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51.
52.
Lilian V. Tose Michael Murgu Boniek G. Vaz Wanderson Romão 《Journal of the American Society for Mass Spectrometry》2017,28(11):2401-2407
Atmospheric solids analysis probe mass spectrometry (ASAP-MS) is a powerful tool for analysis of solid and liquid samples. It is an excellent alternative for crude oil analysis without any sample preparation step. Here, ASAP-MS in positive ion mode, ASAP(+)-MS, has been optimized for analysis of condensed aromatics (CA) standards, crude oil, and paraffinic fraction samples using a Synapt G2-S HDMS. Initially, two methodologies were used to access the chemical composition of samples: (1) using a temperature gradient varying from 150 to 600 °C at a heating rate of 150 °C min–1, and (2) with constant temperature of 300 and 400 °C. ASAP(+)-MS ionized many compounds with a typical petroleum profile, showing a greater signals range of m/z 250–1300 and 200–1400 for crude oil and paraffin samples, respectively. Such performance, mainly related to the detection of high molecular weight compounds (>1000 Da), is superior to that of other traditional ionization sources, such as ESI, APCI, DART, and DESI. Additionally, the CA standards were identified in both forms: radicals, [M]+?, and protonated cations, [M + H]+, with minimum fragmentation. Therefore, ASAP was more efficient in accessing the chemical composition of nonpolar and polar compounds. It is promising in its application with ultrahigh resolution MS instruments, such as FT-ICR MS and Orbitrap, since molecular formulas with greater resolution and mass accuracy (<1 ppm) would be assigned. 相似文献
53.
Cepeda J Balda R Beobide G Castillo O Fernández J Luque A Pérez-Yáñez S Román P Vallejo-Sánchez D 《Inorganic chemistry》2011,50(17):8437-8451
Detailed structural, magnetic, and luminescence studies of six different crystalline phases obtained in the lanthanide/pyrimidine-4,6-dicarboxylate/oxalate system have been afforded: {[Ln(μ-pmdc)(μ-ox)(0.5)(H(2)O)(2)]·3H(2)O}(n) (1-Ln), {[Ln(μ-pmdc)(μ-ox)(0.5)(H(2)O)(3)]·2H(2)O}(n) (2-Ln), {[Ln(μ(3)-pmdc)(μ-ox)(0.5)(H(2)O)(2)]·~2.33H(2)O}(n) (3-Ln), {[Ln(2)(μ(3)-pmdc)(μ(4)-pmdc)(μ-ox)(H(2)O)(3)]·5H(2)O}(n) (4-Ln), {[Ln(μ(3)-pmdc)(μ-ox)(0.5)(H(2)O)(2)]·H(2)O}(n) (5-Ln), and [Ln(pmdc)(1.5)(H(2)O)(2.5)] (6-Ln). The slow generation of the oxalate (ox) anion, obtained from the in situ partial hydrothermal decomposition of the pyrimidine-4,6-dicarboxylate (pmdc) ligand, allows us to obtain good shaped single crystals, while direct addition of potassium oxalate provides the same compounds but as polycrystalline samples. The crystal structures of all compounds are based on the double chelation established by the pmdc and ox ligands to provide distorted 2D honeycomb layers that, in some cases, are fused together, leading to 3D systems, by replacing some of the coordinated water molecules that complete the coordination sphere of the lanthanide by uncoordinated carboxylate oxygen atoms of the pmdc. The presence of channels occupied by crystallization water molecules is also a common feature with the exception of compounds 5-Ln. It is worth noting that compounds 3-Ln present a commensurate crystal structure related to the partial occupancy of the crystallization water molecules placed within the channels. Topological analyses have been carried out, showing a previously nonregistered topology for compounds 4-Ln, named as jcr1. The crystal structures are strongly dependent on the lanthanide ion size and the temperature employed during the hydrothermal synthesis. The lanthanide contraction favors crystal structures involving sterically less hindranced coordination environments for the final members of the lanthanide series. Additionally, reinforcement of the entropic effects at high temperatures directs the crystallization process toward less hydrated crystal structures. The magnetic data of these compounds indicate that the exchange coupling between the lanthanide atoms is almost negligible, so the magnetic behavior is dominated by the spin-orbit coupling and the ligand field perturbation. The luminescence properties that exhibit the compounds containing Nd(III), Eu(III), and Tb(III) have been also characterized. 相似文献
54.
Churchard AJ Banach E Borgschulte A Caputo R Chen JC Clary D Fijalkowski KJ Geerlings H Genova RV Grochala W Jaroń T Juanes-Marcos JC Kasemo B Kroes GJ Ljubić I Naujoks N Nørskov JK Olsen RA Pendolino F Remhof A Románszki L Tekin A Vegge T Zäch M Züttel A 《Physical chemistry chemical physics : PCCP》2011,13(38):16955-16972
The widespread adoption of hydrogen as an energy carrier could bring significant benefits, but only if a number of currently intractable problems can be overcome. Not the least of these is the problem of storage, particularly when aimed at use onboard light-vehicles. The aim of this overview is to look in depth at a number of areas linked by the recently concluded HYDROGEN research network, representing an intentionally multi-faceted selection with the goal of advancing the field on a number of fronts simultaneously. For the general reader we provide a concise outline of the main approaches to storing hydrogen before moving on to detailed reviews of recent research in the solid chemical storage of hydrogen, and so provide an entry point for the interested reader on these diverse topics. The subjects covered include: the mechanisms of Ti catalysis in alanates; the kinetics of the borohydrides and the resulting limitations; novel transition metal catalysts for use with complex hydrides; less common borohydrides; protic-hydridic stores; metal ammines and novel approaches to nano-confined metal hydrides. 相似文献
55.
When thermodynamic properties of a pure substance are transformed to reduced form by using both critical- and triple-point values, the corresponding experimental data along the whole liquid-vapor coexistence curve can be correlated with a very simple analytical expression that interpolates between the behavior near the triple and the critical points. The leading terms of this expression contain only two parameters: the critical exponent and the slope at the triple point. For a given thermodynamic property, the critical exponent has a universal character but the slope at the triple point can vary significantly from one substance to another. However, for certain thermodynamic properties including the difference of coexisting densities, the enthalpy of vaporization, and the surface tension of the saturated liquid, one finds that the slope at the triple point also has a nearly universal value for a wide class of fluids. These thermodynamic properties thus show a corresponding apparently universal behavior along the whole coexistence curve. 相似文献
56.
H. Hirata H. Komatsubara W. Blumund H. S. Rawdon R. Glockerund E. Kaupp F. Foerster G. L. Clark P. K. Frölich A. H. W. Aten L. M. Boerlage V. Kohlschütter A. Good F. Jakober D. J. Brown J. Heyrovsky F. S. Aumonier H. J. S. Sand J. E. Hackford H. S. Lukens A. Schleicher L. Toussaint A. Lassieur S. Wiechowski H. Rom A. Jilek J. Lukas Erich Müller R. Belasio E. Mellana P. Drossbach H. Ginsberg R. Geith 《Analytical and bioanalytical chemistry》1928,75(6):244-255
57.
Pinchasi 《Discrete and Computational Geometry》2002,28(4):607-624
Abstract. For every finite family of (at least five) pairwise intersecting unit circles in the plane, there is an intersection point
that lies on exactly two circles. This proves a conjecture of A. Bezdek. 相似文献
58.
Antonio Salmerón-García Emilio Lopez-Lopez Eva Román José Cabeza Natalia Navas Luís Fermín Capitán-Vallvey 《Chromatographia》2008,67(9-10):767-772
A novel LC method was applied to enhance the peak resolution of two ecdysteroids: 20-hydroxyecdysone and its 3-epimer. An isocratic solvent system of methanol–water (6:4, v/v) was used on a C18 column, and 100 μL of water was injected during the development in such a manner that the eluted solvent peak appeared exactly between the two overlapping peaks. This resulted in the increased retardation of the later-eluted peak, and in a good separation of the two compounds within 4.5 min. 相似文献
59.
An interactive method is proposed for the solution of two-dimensional, laminar flow fields with identifiable regions of recirculation, such as the shear layer driven cavity flow. The method treats the flow field as composed of two regions, with an appropriate mathematical model adopted for each region. The shear layer is computed by the compressible boundary layer equations, and the slowly recirculating flow by the incompressible Navier-Stokes equations. The flow field is solved iteratively by matching the local solutions in the two regions. For this purpose a new matching method utilizing an overlap between the two computational regions is developed, and shown to be most satisfactory. Matching of u, v, as well as u/y is amply accomplished using the present approach, and the stagnation points corresponding to separation and reattachment of the dividing streamline are computed as part of the interactive solution. The interactive method is applied to the test problem of shear layer driven cavity. The computational results are used to show the validity and applicability of the present approach. 相似文献
60.