全文获取类型
收费全文 | 256篇 |
免费 | 3篇 |
国内免费 | 1篇 |
专业分类
化学 | 108篇 |
晶体学 | 65篇 |
力学 | 4篇 |
数学 | 41篇 |
物理学 | 42篇 |
出版年
2023年 | 3篇 |
2022年 | 6篇 |
2021年 | 4篇 |
2020年 | 7篇 |
2019年 | 14篇 |
2018年 | 9篇 |
2017年 | 9篇 |
2016年 | 17篇 |
2015年 | 7篇 |
2014年 | 13篇 |
2013年 | 83篇 |
2012年 | 7篇 |
2011年 | 2篇 |
2009年 | 2篇 |
2008年 | 1篇 |
2007年 | 2篇 |
2006年 | 1篇 |
2005年 | 10篇 |
2004年 | 19篇 |
2003年 | 12篇 |
2002年 | 25篇 |
2000年 | 1篇 |
1999年 | 4篇 |
1996年 | 1篇 |
1979年 | 1篇 |
排序方式: 共有260条查询结果,搜索用时 312 毫秒
1.
We studied the low speed fracture regime (10−4-10−9 m s−1) in different glassy materials (soda-lime glass, glass ceramics) with variable but controlled length scale of heterogeneity. The chosen mechanical system enabled us to work in pure mode I (tensile) and at a fixed load on double cleavage drilled compression specimen. The internal residual stresses of studied samples were carefully relaxed by appropriate thermal treatment. By means of optical and atomic force microscopy techniques fracture surfaces have been examined. We have shown for the first time that the crack front line underwent an out-of-plane oscillating behavior as a result of a reproducible sequence of instabilities. The wavelength of such a phenomenon is in the micrometer range and its amplitude in the nanometer range. These features were observed for different glassy materials providing that a typical length scale characterizing internal heterogeneities was lower than a threshold limit estimated to few nanometers. This effect is the first clear experimental evidence of crack path instabilities in the low speed regime in a uniaxial loading experiment. This phenomenon has been interpreted by referring to the stability criterion for a straight crack propagation as presented by Adda-Bedia et al. [Phys. Rev. Lett. 76 (1996) 1497]. 相似文献
2.
研究了D160大孔吸附树脂对染料木黄酮的吸附性能.结果表明,在pH4.00时,该树脂对染料木黄酮有较好的吸附性能;静态饱和吸附容量为64.5mg/g树脂;用95%乙醇溶液作解吸剂,二次累计解吸率接近100%;表现速率常数k298=1.01×10-4s-1;测得吸附热力学参数分别为:△H=32.2kJ/mol,△S=119J/(mol·K),△G288=-2.03kJ/mol,△G298=-3.22kJ/mol,△G308=4.41kJ/mol.等温吸附服从Freundlich和Langmuir等温吸附规律;研究还表明,提高振荡频率对吸附有利. 相似文献
3.
ABSTRACTA method for combining statistical-based QSAR predictions of two or more binary classification models is presented. It was assumed that all models were independent. This facilitated the combination of positive and negative predictions using a quantitative weight of evidence (qWoE) procedure based on Bayesian statistics and the additivity of the logarithms of the likelihood ratios. Previous studies combined more than one prediction but used arbitrary strengths for positive and negative predictions. In our approach, the combined models were validated by determining the sensitivity and specificity values, which are performance metrics that are a point of departure for obtaining values that measure the weight of evidence of positive and negative predictions. The developed method was experimentally applied in the prediction of Ames mutagenicity. The method achieved a similar accuracy to that of the experimental Ames test for this endpoint when the overall prediction was determined using a combination of the individual predictions of more than one model. Calculating the qWoE value would reduce the requirement for expert knowledge and decrease the subjectivity of the prediction. This method could be applied to other endpoints such as developmental toxicity and skin sensitisation with binary classification models. 相似文献
4.
Abstract A biocompatible zinc (II) complex based on a tetradentate N,N,O,O-type salen ligand was synthesized, characterized and used for the solvent-free ring-opening polymerization (ROP) of L-lactide in bulk at 180?°C to prepare high molecular weight poly(L-lactide) (Mn : 82,600?Da; Mw : 140,000?Da; PDI: 1.70). Poly(L-lactide) (PLLA) was characterized using FTIR, 1H NMR, 13C NMR, GPC, TGA, DSC, WAXD, and MALDI-ToF. Kinetic measurement was carried out and first-order behavior to monomer was observed. The k app was found as 6?±?0.001?×?10?4?s?1. The biocompatibility of the PLLA was confirmed by in vitro cytotoxicity against NIH/3T3 fibroblast cell line and can be used in biomedical applications. 相似文献
5.
Yali Wu 《Linear and Multilinear Algebra》2018,66(6):1268-1276
Cramer’s rule over residue class rings of Bézout domains is given. 相似文献
6.
Two syntheses for 4-nitrocyclohexanol and 4-nitrocyclohexanamine are presented. Both conveniently start from commercially available 4-aminocyclohexanol. 相似文献
7.
The [3 + 2] cycloaddition reaction between sodium azide and various organic nitriles proceeds smoothly in the presence of amine salts as catalyst in dimethylformamide. The corresponding 5-substituted 1-H tetrazoles were obtained under mild condition in good to excellent yields. Supplemental materials are available for this article. Go to the publisher's online edition of Synthetic Communications® to view the free supplemental file. 相似文献
8.
《Current Applied Physics》2014,14(4):563-569
We used an electromagnetic microwave cavity sensor for real time measurement of the glycemia in goat-blood for three animals. We could determine the concentration of d-glucose in blood in the range of 90–550 mg/dl at the resonance frequency near 4.76 GHz with a bandwidth of 300 MHz. The change in microwave reflection coefficient S11 (due to the variation of d-glucose concentration in blood) was about 16.33 dB, 23.92 dB, 7.66 dB and resonance frequency shift was about 21.78 MHz, 36.29 MHz, 20.77 MHz, respectively, for the three different samples. The in vitro results show the measured signal-to-noise ratio of about 32 dB, and the minimum detectable signal level of about 0.025 dB/(mg/dl). The results clearly show the sensitivity and usefulness of this microwave sensor for these types of biological investigations. This proposed system provides a unique approach for real contactless glucose monitoring and, it may serve as a bloodless glucometer for the calibration of different glucose levels. 相似文献
9.
Xin Qi Sook Kyung Kim Su Jung Han Li Xu Ah Young Jee Ha Na Kim 《Supramolecular chemistry》2013,25(6):455-464
We report a small library of fluorophore-triazine tripod fluorescent system that can accommodate a combination of three different functional groups, such as fluorophore (BODIPY), ligand (or ligands) and auxiliary group. Syntheses, photophysical properties as well as binding properties towards metal ions of these BODIPY-triazine derivatives are described. 相似文献
10.
Narinder Singh 《Supramolecular chemistry》2013,25(5):351-357
A series of new p-tert-butylcalix[4]arene-based dipodal receptors are synthesised in high yields. The calix[4]arene units of all the receptors have been found to be present in cone conformation. To optimise the good extraction ability and high transport rate, we synthesised the receptors that differ from each other in their end groups. These receptors extract Cu2+ ion selectively from the buffered aqueous medium containing a mixture of metal ions. The receptor bearing four sp3 nitrogens has by far the greater ability to extract Cu2+ than the other receptors. All these receptors were effectively used for Cu2+ ion transport from the aqueous buffered source phase to the aqueous receiving phase. 相似文献