全文获取类型
收费全文 | 415篇 |
免费 | 15篇 |
专业分类
化学 | 324篇 |
晶体学 | 1篇 |
力学 | 1篇 |
数学 | 42篇 |
物理学 | 62篇 |
出版年
2023年 | 5篇 |
2022年 | 18篇 |
2021年 | 15篇 |
2020年 | 11篇 |
2019年 | 21篇 |
2018年 | 19篇 |
2017年 | 20篇 |
2016年 | 25篇 |
2015年 | 17篇 |
2014年 | 26篇 |
2013年 | 37篇 |
2012年 | 27篇 |
2011年 | 35篇 |
2010年 | 19篇 |
2009年 | 11篇 |
2008年 | 15篇 |
2007年 | 29篇 |
2006年 | 14篇 |
2005年 | 19篇 |
2004年 | 13篇 |
2003年 | 11篇 |
2002年 | 10篇 |
2001年 | 2篇 |
2000年 | 3篇 |
1998年 | 3篇 |
1997年 | 1篇 |
1991年 | 2篇 |
1983年 | 1篇 |
1979年 | 1篇 |
排序方式: 共有430条查询结果,搜索用时 15 毫秒
81.
In this comment, we show that the arguments against the applicability of stationary phase method (SPM) for tunneling time calculations, presented in Letter “Questions concerning the generalized Hartman effect” are not valid for small wave packet energy widths. 相似文献
82.
In this article,the expression for the Drazin inverse of a modified matrix is considered and some interesting results are established.This contributes to certain recent results obtained by Y.Wei [9]. 相似文献
83.
Denysenko D Werner T Grzywa M Puls A Hagen V Eickerling G Jelic J Reuter K Volkmer D 《Chemical communications (Cambridge, England)》2012,48(9):1236-1238
Postsynthetic metal ion exchange in a benzotriazolate-based MFU-4l(arge) framework leads to a Co(II)-containing framework with open metal sites showing reversible gas-phase oxidation properties. 相似文献
84.
Milo S. Jovanovi Nemanja Krgovi Katarina avikin Jelena
ivkovi 《Molecules (Basel, Switzerland)》2022,27(21)
The residue after sieving (“dust”) from the willow gentian underground parts is an unexploited herbal tea by-product, although it contains valuable bioactive compounds. Cyclodextrins as efficient green co-solvents, cage molecules, and multifunctional excipients could improve the extraction and contribute to the added value of the resulting extracts. The objective of this study was to determine the optimal conditions for the extraction of gentiopicroside, isogentisin, and total phenolics (TPC) from willow gentian “dust” using ultrasound-assisted water extraction coupled with hydroxypropyl-β-cyclodextrin (HPβCD). The influence of extraction temperature (X1: 20–80 °C), time (X2: 20–50 min), and HPβCD concentration (X3: 2–4% w/v) was analyzed employing the response surface methodology (RSM). The optimal extraction conditions for simultaneously maximizing the extraction yield of all monitored responses were X1: 74.89 °C, X2: 32.57 min, and X3: 3.01% w/v. The experimentally obtained response values under these conditions (46.96 mg/g DW for gentiopicroside, 0.51 mg/g DW for isogentisin, and 12.99 mg GAE/g DW for TPC) were in close agreement with those predicted, thus confirming the suitability and good predictive accuracy of the developed RSM models. Overall, the developed extraction system could be an applicable alternative strategy to improve the extraction of bioactive compounds from the underutilized “dust” of willow gentian underground parts. 相似文献
85.
Zorica D. Petrović Jelena Đorović Dušica Simijonović Snežana Trifunović Vladimir P. Petrović 《Chemical Papers》2018,72(9):2171-2180
N-Salicylidene and N-vanillidene anil Schiff bases SB-1–5 were evaluated for their iron-coordinating properties. For this purpose, reactions with Fe(III) chloride were performed. The obtained results showed that salicylaldehyde bases SB-1 and SB-2 are the best coordinating ligands among the investigated SBs. The corresponding complexes are obtained in good yield and investigated using UV–Vis spectrophotometry and IR spectroscopy. The inhibitory potential of SB-1–5 against iron-containing enzyme lipoxygenase (LOX) was also tested. Salicylidene bases exerted better activity then vanilliden. The cytotoxic in vitro activities against human breast carcinoma MDA-MB-231 and human colon carcinoma HCT-116 cell lines were determined. Based on these results, SB-1 and SB-2 can be considered as interesting compounds for further in vivo investigations. 相似文献
86.
Neda O. Đorđević Miroslav M. Novaković Dalibor M. Stanković Jelena J. Mutić Snežana B. Pajović 《Natural product research》2018,32(3):247-251
The overall aim of this paper was to compare the multielement composition and antioxidant capacity of two Montenegrin Merlot wines obtained from specific vine clones (VCR1 and VCR 101) along with commercial Merlot wine throughout the consecutive vintages in 2010 and 2011. Elemental composition was analysed using inductively coupled plasma optical emission spectrometry (ICP-OES) and inductively coupled plasma mass spectrometry (ICP-MS). Additionally, antioxidant capacity was assessed by cyclic voltammetry. VCR 1 wine from 2011 stood out for its elemental composition. On the other hand, antioxidant capacity of VCR 101 wines was the highest one for the both vintages. According to the experimental data obtained, all three wines are good source of essential elements and products with a significant antioxidant activity and specific geographical origin. 相似文献
87.
Violeta D. Mitic Jovana Pavlovic Jelena Nikolic Strahinja R. Simonovic Vesna P. Jovanovic Stankov 《Analytical letters》2018,51(6):908-920
Currant fruit extracts were characterized by (2,2-diphenyl-1-picrylhydrazyl) radical scavenging activity, 2,2-azinobis-3 ethyl benzothiazoline-6-sulfonic acid cation decolorization activity, total reducing power, cupric ion reducing antioxidant power, and ferric ion reducing antioxidant power (FRAP) assays to evaluate their antioxidant activity. All five antioxidant assays revealed the highest antioxidant activity to be present for the black currants. The highest concentrations of phenolics were present in the black currants (1690?±?10?mg gallic acid equivalents (GAE)/100?g fresh weight), while the lowest value was obtained in the white currants (579?±?5?mg GAE/100?g fresh weight). The correlation between the total phenolic content and antioxidant activity assays was evaluated using regression analysis. A significant positive correlation was obtained between the total phenols and the cupric ion reducing antioxidant power (r?=?0.97, p?0.05), followed by that between the total phenols and FRAP (r?=?0.93, p?0.05). Hierarchical cluster analysis separated these selected fruit species into two statistically significant clusters with black currants as a distinctive cluster. 相似文献
88.
89.
Jelena Miladinović Rozalija Ninković Milica Todorović 《Journal of solution chemistry》2007,36(11-12):1401-1419
Isopiestic vapor-pressure measurements were made at the temperature 298.15 K for aqueous KCl + MgCl2 solutions using KCl(aq) as the reference standard. The measurements for these ternary solutions were made at KCl ionic strength fractions of y=0.0, 0.1989, 0.3996, 0.5993, 0.7925 and 1.0 (with two additional sets at y=0.0, 0.2021, 0.3998, 0.6125, 0.8209 and 1.0) for the ionic strength range from 0.4014 to 6.2790 mol?kg?1. Our results, and those from two previous isopiestic studies, were combined and used with previously determined parameters for KCl(aq) and those determined here for MgCl2(aq) to evaluate mixing parameters for the Clegg-Pitzer-Brimblecombe model. These combined data were also used to determine the mixing parameters of the Scatchard model. Both sets of model parameters are valid for ionic strengths of I≤12.8 mol?kg?1, where higher-order electrostatic effects have been included in the Clegg-Pitzer-Brimblecombe mixture model. The activity coefficients for KCl and MgCl2 were calculated from these models and the results for KCl were compared to experimental data from Emf measurements. The Scatchard model interaction parameters were used for calculation of the excess Gibbs energy as a function of the ionic strength and ionic strength fraction of KCl. The Zdanovskii-Robinson-Stokes rule of linearity for mixing of isopiestic solutions was tested. 相似文献
90.
Motional heterogeneity and phase separation of functionalized polyester polyurethanes 总被引:1,自引:0,他引:1
The polyester polyurethanes, PU based on isophoronediisocyanate, polycaprolactone, and 1,4-butanediol with different amounts of functional groups introduced into the hard segments via second chain extender, 2,2′-bis-(hydroxymethyl) propionic acid, were investigated by electron spin resonance, ESR, spin label method, wide-angle X-ray diffraction, WAXD, optical microscopy and differential scanning calorimetry, DSC. The objective of this study is to clarify the effect of functional groups on the motional heterogeneity, microphase separation and crystallisation of the polyurethanes. The concentration of carboxylic groups varied from 0 to 0.45 mmol g−1. The temperature-dependent ESR spectra of spin labelled PU hard segments chain ends with stable nitroxide radical 2,2,6,6-tetramethyl-4-aminopiperidin-1-yloxyl are sensitive to the amount of functional groups attached to the hard segments. Composite ESR spectra of functionalized PU, with fast and slow component, suggest that PU hard segments are partitioned in two motionally different environments. According to the ratio of fast and slow component motional heterogeneity increases with an increase of functional groups up to 0.35 mmol g−1 and above this concentration slow component decreases indicating higher degree of phase mixing and stronger effect of soft segments. Polarized micrographs and the extent of ordering from WAXD measurements reveal the changes of phase morphology with the carboxylic groups content in a similar way as shown from the motional behaviour of spin label on the segmental level. The degree of crystallinity and the separation of spherulitic rings are decreasing above a certain concentration of functional groups. The effect of functional groups in PU on the hard and soft segment mixing is discussed in terms of additional noncovalent interactions and chain structure which at critical level of interactions lead to a formation of more open hard segment structure accessible to interaction with the soft segment. 相似文献