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81.
Environmental and food analysis by desorption atmospheric pressure photoionization‐mass spectrometry
Laura Luosujärvi Sanna Kanerva Ville Saarela Sami Franssila Risto Kostiainen Tapio Kotiaho Tiina J. Kauppila 《Rapid communications in mass spectrometry : RCM》2010,24(9):1343-1350
Desorption atmospheric pressure photoionization‐mass spectrometry (DAPPI‐MS) is a versatile surface analysis technique for a wide range of analytes, especially for neutral and non‐polar analytes. Here, a set of analytes typically found in environmental or food samples was analyzed by DAPPI‐MS. The set included five polyaromatic hydrocarbons (PAHs), one N‐PAH, one brominated flame retardant, and nine pesticides, which were studied with three different spray solvents: acetone and toluene in positive ion mode, and anisole in negative ion mode. The analytes showed [M + H]+, M+?, and [M–H]? ions as well as fragmentation and substitution products. Detection limits for the studied compounds ranged from 30 pg to 1 ng (from 0.14 to 5.6 pmol). To demonstrate the feasibility of the use of DAPPI‐MS two authentic samples – a circuit board and orange peel – and a spiked soil sample were analyzed. Tetrabromobisphenol A, imazalil, and PAHs were observed from the three above‐mentioned samples, respectively. The method is best suited for rapid screening analysis of environmental or food samples. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
82.
We study the driven translocation of polymers under time-dependent driving forces using N-particle Langevin dynamics simulations. We consider the force to be either sinusoidally oscillating in time or dichotomic noise with exponential correlation time, to mimic both plausible experimental setups and naturally occurring biological conditions. In addition, we consider both the case of purely repulsive polymer-pore interactions and the case with additional attractive polymer-pore interactions, typically occurring inside biological pores. We find that the nature of the interaction fundamentally affects the translocation dynamics. For the non-attractive pore, the translocation time crosses over to a fast translocation regime as the frequency of the driving force decreases. In the attractive pore case, because of a free energy well induced inside the pore, the translocation time can be a minimum at the optimal frequency of the force, the so-called resonant activation. In the latter case, we examine the effect of various physical parameters on the resonant activation, and explain our observations using simple theoretical arguments. 相似文献
83.
The quadratic assignment problem (QAP) is a challenging combinatorial problem. The problem is NP-hard and in addition, it is considered practically intractable to solve large QAP instances, to proven optimality, within reasonable time limits. In this paper we present an attractive mixed integer linear programming (MILP) formulation of the QAP. We first introduce a useful non-linear formulation of the problem and then a method of how to reformulate it to a new exact, compact discrete linear model. This reformulation is efficient for QAP instances with few unique elements in the flow or distance matrices. Finally, we present optimal results, obtained with the discrete linear reformulation, for some previously unsolved instances (with the size n = 32 and 64), from the quadratic assignment problem library, QAPLIB. 相似文献
84.
Siltanen S Lokki T Tervo S Savioja L 《The Journal of the Acoustical Society of America》2012,131(6):4606-4614
Reflections at rough surfaces change the temporal structure of the reflected signal. This paper shows how to incorporate this temporal behavior in geometric room acoustics modeling. Specifically, a beam tracer is used for calculating the image sources and reflection paths. The roughness of the surfaces is taken into account in post-processing. A single reflection is assumed to distribute the energy according to an exponential function in time based on Biot's rough surface modeling theory. Multiple reflections are modeled with convolutions of exponential functions which are approximated as gamma functions. 相似文献
85.
Suni NM Aalto H Kauppila TJ Kotiaho T Kostiainen R 《Journal of mass spectrometry : JMS》2012,47(5):611-619
In this article, the effect of spray solvent on the analysis of selected lipids including fatty acids, fat-soluble vitamins, triacylglycerols, steroids, phospholipids, and sphingolipids has been studied by two different ambient mass spectrometry (MS) methods, desorption electrospray ionization-MS (DESI-MS) and desorption atmospheric pressure photoionization-MS (DAPPI-MS). The ionization of the lipids with DESI and DAPPI was strongly dependent on the spray solvent. In most cases, the lipids were detected as protonated or deprotonated molecules; however, other ions were also formed, such as adduct ions (in DESI), [M-H](+) ions (in DESI and DAPPI), radical ions (in DAPPI), and abundant oxidation products (in DESI and DAPPI). DAPPI provided efficient desorption and ionization for neutral and less polar as well as for ionic lipids but caused extensive fragmentation for larger and more labile compounds because of a thermal desorption process. DESI was more suitable for the analysis of the large and labile lipids, but the ionization efficiency for less polar lipids was poor. Both methods were successfully applied to the direct analysis of lipids from pharmaceutical and food products. Although DESI and DAPPI provide efficient analysis of lipids, the multiple and largely unpredictable ionization reactions may set challenges for routine lipid analysis with these methods. 相似文献
86.
We analyze the coupling between surface plasmon polaritons in a metal grating and the guided modes of a dielectric waveguide. Our model structure is a gold wire grating on a slab waveguide made of silicon nitride on silica wafer. The excitation of guided-mode resonances, surface plasmon polariton modes and hybrid waveguide-plasmon modes are observed in numerical simulations. Our experiments verify the existence of the predicted modes. These hybrid modes add significant degrees of freedom in designing structures for plasmonic applications. 相似文献
87.
Turkka Salminen Mikko Hahtala Ilkka Sepp?l? Pekka Laukkanen Tapio Niemi 《Applied Physics A: Materials Science & Processing》2010,101(4):735-738
Thin films of yttria stabilized zirconia were deposited onto silicon substrates using high repetition rate picosecond pulse
lasers. The applied lasers covered the repetition rate range from 10 kHz to 4 MHz. We found that the laser pulse overlapping
which results from increased repetition rates led to considerable changes in the ablation process. Defect formation and local
heating lead to lower ablation thresholds and, with sufficiently high repetition rates, to melting of the target and even
to thermal evaporation. We found that yttria-stabilized zirconia (YSZ) films deposited with picosecond pulses at 1064 nm wavelength
below repetition rates of 2 MHz have rough, nanostructured morphology and the same atomic ratio of yttrium and zirconium as
the target. Films deposited with 2 MHz and higher repetition rates with high number of overlapping pulses are very smooth,
but are yttrium deficient, providing evidence of the importance of the thermal processes. 相似文献
88.
Lene Tapio Sreedhar Subramanian Johan Sjöblom 《Journal of Dispersion Science and Technology》2017,38(3):355-360
The main goal of this paper is to compare the ability of different organic solvents to desorb asphaltenes from stainless steel surfaces. The asphaltenes were extracted from a North Sea crude oil by precipitation. The organic solvents are characterized based on their Hansen solubility parameters (HSPs). The adsorption of asphaltenes was followed by means of a Quartz Crystal Microbalance with Dissipation (QCM-D). The asphaltene desorption efficiency of the solvents tested varied between 20% and 70%, with pyridine as the most efficient solvent. Carbon disulfide was found to be a poor desorption solvent, indicating the importance of solvent polarity. A simple model based on the HSPs seemed to give a good quantitative explanation of experimental desorption experiments. 相似文献
89.
As a part of our studies in the conversion of triterpenoids into steroids we have reported1 that the Jones oxidation of some triterpenoid hemiacetals (1) gives acyloxy acids (2) instead of the desired 1,5-diketones (3). We now report2 the shortest route yet for the reconstruction of a triterpenoid ring A ketone (4) into a steroidal enone (7) involving as key steps the exhaustive Baeyer-Villiger oxidation3 of triterpenoid ketones (4) into δ-lactones (5) and mild chromium(VI) oxidation of cyclic hemiacetals (1) into diketones (3). 相似文献
90.
Esa Toukoniitty Päivi Mäki-Arvelaa Rainer Sjöholm Reko Leino Tapio Salmi Dmitry Yu. Murzin 《Reaction Kinetics and Catalysis Letters》2002,75(1):21-30
Three different modifiers, (-)-cinchonidine, 10,11-dihydrocinchonidine and (+)-cinchonine were investigated in the enantioselective hydrogenation of an unsymmetrical dione, 1-phenyl-1,2-propanedione, over a commercial Pt/Al2O3 catalyst. The catalytic activity, as well as the regio- and enantioselectivity in the hydroxyketones and diols formed were compared. 相似文献