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排序方式: 共有393条查询结果,搜索用时 15 毫秒
41.
Stelling A Salzer R Kirsch M Sobottka SB Geiger K Koch E Schackert G Steiner G 《Analytical and bioanalytical chemistry》2011,400(9):2745-2753
Established methods for characterization of tissue and diagnostics, for example histochemistry, magnetic resonance imaging
(MRI), X-ray tomography, or positron emission tomography (PET), are mostly not suitable for intra-operative use. However,
there is a clear need for an intra-operative diagnostics especially to identify the borderline between normal and tumor tissue.
Currently, vibrational spectroscopy techniques (both Raman and infrared) complement the standard methods for tissue diagnostics.
Vibrational spectroscopy has the potential for intra-operative use, because it can provide a biochemically based profile of
tissue in real time and without requiring additional contrast agents, which may perturb the tissue under investigation. In
addition, no electric potential needs to be applied, and the measurements are not affected by electromagnetic fields. Currently,
promising approaches include Raman fiber techniques and nonlinear Raman spectroscopy. Infrared spectroscopy is also being
used to examine freshly resected tissue ex vivo in the operating theater. The immense volume of information contained in Raman
and infrared spectra requires multivariate analysis to extract relevant information to distinguish different types of tissue.
The promise and limitations of vibrational spectroscopy methods as intra-operative tools are surveyed in this review. 相似文献
42.
Schmidt CM Weitz E Geiger FM 《Langmuir : the ACS journal of surfaces and colloids》2006,22(23):9642-9650
Preventing a build-up of indoor pollutant concentrations has emerged as a major goal in environmental chemistry. Here, we have applied chemical ionization mass spectrometry to study the interaction of acetone, a common indoor air pollutant, with Degussa P25 TiO2, an inexpensive catalyst that is widely used for the degradation of volatile organic compounds into CO2 and water. To better understand the adsorption of acetone onto Degussa P25, the necessary first step for its degradation, the experiments were carried out at room temperature in the absence of UV light. This allowed for the deconvolution of the nonreactive and reactive thermal binding processes on Degussa P25 at acetone partial pressures (10(-7)-10(-4) Torr) commonly found in indoor environments. On average, 30% of the adsorbed acetone is bound irreversibly, resulting in a surface coverage of irreversibly bound acetone of approximately 1 x 10(12) molecules/cm2 at 3-4 x 10(-5) Torr. Equilibrium and dynamic experiments yield a sticking coefficient of approximately 1 x 10(-4) that is independent of the acetone partial pressures examined here. Equilibrium binding constants and free energies of adsorption are reported. 相似文献
43.
A fast Pareto genetic algorithm approach for solving expensive multiobjective optimization problems 总被引:1,自引:0,他引:1
We present a new multiobjective evolutionary algorithm (MOEA), called fast Pareto genetic algorithm (FastPGA), for the simultaneous
optimization of multiple objectives where each solution evaluation is computationally- and/or financially-expensive. This
is often the case when there are time or resource constraints involved in finding a solution. FastPGA utilizes a new ranking
strategy that utilizes more information about Pareto dominance among solutions and niching relations. New genetic operators
are employed to enhance the proposed algorithm’s performance in terms of convergence behavior and computational effort as
rapid convergence is of utmost concern and highly desired when solving expensive multiobjective optimization problems (MOPs).
Computational results for a number of test problems indicate that FastPGA is a promising approach. FastPGA yields similar
performance to that of the improved nondominated sorting genetic algorithm (NSGA-II), a widely-accepted benchmark in the MOEA
research community. However, FastPGA outperforms NSGA-II when only a small number of solution evaluations are permitted, as
would be the case when solving expensive MOPs. 相似文献
44.
45.
Hermann Ehrlich Thomas Hanke René Born Christiane Fischer Andrej Frolov Tobias Langrock Ralf Hoffmann Uwe Schwarzenbolz Thomas Henle Paul Simon Dorin Geiger Vasily V. Bazhenov Hartmut Worch 《Journal of membrane science》2009
In the present work, we show for the first time, that N?-carboxymethyllysine is the major product of the in vitro non-enzymatic glycation reaction between fibrillar collagen and glucuronic acid. Dual diffusion membrane system was effectively used for oriented crystal growth of octacalcium phosphate/hydroxyapatite on the biomimetically carboxymethylated collagen fibrils. We hypothesize that the function of biomimetically carboxymethylated collagen is to increase the local concentration of corresponding ions in such a way that a critical nucleus of ions can be formed, leading to the formation of the mineral under specific micro-environment conditions achieved by using diffusion membrane system. 相似文献
46.
When regions of three-phase flow arise in an oil reservoir, each of the flow parameters, i.e. capillary pressures and relative
permeabilities, are generally functions of two phase saturations and depend on the wettability state. The idea of this work
is to generate consistent pore-scale based three-phase capillary pressures and relative permeabilities. These are then used
as input to a 1-D continuum core- or reservoir-scale simulator. The pore-scale model comprises a bundle of cylindrical capillary
tubes, which has a distribution of radii and a prescribed wettability state. Contrary to a full pore-network model, the bundle
model allows us to obtain the flow functions for the saturations produced at the continuum-scale iteratively. Hence, the complex
dependencies of relative permeability and capillary pressure on saturation are directly taken care of. Simulations of gas
injection are performed for different initial water and oil saturations, with and without capillary pressures, to demonstrate
how the wettability state, incorporated in the pore-scale based flow functions, affects the continuum-scale displacement patterns
and saturation profiles. In general, wettability has a major impact on the displacements, even when capillary pressure is
suppressed. Moreover, displacement paths produced at the pore-scale and at the continuum-scale models are similar, but they
never completely coincide. 相似文献
47.
F. L. Dickert Ulrich Geiger Karin Weber 《Analytical and bioanalytical chemistry》1999,364(1-2):128-132
Advances in robustness, selectivity and sensitivity in organic solvent vapour detection can be achieved by the application of β-cyclodextrines as coatings for mass sensitive chemical sensors. Linking the cyclodextrines with e.g. diiodooctane combines the molecular recognition capabilities of host-guest chemistry with the high stability of polymeric layers. Special increase in selectivity is achieved with anhydro cyclodextrines, since their flattened conus is adapted to benzene derivatives as can also be shown by computer modelling. Furthermore methylation elongates the cavity, guaranteeing an optimised engulfing of the analytes. In this way even a differentiation between p- and m-xylene vapours and a QMB detection limit of some μL/L is possible. 相似文献
48.
Sebastian Geiger Thomas Driesner Christoph A. Heinrich Stephan K. Matthäi 《Transport in Porous Media》2006,63(3):399-434
We present a new finite element – finite volume (FEFV) method combined with a realistic equation of state for NaCl–H2O to model fluid convection driven by temperature and salinity gradients. This method can deal with the nonlinear variations
in fluid properties, separation of a saline fluid into a high-density, high-salinity brine phase and low-density, low-salinity
vapor phase well above the critical point of pure H2O, and geometrically complex geological structures. Similar to the well-known implicit pressure explicit saturation formulation,
this approach decouples the governing equations. We formulate a fluid pressure equation that is solved using an implicit finite
element method. We derive the fluid velocities from the updated pressure field and employ them in a higher-order, mass conserving
finite volume formulation to solve hyperbolic parts of the conservation laws. The parabolic parts are solved by finite element
methods. This FEFV method provides for geometric flexibility and numerical efficiency. The equation of state for NaCl–H2O is valid from 0 to 750°C, 0 to 4000 bar, and 0–100 wt.% NaCl. This allows the simulation of thermohaline convection in high-temperature
and high-pressure environments, such as continental or oceanic hydrothermal systems where phase separation is common. 相似文献
49.
K. Geiger 《Rheologica Acta》1988,27(2):209-211
Zusammenfassung Basierend auf dem das Fließverhalten strukturviskoser Fluide sehr genau beschreibenden sogenannten Carreau-Ansatz wird eine Näherungsformel für die Drehmoment-Schergeschwindigkeit-Charakteristik (scheinbare Fließkurve) des Platte-Platte-Rotationsrheometers (PPR) im stationären Versuch vorgeschlagen. Die gewonnenen Resultate können in die Auswertungseinheit des Platte-Platte-Systems leicht integriert werden und damit das Anwendungsgebiet des PPR-Systems für konzentrierte Polymerlösungen und Polymerschmelzen beträchtlich erweitern.
A new simplified, but very accurate, formula is proposed for the torque-rate characteristic (apparent flow curve) of the parallel-disk rotational rheometer (PDR) in steady-shear mode, based on the Carreau formula for the viscosity of pseudoplastic fluids. The results can easily be incorporated into the evaluation of the parallel-disk system and therefore the application field of the PDR-system can be extended considerably for concentrated polymer solutions and polymer melts.相似文献
50.
Buchbinder AM Ray NA Lu J Van Duyne RP Stair PC Weitz E Geiger FM 《Journal of the American Chemical Society》2011,133(44):17816-17823
This work characterizes the adsorption, structure, and binding mechanism of oxygenated organic species from cyclohexane solution at the liquid/solid interface of optically flat alumina-supported palladium nanoparticle surfaces prepared by atomic layer deposition (ALD). The surface-specific nonlinear optical vibrational spectroscopy, sum-frequency generation (SFG), was used as a probe for adsorption and interfacial molecular structure. 1-Hexanoic acid is an overoxidation product and possible catalyst poison for the aerobic heterogeneous oxidation of 1-hexanol at the liquid/solid interface of Pd/Al(2)O(3) catalysts. Single component and competitive adsorption experiments show that 1-hexanoic acid adsorbs to both ALD-prepared alumina surfaces and alumina surfaces with palladium nanoparticles, that were also prepared by ALD, more strongly than does 1-hexanol. Furthermore, 1-hexanoic acid adsorbs with conformational order on ALD-prepared alumina surfaces, but on surfaces with palladium particles the adsorbates exhibit relative disorder at low surface coverage and become more ordered, on average, at higher surface coverage. Although significant differences in binding constant were not observed between surfaces with and without palladium nanoparticles, the palladium particles play an apparent role in controlling adsorbate structures. The disordered adsorption of 1-hexanoic acid most likely occurs on the alumina support, and probably results from modification of binding sites on the alumina, adjacent to the particles. In addition to providing insight on the possibility of catalyst poisoning by the overoxidation product and characterizing changes in its structure that result in only small adsorption energy changes, this work represents a step toward using surface science techniques that bridge the complexity gap between fundamental studies and realistic catalyst models. 相似文献