全文获取类型
收费全文 | 530篇 |
免费 | 22篇 |
国内免费 | 2篇 |
专业分类
化学 | 415篇 |
晶体学 | 2篇 |
数学 | 48篇 |
物理学 | 89篇 |
出版年
2023年 | 3篇 |
2022年 | 31篇 |
2021年 | 48篇 |
2020年 | 20篇 |
2019年 | 16篇 |
2018年 | 12篇 |
2017年 | 16篇 |
2016年 | 30篇 |
2015年 | 19篇 |
2014年 | 31篇 |
2013年 | 36篇 |
2012年 | 41篇 |
2011年 | 30篇 |
2010年 | 39篇 |
2009年 | 20篇 |
2008年 | 20篇 |
2007年 | 18篇 |
2006年 | 15篇 |
2005年 | 16篇 |
2004年 | 13篇 |
2003年 | 6篇 |
2002年 | 4篇 |
2001年 | 2篇 |
2000年 | 4篇 |
1999年 | 4篇 |
1998年 | 2篇 |
1996年 | 4篇 |
1995年 | 7篇 |
1994年 | 5篇 |
1993年 | 4篇 |
1992年 | 3篇 |
1991年 | 2篇 |
1990年 | 4篇 |
1989年 | 2篇 |
1988年 | 3篇 |
1987年 | 2篇 |
1986年 | 2篇 |
1985年 | 2篇 |
1983年 | 2篇 |
1977年 | 1篇 |
1976年 | 1篇 |
1972年 | 1篇 |
1964年 | 1篇 |
1963年 | 1篇 |
1961年 | 1篇 |
1959年 | 1篇 |
1934年 | 1篇 |
1923年 | 1篇 |
1916年 | 1篇 |
1907年 | 2篇 |
排序方式: 共有554条查询结果,搜索用时 218 毫秒
21.
22.
We study various variations on selective separability in non-regular topological spaces. We use the notions of θ-closure and θ-density to define selective versions of θ-separability. These properties are also related to topological games. 相似文献
23.
Karolina Wieszczycka Agata Gorzelańczyk Joanna Zembrzuska 《Research on Chemical Intermediates》2013,39(3):853-868
Photodegradation of the oximes of alkyl-2-, -3-, and -4-pyridylketones and identification of possible degradation products using LC–MS/MS and GC–MS techniques were performed. The influence of copper(II) and iron(III) ions on the stability of the oxime under UV–Vis radiation exposure were also studied. It was found that the photodegradation of the pyridylketoximes resulted in the photoisomerization, photofragmentation and photosubstitution to a pyridine ring. Based on these results, a hypothetical mechanism of photodegradation of pyridylketoximes was proposed. 相似文献
24.
Przemysław Koźmiński Ewa Gniazdowska Leon Fuks Agata Oszczak 《Journal of Radioanalytical and Nuclear Chemistry》2012,292(1):67-74
Easy and efficient way to modify of the C-terminus of the peptide using amino acid lysine has been proposed and experimentally
verified. The synthesis yield was high (≥85%) and it was found that reactions can be carried out even with microgram amounts
of the peptide. Using Fmoc-alanine (as the peptide model) with modified C-terminus the procedure of peptide labelling with
monovalent and trivalent 99mTc complexes has been elaborated. 相似文献
25.
Agata Górniak Bożena Karolewicz Ewa Żurawska-Płaksej Janusz Pluta 《Journal of Thermal Analysis and Calorimetry》2013,111(3):2125-2132
The objective of the present investigation was to study the effect of eutectic formation on in vitro dissolution of simvastatin (SIM) released from mixtures with acetylsalicylic acid (ASA) prepared by a grinding method. SIM–ASA mixtures were characterized by means of differential scanning calorimetry (DSC), infrared spectroscopy (IR), X-ray powder diffractometry (XRPD), and in vitro dissolution tests. IR spectroscopy and XRPD studies indicated no interaction between SIM and ASA in the solid state. The DSC investigation has revealed that SIM and ASA form a simple eutectic system containing 66.6 % w/w of SIM at the eutectic point. In vitro dissolution studies of SIM and its mixtures with ASA were carried out. The eutectic mixture shows an appreciable increase in the dissolution rate in comparison with other ratios and SIM in 0.5 % w/v sodium lauryl sulfate. The dissolution enhancement of SIM was related to the effective wetting of the drug particles with a significantly reduced size released from eutectic composition. In conclusion, dissolution of SIM can be enhanced through eutectic formation with ASA by means of simple mechanical activation (a grinding method). 相似文献
26.
New synthesized 1,4‐disubstituted thiosemicarbazide derivatives were analyzed in the RP system, modified with the addition of salts; chaotropic (sodium hexafluorophosphate – Na PF6), cosmotropic (sodium phosphate – NaH2PO4), and neutral (NaCl) on Zorbax XDB C18 column. The effect of the eluent composition on the analytes retention (k), system efficiency (N), peak symmetry (As), and LOD values were all examined and compared to unmodified organic‐aqueous mobile phase system. It was established that eluent modified with chaotropic salts addition was also the most advantageous according to other peak parameters such as the theoretical plates numbers and asymmetry factors. The lower LOD values were achieved in comparison to unmodified organic‐aqueous eluent system. Compatibility of lipophilicity parameters calculated by the use of computer software with experimental ones measured by RP‐HPLC was also the best for chaotropic modified mobile phase. To explain the observed phenomena, molecular modeling was performed for chosen representative compound in different environment representing examined mobile phase composition. 相似文献
27.
Magdalena Połosak Agata Piotrowska Seweryn Krajewski Aleksander Bilewicz 《Journal of Radioanalytical and Nuclear Chemistry》2013,295(3):1867-1872
The aim of this study was to evaluate acyclic ligands which can be applied for labeling proteins such as monoclonal antibodies and their fragments with scandium radionuclides. Recently, scandium isotopes (47Sc, 44Sc) are more available and their properties are convenient for radiotherapy or PET imaging. They can be used together as “matched pair” in theranostic approach. Because proteins denaturize at temperature above 42 °C, ligands which efficiently form complexes at room temperature, are necessary for labelling such biomolecules. For complexation of scandium radionuclides open chain ligands DTPA, HBED, BAPTA, EGTA, TTHA and deferoxamine have been chosen. We found that the ligands studied (except HBED) form strong complexes within 10 min and that the radiolabelling yield varies between 96 and 99 %. The complexes were stable in isotonic NaCl, but stability of 46Sc-TTHA, 46Sc-BAPTA and 46Sc-HBED in PBS buffer was low, due to formation by Sc3+stronger complexes with phosphates than with the studied ligands. From the radiolabelling studies with n.c.a. 47Sc we can conclude that the most stable complexes are formed by the 8-dentate DTPA and EGTA ligands. 相似文献
28.
Abstract This paper presents a new analysis of all (old and new) quasi-elastic neutron scattering results obtained for seven members of the PAA series (n = 1,…, 7). The analysis is based upon a discussion of the parameter p, which is the deviation of the intensity of the elastic component from the intensity demanded by a reorientational model. If the value of this parameter is negative, it may be interpreted as an indication of an additional motion which has not been taken into account in the model. The first model analysed in this way for all seven substances in the nematic phase was that of the rotational diffusion of the whole molecule in its stretched (trans) conformation, around the long axis. A very large negative values of p (p ? -60 per cent) was obtained, clearly showing that some motions have been neglected. The second model was that of the rotational diffusion of moieties consisting of benzene rings plus alkoxy side-chains. The diffusion occurs around the benzene para-axes, and the alkoxy side-chains are assumed to be in their trans conformations. Less negative values of p (p ? -10 per cent) were obtained, indicating that other motions still exist. Since these must take place in the alkyl chains, we make a third step in the analysis, in which we retain the second model but now take substances which are alkyl-deuterated (which means masking for the neutron incoherent scattering method). Now values of p which are nearly zero are obtained which means that the motions previously ignored indeed exist in the alkyl chains. An even-odd effect observed in the dependence of p on n indicates that even molecules are more mobile than odd ones, probably due to less steric hindrance in more ordered, even substances. A critical discussion on reorientational correlation times is also presented. 相似文献
29.
In our investigation, the chemical composition and bioactive potential of leaf buds of raspberry, blackberry, and a raspberry-blackberry hybrid were determined. Antioxidant and antimicrobial properties were tested in water (W), ethanol-water (EW), and glycerol-water (GW) extracts from the buds. These plant organs contain relatively large amounts of minerals, especially Fe. The total antioxidant capacity (TAC) measured by the ABTS and DPPH methods ranged from 2.86 to 12.19 and 6.75 to 24.26 mmol per 100 g fresh weight (FW) of buds, respectively. TAC values were generally higher in the raspberry than in the case of blackberry and raspberry-blackberry hybrid extracts. The antioxidant properties of the extracts were strongly positively correlated with their content of total phenolic (TP). No such relationship was noted for ascorbic acid (AA), whose concentration in all extracts was at a similarly low level. Antioxidant properties determined in vitro were confirmed for the GW extract from raspberry leaf buds in biological test based on the growth parameters of Δsod1 Saccharomyces cerevisiae mutant cells in hypertonic medium. The extracts also exhibited strong antibacterial properties against Staphylococcus aureus and Enterococcus faecalis and weaker against Enterobacter aerogenes. The studied leaf buds could be therefore an unconventional source of minerals, natural antioxidants and antibacterial compounds with potential applications in the food, pharmaceutical, and cosmetics industries. 相似文献
30.
Ewa Ostrowska-Ligęza Ewa Jakubczyk Agata Górska Magdalena Wirkowska Joanna Bryś 《Journal of Thermal Analysis and Calorimetry》2014,118(2):911-918
The influence of adverse conditions of environment in the case of baby formulas, which are multiple mixtures, should be minimised. Water activity (a w) and moisture content, correlated through sorption isotherms, and glass transition temperature have been considered relevant parameters to describe food stability. The aim of the study was to analyse water activity and glass transition temperature as the function of water content for samples of baby formulas. Three types of baby formulas (mixture, agglomerate, coated agglomerate) were determined by sorption isotherms, DSC and MDSC. DSC curves of mixture, agglomerate and coated agglomerate did not show differences in shape and course. The glass transition temperature of powders stored at different water activities was measured and it decreased with the increase in moisture content, confirming the strong plasticising effect of water on this property. Critical water activities varied from 0.14 to 0.68 and critical moisture contents varied from 0.032 to 0.062 g g?1 powder. 相似文献