全文获取类型
收费全文 | 217篇 |
免费 | 9篇 |
国内免费 | 20篇 |
专业分类
化学 | 203篇 |
晶体学 | 1篇 |
物理学 | 42篇 |
出版年
2024年 | 1篇 |
2023年 | 3篇 |
2022年 | 8篇 |
2021年 | 6篇 |
2020年 | 4篇 |
2019年 | 2篇 |
2018年 | 10篇 |
2017年 | 5篇 |
2016年 | 4篇 |
2015年 | 9篇 |
2014年 | 8篇 |
2013年 | 15篇 |
2012年 | 11篇 |
2011年 | 9篇 |
2010年 | 7篇 |
2009年 | 9篇 |
2008年 | 7篇 |
2007年 | 12篇 |
2006年 | 14篇 |
2005年 | 10篇 |
2004年 | 10篇 |
2003年 | 8篇 |
2002年 | 7篇 |
2001年 | 6篇 |
2000年 | 7篇 |
1999年 | 6篇 |
1998年 | 6篇 |
1997年 | 5篇 |
1996年 | 3篇 |
1995年 | 4篇 |
1994年 | 2篇 |
1993年 | 2篇 |
1992年 | 3篇 |
1990年 | 1篇 |
1987年 | 5篇 |
1986年 | 1篇 |
1984年 | 2篇 |
1982年 | 1篇 |
1981年 | 3篇 |
1980年 | 1篇 |
1979年 | 6篇 |
1978年 | 2篇 |
1977年 | 1篇 |
排序方式: 共有246条查询结果,搜索用时 15 毫秒
41.
采用模板法制备了CuO-CeO2-SiO2和稀土掺杂的CuO-Ce0.9M0.1O2-SiO2 (M=La, Pr, Nd)催化剂. 运用X射线衍射(XRD), N2吸附-脱附, 透射电镜(TEM), 拉曼(Raman)光谱, X射线光电子能谱(XPS)和氢气-程序升温还原(H2-TPR)等手段对催化剂的结构进行表征, 并考察稀土掺杂对氯化氢催化氧化制氯气性能的影响. 结果表明, 稀土掺杂进入CeO2晶格中形成良好的固溶体结构, 获得更小的晶粒尺寸和更高的比表面积, 并且显著提高了固溶体的表面氧空位浓度. 稀土掺杂显著影响了催化剂的氯化氢催化氧化活性, 活性顺序为: CuOCe0.9La0.1O2-SiO2>CuO-Ce0.9Nd0.1O2-SiO2>CuO-Ce0.9Pr0.1O2-SiO2>CuO-CeO2-SiO2, 固溶体氧空位浓度的高低与氯化氢氧化活性直接相关. 通过与Ce0.9M0.1O2-SiO2催化剂的结构和性能的对比, 发现氧空位浓度的提高并不能增强在固溶体表面发生的氯化氢氧化反应. 动力学测试显示, 稀土掺杂后, 氧分子的吸附成为反应过程的决速步骤. 但在V(O2):V(HCl)=1 条件下, 更高的氧空位浓度导致了固溶体更低的氯化氢氧化反应速率. 结合机理分析认为, CuO-Ce0.9M0.1O2-SiO2催化剂更高的氧空位浓度增强了固溶体表面的“氧溢流”, 加快了氯化氢氧化的整体反应速率, 这是CuO-Ce0.9M0.1O2-SiO2具备高活性的关键. 相似文献
42.
A distinct approach for the synthesis of α-aminonitriles has been discovered by three-component reaction of nitroarenes, aldehydes, and TMSCN using indium in dilute aqueous HCl at room temperature. The products were formed in high yields (86-96%) within a short period of time (5-20 min). This one-pot conversion consists of the following steps: (i) reduction of nitro compounds to amines, (ii) formation of imines from amines and aldehydes and (iii) addition of cyanide anion to the imines. 相似文献
43.
HCl是一种有毒有害气体,对其高灵敏度探测具有非常重要的意义,然而到目前为止,采用激光光谱的手段对其探测的研究报道很少。石英增强光声光谱(QEPAS)是近年来发展起来的一种痕量气体探测技术,具有系统体积小、价格低廉、探测灵敏度高等优点。以5 000 ppm HCl∶N2混合气作为待测目标,采用输出波长为1 742.38 nm的分布反馈连续波单纵模半导体激光器,开展对基于QEPAS技术的HCl高灵敏度探测研究。为了提高信噪比和简化数据处理过程,QEPAS传感器系统采用波长调制和2次谐波探测技术。研究中,首先对声波探测系统中微共振腔强声波增强特性进行了讨论,选择了“共轴”形式的声波微共振腔,并对其尺寸进行了优化,选择的微共振管长度为4 mm、内径为0.5 mm。实验中研究了激光波长调制深度对QEPAS系统产生的信号幅度的影响,当QEPAS系统积分时间为1 s、激光波长调制深度为0.23 cm-1时,获得了815 ppb的优异检测极限,归一化噪声等效吸收系数为7.41×10-9 cm-1·W·Hz-1/2。在后续的实验中,可在待测HCl气体中加入水汽分子,提高HCl分子的热弛豫速率,进一步提高HCl-QEPAS传感器系统的信号强度。 相似文献
44.
Zhimei Tian Na Zhang Chongfu Song Chang Wang 《International journal of quantum chemistry》2024,124(1):e27262
The interaction behavior of HCl and (ZnS)n (n = 1–12) clusters and HCl effect on Hg0 adsorbed by (ZnS)n have been studied theoretically. The combined genetic algorithm and density functional theory (GA-DFT) method has been used to obtain the structures of (ZnS)nHCl and (ZnS)nHgHCl (n = 1–12) clusters. The structural properties of (ZnS)nHCl and (ZnS)nHgHCl have been analyzed. The adsorption energies and interaction energies have been calculated. Bond length and bond order analysis has revealed that S H and Zn Cl bonds form after HCl adsorbed on (ZnS)n clusters, while Hg0 can only weakly bind with (ZnS)nHCl clusters. According to thermodynamic adsorption analysis, the formation of (ZnS)nHCl clusters from (ZnS)n and HCl are spontaneous because of their negative Gibbs free energy changes. The formation of (ZnS)nHgHCl from (ZnS)nHCl and Hg are nonspontaneous for n = 1–4 and 9, and the Gibbs free energy changes have small negative values for other sizes. Electron localization function and noncovalent interaction (NCI) analysis of (ZnS)10HgHCl manifest that Hg and its nearest Zn form zinc amalgam. Projected density of state study has been performed to obtain the interaction nature of HCl and (ZnS)n clusters and Hg0 adsorption on (ZnS)nHCl clusters. Based on our study, HCl is chemical adsorbed by (ZnS)n clusters except (ZnS)4 cluster. After (ZnS)n adsorbs HCl, Hg0 can physically adsorb on (ZnS)nHCl clusters. The strength of Hg0 on (ZnS)nHCl is comparable to that of Hg0 on (ZnS)n, indicating that HCl can hardly affect the adsorption of Hg0 on ZnS clusters. 相似文献
45.
《Analytical letters》2012,45(6):1153-1162
Abstract A procedure is described for the assay of phenylpropanolamine hydrochloride & isopropamide by HPLC using CROWNPAK column and detection at 200 nm. The system was aqueous perchloric acid as mobile phase containing 5 % methanol. Linearity studies were carried out using peak height measurements. There was > 99 % recovery and coefficient of variation was < 2% for formulation. The procedure was rapid, accurate, precise and specific for the assay of phenylpropanolamine HCl in presence of isopropamide. 相似文献
46.
Nondestructive three‐dimensional refractive‐index measurements are used for the determination of both crystallinity and orientation in thin polymer films. The prism waveguide coupler is particularly suitable for three‐dimensional isotropic and anisotropic thin‐film studies because of the quantitative character of the information obtained and the ease of data acquisition. It has been limited, however, to measuring the refractive index of optically transparent or weakly absorbing films. This study shows that a modified prism waveguide coupler can be used to determine the complex refractive index over a range from transparent to highly absorbing films from the internally reflected light intensity. Thus, both the refractive index, n, and the extinction coefficient, k, can be obtained. This method is used to determine the anisotropic three‐dimensional n and k values of spin‐coated emeraldine base and hydrogen chloride doped emeraldine salt polyaniline films. © 2001 John Wiley & Sons, Inc. J Polym Sci Part B: Polym Phys 39: 2481–2490, 2001 相似文献
47.
建立了动物组织中金霉素残留测定的高效液相色谱柱后衍生法,研究了镁离子和草酸体系对金霉素荧光强度的影响。结果表明,镁离子浓度和草酸浓度为1∶1.2时,金霉素的荧光强度最强。动物组织样品以5%高氯酸提取,正己烷脱脂,C18净化,Hy-persil ODS C18(250×4.6 mm,5μm)分离,流动相为甲醇∶0.05 mol/L草酸=80∶20(V/V),流速为0.7 mL/min,柱后0.05 mol/L乙酸镁衍生,流速为0.1 mL/min,紫外检测器和荧光检测器同时测定,提高了金霉素残留定量灵敏度。紫外检测波长365nm,荧光检测波长eλx=360 nm,eλm=520 nm。 相似文献
48.
Noha M. Soliman Faiyaz Shakeel Nazrul Haq Fars K. Alanazi Sultan Alshehri Mohsen Bayomi Ahmed S. M. Alenazi Ibrahim A. Alsarra 《Molecules (Basel, Switzerland)》2022,27(14)
Various chitosan (CS)-based nanoparticles (CS-NPs) of ciprofloxacin hydrochloride (CHCl) have been investigated for therapeutic delivery and to enhance antimicrobial efficacy. However, the Box–Behnken design (BBD)-supported statistical optimization of NPs of CHCl has not been performed in the literature. As a result, the goal of this study was to look into the key interactions and quadratic impacts of formulation variables on the performance of CHCl-CS-NPs in a systematic way. To optimize CHCl-loaded CS-NPs generated by the ionic gelation process, the response surface methodology (RSM) was used. The BBD was used with three factors on three levels and three replicas at the central point. Tripolyphosphate, CS concentrations, and ultrasonication energy were chosen as independent variables after preliminary screening. Particle size (PS), polydispersity index (PDI), zeta potential (ZP), encapsulation efficiency (EE), and in vitro release were the dependent factors (responses). Prepared NPs were found in the PS range of 198–304 nm with a ZP of 27–42 mV. EE and drug release were in the range of 23–45% and 36–61%, respectively. All of the responses were optimized at the same time using a desirability function based on Design Expert® modeling and a desirability factor of 95%. The minimum inhibitory concentration (MIC) of the improved formula against two bacterial strains, Pseudomonas aeruginosa and Staphylococcus aureus, was determined. The MIC of the optimized NPs was found to be decreased 4-fold compared with pure CHCl. The predicted and observed values for the optimized formulation were nearly identical. The BBD aided in a better understanding of the intrinsic relationship between formulation variables and responses, as well as the optimization of CHCl-loaded CS-NPs in a time- and labor-efficient manner. 相似文献
49.
The reactions between OH radicals and hydrogen halides (HCl, HBr, HI) have been studied between 298 and 460 K by using a discharge flow-electron paramagnetic resonance technique. The rate constants were found to be kHCl(298 K) = (7.9 ± 1.3) × 10−13 cm3 molecule−1 s−1 with a weak positive temperature dependence, kHBr (298-460 K) = (1.04 ± 0.2) × 10−11 cm3 molecule−1 s−1, and kHI(298 K) = (3.0 ± 0.3) × 10−11 cm3 molecule−1 s−1, respectively. The homogeneous nature of these reactions has been experimentally tested. 相似文献
50.
Oxidation of acetylacetone (AA) by bromamine-B (BAB) in HC1 medium (0.1 to 0.6 mol dm−3) at constant ionic strength has been investigated at 40°C. The rate is first order in [BAB]0 and fractional order each in [AA]0 and [H+]. The reaction is also catalysed by chloride ion. Michaelis-Menten type of kinetics is observed. Decrease in dielectric constant
of medium increases the rate. A solvent isotope effect κ′H2O/κ′D2O = 0.96 has been noted. Activation parameters for the rate limiting step have been computed. The mechanism involves the enol
form of the diketone. 相似文献