全文获取类型
收费全文 | 334篇 |
免费 | 12篇 |
国内免费 | 5篇 |
专业分类
化学 | 303篇 |
力学 | 3篇 |
数学 | 11篇 |
物理学 | 34篇 |
出版年
2024年 | 4篇 |
2023年 | 5篇 |
2022年 | 44篇 |
2021年 | 26篇 |
2020年 | 29篇 |
2019年 | 19篇 |
2018年 | 11篇 |
2017年 | 10篇 |
2016年 | 14篇 |
2015年 | 11篇 |
2014年 | 17篇 |
2013年 | 38篇 |
2012年 | 11篇 |
2011年 | 11篇 |
2010年 | 14篇 |
2009年 | 11篇 |
2008年 | 8篇 |
2007年 | 3篇 |
2006年 | 8篇 |
2005年 | 4篇 |
2004年 | 14篇 |
2003年 | 5篇 |
2002年 | 7篇 |
2001年 | 1篇 |
2000年 | 1篇 |
1999年 | 1篇 |
1998年 | 1篇 |
1997年 | 6篇 |
1996年 | 2篇 |
1994年 | 2篇 |
1993年 | 3篇 |
1991年 | 1篇 |
1990年 | 2篇 |
1989年 | 1篇 |
1988年 | 1篇 |
1987年 | 1篇 |
1981年 | 1篇 |
1976年 | 2篇 |
1975年 | 1篇 |
排序方式: 共有351条查询结果,搜索用时 13 毫秒
1.
Mohamed Hilmy Elnagdi Ramadan Maawad Abdel-Motaleb Mona Mustafa Mohamed Foad Zayed Eman Moustafa Kamel 《Journal of heterocyclic chemistry》1987,24(6):1677-1681
The behaviour of several 2-amino-3-cyano-4H-pyran derivatives toward a variety of nucleophilic reagents is reported. 相似文献
2.
Toluene was methylated with methanol and disproportionated using catalysts containing different Pt contents (0.2, 0.4 and 0.6%) supported on H‐ZSM‐5 or H‐mordenite (H‐M) zeolites in a fixed‐bed flow‐reactor operated atmospherically at temperatures of 300–500 °C in a flow of hydrogen. Platinum dispersion in the zeolite supports and acid sites strength distribution were evaluated using hydrogen chemisorption (1:1 stoichiometry) and ammonia temperature programmed desorption (TPD) in a differential scanning calorimeter (DSC). Toluene methylation was much faster on all catalysts than toluene disproportionation (DISP). Both reactions were more accelerated using H‐ZSM‐5 containing catalysts than H‐M containing catalysts. The yield of xylenes, and in particular para‐xylene, was significantly influenced by the yield of trimethylbenzenes (TMBs) in product. The selectivities for para‐, ortho‐ and meta‐xylenes production were found largely dependent on the Pt content in the catalysts, particularly when supported on H‐ZSM5‐zeolite. However, using Pt/H‐M catalysts, these selectivities were not strictly controlled by Pt content in the catalysts. 相似文献
3.
Abou El-Nasr EA Fujii A Yahagi T Ebata T Mikami N 《The journal of physical chemistry. A》2005,109(11):2498-2504
Geometric structures and excited-state proton dislocation of size-selected salicylic acid clusters (salicylic acid and 5-methoxysalicylic acid) with water were studied by using laser spectroscopic techniques. Fluorescence excitation, dispersed fluorescence, and infrared (IR) spectra of those clusters in supersonic jets were examined for both the electronic ground (S0) and first excited (S1) states. The geometric structures of the clusters were determined on the basis of the IR spectra of the OH stretch region with the help of quantum chemical calculations. The hydroxyl group of the water moiety in the clusters forms a ring involving the carboxylic group of the salicylic acid moiety. The IR spectra in S0 show that the intramolecular hydrogen bond in the salicylic acid moiety is still held upon cluster formation, but the phenolic OH stretch band intensity is remarkably weaken in the clusters. The IR spectra in the S1 state and dispersed fluorescence spectra indicated that the intramolecular excited state proton dislocation is hardly affected by the microsolvation with water, in contrast with the strong suppression of the dislocation in the self-solvation. 相似文献
4.
Jacqueline Ficini Jean dAngelo Arnaud Eman Anne Marie Touzin 《Tetrahedron letters》1976,17(9):683-686
5.
Shoaib Khan Shahid Iqbal Mazloom Shah Wajid Rehman Rafaqat Hussain Liaqat Rasheed Hamad Alrbyawi Ayed A. Dera Mohammed Issa Alahmdi Rami Adel Pashameah Eman Alzahrani Abd-ElAziem Farouk 《Molecules (Basel, Switzerland)》2022,27(20)
A unique series of sulphonamide derivatives was attempted to be synthesized in this study using a new and effective method. All of the synthesized compounds were verified using several spectroscopic methods, including FTIR, 1H-NMR, 13C-NMR, and HREI-MS, and their binding interactions were studied using molecular docking. The enzymes urease and α-glucosidase were evaluated against each derivative (1–15). When compared to their respective standard drug such as acarbose and thiourea, almost all compounds were shown to have excellent activity. Among the screened series, analogs 5 (IC50 = 3.20 ± 0.40 and 2.10 ± 0.10 µM) and 6 (IC50 = 2.50 ± 0.40 and 5.30 ± 0.20 µM), emerged as potent molecules when compared to the standard drugs acarbose (IC50 = 8.24 ± 0.08 µM) and urease (IC50 = 7.80 ± 0.30). Moreover, an anti-microbial study also demonstrated that analogs 5 and 6 were found with minimum inhibitory concentrations (MICs) in the presence of standard drugs streptomycin and terinafine. 相似文献
6.
Hussein H. Elganzory Fahad M. Alminderej Mohamed N. El-Bayaa Hanem M. Awad Eman S. Nossier Wael A. El-Sayed 《Molecules (Basel, Switzerland)》2022,27(20)
New 1,3,4-thiadiazole thioglycosides linked to a substituted arylidine system were synthesized via heterocyclization via click 1,3-dipolar cycloaddition. The click strategy was used for the synthesis of new 1,3,4-thiadiazole and 1,2,3-triazole hybrid glycoside-based indolyl systems as novel hybrid molecules by reacting azide derivatives with the corresponding acetylated glycosyl terminal acetylenes. The cytotoxic activities of the compounds were studied against HCT-116 (human colorectal carcinoma) and MCF-7 (human breast adenocarcinoma) cell lines using the MTT assay. The results showed that the key thiadiazolethione compounds, the triazole glycosides linked to p-methoxyarylidine derivatives and the free hydroxyl glycoside had potent activity comparable to the reference drug, doxorubicin, against MCF-7 human cancer cells. Docking simulation studies were performed to check the binding patterns of the synthesized compounds. Enzyme inhibition assay studies were also conducted for the epidermal growth factor receptor (EGFR), and the results explained the activity of a number of derivatives. 相似文献
7.
Salma Eldesouki Rama Qadri Rashid Abu Helwa Hiba Barqawi Yasser Bustanji Eman Abu-Gharbieh Waseem El-Huneidi 《Molecules (Basel, Switzerland)》2022,27(21)
Kahweol and cafestol are two diterpenes extracted from Coffea arabica beans that have distinct biological activities. Recent research describes their potential activities, which include anti-inflammatory, anti-diabetic, and anti-cancer properties, among others. The two diterpenes have been shown to have anticancer effects in various in vitro and in vivo cancer models. This review aims to shed light on the recent developments regarding the potential effects of kahweol and cafestol on various cancers. A systematic literature search through Google Scholar and PubMed was performed between February and May 2022 to collect updates about the potential effects of cafestol and kahweol on different cancers in in vitro and in vivo models. The search terms “Kahweol and Cancer” and “Cafestol and Cancer” were used in this literature review as keywords; the findings demonstrated that kahweol and cafestol exhibit diverse effects on different cancers in in vitro and in vivo models, showing pro-apoptotic, cytotoxic, anti-proliferative, and anti-migratory properties. In conclusion, the diterpenes kahweol and cafestol display significant anticancer effects, while remarkably unaffecting normal cells. Our results show that both kahweol and cafestol exert their actions on various cancers via inducing apoptosis and inhibiting cell growth. Additionally, kahweol acts by inhibiting cell migration. 相似文献
8.
Mohammed Alqarni Nader Ibrahim Namazi Sameer Alshehri Ibrahim A. Naguib Amal M. Alsubaiyel Kumar Venkatesan Eman Mohamed Elmokadem Mahboubeh Pishnamazi Mohammed A. S. Abourehab 《Molecules (Basel, Switzerland)》2022,27(14)
Industrial-based application of supercritical CO2 (SCCO2) has emerged as a promising technology in numerous scientific fields due to offering brilliant advantages, such as simplicity of application, eco-friendliness, and high performance. Loxoprofen sodium (chemical formula C15H18O3) is known as an efficient nonsteroidal anti-inflammatory drug (NSAID), which has been long propounded as an effective alleviator for various painful disorders like musculoskeletal conditions. Although experimental research plays an important role in obtaining drug solubility in SCCO2, the emergence of operational disadvantages such as high cost and long-time process duration has motivated the researchers to develop mathematical models based on artificial intelligence (AI) to predict this important parameter. Three distinct models have been used on the data in this work, all of which were based on decision trees: K-nearest neighbors (KNN), NU support vector machine (NU-SVR), and Gaussian process regression (GPR). The data set has two input characteristics, P (pressure) and T (temperature), and a single output, Y = solubility. After implementing and fine-tuning to the hyperparameters of these ensemble models, their performance has been evaluated using a variety of measures. The R-squared scores of all three models are greater than 0.9, however, the RMSE error rates are 1.879 × 10−4, 7.814 × 10−5, and 1.664 × 10−4 for the KNN, NU-SVR, and GPR models, respectively. MAE metrics of 1.116 × 10−4, 6.197 × 10−5, and 8.777 × 10−5errors were also discovered for the KNN, NU-SVR, and GPR models, respectively. A study was also carried out to determine the best quantity of solubility, which can be referred to as the (x1 = 40.0, x2 = 338.0, Y = 1.27 × 10−3) vector. 相似文献
9.
Rabab M. Amer Amira Kamel Eltokhy Rasha Osama Elesawy Amany Nagy Barakat Eman Basha Omnia Safwat Eldeeb Alshimaa Aboalsoud Nancy Mohamed Elgharabawy Radwa Ismail 《Molecules (Basel, Switzerland)》2022,27(12)
Introduction. Vigabatrin (VGB) is an antiepileptic drug that acts to irreversibly inhibit the γ-aminobutyric acid (GABA) transaminase enzyme, elevating GABA levels. Broad studies have established that long-term treatment and/or high doses of VGB lead to variable visual defects. However, little attention has been paid to its other side effects, especially those demonstrating cerebellar involvement. Sodium glucose-linked co-transporter 2 (SGLT2) inhibitors are antidiabetic agents with protective effects far greater than expected based on their anti-hyperglycemic effect. Method. Our study herein was designed to investigate the possible ameliorative effect of empagliflozin, the SGLT2 inhibitors, in VGB-induced cerebellar toxicity. A total of 40 male Wistar rats were allocated equally into 4 groups: Group I: control group; Group II: VGB group; Group III empagliflozin treated VGB group; and Group IV: empagliflozin treated group. All groups were subjected to the detection of cerebellar messenger RNA gene expression of silent mating type information regulation 2 homolog 1 (SIRT1) and Nucleoporin p62 (P62). Mammalian target of rapamycin (mTOR), adenosine monophosphate-activated protein kinase (AMPK), and beclin1 levels were assessed by the ELISA technique while malondialdehyde (MDA) level and superoxide dismutase (SOD) activity were detected spectrophotometrically. Immuno-histochemical studies, focusing on glial fibrillary acidic protein (GFAP) and S100 were performed, and the optical color density and the mean area percentage of GFAP positive astrocytes and the number of S 100 positive cells were also counted. Results. Following empagliflozin treatment, we documented significant upregulation of both SIRT1 and P62 mRNA gene expression. Additionally, AMPK, Beclin1 levels, and SOD activity were significantly improved, while both mTOR and MDA levels were significantly reduced. Conclusions. We concluded for the first time that empagliflozin efficiently ameliorated the VGB-induced disrupted mTOR/AMPK/SIRT-1 signaling axis with subsequent improvement of the autophagy machinery and mitigation of the oxidative and inflammatory cellular environment, paving the way for an innovative therapeutic potential in managing VGB-induced neurotoxicity. 相似文献
10.
Tarfah Al-Warhi Adil Aldhahrani Fayez Althobaiti Eman Fayad Ola A. Abu Ali Sarah Albogami Ali H. Abu Almaaty Amgad I. M. Khedr Syed Nasir Abbas Bukhari Islam Zaki 《Molecules (Basel, Switzerland)》2022,27(12)
A novel series of amides based TMP moiety was designed, synthesized and evaluated for their antiproliferative as well as enzyme inhibition activity. Compounds 6a and 6b showed remarkable cytotoxic activity against HepG2 cells with IC50 values 0.65 and 0.92 μM, respectively compared with SAHA and CA-4 as reference compounds. In addition, compound 6a demonstrated good HDAC-tubulin dual inhibition activity as it showed better HDAC activity as well as anti-tubulin activity. Moreover, compound 6a exhibited G2/M phase arrest and pre-G1 apoptosis as demonstrated by cell cycle analysis and Annexin V assays. Further apoptosis studies demonstrated that compound 6a boosted the level of caspase 3/7. Caspase 3/7 activation and apoptosis induction were evidenced by decrease in mitochondrial permeability suggesting that activation of caspase 3/7 may occur via mitochondrial apoptotic pathway. 相似文献