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排序方式: 共有102条查询结果,搜索用时 15 毫秒
11.
12.
Vugts DJ Koningstein MM Schmitz RF de Kanter FJ Groen MB Orru RV 《Chemistry (Weinheim an der Bergstrasse, Germany)》2006,12(27):7178-7189
A broad range of differently substituted dihydropyrimidines and thiazines can be efficiently prepared by using a four-component reaction between phosphonates, nitriles, aldehydes, and iso(thio)cyanates. The scope and limitations of this multicomponent reaction are fully described. Variation of all four components has been investigated. The nitrile and aldehyde inputs can be varied extensively, but variation of the phosphonate input remains limited. An interesting rearrangement leading to phosphoramidates has been observed. Furthermore, the multicomponent reaction seems to be restricted to the use of isocyanates with strongly electron-withdrawing substituents, but an interesting additional exchange reaction under microwave conditions leads to dihydropyrimidines with less electron-withdrawing substituents at N3. In addition, a diastereoselective formation of dihydropyrimidines has been observed when using a chiral aldehyde as the input. Finally, by changing the isocyanate component to an isothiocyanate, thiazines are efficiently formed instead of the corresponding thio-dihydropyrimidines. 相似文献
13.
14.
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
15.
We describe a finite element method for computation of numerical approximations of the solution of the second order singularly perturbed two-point boundary value problem on [?1, 1] On a quasi-uniform mesh we construct exponentially fitted trial spaces which consist of piece-wise polynomials and of exponentials which fit locally to the singular solution of the equation or its adjoint. We discretise the Galerkin form for the boundary problem using such exponentially fitted trial spaces. We derive rigorous bounds for the error of discretisation with respect to the energy norm and we obtain superconvergence at the mesh-points, the error depending on ?, the mesh-width and the degree of the piece-wise polynomials. 相似文献
16.
M.-Carmen Estevez Marinus A. OtteAuthor VitaeBorja SepulvedaAuthor Vitae Laura M. LechugaAuthor Vitae 《Analytica chimica acta》2014
Motivated by potential benefits such as sensor miniaturization, multiplexing opportunities and higher sensitivities, refractometric nanoplasmonic biosensing has profiled itself in a short time span as an interesting alternative to conventional Surface Plasmon Resonance (SPR) biosensors. This latter conventional sensing concept has been subjected during the last decades to strong commercialization, thereby strongly leaning on well-developed thin-film surface chemistry protocols. Not surprisingly, the examples found in literature based on this sensing concept are generally characterized by extensive analytical studies of relevant clinical and diagnostic problems. In contrast, the more novel Localized Surface Plasmon Resonance (LSPR) alternative finds itself in a much earlier, and especially, more fundamental stage of development. Driven by new fabrication methodologies to create nanostructured substrates, published work typically focuses on the novelty of the presented material, its optical properties and its use – generally limited to a proof-of-concept – as a label-free biosensing scheme. Given the different stages of development both SPR and LSPR sensors find themselves in, it becomes apparent that providing a comparative analysis of both concepts is not a trivial task. Nevertheless, in this review we make an effort to provide an overview that illustrates the progress booked in both fields during the last five years. First, we discuss the most relevant advances in SPR biosensing, including interesting analytical applications, together with different strategies that assure improvements in performance, throughput and/or integration. Subsequently, the remaining part of this work focuses on the use of nanoplasmonic sensors for real label-free biosensing applications. First, we discuss the motivation that serves as a driving force behind this research topic, together with a brief summary that comprises the main fabrication methodologies used in this field. Next, the sensing performance of LSPR sensors is examined by analyzing different parameters that can be invoked in order to quantitatively assess their overall sensing performance. Two aspects are highlighted that turn out to be especially important when trying to maximize their sensing performance, being (1) the targeted functionalization of the electromagnetic hotspots of the nanostructures, and (2) overcoming inherent negative influence that stem from the presence of a high refractive index substrate that supports the nanostructures. Next, although few in numbers, an overview is given of the most exhaustive and diagnostically relevant LSPR sensing assays that have been recently reported in literature, followed by examples that exploit inherent LSPR characteristics in order to create highly integrated and high-throughput optical biosensors. Finally, we discuss a series of considerations that, in our opinion, should be addressed in order to bring the realization of a stand-alone LSPR biosensor with competitive levels of sensitivity, robustness and integration (when compared to a conventional SPR sensor) much closer to reality. 相似文献
17.
J. J. Scholtz A. Driessen R. V.D. Berg H. V. Groen H. Verhoog J. J. De Kleuver 《高压研究》2013,33(1-6):874-876
Abstract We constructed a diamond anvil cell for pressures up to 100 GPa in magnetic fields up to 12 T. The cell can be operated at any temperature between 10 and 350 K. Loading by condensation of gases is possible. 相似文献
18.
Henk Hiemstra Wim J. Klaver Marinus J. Moolenaar W.Nico Speckamp 《Tetrahedron letters》1984,25(47):5453-5456
The combination of a silicon directed N-acyliminium ion cyclization reaction and a subsequent SN2′ substitution of an imide nitrogen with lithium dimethyl cuprate constitutes a novel approach to functionalized transfused carbobicycles. 相似文献
19.
Wang J Groen JC Yue W Zhou W Coppens MO 《Chemical communications (Cambridge, England)》2007,(44):4653-4655
Hierarchically structured composites (TUD-C) with ZSM-5 crystals embedded in a well-connected mesoporous matrix were synthesized by using only one organic templating/scaffolding molecule (TPAOH). 相似文献
20.
Considerations for applying LDA to bubbly flows with bubbles about 3 to 4 mm in diameter were investigated by means of detailed experiments in the model
geometry of a train of bubbles. Both forward scatter and backscatter LDA were studied. The validity of phase discrimination via burst amplitude was tested and special attention was paid to the impact
of bubble interface response to the laser beams.
Forward and backscatter measurements can be compared well. In both configurations, predominantly the liquid phase is “seen”
by LDA. A bubble itself only leads to a velocity realization in special conditions. In those cases the Doppler shift is determined
by the motion of the bubble interface which consists of the motion of the center of gravity of the bubble as well as shape
oscillations. In backscatter bubbles only give velocity realizations when their “cheeks” pass through the measuring volume
virtually perpendicularly.
It is shown that the bubble-caused velocity realization frequency is very low for bubbles of the size used. Phase discrimination
on burst amplitude does not hold. In ambient cases such as bubble columns one can assume that only the liquid phase is being
studied.
Received: 4 May 1998/Accepted: 30 September 1998 相似文献