首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   484篇
  免费   24篇
  国内免费   2篇
化学   365篇
晶体学   4篇
力学   21篇
数学   43篇
物理学   77篇
  2024年   5篇
  2023年   8篇
  2022年   47篇
  2021年   44篇
  2020年   29篇
  2019年   23篇
  2018年   25篇
  2017年   16篇
  2016年   30篇
  2015年   14篇
  2014年   18篇
  2013年   41篇
  2012年   39篇
  2011年   41篇
  2010年   31篇
  2009年   18篇
  2008年   15篇
  2007年   20篇
  2006年   14篇
  2005年   9篇
  2004年   5篇
  2003年   8篇
  2002年   1篇
  2001年   2篇
  1999年   1篇
  1996年   2篇
  1995年   1篇
  1993年   1篇
  1988年   1篇
  1987年   1篇
排序方式: 共有510条查询结果,搜索用时 15 毫秒
51.
Domestically produced diagnostic cold kits, viz. glucoheptonate (GH), diisopropyliminodiacetic acid (DISIDA), dimercaptosuccinic acid (DMSA), diethylenetriamine-pentaacetic acid (DTPA), methylenediphosphonate (MDP) and Sn-colloid were labeled with99mTc and their in-vivo distribution in experimental animals (rats) was evaluated prior to use in humans for diagnostic scanning. The biodistribution pattern was found in accordance with the latest guidelines of the International Atomic Energy Agency (IAEA), which serve as a standard for small scale producers.  相似文献   
52.
Designed and synthesized a new highly water soluble N,N1-bis(2-((5-((dimethylamino)methyl)furan-2-yl)methylthio)ethyl)-perylene -3,4,9,10-tetracarboxylic diimide from 2-((5-((dimethylamino)methyl)furan-2-yl)methylthio)ethanamine and perylene-3,4,9,10- tetracarboxylic dianhydride.The compound was characterized by 1H,13C,2D NMR,mass and IR techniques.The compound is highly fluorescent with good solubility in water and other polar solvents.  相似文献   
53.
Journal of Solution Chemistry - The development of a meaningful dissolution procedure for drug products with limited water solubility has been a challenge to both the pharmaceutical industry and...  相似文献   
54.
Ali I  Gupta VK  Singh P  Pant HV 《Talanta》2006,68(3):928-931
Domperidone is a dopamine D2 receptor antogonist, which has been used as antiemetic agent in human beings. It has been found in wastewater released by some pharmaceutical industries leading to the contamination of surface and ground water. Therefore, a sensitive, inexpensive and reproducible HPLC-SPE method was developed for the analysis of domperidone in the wastewater. The column used was Waters symmetry C18 (15 cm × 0.46 mm, 5 μm). The mobile phase used was phosphate buffer (50 mM, pH 3.5) acetonitrile (80:20, v/v) at the flow rate 2.0 mL/min. The detection was achieved by using UV mode at 230 nm. The retention, separation and resolution factors were 2.63, 3.00 and 3.20, respectively. The percentage recovery of domperidone from wastewater was 95.0%. Celiprolol was used as the internal standard to access the percentage extraction of domperidone from wastewater.  相似文献   
55.
The fabrication of nanoparticles has been perused as a topic of critical importance in the present decades. Biosynthesis of nanoparticles employs plants extract instead of harmful chemicals. These plant extracts act as reducing and capping agents which is the most appropriate and eco-friendly method among all the preparative routs. In present study, the magnetite nanoparticles (Fe3O4-NPs) were fabricated using rapid, single step and benign biosynthetic rout by reduction of ferric nitrate nonahydrate solution with Ferocactus echidne aqueous extract containing ascorbic acid as a main reducing and capping agent. The structural and morphological properties of prepared iron oxide nanoparticles were investigated by Powder X-ray diffraction and scanning electron microscopy. The size of the synthesized nanoparticles was approximately 15 ± 2 nm as determined by Scherrer equation. The biosynthetically fabricated nanoparticles were employed as catalyst for pyrolysis of nutshells to produce biofuel. Catalytic pyrolysis of biomass yields biofuel as an alternative source of energy and chemical feed stock. Effect of temperature, heating rate, and amount of catalyst were investigated on conversion percentage and product yields. Aniline point, carbon residue, and cetane number of prepared bio-oil were also determined.  相似文献   
56.
We investigate the impact of Ni insertion on the structural,optical,and magnetic properties of Ba0.8La0.2Fe12-xNixO19hexaferrites(Ni substituted La-BaM hexaferrites).Samples were prepared using the conventional co-precipitation method and sintered at 1000℃for 4 hours to assist the crystallization process.An analysis of the structure of the samples was carried out using an x-ray diffraction(XRD)spectrometer.The M-type hexagonal structure of all the samples was confirmed using XRD spectra.The lattice parameters a and c were found to be in the ranges of 5.8925±0.001 nm–5.8952±0.001 nm and 23.2123±0.001 nm–23.2219±0.001 nm,respectively.The M-type hexagonal nature of the prepared samples was also indicated by the presence of corresponding FT-IR bands and Raman modes in the FT-IR and Raman spectra,respectively.EDX results confirmed the successful synthesis of the samples according to the required stoichiometric ratio.A UV-vis spectrometer was used to record the absorption spectra of the prepared samples in the wavelength range of 200 nm–1100 nm.The optical energy bandgap of the samples was found to be in the range of 1.21 eV–3.39 eV.The M–H loops of the samples were measured at room temperature at an applied magnetic field range of 0 kOe–60 kOe.A high saturation magnetization of 99.92 emu/g was recorded in the sample with x=0 at a microwave operating frequency of 22.2 GHz.This high value of saturation magnetization is due to the substitution of La3+ions at the spin-up(12k,2a,and 2b)sites.The Ni substitution is proven to be a potential candidate for the tuning of the optical and magnetic parameters of M-type hexaferrites.Therefore,we suggest that the prepared samples are suitable for use in magneto-optic applications.  相似文献   
57.
The study is focused on examining 2,5-Substituted 4-Pyrone based compounds through quantum chemical and topological analysis techniques, evaluating the properties of these compounds, including their geometrical structure, intermolecular interactions and assess their possible applications. Additionally, the molecular stability, charge delocalization and UV-Visible data was investigated and compared with the calculated energy and oscillator strength using the TD-DFT approach. The researchers observed that charge transfer occurred within the molecule, indicated by the HOMO and LUMO energies. It was also found that the compound exhibited planarity and higher chemical reactivity. The calculated Mulliken charges and molecular electrostatic potential were used to interpret the Fukui index data that help predict reactive sites and understand the reactivity patterns of specific atoms in a compound. The study is aimed to understand the role of NCI in the molecule under investigation using electron localization functions and localized orbit locator methods. Molecular docking and ADMET studies were conducting involving a detailed MD simulation of a protein-ligand complex using the OPLS3e force field and the SPC water model. These findings could prove to be beneficial in developing new therapeutic agents with various pharmacological effects and potential toxicities.  相似文献   
58.
β-Sitosterol-3-O-(6?-O-13?-octadecenoyl)-β-D-glucoside (1), a new acyl β-sitosteryl glucoside, along with three known compounds β-sitosterol-3-O-β-D-glucoside (2), β-sitosterol (3) and methyl gallate (4) have been isolated from the ethyl acetate soluble fraction of methanolic extract of Ailanthus altissima fruits. Their structures were elucidated through spectroscopic data including 2D NMR, ESI-MS, methanolysis and oxidative cleavage of double bond. Antibacterial, antifungal, cytotoxic, phytotoxic and insecticidal activities were evaluated of compound 1, crude extract and its fractions so far for the first time. Pharmacological activities results showed that n-butanol fraction was good active against Pseudomonas aeruginosa and Salmonella typhi bacteria, and moderate active against Microsporum canis fungus. Crude extract, n-butanol and aqueous fractions showed good cytotoxicity. Moreover, compound 1, extract and all fractions showed notable phytotoxicity at higher concentrations, whereas all inactive against assayed insects.  相似文献   
59.
Results of phase transformations, enthalpy released and specific heat of Ge22Se78–xBix(x=0, 4 and 8) chalcogenide glasses, using differential scanning calorimetry (DSC), under non-isothermal condition have been reported and discussed. The glass transition temperature, T g, is found to increase with an average coordination number and heating rates. Following Gibbs—Dimarzio equation, the calculated values of T g (i.e. 462.7, 469.7 and 484.4 K) and the experimental values (i.e. 463.1, 467.3 and 484.5 K) increase with Bi concentration. Both values of T g, at a heating rate of 5 K min–1, are found to be in good agreement. The glass transition activation energy increases i.e. 102±2, 109±3 and 115±8 kJ mol–1 with Bi concentration. The demand for thermal stability has been ensured through the temperature difference T cT g and the enthalpy released during the crystallization process. Below T g, specific heat has been observed to be temperature independent but highly compositional dependent. The growth kinetic has been investigated using the Kissinger, Ozawa, Matusita and modified JMA equations. Results indicate that the crystallization ability is enhanced, the activation energy of crystallization increases with increasing the Bi content and the crystal growth of these glasses occur in 3 dimensions.This revised version was published online in November 2005 with corrections to the Cover Date.  相似文献   
60.
Topological indices are numerical parameters of a molecular graph, which characterize its topology and are usually graph invariant. In quantitative structure–activity relationship/quantitative structure–property relationship study, physico‐chemical properties and topological indices such as Randić, atom–bond connectivity (ABC), and geometric–arithmetic (GA) index are used to predict the bioactivity of chemical compounds. Graph theory has found a considerable use in this area of research. In this paper, we study hex‐derived networks HDN1(n) and HDN2(n), which are generated by hexagonal network of dimension n and derive analytical closed results of general Randić index Rα(G) for different values of α, for these networks of dimension n. We also compute the general first Zagreb, ABC, GA, ABC4, and GA5 indices for these hex‐derived networks for the first time and give closed formulae of these degree‐based indices for hex‐derived networks. Copyright © 2016 John Wiley & Sons, Ltd.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号