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41.
AHP中增加一组元素的严格保序性条件 总被引:7,自引:0,他引:7
给出了左主特征向量法(LEM)下增加一组元素严格保序的充要条件,通过研究在右主特征向量法(REM),左主特征向量法(LEM),几何平均特征向量法(GMEM)下增加一组元素严格保序的条件之间的关系,从而给出GMEM下增加一组元素严格保序的充分条件。 相似文献
42.
边界层流中当地感受性过程的数值研究 总被引:1,自引:1,他引:0
边界层流中当地感受性问题的研究对层流向湍流转捩过程的预测与控制起着非常关键的作用,尤其是对边界层内诱导产生三维Tollmien-Schlichting(T-S)波成因过程的探讨具有更加重要的理论意义.采用高精度、高分辨率变间距的紧致有限差分方法,直接数值模拟了在自由来流湍流与二维壁面局部粗糙相互作用下边界层内的当地感受性问题.数值计算发现,在自由来流湍流与二维壁面局部粗糙作用下,边界层内诱导形成的当地感受性过程是真实存在的;且被激发的一组三维T-S波波包沿流向发展的过程中流向涡结构将逐渐形成,其强度将越演越烈.数值结果还显示,边界层内被诱导产生当地感受性过程的波长转换机制仅使流向波数发生改变,而展向波数保持不变;以及自由来流湍流运动方向的改变将决定三维T-S波波包的传播方向,但其传播速度的大小都近似为无穷远来流速度的1/3.另外,还建立了自由来流湍流的强度和运动方向以及二维壁面局部粗糙的长度和高度与边界层内的当地感受性问题之间的关系等.这一课题的深入研究,将在进一步理解和认识层流向湍流转捩的理论机制,以及湍流的形成机理等方面均起到十分重要的作用. 相似文献
43.
Bülent Karaszen Süleyman Yldz Murat Uzunca 《Mathematical Methods in the Applied Sciences》2021,44(1):476-492
In this paper, we present two different approaches for constructing reduced‐order models (ROMs) for the two‐dimensional shallow water equation (SWE). The first one is based on the noncanonical Hamiltonian/Poisson form of the SWE. After integration in time by the fully implicit average vector field method, ROMs are constructed with proper orthogonal decomposition(POD)/discrete empirical interpolation method that preserves the Hamiltonian structure. In the second approach, the SWE as a partial differential equation with quadratic nonlinearity is integrated in time by the linearly implicit Kahan's method, and ROMs are constructed with the tensorial POD that preserves the linear‐quadratic structure of the SWE. We show that in both approaches, the invariants of the SWE such as the energy, enstrophy, mass and circulation are preserved over a long period of time, leading to stable solutions. We conclude by demonstrating the accuracy and the computational efficiency of the reduced solutions by a numerical test problem. 相似文献
44.
Patrícia S.M. Santos 《Talanta》2010,82(4):1616-1621
Very different filtration and preservation procedures may be found in the literature on the study of the rainwater dissolved organic fraction. Thus, the influence of sample filtration and preservation procedures on the fluorescence of rainwater dissolved organic matter (DOM) was studied in this work. Rainwater was filtered through different filters (quartz 0.22 μm or PVDF 0.45 μm) and excitation (λem = 415 nm) and synchronous (Δλ = 70 nm) fluorescence spectra were obtained at the same day of collection, or after preservation by refrigeration (1-7 days) or by freezing (1-4 weeks). The excitation-emission matrix (EEM) spectra of rainwater showed six types of fluorescent bands: two corresponding to humic-like bands, and four resembling proteins. Then, the excitation and synchronous spectra were chosen in order to monitor changes in the humic-like and protein-like bands, respectively. The filtration procedures adopted in this work did not affect the fluorescence properties of the rainwater samples. However, these properties were differently preserved by refrigeration or freezing: after refrigeration, filtered rainwater maintained the original fluorescent properties for at least 4 days, while after freezing fluorescent properties were not always preserved since it occurred a decrease of protein-like fluorescence intensity. 相似文献
45.
Mikhail K. Kolev Miglena N. Koleva Lubin G. Vulkov 《Numerical Methods for Partial Differential Equations》2013,29(4):1121-1148
Two numerical methods for a one‐dimensional haptotaxis model, which exploit the use of van Leer flux limiter, are developed and analyzed. Sufficient conditions time step size and flux limiting are given for such formulation to ensure the non‐negativity of the discrete solution and second‐order accuracy in space. Another advantage is that we avoid solving large nonlinear systems of algebraic equations. The discrete preservation of total conservation of cell density, concentration, and logarithmic density is also verified for the numerical solution. Numerical results concerning accuracy, convergence rate, positivity, and conservation properties are presented and discussed. Similar approach could be applied efficiently in the corresponding two‐ and three‐dimensional problems. © 2012 Wiley Periodicals, Inc. Numer Methods Partial Differential Eq 2013 相似文献
46.
47.
Olga
wider Micha Wjcicki Marzena Bujak Edyta Juszczuk-Kubiak Magdalena Szczepaska Marek . Roszko 《Molecules (Basel, Switzerland)》2021,26(19)
Salt concentrations in brine and temperature are the major environmental factors that affect activity of microorganisms and, thus may affect formation of biogenic amines (BAs) during the fermentation process. A model system to ferment cucumbers with low salt (0.5%, 1.5% or 5.0% NaCl) at two temperatures (11 or 23 °C) was used to study the ability of indigenous microbiota to produce biogenic amines and metabolize amino acid precursors. Colony counts for presumptive Enterococcus and Enterobacteriaceae increased by 4 and up to 2 log of CFU∙mL−1, respectively, and remained viable for more than 10 days. 16S rRNA sequencing showed that Lactobacillus and Enterobacter were dominant in fermented cucumbers with 0.5% and 1.5% salt concentrations after storage. The initial content of BAs in raw material of 25.44 ± 4.03 mg∙kg−1 fluctuated throughout experiment, but after 6 months there were no significant differences between tested variants. The most abundant BA was putrescine, that reached a maximum concentration of 158.02 ± 25.11 mg∙kg−1. The Biogenic Amines Index (BAI) calculated for all samples was significantly below that needed to induce undesirable effects upon consumption. The highest value was calculated for the 23 °C/5.0% NaCl brine variant after 192 h of fermentation (223.93 ± 54.40). Results presented in this work indicate that possibilities to control spontaneous fermentation by changing salt concentration and temperature to inhibit the formation of BAs are very limited. 相似文献
48.
Meagan McCloskey David J. Yurkowski Christina A. D. Semeniuk 《Isotopes in environmental and health studies》2018,54(2):196-208
Stable isotope ecology typically involves sacrificing the animal to obtain tissues. However, with threatened species or in long-term longitudinal studies, non-lethal sampling techniques should be used. The objectives of this study were to (1) determine if caudal fin tissue could be used as a non-lethal proxy to liver and muscle for stable isotope analysis, and (2) assess the effects of ethanol preservation on δ15N and δ13C in fin tissue of juvenile yellow perch Perca flavescens. The δ13C of caudal fin was not significantly different from liver (t23?=??0.58; p?=?0.57), and was more correlated with δ15N in liver (r2?=?0.78) than muscle (r2?=?0.56). Ethanol preservation enriched 15N and 13C for caudal fins, but by using our developed regression models, these changes in δ15N and δ13C can now be corrected. Overall, caudal fin tissue is a more reliable proxy to liver than muscle for δ15N and δ13C in yellow perch. 相似文献
49.
Prof. Piero Baglioni Dr. David Chelazzi 《Chemistry (Weinheim an der Bergstrasse, Germany)》2021,27(42):10798-10806
Colloid science is contributing solutions to counteract the degradation of artifacts, favoring their transfer to future generations. Advanced materials such as nanoparticles, coatings, gels and microemulsions have been assessed in conservation, spanning from archeological sites to modern and contemporary art. We give an overview of the fundamental milestones and latest innovations in conservation science, targeting solutions and tools for remedial conservation based on green nanomaterials and hybrid systems. Future perspectives and outstanding challenges in this exciting field are then outlined. 相似文献
50.
The QuEChERS method was applied to the determination of pesticide residues in vine (Vitis vinifera) leaves by LC-MSMS. The method was validated in-house for 33 pesticides representing 17 different chemical groups, that are most commonly used in grape production. Recoveries for the pesticides tested ranged from 75 to 104%, and repeatability and reproducibility relative standard deviations (RSDr% and RSDRw%) were less than 20%. The method was applied to the analysis of pesticide residues in 17 market brands of vine leaves processed according to three different preservation methods and sampled from the Lebanese market. Dried vine leaves were more contaminated with pesticide residues than those preserved in brine or stuffed vine leaves. The systemic fungicides were the most frequently detected among all the phytosanitary compounds usually applied to grape production. Brine-preserved and stuffed vine leaves contained lower concentrations of the residues but still contained a cocktail of different pesticides. 相似文献