全文获取类型
收费全文 | 1125篇 |
免费 | 76篇 |
国内免费 | 121篇 |
专业分类
化学 | 886篇 |
晶体学 | 11篇 |
力学 | 17篇 |
综合类 | 22篇 |
数学 | 104篇 |
物理学 | 282篇 |
出版年
2024年 | 4篇 |
2023年 | 30篇 |
2022年 | 69篇 |
2021年 | 54篇 |
2020年 | 47篇 |
2019年 | 63篇 |
2018年 | 67篇 |
2017年 | 52篇 |
2016年 | 70篇 |
2015年 | 40篇 |
2014年 | 73篇 |
2013年 | 90篇 |
2012年 | 66篇 |
2011年 | 75篇 |
2010年 | 51篇 |
2009年 | 54篇 |
2008年 | 53篇 |
2007年 | 57篇 |
2006年 | 37篇 |
2005年 | 39篇 |
2004年 | 39篇 |
2003年 | 28篇 |
2002年 | 22篇 |
2001年 | 23篇 |
2000年 | 17篇 |
1999年 | 17篇 |
1998年 | 10篇 |
1997年 | 11篇 |
1996年 | 8篇 |
1995年 | 12篇 |
1994年 | 5篇 |
1993年 | 8篇 |
1992年 | 6篇 |
1991年 | 6篇 |
1990年 | 1篇 |
1989年 | 3篇 |
1987年 | 2篇 |
1986年 | 7篇 |
1985年 | 1篇 |
1984年 | 2篇 |
1983年 | 1篇 |
1981年 | 1篇 |
1979年 | 1篇 |
排序方式: 共有1322条查询结果,搜索用时 126 毫秒
61.
N-(4-(substituted)-3-(trifluoromethyl) phenyl) isobutyramides and their N-ethyl analogues (flutamides) are versatile scaffolds with a wide spectrum of biological activities. A series of new N-(4-(substituted)-3-(trifluoromethyl) phenyl) isobutyramides (8a-t) and their N-ethyl analogous (9a-t) were synthesized and characterized. The inhibitory potential of the synthesized compounds on the viability of three human cancer cell lines HEP3BPN 11 (liver), MDA-MB 453 (breast), and HL 60 (leukemia) were assessed. Among all the compounds 8 L, 8q, 9n and 9p showed higher inhibitory activity on the viability of HL 60 than the standard methotrexate. These lead molecules were then tested for their potential to inhibit the activity of proangiogenic cytokines. The compound 9n showed significantly better inhibition against two cytokines viz. TNFα and Leptin as compared to the standard suramin, while 9p has activity comparable to suramin against IGF1, VEGF, FGFb, and Leptin. The 8q is found to be strong antiangiogenic agent against IGF1, VEGF and TGFβ; while 8 L has showed activity against TNFα, VEGF, and Leptin inhibition. Furthermore antioxidant potential of 8a–t and 9a-t compounds was screened using DPPH, OH and SOR radical scavenging activities. The OH radical scavenging activity of 8c and DPPH activities of 9n as well as 9o are significant as compared to respective standards ascorbic acid and α-tocopherol. The 8c, 9p and 9 h have also exhibited potential antioxidant activity. Additionally, we present in silico molecular docking data to provide the structural rationale of observed TNFα inhibition against newly synthesized compounds. Overall, the synthesized flutamide derivatives have not only anticancer activity, but also possess dual inhibitory effect (anti-angiogenesis and antioxidant) and hence can act as a promising avenue to develop further anticancer agents. 相似文献
62.
Enas Mahmoud Amer Saber H. Saber Ahmad Abo Markeb Amal A. Elkhawaga Islam M. A. Mekhemer Abdel-Naser A. Zohri Turki S. Abujamel Steve Harakeh Elham A. Abd-Allah 《Molecules (Basel, Switzerland)》2021,26(8)
Beta glucan (β-glucan) has promising bioactive properties. Consequently, the use of β-glucan as a food additive is favored with the dual-purpose potential of increasing the fiber content of food products and enhancing their health properties. Our aim was to evaluate the biological activity of β-glucan (antimicrobial, antitoxic, immunostimulatory, and anticancer) extracted from Saccharomyces cerevisiae using a modified acid-base extraction method. The results demonstrated that a modified acid-base extraction method gives a higher biological efficacy of β-glucan than in the water extraction method. Using 0.5 mg dry weight of acid-base extracted β-glucan (AB extracted) not only succeeded in removing 100% of aflatoxins, but also had a promising antimicrobial activity against multidrug-resistant bacteria, fungi, and yeast, with minimum inhibitory concentrations (MIC) of 0.39 and 0.19 mg/mL in the case of resistant Staphylococcus aureus (MRSA) and Pseudomonas aeruginosa, respectively. In addition, AB extract exhibited a positive immunomodulatory effect, mediated through the high induction of TNFα, IL-6, IFN-γ, and IL-2. Moreover, AB extract showed a greater anticancer effect against A549, MDA-MB-232, and HepG-2 cells compared to WI-38 cells, at high concentrations. By studying the cell death mechanism using flow-cytometry, AB extract was shown to induce apoptotic cell death at higher concentrations, as in the case of MDA-MB-231 and HePG-2 cells. In conclusion, the use of a modified AB for β-glucan from Saccharomyces cerevisiae exerted a promising antimicrobial, immunomodulatory efficacy, and anti-cancer potential. Future research should focus on evaluating β-glucan in various biological systems and elucidating the underlying mechanism of action. 相似文献
63.
Flavio Sabatelli Jacopo Segato Leonardo Belpassi Alessandro Del Zotto Daniele Zuccaccia Paola Belanzoni 《Molecules (Basel, Switzerland)》2021,26(9)
The coordination ability of the [(ppy)Au(IPr)]2+ fragment [ppy = 2-phenylpyridine, IPr = 1,3-bis(2,6-di-isopropylphenyl)-imidazol-2-ylidene] towards different anionic and neutral X ligands (X = Cl−, BF4−, OTf−, H2O, 2-butyne, 3-hexyne) commonly involved in the crucial pre-equilibrium step of the alkyne hydration reaction is computationally investigated to shed light on unexpected experimental observations on its catalytic activity. Experiment reveals that BF4− and OTf− have very similar coordination ability towards [(ppy)Au(IPr)]2+ and slightly less than water, whereas the alkyne complex could not be observed in solution at least at the NMR sensitivity. Due to the steric hindrance/dispersion interaction balance between X and IPr, the [(ppy)Au(IPr)]2+ fragment is computationally found to be much less selective than a model [(ppy)Au(NHC)]2+ (NHC = 1,3-dimethylimidazol-2-ylidene) fragment towards the different ligands, in particular OTf− and BF4−, in agreement with experiment. Effect of the ancillary ligand substitution demonstrates that the coordination ability of Au(III) is quantitatively strongly affected by the nature of the ligands (even more than the net charge of the complex) and that all the investigated gold fragments coordinate to alkynes more strongly than H2O. Remarkably, a stabilization of the water-coordinating species with respect to the alkyne-coordinating one can only be achieved within a microsolvation model, which reconciles theory with experiment. All the results reported here suggest that both the Au(III) fragment coordination ability and its proper computational modelling in the experimental conditions are fundamental issues for the design of efficient catalysts. 相似文献
64.
Luana Malacaria Giuseppina Anna Corrente Amerigo Beneduci Emilia Furia Tiziana Marino Gloria Mazzone 《Molecules (Basel, Switzerland)》2021,26(9)
This review focuses on the ability of some natural antioxidant molecules (i.e., hydroxycinnamic acids, coumarin-3-carboxylic acid, quercetin, luteolin and curcumin) to form Al(III)- and Fe(III)-complexes with the aim of evaluating the coordination properties from a combined experimental and theoretical point of view. Despite the contributions of previous studies on the chemical properties and biological activity of these metal complexes involving such natural antioxidants, further detailed relationships between the structure and properties are still required. In this context, the investigation on the coordination properties of Al(III) and Fe(III) toward these natural antioxidant molecules might deserve high interest to design water soluble molecule-based metal carriers that can improve the metal’s intake and/or its removal in living organisms. 相似文献
65.
研究采用视频分析法,利用NVivo软件,以东芝杯教学技能创新大赛的化学组选手为对象,从教学理念、教学情境、实验设计和教学手段等4个维度,评价卓越职前化学教师课堂教学的创新能力。结果发现:教学理念新颖,但具体落实尚有不足;情境创设生动,但主题与学生的联系不够紧密;实验设计别致,但在水平上还有提升空间;教学技术手段先进,但还需要深度融合。研究为创新型卓越化学教师的培养提供了启示。 相似文献
66.
Thermosetting resin matrix is the key component of advanced wave-transparent composites,where low dielectric constant,excellent processability,high thermal stability,as well as good bonding ability are required for resins.Herein,we prepared a series of phenylethynyl terminated polyimide(PI)resins by grafting amine-functionalized hyperbranched polysiloxane(HBPSi)to PI chains during the in situ polymerization.The effects of HBPSi on the processability of oligomers,molecular packing,thermal stability,dielectric property and bonding ability to reinforce Kevlar fibers of the cured PI/HBPSi composite resins have been examined in detail.The dielectric constants of the cured composite resins were greatly reduced from 3.29 to 2.19 without compromising its processability and thermal stability.Meanwhile,the 10 wt%HBPSi-containing PI resin demonstrated better bonding ability to reinforce fibers with the interfacial shear strength(IFSS)of 37.64 MPa,compared with that of neat PI-6 matrix(27.34 MPa),and better adhesion to metal with the lap shear strength of 10.48 MPa,50%higher than that of neat resin PI-6(6.98 MPa).These resultant PI/HBPSi composite resins exhibit excellent comprehensive properties,indicating their great potential as low-dielectric constant resin matrix in radar radome. 相似文献
67.
基于透明质酸构筑的药物递送载体及其应用 总被引:1,自引:0,他引:1
传统纳米药物控释载体主要通过细胞胞吞作用实现药物递送,其主要过程为被动靶向机制,因此会影响纳米载体在肿瘤组织的富集和治疗效果。近年来生物大分子透明质酸因其优异的水溶性、生物相容性、可降解性和肿瘤靶向性备受科研工作者青睐,已被广泛用于药物控释载体的构筑中,并成为靶向肿瘤治疗纳米载体领域的研究热点。本文根据透明质酸基纳米载体治疗机制的不同,从透明质酸基纳米载体在化疗、光热治疗、光动力治疗以及联合治疗的应用方面对其性能进行了总结和评述,并在此基础上展望了未来透明质酸基纳米治疗载体的研究方向和发展趋势。 相似文献
68.
Li Yuan Sidi Huang Yinhui Hu Yuzheng Zhang Aijuan Gu Guozheng Liang Guoqiang Chen Yongming Gao Steven Nutt 《先进技术聚合物》2014,25(7):752-759
Self‐healing cyanate ester resins (CE) were developed by adding low molecular weight poly(phenylene oxide) (PPO) resin, yielding a high performance CE/PPO system via a low‐temperature process. The addition of PPO improved the flexural strength and fracture toughness of the CE matrix without sacrificing thermal properties. CE/PPO formulations with 5, 10, and 15 wt.% PPO showed 43%, 65%, and 105% increase in fracture toughness due to a combination of crack deflection, crack pinning, and matrix cavitation around second‐phase particles. When PPO was introduced into the CE, dielectric properties were either unchanged or declined. During thermal treatment to heal damaged CE, liquid PPO flowed into cracks, and during subsequent cooling, solidified to bond the crack surfaces. The self‐healing efficiency for CE with 15 wt.% PPO after heating to 220°C for 1 h exhibited a recovery of 73% in toughness and 81% in microtensile strength. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献
69.
以萘普生(NPX)为前体, 分别与芳基钌(Ru)、 锇(Os)及铱(Ir)二聚体反应制备了3个单核配合物[Ru(η 6-p-cymene)(NPX-bpy)Cl]Cl(1), [Os(η 6-p-cymene)(NPX-bpy)Cl]Cl(2)和[Ir(η 5-Cp *)·(NPX-bpy)Cl]Cl(3). 利用元素分析、 电喷雾质谱和核磁共振波谱对3个配合物的组成和结构进行了表征, 并研究了其细胞毒性. 结果表明, 3个配合物对几种肿瘤细胞株均无毒性(IC50>100 μmol/L), 仅配合物1对NB-4细胞有中等程度的毒性(IC50=45.2 μmol/L), 且毒性大于配合物2和3, 这可能与配合物1在细胞核内具有更高的富集量有关. 此外, 3个配合物均可有效抑制COX-2的表达, 保留了萘普生的抗炎性质, 实现了金属配合物抗癌及抗炎的多功能化应用. 相似文献
70.
Anna Kryshchyshyn-Dylevych Myroslav Garazd Andrew Karkhut Sviatoslav Polovkovych 《合成通讯》2020,50(18):2830-2838
AbstractA mild and efficient method for the synthesis of 1-oxo-9H-thiopyrano[3,4-b]indole-3-carboxylic acids and dimerized 3-(4-carboxy-1H-3-indolyl)-2-propenoic acids via alkaline hydrolysis of 3-(rhodanin-5-yl)-1H-indole-2-carboxylic acids derivatives was elaborated. Anticancer activity screening in NCI60-cell lines assay allowed identification of 5-fluoro-3-(4-oxo-2-thioxothiazolidin-5-ylidenemethyl)-1H-indole-2-carboxylic acid methyl ester 2a with significant antimitotic activity at micromolar and submicromolar concentrations. 相似文献