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   139篇
  免费   2篇
化学   90篇
晶体学   2篇
力学   2篇
数学   2篇
物理学   45篇
  2024年   1篇
  2023年   3篇
  2022年   9篇
  2021年   10篇
  2020年   9篇
  2019年   8篇
  2018年   7篇
  2017年   6篇
  2016年   3篇
  2015年   1篇
  2014年   4篇
  2013年   10篇
  2012年   5篇
  2011年   7篇
  2010年   5篇
  2009年   10篇
  2008年   11篇
  2007年   7篇
  2006年   5篇
  2005年   1篇
  2004年   2篇
  2003年   1篇
  2002年   2篇
  1997年   1篇
  1991年   2篇
  1990年   1篇
  1989年   3篇
  1981年   1篇
  1979年   1篇
  1978年   1篇
  1976年   2篇
  1950年   2篇
排序方式: 共有141条查询结果,搜索用时 15 毫秒
71.
Simple, sensitive, rapid, and accurate high-performance liquid chromatographic (HPLC) method is developed and validated for the simultaneous determination of diltiazem, metformin, pioglitazone, and rosiglitazone hydrochloride in raw materials, their pharmaceutical formulations, and human serum. In HPLC, all the above drugs were chromatographed using acetonitrile-methanol-water (30:20:50, v/v, pH 2.59 ± 0.02) as the mobile phase at a flow rate of 1.0 mL/min at ambient temperature. The separation is carried out on a Hiber, 250-4.6 RP-18 column, equipped with a UV-vis detector at 230 nm. All the antidiabetic drugs eluted at different retention time and each showed a good resolution from diltiazem. The method is successfully applied to pharmaceutical formulations because no chromatographic interferences from the tablet excipients are found. The method is found to be linear, accurate, and precise with apposite detection and quantification limit. Suitability of the method for the quantitative determination of the drugs is proven by validation in accordance with the requirements laid down by International Conference on Harmonization (ICH) guidelines. The validation results, together with statistical treatment of the data, demonstrated the reliability of this method.  相似文献   
72.
The use of the molecular imprinting technique to produce polymers with high specificity for a given “molecular template” has undergone a rapid and expansive evolution since the inception of the idea over half a century ago. It was only a matter of time before the seemingly inevitable “marriage” of this concept with another modern research obsession, the generation of “smart” polymers, capable of reacting quickly, accurately and reproducibly to changes in their environment. Many advances have since been made, concerning the quality and diversity of these systems and polymers responsive to temperature, pH and a host of other environmental cues now exist. This article provides a succinct overview of the process and outcomes of “smart” molecular imprinting, followed by a detailed assessment of recent developments and applications in such field.

  相似文献   

73.
Investigating the dynamic characteristics of nonlinear models that appear in ocean science plays an important role in our lifetime. In this research, we study some features of the paired Boussinesq equation that appears for two-layered fluid flow in the shallow water waves. We extend the modified expansion function method (MEFM) to obtain abundant solutions, as well as to find new solutions. By using this newly modified method one can obtain novel and more analytic solutions comparing to MEFM. Also, numerical solutions via the Adomian decomposition scheme are discussed and favorable comparisons with analytical solutions have been done with an outstanding agreement. Besides, the instability modulation of the governing equations are explored through the linear stability analysis function. All new solutions satisfy the main coupled equation after they have been put into the governing equations.  相似文献   
74.
Shock tube experiments have been carried out on 2-methyl-1-butene (2M1B), 2-methyl-2-butene (2M2B), and 3-methyl-1-butene (3M1B)—the three isomers of methyl butene compound. Carbon monoxide (CO) time-histories and ignition delay times are obtained behind reflected shockwaves over the temperature range of 1350-1630 K and pressures of 8.3-10.5 atm with stoichiometric mixtures of 0.075% fuel in O2/Ar. Comparative ignition study reveals that 3M1B ignites significantly faster than the other two isomers, while 2M1B dissociates earlier but ignites later than 2M2B. Possible mechanisms for this behavior are discussed with ignition delay time sensitivity and reaction path analysis. In addition, time-resolved CO measurements are compared with three different reaction mechanisms from the literature. Sensitivity analyses have been carried out to identify important reactions that need attention to accurately predict the chemistry of these isomers. Further investigation into the rates of unimolecular fuel decomposition reactions and C3H3 + O2 = CH2CO + HCO reaction are suggested based on the current investigation.  相似文献   
75.
76.
This paper deals with the existence of proper conformal Killing vectors(CKVs) in Kantowski-Sachs metric.Subject to some integrability conditions, the general form of vector filed generating CKVs and the conformal factor is presented. The integrability conditions are solved generally as well as in some particular cases to show that the nonconformally flat Kantowski-Sachs metric admits two proper CKVs, while it admits a 15-dimensional Lie algebra of CKVs in the case when it becomes conformally flat. The inheriting conformal Killing vectors(ICKVs), which map fluid lines conformally, are also investigated.  相似文献   
77.
In this Letter, the solution of non-homogeneous orthotropic elastic cylinder for plane strain problems is developed. The dynamical problem of an orthotropic cylinder containing: (i) an isotropic core and (ii) a rigid core are considered. The elastic constants and density are taken as a power function of the radial coordinate. Analytical expressions for the component of the displacement and the components of the stresses in different cases are obtained. The numerical calculations are carried out for the component of displacement and the components of the stresses through the radial of the cylinder. The results indicate that the effect of inhomogeneity is very pronounced. Those cases have been illustrated and discussed by figures.  相似文献   
78.
We reported here the level structure in the ood proton nucleus Ho151. High spin states in Ho151 have been populated in the Sn122 (Cl35, xyzγ) reaction. The level structure has been established up to an energy of 9.9 MeV and spin value I = 63/2. The systematic behavior of the level pattern of Ho151 nucleus is discussed in the context of the high-spin structure in the neighbouring nuclei. Most of the proposed level configurations can be explained by the coupling of h 11/2 protons to f 7/2 and/or h 9/2 neutrons.  相似文献   
79.
A simple, sensitive, selective, precise and stability-indicating high-performance thin-layer chromatographic (HPTLC) method for densitometric determination of moxifloxacin both as a bulk drug and from pharmaceutical formulation was developed and validated as per the International Conference on Harmonization (ICH) guidelines. The method employed TLC aluminium plates pre-coated with silica gel 60F-254 as the stationary phase and the mobile phase consisted of n-propanol-ethanol-6 M ammonia solution (4:1:2, v/v/v). Densitometric analysis of moxifloxacin was carried out in the absorbance mode at 298 nm. Compact spots for moxifloxacin were found at Rf value of 0.58 ± 0.02. The linear regression analysis data for the calibration plots showed good linear relationship with r = 0.9925 in the working concentration range of 100-800 ng spot−1. The method was validated for precision, accuracy, ruggedness, robustness, specificity, recovery, limit of detection (LOD) and limit of quantitation (LOQ). The LOD and LOQ were 3.90 and 11.83 ng spot−1, respectively. Drug was subjected to acid and alkali hydrolysis, oxidation, dry heat, wet heat treatment and photodegradation. All the peaks of degradation products were well resolved from the standard drug with significantly different Rf values. Statistical analysis proves that the developed HPTLC method is reproducible and selective. As the method could effectively separate the drug from its degradation products, it can be employed as stability-indicating one. Moreover, the proposed HPTLC method was utilized to investigate the kinetics of the acidic and alkaline degradation processes at different temperatures. Arrhenius plot was constructed and apparent pseudo-first-order rate constant, half-life and activation energy were calculated. In addition the pH-rate profile for degradation of moxifloxacin in constant ionic strength buffer solutions within the pH range 1.2-10.8 was studied.  相似文献   
80.
Prostate cancer (PCa) is the most common cancer in men, accounting for approximately 10% of all new cases in the United States. Plant-derived bioactive compounds, such as pentacyclic triterpenoids (PTs), have the ability to inhibit PCa cell proliferation. We isolated and characterized nummularic acid (NA), a potent PT, as a major chemical constituent of Ipomoea batatas, a medicinal food plant used in ethnomedicine for centuries. In the current study, in vitro antiproliferative potential against PCa cells (DU145 and PC3) via 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl-2H-tetrazolium bromide (MTT) assay; Western blot protein expression analysis; absorption, distribution, metabolism, excretion (ADME); pharmacokinetic prediction studies; and bisphenol A (BPA)-induced prostate inhibition in Sprague Dawley rats were conducted to gauge the anti-cancer ability of NA. Significant (p < 0.05 and p < 0.01) time- and dose-dependent reductions in proliferation of PCa cells, reduced migration, invasion, and increased apoptotic cell population were recorded after NA treatment (3–50 µM). After 72 h of treatment, NA displayed significant IC50 of 21.18 ± 3.43 µM against DU145 and 24.21 ± 3.38 µM against PC3 cells in comparison to the controls cabazitaxel (9.56 ± 1.45 µM and 12.78 ± 2.67 µM) and doxorubicin (10.98 ± 2.71 µM and 15.97 ± 2.77 µM). Further deep mechanistic studies reveal that NA treatment considerably increased the cleavage of caspases and downstream PARP, upregulated BAX and P53, and downregulated BCL-2 and NF-κB, inducing apoptosis in PCa cells. Pharmacokinetic and ADME characterization indicate that NA has a favorable physicochemical nature, with high gastrointestinal absorption, low blood–brain barrier permeability, no hepatotoxicity, and cytochrome inhibition. BPA-induced perturbations of prostate glands in Sprague Dawley rats show a potential increase (0.478 ± 0.28 g) in prostate weight compared to the control (0.385 ± 0.13 g). Multi-dose treatment with NA (10 mg/kg) significantly reduced the prostate size (0.409 ± 0.21 g) in comparison to the control. NA-treated groups exhibited substantial restoration of hematological and histological parameters, reinstatement of serum hormones, and suppression of inflammatory markers. This multifaceted analysis suggests that NA, as a novel small molecule with a strong pharmacokinetic and pharmacological profile, has the potential to induce apoptosis and death in PCa cells.  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