全文获取类型
收费全文 | 242篇 |
免费 | 30篇 |
国内免费 | 105篇 |
专业分类
化学 | 306篇 |
晶体学 | 9篇 |
力学 | 13篇 |
数学 | 6篇 |
物理学 | 43篇 |
出版年
2024年 | 2篇 |
2023年 | 7篇 |
2022年 | 18篇 |
2021年 | 30篇 |
2020年 | 24篇 |
2019年 | 28篇 |
2018年 | 13篇 |
2017年 | 25篇 |
2016年 | 15篇 |
2015年 | 22篇 |
2014年 | 17篇 |
2013年 | 30篇 |
2012年 | 24篇 |
2011年 | 21篇 |
2010年 | 23篇 |
2009年 | 17篇 |
2008年 | 17篇 |
2007年 | 7篇 |
2006年 | 12篇 |
2005年 | 4篇 |
2004年 | 11篇 |
2003年 | 2篇 |
2002年 | 3篇 |
1999年 | 2篇 |
1998年 | 1篇 |
1997年 | 1篇 |
1991年 | 1篇 |
排序方式: 共有377条查询结果,搜索用时 62 毫秒
1.
Qingbiao Yang Zhenyu Li Youliang Hong Yiyang Zhao Shilun Qiu Ce Wang Yen Wei 《Journal of Polymer Science.Polymer Physics》2004,42(20):3721-3726
Although there have been many reports on the preparation and applications of various polymer nanofibers with the electrospinning technique, the understanding of synthetic parameters in electrospinning remains limited. In this article, we investigate experimentally the influence of solvents on the morphology of the poly(vinyl pyrrolidone) (PVP) micro/nanofibers prepared by electrospinning PVP solution in different solvents, including ethanol, dichloromethane (MC) and N,N‐dimethylformamide (DMF). Using 4 wt % PVP solutions, the PVP fibers prepared from MC and DMF solvents had a shape like a bead‐on‐a‐string. In contrast, smooth PVP nanofibers were obtained with ethanol as a solvent although the size distribution of the fibers was somewhat broadened. In an effort to prepare PVP nanofibers with small diameters and narrow size distributions, we developed a strategy of using mixed solvents. The experimental results showed that when the ratio of DMF to ethanol was 50:50 (w/w), regular cylindrical PVP nanofibers with a diameter of 20 nm were successfully prepared. The formation of these thinnest nanofibers could be attributed to the combined effects of ethanol and DMF solvents that optimize the solution viscosity and charge density of the polymer jet. In addition, an interesting helical‐shaped fiber was obtained from 20 wt % PVP solution in a 50:50 (w/w) mixed ethanol/DMF solvent. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 3721–3726, 2004 相似文献
2.
John B. Little 《Geometriae Dedicata》2004,104(1):233-234
We correct an error in Example (3.4) in Geom. Dedicata
31 (1989), 19–35. 相似文献
3.
4.
Published data on silicon carbide nanotubes (SiC-NT) are analyzed. According to theoretical calculations, single-layer SiC-NTs
do not dissociate, but they have not yet been detected experimentally. According to the experimental data, metastable SiC-NTs
with walls consisting of several layers and nanotube fibers were produced. The optimized structure of single-layer SiC-NTs
was calculated by the RHF/6-31G quantum-chemical method. The possibility of obtaining SiC-NTs by gas-phase chemical deposition
from methyltrichlorosilane in the temperature range of 800–1000 °C was investigated. Nanofibers and polygrained SiC nanotubes
were obtained, but ordinary layer SiC nanotubes were not detected. To remove the inconsistencies it was first proposed to
classify the nanotubes according to the structure of their walls, separating all the SiC-NTs into three types: 1) ordinary
layer nanotubes with rolled layers, similar to carbon nanotubes; 2) polynanocrystalline nanotubular fibers or nanotubes with
walls consisting of linked differently oriented nanograins; 3) monocrystalline synthetic nanotubes with ideal crystalline
walls. It was concluded that the ordinary SiC-NTs of the first type are unstable with the exception of one-or two-layer nanotubes;
stable SiC-NTs of the first type and SiC-NTs of the third type have not yet been discovered; only nanotubular fibers of the
second type were obtained experimentally.
__________
Translated from Teoreticheskaya i éksperimental’naya Khimiya, Vol. 42, No. 1, pp. 3–13, January–February, 2006. 相似文献
5.
A food web model with a closed nutrient cycle is presented and analyzed via Monte Carlo simulations. The model consists of three trophic levels, each of which is populated by animals of one distinct species. While the species at the intermediate level feeds on the basal species, and is eaten by the predators living at the highest level, the basal species itself uses the detritus of animals from higher levels as the food resource. The individual organisms remain localized, but the species can invade new lattice areas via proliferation. The impact of different proliferation strategies on the viability of the system is investigated. From the phase diagrams generated in the simulations it follows that in general a strategy with the intermediate level species searching for food is the best for the survival of the system. The results indicate that both the intermediate and top level species play a critical role in maintaining the structure of the system. 相似文献
6.
Size‐dependent mechanical properties of glassy polymer nanofibers via molecular dynamics simulations
下载免费PDF全文
![点击此处可从《Journal of Polymer Science.Polymer Physics》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Shengwei Deng Arkadii Arinstein Eyal Zussman 《Journal of Polymer Science.Polymer Physics》2017,55(6):506-514
The microstructure of polymer matrix under cylindrical confinement is key to understanding the size‐dependent thermomechanical behavior of electrospun nanofibers. Coarse‐grained molecular dynamics simulation was applied here to probe polymer systems under cylindrical confinement, prepared with or without pre‐stretching. Simulation results showed that below a certain radius, a noticeable increase of the elastic modulus is observed with the decrease of the radius of cylindrical confinement. This size‐dependent mechanical behavior correlated to the degree of polymer chain orientation. Modulation of density and bond orientation in the radial direction was observed: the density and bond orientation began to oscillate, increasing the oscillation amplitudes with decreases in the radius. Such behavior suggests that the cylindrical confinement enhances the bond alignment of the entire fiber and not in the near‐surface layers only. The unstretched fibers had uniform density distribution along the fiber axis, while the stretched fibers demonstrated a fluctuation in density distribution. The crossover radius of size‐dependent behavior was two orders of magnitude smaller than observed in real experiments, demonstrating that the confinement affects some internal fiber scale, which exceeds the scale of individual macromolecules, and this internal scale may be related to supramolecular structures of the polymer matrix rather than the individual macromolecules. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2017 , 55, 506–514 相似文献
7.
Bentolhoda Hadavi Moghadam Akbar Khodaparast Haghi Shohreh Kasaei 《Journal of Macromolecular Science: Physics》2015,54(11):1404-1425
Comparative studies between response surface methodology (RSM) and artificial neural network (ANN) methods to find the effects of electrospinning parameters on the porosity of nanofiber mats is described. The four important electrospinning parameters studied included solution concentration (wt.%), applied voltage (kV), spinning distance (cm) and volume flow rate (mL/h). It was found that the applied voltage and solution concentration are the two critical parameters affecting the porosity of the nanofiber mats. The two approaches were compared for their modeling and optimization capabilities with the modeling capability of RSM showing superiority over ANN, having comparatively lower values of errors. The mean relative error for the RSM and ANN models were 1.97% and 2.62% and the root mean square errors (RMSE) were 1.50 and 1.95, respectively. The superiority of the RSM-based approach is due to its high prediction accuracy and the ability to compute the combined effects of the electrospinning factors on the porosity of the nanofiber mats. 相似文献
8.
Anahita Fathi Azarbayjani Naimeh Talebi Kambiz Diba 《International Journal of Polymer Analysis and Characterization》2019,24(3):227-235
Hydroquinone (HQ) loaded polymer solution was electrospun for its topical application. Nanofibers were then investigated in terms of stability, drug release, and antifungal activity. The effect of chitosan (CS) was investigated on the viscosity, stability, drug release, and antifungal activity of the developed formulation. Results indicate a significantly stable HQ-loaded nanofiber formulation. The addition of CS caused hydration of the drug delivery system and enhanced drug release but reduced its stability. HQ-loaded nanofiber mat showed significant antifungal activity, however, there was no inhibition zone in samples containing CS. 相似文献
9.
The contribution of electrospun nanofibrous membranes (e.NFMs) in the biosensing platforms opens up a new prospect for the invention of faster and more sensitive analytical devices. In this paper, we utilized e.NFM of polyethersulfone (PES) as a solid substrate for the protein immobilization through two different approaches: physical and covalent. Scanning electron microscopy (SEM) and Fourier‐transform‐infrared (FTIR) tests were performed to study the effect of plasma treatment on protein immobilization efficacy. Moreover, taking advantage of ELISA technique, the influence of different parameters, namely, nanofibers diameter, membrane thickness, plasma treatment time, an incubation time of ethyl‐3‐(3‐dimethylaminopropyl)‐carbodiimide/N‐hydroxysuccinimide (EDC/NHS), and their ratio on antibody immobilization efficacy through two mentioned approaches, was also assessed. 相似文献
10.
This study dedicates to foaming of biocompatible blends of polylactic acid and thermoplastic polyurethane reinforced with bio-degradable cellulose nanofibers. This research primarily was associated with fabrication of PLA-TPU nanocomposites using a low weight fraction of cellulose nanofibers as a biodegradable reinforcement. Microstructural and mechanical properties of fabricated nanocomposites were examined and diffractometry was utilized to verify formation of percolated nanocomposites. Microcellular foaming was then performed with CO2 as a blowing agent. Central composite design was applied in designing the experiments to evaluate the effects of main operating variables consisting of saturation pressure and time, heating time and foaming temperature. The results demonstrated that high saturation pressure and time promoted low cell diameters (below 5 μm) and high cell densities (above 109 cell/cm3) due to the grown degree of crystallinity and higher PLA-TPU miscibility. Accordingly, adding TPU and CNF to the matrix create high crystalline foamed samples decorated with low bulk density. 相似文献