Stone Dimitris Papanastasiou Jaime E. Rodriguez Wolfgang Mueller Harikrishnan Sukumar Gary A. Eiceman 《International Journal for Ion Mobility Spectrometry》2008,11(1-4):51-60
Chlorophenols (CPs) as a mixture of fourteen congeners from mono- to pentachlorophenol were determined using liquid chromatography/electrospray ionization/ion mobility spectrometry (LC/ESI/IMS) to describe the response and analytical performance of a mobility spectrometer as a detector for liquid chromatography. The mobility spectrometer was equipped with an interface so that flows from a large bore column could be electrosprayed directly into the drift tube at flow rates up to 500 μL/min without splitting of flow. A linear gradient of the mobile phase from 40% to 90% methanol and 60% to 10% acetic acid (AcOH)–ammonium acetate buffer solution over 40 min with a C18 column provided baseline separations though mobility spectra for CPs were influenced by mobile phase composition. Product ions formed from CPs with ESI included phenoxide anions CPO?, AcOH·CPO?, CPOH·CPO?, and Na+·(CPO?)2 and were found to be governed by the drift gas temperature. Ions were identified using LC/ESI/mass spectrometry (MS) and supported by results from computational modeling. Quantitative response was affected by congener structure through the acidities of the OH moiety and by the composition of the mobile phase. Limits of detection ranged from 0.135 mg/L for 2,3,5-trichlorophenol and pentachlorophenol to 2.23 mg/L for 2-chlorophenol; corresponding linear ranges were 20 and 70. 相似文献
82.
Let \(\mathcal{S}\) be a finite additively written commutative semigroup, and let \(\exp(\mathcal{S})\) be its exponent which is defined as the least common multiple of all periods of the elements in \(\mathcal{S}\) . For every sequence T of elements in \(\mathcal{S}\) (repetition allowed), let \(\sigma(T) \in\mathcal{S}\) denote the sum of all terms of T. Define the Davenport constant \(\mathsf{D}(\mathcal{S})\) of \(\mathcal{S}\) to be the least positive integer d such that every sequence T over \(\mathcal{S}\) of length at least d contains a proper subsequence T′ with σ(T′)=σ(T), and define \(\mathsf{E}(\mathcal{S})\) to be the least positive integer ? such that every sequence T over \(\mathcal{S}\) of length at least ? contains a subsequence T′ with \(|T|-|T'|= \lceil\frac{|\mathcal{S}|}{\exp(\mathcal{S})} \rceil \exp(\mathcal{S})\) and σ(T′)=σ(T). When \(\mathcal{S}\) is a finite abelian group, it is well known that \(\lceil\frac{|\mathcal{S}|}{\exp(\mathcal{S})} \rceil\exp (\mathcal{S})=|\mathcal{S}|\) and \(\mathsf{E}(\mathcal{S})=\mathsf{D}(\mathcal{S})+|\mathcal{S}|-1\) . In this paper we investigate whether \(\mathsf{E}(\mathcal{S})\leq \mathsf{D}(\mathcal{S})+ \lceil\frac{|\mathcal{S}|}{\exp(\mathcal {S})} \rceil \exp(\mathcal{S})-1\) holds true for all finite commutative semigroups \(\mathcal{S}\) . We provide a positive answer to the question above for some classes of finite commutative semigroups, including group-free semigroups, elementary semigroups, and archimedean semigroups with certain constraints. 相似文献
83.
Adhikari D Zhao G Basuli F Tomaszewski J Huffman JC Mindiola DJ 《Inorganic chemistry》2006,45(4):1604-1610
The lithium salt (L)Li(THF) (L- = bis(3,5-di-tertbutylpyrazol-1-yl)-1-CH2NAr, Ar = 2,6-iPr2C6H3) can be readily prepared from lithium bis(3,5-di-tertbutylpyrazol-1-yl)methide and the N-methyleneaniline H2C=NAr. This N,N,N'-heteroscorpionate lithium reagent can be transmetalated with Tl(OTf), FeCl2(THF)(1.5), and CoCl2 to yield the (L)Tl, (L)FeCl, and (L)CoCl complexes, respectively. Single crystal structural data for compounds (L)Li(THF), (L)Tl, (L)FeCl, and (L)CoCl reveal in each case the hapticity of the sterically demanding, monoanionic L- ligand to be kappa3-N3. 相似文献
84.
85.
Nitin Labhsetwar R. B. Biniwale Rakesh Kumar S. Rayalu Sukumar Devotta 《Catalysis Surveys from Asia》2006,10(1):55-64
Catalytic control of auto-exhaust emissions is one of the most successful applications of heterogeneous catalysis, both in commercial and environmental point of views. Although noble metal-based catalysts have dominated this area, efforts were always put in towards development of low cost non-noble metal-based catalysts. With the recent need of closed-coupled catalytic converter, thermal stability requirements have also become more severe, leading to the search for stable catalytic materials. Mixed oxides, including those perovskite type compounds with ABO3 structure have been extensively studied, mainly for their catalytic and electrical properties. Low surface area of these catalysts has so far been the most important limitation for their catalytic applications involving high space velocities, e.g. auto-exhaust catalysis. Various synthesis routes have been earlier attempted to improve their surface area, yet this was much inferior than the noble metal catalysts, dispersed on high surface area alumina. The in situ synthesis of these oxides on alumina is often associated with the formation of undesired phases, due to the reactive nature of perovskite precursors. However, alumina washcoat, commonly used for improving the surface area of ceramic and metallic catalyst supports, can be modified for perovskite applications. In situ synthesis of stabilized perovskites on modified alumina-washcoated supports offer high surface area and excellent catalyst adhesion. Although, it is difficult to ascertain the presence of pure perovskite type materials on support, such improved synthesis has resulted in remarkable improvement in their catalytic activity for their applications in auto-exhaust catalytic converters. This review presents our work on synthesis of various improved perovskite-type mixed oxides supported on modified alumina-washcoated cordierite honeycomb, their characterization, and detailed catalytic evaluations for possible application in automobile pollution control. 相似文献
86.
A new heat-resistant polymer has been synthesized from N-(4-carboxy phenyl) trimellitimide and benzidine. The polymer was characterized by nitrogen analysis, IR spectroscopy, density, viscosity, and x-ray measurements. The polymer was found to be insoluble in all polar organic solvents and only soluble in formic acid and concentrated H2SO4. The solubility parameter value has been determined. Thermal studies show that the polymer is thermostable up to 300°C. The electrical properties have also been measured. 相似文献
87.
Structural Chemistry - The current study primarily involves the investigation of reducing properties of dithia-substituted bicyclic hydrocarbons. Adiabatic electron affinities (AEA) of the selected... 相似文献
88.
89.
N. Sukumar 《Foundations of Chemistry》2009,11(1):7-20
The concept of molecular structure is fundamental to the practice and understanding of chemistry, but the meaning of this
term has evolved and is still evolving. The Born–Oppenheimer separation of electronic and nuclear motions lies at the heart
of most modern quantum chemical models of molecular structure. While this separation introduces a great computational and
practical simplification, it is neither essential to the conceptual formulation of molecular structure nor universally valid.
Going beyond the Born–Oppenheimer approximation introduces new paradigms, bringing fresh insight into the chemistry of fluxional
molecules, proteins, superconductors and macroscopic dielectrics, thus opening up new avenues for exploration. But it requires
that our ideas of molecular structure need to evolve beyond simple ball-and-stick-type models.
相似文献
N. SukumarEmail: |
90.
An expression for the induced spin-orbit potential in a heavy-ion collision is derived by making and adiabatic approximation to the effective interaction in second-order perturbation theory. An explicit form for the induced spin-orbit interaction for the case of a projectile of arbitrary ground state spin S is given and is shown to be equivalent to the result obtained using the methods of geometrical magnetism. 相似文献