全文获取类型
收费全文 | 617篇 |
免费 | 23篇 |
国内免费 | 1篇 |
专业分类
化学 | 366篇 |
晶体学 | 3篇 |
力学 | 34篇 |
数学 | 136篇 |
物理学 | 102篇 |
出版年
2023年 | 7篇 |
2022年 | 11篇 |
2021年 | 35篇 |
2020年 | 14篇 |
2019年 | 19篇 |
2018年 | 29篇 |
2017年 | 25篇 |
2016年 | 27篇 |
2015年 | 19篇 |
2014年 | 33篇 |
2013年 | 63篇 |
2012年 | 45篇 |
2011年 | 56篇 |
2010年 | 28篇 |
2009年 | 31篇 |
2008年 | 43篇 |
2007年 | 25篇 |
2006年 | 25篇 |
2005年 | 15篇 |
2004年 | 21篇 |
2003年 | 11篇 |
2002年 | 6篇 |
2001年 | 9篇 |
2000年 | 10篇 |
1999年 | 6篇 |
1998年 | 6篇 |
1997年 | 5篇 |
1994年 | 1篇 |
1993年 | 3篇 |
1992年 | 1篇 |
1987年 | 2篇 |
1985年 | 1篇 |
1984年 | 1篇 |
1981年 | 2篇 |
1980年 | 1篇 |
1979年 | 2篇 |
1973年 | 1篇 |
1940年 | 2篇 |
排序方式: 共有641条查询结果,搜索用时 234 毫秒
21.
22.
In this paper, a model to estimate the weights of mutually dependent criteria, based on cause-effect assessments of a group of professionals, is developed for problem of multiple criteria decision making (MCDM). Here, both DEMATEL (Decision Making Trial and Evaluation Laboratory) and TOPSIS (Technique for Order Performance by Similarity to Ideal Solution) models are combined and extended to handle fuzzy evaluations where the first is used to set the weights of the interdependent criteria and the second for drawing a decision from a group of professionals who use linguistic ratings in their evaluation. The presented model is characterized by the capability to estimate the criteria weights when the criteria are interrelated. The strict determination of the criteria weights prior to the assessment process is eliminated as they are computed by the DEMATEL part. A classical case-study of optimal sore throat treatment in primary care unit is used to demonstrate the efficiency of the proposed model. 相似文献
23.
Raoudha Abderrahim Khaled Boujlel 《Phosphorus, sulfur, and silicon and the related elements》2013,188(5):995-999
The imidates derived from 3-aminotriazole 1 react with isocyanates and isothiocyanates to give corresponding 1,2,4-triazolo-1,3,5-triazin-4-ones and 1,2,4-triazolo-1,3,5-triazin-4-thiones in a 60–75% overall yield. If the condensation is realized at r.t., then the intermediate 2 can be isolated. 相似文献
24.
Noureddine Raouafi Khaled Boujlel Mohamed Lamine BenKhoud 《Phosphorus, sulfur, and silicon and the related elements》2013,188(7):1387-1395
The condensation of N1-benzimidazolyl amidines 1 with tris(dimethy- lamino)phosphine leads to the corresponding [1,2a]Benzimidazolo-1,3,5,2-triazaphosphorines 3 . The N2-phosphoroamidine intermediates 2′ are isolated and yielded the corresponding cyclic compounds 4 upon heating. The oxidation by sulfur of the compounds 3 gives the thiooxide derivatives 4 . The structure of these compounds is unambiguously confirmed by IR, 1H, 31P, and 13C NMR spectroscopy and by MS for some products. 相似文献
25.
26.
The present review highlights the synthetic procedures reported for the preparation of oxazolo[3,2-a]pyridines as a class of 5-6 bicyclic heterocycles with a nitrogen atom at the ring junction. The different sections included the synthesis of the investigated analogs through the reactions of (1) β-ketoesters with α,β-unsaturated ketones (2) δ-oxoacids or esters or unsaturated carboxylic acids with glycinol derivatives (3) unsaturated ketoesters with enamines (4) ethoxymethylenes with amidoglycinol derivatives (5) pyridinium salts with phenylglycinol (6) Multicomponent reactions, and (7) Synthesis of tetracyclic systems. The aim of the present study is to demonstrate a synopsis of the synthesis of compounds containing oxazolo[3,2-a]pyridine skeleton with high yields using readily and accessible starting materials, and efficient synthetic routes until now. The stereochemistry of the obtained enantiopure heterocycles, the isolation of the isomers and the reaction mechanisms of the unexpected products are discussed. 相似文献
27.
Inhibition of 304 stainless steel corrosion in acidic chloride pickling (1.0 M HCl) solutions by newly synthesized oxazocine derivative 4 as a corrosion inhibitor have been studied using weight loss, potentiodynamic polarization, and atomic absorption spectroscopy investigations. Potentiodynamic polarization curves show that the inhibitor behaves as a mixed-type. The adsorption of the inhibitor on the metal surface in the acid solution was found to obey Langmuir’s adsorption isotherm. The inhibition mechanism of the investigated inhibitor was discussed in terms of its adsorption on the metal surface. The relationship between the molecular structure and the inhibition efficiency was elucidated by quantum chemical calculations. 相似文献
28.
Journal of Radioanalytical and Nuclear Chemistry - Four different grain size fractions (0.2–0.5, 0.5–1, 1–1.8, 1.8–2 mm) of red brick and cement mortar samples at... 相似文献
29.
Khaled D. Khalil Sayed M. Riyadh Mariusz Jaremko Thoraya A. Farghaly Mohamed Hagar 《Molecules (Basel, Switzerland)》2021,26(12)
Recently, the development of nanocatalysts based on naturally occurring polysaccharides has received a lot of attention. Chitosan (CS), as a biodegradable and biocompatible polysaccharide, is considered to be an excellent template for the design of a hybrid biopolymer-based metal oxide nanocomposite. In this case, lanthanum oxide nanoparticles doped with chitosan at different weight percentages (5, 10, 15, and 20 wt% CS/La2O3) were prepared via a simple solution casting method. The prepared CS/La2O3 nanocomposite solutions were cast in a Petri dish in order to produce the developed catalyst, which was shaped as a thin film. The structural features of the hybrid nanocomposite film were studied by FTIR, SEM, and XRD analytical tools. FTIR spectra confirmed the presence of the major characteristic peaks of chitosan, which were modified by interaction with La2O3 nanoparticles. Additionally, SEM graphs showed dramatic morphological changes on the surface of chitosan, which is attributed to surface adsorption with La2O3 molecules. The prepared CS/La2O3 nanocomposite film (15% by weight) was investigated as an effective, recyclable, and heterogeneous base catalyst in the synthesis of pyridines and pyrazoles. The nanocomposite used was sufficiently stable and was collected and reused more than three times without loss of catalytic activity. 相似文献
30.
Md Shahadat Hossan Mohammed Khaled Bin Break Tracey D. Bradshaw Hilary M. Collins Christophe Wiart Teng-Jin Khoo Ahmed Alafnan 《Molecules (Basel, Switzerland)》2021,26(8)
Cardamonin is a polyphenolic natural product that has been shown to possess cytotoxic activity against a variety of cancer cell lines. We previously reported the semi-synthesis of a novel Cu (II)–cardamonin complex (19) that demonstrated potent antitumour activity. In this study, we further investigated the bioactivity of 19 against MDA-MB-468 and PANC-1 cancer cells in an attempt to discover an effective treatment for triple-negative breast cancer (TNBC) and pancreatic cancer, respectively. Results revealed that 19 abolished the formation of MDA-MB-468 and PANC-1 colonies, exerted growth-inhibitory activity, and inhibited cancer cell migration. Further mechanistic studies showed that 19 induced DNA damage resulting in gap 2 (G2)/mitosis (M) phase arrest and microtubule network disruption. Moreover, 19 generated reactive oxygen species (ROS) that may contribute to induction of apoptosis, corroborated by activation of caspase-3/7, PARP cleavage, and downregulation of Mcl-1. Complex 19 also decreased the expression levels of p-Akt and p-4EBP1, which indicates that the compound exerts its activity, at least in part, via inhibition of Akt signalling. Furthermore, 19 decreased the expression of c-Myc in PANC-1 cells only, which suggests that it may exert its bioactivity via multiple mechanisms of action. These results demonstrate the potential of 19 as a therapeutic agent for TNBC and pancreatic cancer. 相似文献