全文获取类型
收费全文 | 1048篇 |
免费 | 41篇 |
国内免费 | 109篇 |
专业分类
化学 | 1078篇 |
晶体学 | 9篇 |
力学 | 2篇 |
综合类 | 12篇 |
数学 | 44篇 |
物理学 | 53篇 |
出版年
2023年 | 15篇 |
2022年 | 74篇 |
2021年 | 76篇 |
2020年 | 65篇 |
2019年 | 60篇 |
2018年 | 71篇 |
2017年 | 40篇 |
2016年 | 55篇 |
2015年 | 32篇 |
2014年 | 48篇 |
2013年 | 99篇 |
2012年 | 111篇 |
2011年 | 40篇 |
2010年 | 37篇 |
2009年 | 58篇 |
2008年 | 50篇 |
2007年 | 37篇 |
2006年 | 35篇 |
2005年 | 26篇 |
2004年 | 18篇 |
2003年 | 19篇 |
2002年 | 19篇 |
2001年 | 18篇 |
2000年 | 10篇 |
1999年 | 17篇 |
1998年 | 8篇 |
1997年 | 7篇 |
1996年 | 6篇 |
1995年 | 11篇 |
1994年 | 7篇 |
1993年 | 6篇 |
1992年 | 4篇 |
1991年 | 6篇 |
1990年 | 5篇 |
1989年 | 3篇 |
1988年 | 1篇 |
1987年 | 1篇 |
1986年 | 1篇 |
1985年 | 1篇 |
1984年 | 1篇 |
排序方式: 共有1198条查询结果,搜索用时 593 毫秒
61.
New water-soluble methylimidazolium ionic liquids (MIILs) bearing N,N′-bis-(salicylidene)-R,R-1,2-diaminocyclohexane (saldach) scaffold, H2(R1)2saldach(2-MeIm+X−)2 (4a: R1=H, X=Cl–; 4b: R1=H, X=PF6–; 4c: R1=H, X=BF4–; 4d: R1=iPr, X=Cl–; 4e: R1=iPr, X=PF6–; 4f: R1=iPr, X=BF4–), and their Fe(III) complexes have been synthesized and structurally characterized as well as their profile of antimicrobial susceptibility was identified. The new saldach-supported MIILs demonstrated a distinctly enhanced biocidal effect toward methicillin resistant Staphylococcus aureus (MRSA) and multidrug-resistant Escherichia coli (MDREC). Compound 4d is the most potent antibacterial agent and could inhibit the growth of all micro-organisms, except A. flavus, more effectively than standard antibiotics. 相似文献
62.
Hermina Iulia Petkes Emese Gál Luiza Găină Mihaela Sabou Cornelia Majdik Luminiţa Silaghi-Dumitrescu 《Comptes Rendus Chimie》2014,17(10):1050-1056
The synthesis of new phenothiazinyl- and phenyl-nitrones under classical versus microwave heating conditions is described. Better yields were obtained under microwave irradiation in the condensation reactions of phenothiazyl-carbaldehyde with hydroxylamine derivatives. The structures of the new phenothiazinyl-nitrones were assigned on the basis of MS, FT–IR and NMR spectra. The new nitrones and some known phenyl-nitrones were screened for their antibacterial and antifungal activity against several Candida species, Gram negative bacteria, such as E. coli, Citrobacter spp, Morganella spp, Pseudomonas aeruginosa, Klebsiella pneumoniae (± ESBL), Proteus spp, Acinetobacter spp and the Gram positive bacterium Staphylococcus aureus, with moderate results. 相似文献
63.
《Arabian Journal of Chemistry》2022,15(10):104133
A comparative study between methanolic extract and n-hexane fraction of Typha domingensis (Typhaceae) was conducted for the evaluation of phytochemical potential, in vitro biological activities, and in-silico molecular docking studies. The phytochemical composition was estimated by total phenolic and total flavonoid contents, and by GC–MS analysis. Several biological activities were performed such as antioxidant assays (ABTS, FRAP, DPPH, & CUPRAC), enzyme inhibition activity (Tyrosinase, Acetylcholinesterase & Butyrylcholinesterase), thrombolytic activity, and antimicrobial activity (antibacterial & antiviral) to evaluate the medicinal importance of Typha domingensis. The results of the comparative study showed that methanolic extract has more total phenolic and total flavonoid contents (95.72 ± 5.76 mg GAE/g, 131.66 ± 7.92 mg QE/g, respectively) as compared to n-hexane fraction which confirms its maximum antioxidant potential (ABTS 114.31 ± 8.17, FRAP 116.84 ± 3.01, DPPH 283.54 ± 7.3 & CUPRAC 284.16 ± 6.5 mg TE/g). In the case of in vitro enzyme inhibition study and thrombolytic activity, better results were observed for methanolic extract. Almost similar antimicrobial patterns were observed for both methanolic extract and n-hexane fraction of Typha domingensis. The major bioactive phytochemicals identified by GC–MS were further analyzed for in-silico molecular docking studies to determine the binding affinity between ligands and the enzymes. The docking study indicated that most of the bioactive compounds showed a better binding affinity with enzymes as compared to the standard compounds (kojic acid & galantamine). The results of this study recommended that Typha domingensis has promising pharmaceutical importance and it should be further analyzed for the isolation of bioactive phytochemicals which may be useful for the treatment of several diseases. 相似文献
64.
《Arabian Journal of Chemistry》2022,15(11):104225
Cinnamomum camphora leaf essential oil (CEO) was extracted using enzymatic-ultrasound pretreatment followed by microwave assisted extraction (EUP-MAE) method and simultaneously studied as a mycelial growth inhibitor against five important pathogens which cause potato dry rot. The optimum EUP-MAE conditions with a real CEO yield of 19.23 ± 0.12 mg/g were obtained through Plackett–Burman design and Box–Behnken design as follows: 3 % of enzyme dosage, 2 h of pretreatment time, 5 of pH, 210 W of ultrasound power, 50 °C pretreatment temperature, 16 mL/g of water to solid ratio, 30 min of microwave time and 500 W of microwave power. Compared to the reference methods, EUP-MAE possessed a highest CEO yield than these of ultrasound-microwave assisted extraction (U-MAE) and traditional hydrodistillation (HD). Gas chromatography-mass spectrometry (GC–MS) analysis demonstrated that eucalyptol, camphor, and α-terpineol were the three main constituents of CEO. Results from in vitro antifungal activity assay revealed that the mycelial growths of all the five tested Fusarium solani, Fusarium culmorum, Fusarium trichothecioides, Fusarium sporotrioides, and Fusarium avenaceum were apparently affected by CEO. These findings not only provide a potential paradigm for the separation of plant essential oil, but also guarantee a promising utilization of the CEO for potato protection to control the Fusarium spp. 相似文献
65.
Structures and Bioactivities of Steroidal Saponins Isolated from the Genera Dracaena and Sansevieria
Zaw Min Thu Sann Myint Oo Thinn Myat Nwe Hnin Thanda Aung Chabaco Armijos Faiq H. S. Hussain Giovanni Vidari 《Molecules (Basel, Switzerland)》2021,26(7)
The species Dracaena and Sansevieria, that are well-known for different uses in traditional medicines and as indoor ornamental plants with air purifying property, are rich sources of bioactive secondary metabolites. In fact, a wide variety of phytochemical constituents have been isolated so far from about seventeen species. This paper has reviewed the literature of about 180 steroidal saponins, isolated from Dracaena and Sansevieria species, as a basis for further studies. Saponins are among the most characteristic metabolites isolated from the two genera. They show a great variety in structural motifs and a wide range of biological activities, including anti-inflammatory, anti-microbial, anti-proliferative effects and, in most case, remarkable cytotoxic properties. 相似文献
66.
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
67.
Ana Margarida Silva Diana Pinto Iva Fernandes Victor de Freitas María de la Luz Cdiz-Gurrea Paulo Costa Cristina Delerue-Matos Francisca Rodrigues 《Molecules (Basel, Switzerland)》2021,26(8)
During kiwiberry production, different by-products are generated, including leaves that are removed to increase the fruit’s solar exposure. The aim of this work was to extract bioactive compounds from kiwiberry leaf by employing microwave-assisted extraction (MAE). Compatible food solvents (water and ethanol) were employed. The alcoholic extract contained the highest phenolic and flavonoid contents (629.48 mg of gallic acid equivalents (GAE) per gram of plant material on dry weight (dw) (GAE/g dw) and 136.81 mg of catechin equivalents per gram of plant material on dw (CAE/g dw), respectively). Oppositely, the hydroalcoholic extract achieved the highest antioxidant activity and scavenging activity against reactive oxygen and nitrogen species (IC50 = 29.10 μg/mL for O2•−, IC50 = 1.87 μg/mL for HOCl and IC50 = 1.18 μg/mL for •NO). The phenolic profile showed the presence of caffeoylquinic acids, proanthocyanidin, and quercetin in all samples. However, caffeoylquinic acids and quercetin were detected in higher amounts in the alcoholic extract, while proanthocyanidins were prevalent in the hydroalcoholic extract. No adverse effects were observed on Caco-2 viability, while the highest concentration (1000 µg/mL) of hydroalcoholic and alcoholic extracts conducted to a decrease of HT29-MTX viability. These results highlight the MAE potentialities to extract bioactive compounds from kiwiberry leaf. 相似文献
68.
69.
以2-胺基苯甲酸为原料,通过环化、缩合、肼解、环化、硫醚化和氧化等步骤,合成了10个含喹唑啉酮取代1,3,4-噁二唑(噻二唑)化合物。通过1H NMR、13C NMR、MS 和元素分析进行确证其结构。初步抑菌活性测试表明,化合物浓度在50 μg/mL时,对葡萄座腔菌(Botryosphaeria dothidea)、拟茎点霉菌(Phomopsis sp.)和灰霉菌(B. cinerea)具有中等抑制活性。另外,目标化合物对猕猴桃溃疡病(Pseudomonas syringae pv. actinidia)均具有一定的抑制活性,其中化合物6a和6b对猕猴桃溃疡病的EC50值为11.7 μg/mL和20.5 μg/mL,优于对照药剂叶枯唑(24.5 μg/mL)。这类化合物具有较好抗菌的生物活性,在此基础上进行结构优化,有望发现较高活性化合物。 相似文献
70.
In this study,a promising strategy has been developed to promote bone regeneration by combining antioxidant activities and osteoimmunomodulatory properties.Herein,an L-arginine/nanofish bone(Arg/NFB) nanocomplex has been prepared and evaluated in vitro and in vivo.The Arg/NFB nanocomplex possesses good antioxidant activities and could modulate the polarization of non-activated macrophage into different types and induce the secretion of pre-inflammato ry,anti-inflammatory,osteogenic as well as angiogenic cytokines.Additionally,the regulated immune microenvironment can enhance the osteogenic differentiation of mouse embryo osteoblast precursor cells(MC3 T3-E1) and angiogenic capacity of human umbilical vein endothelial cells(HUVECs),leading to the improved formation of mineralized nodules,alkaline phosphatase activity and angiogenic effects.In vivo results with cranial defect models reveal that the treatment of Arg/NFB nanocomplex exhibited significant improvement of new bone formation and angiogenesis.All the results demonstrate Arg/NFB nanocomplex with antioxidant activities and osteoimmunomodulatory properties could be a new idea for developing the next generation of bone regeneration biomaterials. 相似文献