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   125篇
  免费   8篇
化学   117篇
力学   5篇
物理学   11篇
  2023年   1篇
  2022年   2篇
  2021年   1篇
  2020年   2篇
  2019年   11篇
  2018年   3篇
  2017年   1篇
  2016年   5篇
  2015年   6篇
  2014年   10篇
  2013年   7篇
  2012年   6篇
  2011年   6篇
  2010年   6篇
  2009年   7篇
  2008年   11篇
  2007年   9篇
  2006年   9篇
  2005年   11篇
  2004年   5篇
  2003年   5篇
  2002年   1篇
  2001年   1篇
  1999年   2篇
  1987年   1篇
  1981年   2篇
  1973年   1篇
  1969年   1篇
排序方式: 共有133条查询结果,搜索用时 0 毫秒
31.
Oroxylum indicum, of the Bignoniaceae family, has various ethnomedical uses such as an astringent, anti-inflammatory, anti-bronchitis, anti-helminthic and anti-microbial, including anticancer properties. The druggability of OI stem bark extract was determined by its molecular docking interactions with PARP and Caspase-3, two proteins involved in cell survival and death. Note that 50 µg/mL of Oroxylum indicum extract (OIE) showed a significant (p < 0.05%) toxicity to HSC-3 cells. MTT aided cell viability and proliferation assay demonstrated that 50 µg/mL of OIE displayed significant (p < 0.5%) reduction in cell number at 4 h of incubation time. Cell elongation and spindle formation was noticed when HSC-3 cells were treated with 50 µg/mL of OIE. OIE initiated DNA breakage and apoptosis in HSC-3 cells, as evident from DNA ladder assay and calcein/EB staining. Apoptosis potential of OIE is confirmed by flow cytometer and triple-staining (live cell/apoptosis/necrosis) assay. Caspase-3/7 fluorescence quenching (LANCE) assay demonstrated that 50 µg/mL of OIE significantly enhanced the RFU of caspases-3/7, indicating that the apoptosis potential of OIE is probably through the activation of caspases. Immuno-cytochemistry of HSC-3 cells treated with 50 µg/mL of OIE showed a significant reduction in mitochondrial bodies as well as a reduction in RFU in 60 min of incubation time. Immunoblotting studies clearly showed that treatment of HSC-3 cells with OI extract caused caspase-3 activation and PARP deactivation, resulting in apoptotic cell death. Overall, our data indicate that OIE is an effective apoptotic agent for human squamous carcinoma cells and it could be a future cancer chemotherapeutic target.  相似文献   
32.
Aquilaria sinensis (Lour.) Spreng is known for its resinous secretion (agarwood), often secreted in defense against injuries. We investigated the effects of A. sinensis flower extract (AF) on peroxisome proliferator-activated receptors alpha and gamma (PPARα and PPARγ), liver X receptor (LXR), glucose uptake, and lipid accumulation (adipogenesis). Activation of PPARα, PPARγ and LXR was determined in hepatic (HepG2) cells by reporter gene assays. Glucose uptake was determined in differentiated muscle (C2C12) cells using 2-NBDG (2-deoxy-2-[(7-nitro-2,1,3-benzoxadiazol-4-yl)amino]-D-glucose). Adipogenesis was determined in adipocytes (3T3-L1 cells) by Oil red O staining. At a concentration of 50 µg/mL, AF caused 12.2-fold activation of PPARα and 5.7-fold activation of PPARγ, while the activation of LXR was only 1.7-fold. AF inhibited (28%) the adipogenic effect induced by rosiglitazone in adipocytes and increased glucose uptake (32.8%) in muscle cells at 50 μg/mL. It was concluded that AF acted as a PPARα/γ dual agonist without the undesired effect of adipogenesis and exhibited the property of enhancing glucose uptake. This is the first report to reveal the PPARα/γ dual agonistic action and glucose uptake enhancing property of AF along with its antiadipogenic effect, indicating its potential in ameliorating the symptoms of metabolic syndrome.  相似文献   
33.
The dispersal of CuO catalyst on the surface of the semiconducting SnO2 film is found to be of vital importance for improving the sensitivity and the response speed of a SnO2 gas sensor for H2S gas detection. Ultra-thin CuO islands (8 nm thin and 0.6 mm diameter) prepared by evaporating Cu through a mesh and subsequent oxidation yield a fast response speed and recovery. Ultimately nanoparticles of Cu (average size = 15 nm) prepared by a chemical technique using a reverse micelle method involving the reduction of Cu(NO3)2 by NaBH4 exhibited significant improvement in the gas sensing characteristics of SnO2 films. A fast response speed of ∼14 s and a recovery time of ∼60 s for trace level ∼20 ppm H2S gas detection have been recorded. The sensor operating temperature (130° C) is low and the sensitivity (S = 2.06 × 103) is high. It is found that the spreading over of CuO catalyst in the nanoscale range on the surface of SnO2 allows effective removal of excess adsorbed oxygen from the uncovered SnO2 surface due to spill over of hydrogen dissociated from the H2S-CuO interaction.  相似文献   
34.
Sintered ceramic powders of calcium-doped lead titanate [Pb1−xCaxTiO3] ceramics with different Ca dopant concentration in the range (x=0-0.35) have been prepared using a sol-gel chemical route. The sol-gel technique is known to offer better purity and homogeneity, and can yield stoichiometric powders with improved properties at relatively lower processing temperature in comparison to conventional solid-state reaction. X-ray diffraction (XRD) and Raman spectroscopy studies have been carried out to identify the crystallographic structure and phase formation. The infrared absorption spectra in the mid-IR region (400-4000 cm−1) show the band corresponding to the Ti-O bond at ∼576 cm−1 and is found to shift to a higher wave number 592 cm−1 with increasing Ca content. The dielectric properties as a function of frequency, and phase transition studies on sintered ceramic Pb0.65Ca0.35TiO3 has been investigated in detail over a wide temperature range 30-600 °C and the results are discussed.  相似文献   
35.
Summary Considering the analogy of a liquid surface to a stretched membrane, the theory of large elastic deformations is used to calculate the deformed shapes of sessile and pendent liquid drops of some polymers. In particular, the liquid drops are treated as highly deformable liquid-filled membranes that follow a neo-Hookean constitutive equation. Since, with the advent of sophisticated pressure transducers, it is easier to measure pressure accurately than to determine the curvature of the liquid drop geometry, the problem is formulated in terms of the pressure prescribed at the tip of the liquid drop with a varying hydrostatic pressure. The governing equations consisting of a non-linear ordinary differential equation and aVolterra type integral equation are solved numerically on a digital computer.Based on the solution of the governing equations, a procedure to estimate the surface tension of a polymer from the shape factor versus pressure curves is illustrated. Also, by increasing the pressure and by balancing the vertical component of the surface tension against the weight of a pendent liquid drop the size of a drop separated from a liquid column is predicted.
Zusammenfassung Mit Rücksicht auf die Analogie zwischen einer flüssigen Oberfläche und einer gespannten Membrane wird die Theorie der großen elastischen Deformationen angewendet, um die deformierte Gestalt von sitzenden und hängenden flüssigen Tropfen einiger Polymere zu kalkulieren. Im besonderen werden die flüssigen Tropfen als sehr deformierbare liquid gefüllte Membranen behandelt, die einer neo-Hookeschen konstitutiven Gleichung folgen. Das Problem ist so formuliert, daß der Druck an der Spitze eines flüssigen Tropfens als ein veränderlicher hydrostatischer Druck ausgedrückt wird, weil mit den neuen hochentwickelten Druckvermittlern es leichter ist, den Druck direkt zu messen, als die Krümmung eines flüssigen Tropfens von seiner Geometrie zu bestimmen. Die Gleichungen, von denen die Geometrie eines Tropfens bestimmt werden, bestehen aus einer nichtlinearen Differentialgleichung und einerVolterra-Integralgleichung. Diese Gleichungen werden mit Hilfe eines Computers gelöst.Aufgrund der Lösung dieser Gleichungen wird ein Verfahren entwickelt, das die Bestimmung der Oberflächenspannung eines Polymers von dem Formfaktor Gegendruckkurven ermöglicht. Die Größe eines von der flüssigen Säule getrennten Tropfens kann mit Hilfe von erhöhtem Druck durch Kräfteausgleich vorherbestimmt werden.


This work is an extension of the work performed under the National Science Foundation Grant No. GK-4842.

With 8 figures  相似文献   
36.
The first use of the spirodiepoxide functional group in total synthesis, a study culminating in an efficient synthesis of the potent proteasome inhibitor epoxomicin, is described. Spirodiepoxides derived from allenes by oxidation are shown to give syn disubstituted ketones and their derivatives, including ortho ester, oxazoline, azido epoxide, as well as sulfonamide-, amide-, and azide-containing hydroxy ketones.  相似文献   
37.
The LRS Bianchi type-I and type-II string cosmological models are studied when the source for the energy momentum tensor is a bulk viscous stiff fluid containing one dimensional strings together with zero-mass scalar field. We have obtained the solutions of the field equations assuming a functional relationship between metric coefficients when the metric is Bianchi type-I and constant deceleration parameter in case of Bianchi type-II metric. The physical and kinematical properties of the models are discussed in each case. The effects of Viscosity on the physical and kinematical properties are also studied.  相似文献   
38.
A three-component Mannich-type reaction of aromatic aldehydes, anilines, and cyclohexanone in the presence of Amberlyst-15 affords the corresponding β-amino ketones in good yields at room temperature. The conversion is highly diastereoselective, favoring the formation of anti-isomers.  相似文献   
39.
A novel tea bag methodology for resolution of methyl esters of N-acetyl-α-amino acids in reverse micellar medium of bis (2-ethylhexyl) sulfosuccinate sodium salt (AOT) in isooctane-chloroform using immobilized enzymes or microbial cells is presented. The methodology effectively solves the problems of substrate solubility, product separation and surfactant recycling and provides products in high yields (80 to 90%) and excellent optical purities (% ee 97 to >99%).  相似文献   
40.
A novel pentacyclic heterocycle has been synthesized starting from D ‐glucose involving two crucial conversions: the intramolecular cycloaddition of O‐allyloxy furanaldoxime derived from D ‐glucose to furanopyran‐2‐isoxazoline and its diastereoselective reductive cleavage to the corresponding cis‐1,3‐amino alcohol. The antibacterial and antifungal activities of the synthesized heterocycle have been examined.  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