全文获取类型
收费全文 | 197篇 |
免费 | 9篇 |
国内免费 | 46篇 |
专业分类
化学 | 206篇 |
晶体学 | 9篇 |
物理学 | 37篇 |
出版年
2024年 | 2篇 |
2023年 | 2篇 |
2022年 | 5篇 |
2021年 | 8篇 |
2020年 | 9篇 |
2019年 | 8篇 |
2018年 | 4篇 |
2017年 | 13篇 |
2016年 | 10篇 |
2015年 | 4篇 |
2014年 | 4篇 |
2013年 | 15篇 |
2012年 | 16篇 |
2011年 | 20篇 |
2010年 | 10篇 |
2009年 | 11篇 |
2008年 | 14篇 |
2007年 | 13篇 |
2006年 | 9篇 |
2005年 | 10篇 |
2004年 | 6篇 |
2003年 | 6篇 |
2002年 | 4篇 |
2001年 | 9篇 |
2000年 | 3篇 |
1999年 | 5篇 |
1998年 | 2篇 |
1997年 | 3篇 |
1996年 | 7篇 |
1995年 | 7篇 |
1994年 | 3篇 |
1993年 | 2篇 |
1992年 | 3篇 |
1991年 | 2篇 |
1990年 | 3篇 |
排序方式: 共有252条查询结果,搜索用时 31 毫秒
211.
A method for the selective hydration of nitrile to amide by employing commercially available acetaldoxime and inexpensive oxometallate such as molybdate, vanadate, and tungstate in environmentally friendly water is described. Under this protocol, nitriles including aromatic nitriles, heterocyclic nitriles, and aliphatic nitriles were converted into the corresponding amides in good to excellent yields.
[Supplementary materials are available for this article. Go to the publisher's online edition of Synthetic Communications® for the following free supplemental resource(s): Full experimental and spectral details.] 相似文献
212.
I. A. Darwish A. S. Khedr H. F. Askal R. M. Mahmoud 《Journal of Applied Spectroscopy》2006,73(6):792-797
Three simple and sensitive spectrophotometric methods (A–C) for determination of amantadine hydro-chloride have been developed
and validated. The first method (A) is based on the oxidation of the drug by ammonium molybdate. The second method (B) was
based on the charge-transfer complexation reaction between the amantadine base as an electron donor and iodine as a σ-acceptor.
The third method (C) is based on the reaction of N-alkylvinylamine formed from the interaction of the free amino group in
amantadine molecule and acetalde-hyde with chloranil to give colored vinylamino-substituted benzoquinone. The colored products
of these reactions were measured at their corresponding maximum absorption peaks. Different variables affecting the reactions
were carefully studied and optimized. Under the optimum conditions, linear relationships with good correlation coefficients
0.9993–0.9998 were found between the reading and the corresponding concentration of the drug in the range 2–90 μg·ml−1. The limits of detection ranged from 0.16 to 1.91 μg·ml−1. The precision of the methods was satisfactory: the values of relative standard deviation did not exceed 1.63%. The proposed
methods were successfully applied to the analysis of amantadine HCl in its capsules with good accuracy and precision; the
label claim percentages ranged from 99.8 to 100.5 ± (0.52–1.22) %. The results obtained by the proposed spectrophotometric
methods were comparable with those obtained by the official method.
Published in Zhurnal Prikladnoi Spektroskopii, Vol. 73, No. 6, pp. 707–712. 相似文献
213.
建立激光拉曼光谱法测定模拟高放废液中钼酸根的分析方法。考察了拉曼光谱法测量钼酸根的主要影响因素。以硝酸根作为内标物,在选定的实验条件下,钼酸根与硝酸根的拉曼光谱特征峰强度比值与钼酸根浓度呈良好的线性关系,钼酸根浓度分别为0.002~0.08,0.05~0.80 mol/L时,线性方程分别为y=247c–0.178 8,y=11.36c–0.112 8,r~20.999,方法检出限为0.001 mol/L。采用该方法测定模拟高放废液中的钼酸根,测定值与配制值相比,相对误差小于5%,测量结果的相对标准偏差小于4%(n=6)。该方法操作简便、检测快速、制样简单、取样量小。 相似文献
214.
Enrico Cavalli Philippe Boutinaud Pieter Dorenbos 《Journal of solid state chemistry》2008,181(5):1025-1031
The luminescence properties of KLa(MoO4)2 (KLM) single crystals doped with Pr3+ have been measured in the 10-600 K temperature range in order to investigate the mechanisms involved in the radiationless processes. At variance with previously studied scheelite-like molybdates activated with Pr3+, no effects attributed to the formation of intervalence charge transfer states have been observed. The model proposed in order to account for this behaviour allows the determination of the energy of the Pr3+ levels relative to the valence and conduction bands of the host. This model has firstly been confirmed for Tb3+-doped KLM, for which suitable experimental data are available, and then extended to the other rare earth ions on the basis of the systematic nature of the lanthanide energy levels properties. The obtained conclusions are finally supported in the light of the comparison with some other representative cases. 相似文献
215.
Red phosphors gadolinium tungstate and molybdate with the formula Gd(2−x)MO6:Eux3+ (M=Mo, W) were successfully synthesized by the solid-state reaction at 900 and 1300 °C for 4 h, respectively. The products were characterized by an X-ray powder diffractometer (XRD), TG-DSC, FT-IR, PL, UV-vis and SEM. Room-temperature photoluminescence indicated that the as-prepared Gd(2−x)MO6:Eux3+ (M=Mo, W) had a strong red emission, which is due to the characteristic transitions of Eu3+ (5D0→7FJ, J=0, 1, 2, 3, 4) for these phosphors. Meanwhile, the 5D0→7F2 is in the dominant position. The emission quantum efficiency of Eu3+ in the Gd(2−x)MO6:Eux3+ (M=Mo, W) system has been investigated. The XRD results indicate that both Gd2WO6 and Gd2MoO6 belong to the monoclinic system with space group C2/c [A. Bril, G. Blasse, J. Chem. Phys. 45 (1966) 2350-2356] and I2/a [A. Bril, G. Blasse, J. Chem. Phys. 45 (1966) 2350-2356], respectively. SEM images indicate that the shape of Gd1.96WO6:Eu0.043+ is aggregated small particles with a mean diameter of about 300 nm, and the shape of Gd1.96MoO6:Eu0.043+ is block-like structures. 相似文献
216.
In a hydrochloric acid medium, benzhexol hydrochloride, cyproheptadine hydrochloride, and maprotiline hydrochloride, can react
with ammonium molybdate to form ion-association complexes by virtue of electrostatic attraction and hydrophobic interaction
which result in a significant enhancement of the resonance light scattering intensity. The maximum scattering wavelengths
were found at 364 nm, 364 nm, and 381 nm for benzhexol hydrochloride, cyproheptadine hydrochloride, and maprotiline hydrochloride
systems, respectively. Spectral characteristics of the three systems, influencing factors, and optimum conditions were investigated.
The reason of resonance light-scattering enhancement and the mechanism of interactions between the drugs and ammonium molybdate
were also discussed. Based on the linear relationship between the enhanced intensity of resonance light scattering and the
concentration of drugs, a highly sensitive method for the determination of the three drugs was developed, the detection limits
being 0.0110 μmol L−1, 0.0038 μmol L−1, and 0.0155 μmol L−1 for benzhexol hydrochloride, cyproheptadine hydrochloride, and maprotiline hydrochloride, respectively. The method was successfully
applied to the determination of the investigated drugs in pharmaceutical, serum, and urine samples. 相似文献
217.
[4,4′-bpyH_2][4,4′-bpyH][Cr(OH)_6(Mo_6O_(18))]和[4,4′-bpyH]_3[Al(OH)_6(Mo_6O_(18))]·2H_2O的合成及晶体结构(英文)
通过水热方法合成了两种新的B-Anderson型多钼氧酸盐[4 ,4′-bpyH2][4 ,4′-bpy H][Cr( OH)6( Mo6O18)](1)和[4 ,4′-bpyH]3[Al(OH)6( Mo6O18)].2 H2O(2) ,通过元素分析、IR光谱和单晶X射线衍射对其进行了表征.化合物1和2都是分离结构.化合物1分子由2个晶体学独立1/2 B-Anderson类型[Cr(OH)6( Mo6O18)]3 -多阴离子,1个双质子化的[4 ,4′-bpyH2]2 +阳离子和1个单质子化的[4 ,4′-bpyH]+阳离子组成,化合物2则是由1个晶体学独立完整的B-Anderson型[ Al( OH)6( Mo6O18)]3 -多阴离子, 3个单质子化的[4 ,4′-bpyH]+阳离子和2个晶格水分子组成.借助4 ,4′-bpy分子间的π-π堆积作用,化合物1和2形成三维超分子结构. 相似文献
218.
The synergistic effect of benzotriazole (BTAH) and molybdate on the inhibition of copper tarnish was studied in this paper. The antitarnish treatment of copper was conducted with BTAH solution containing molybdate. The surface morphology observation and composition analysis were investigated by SEM with energy dispersive X‐ray (EDX) spectroscopy. The addition of molybdate improved the protection of BTAH significantly. The BTAH + molybdate treated copper specimen has higher N concentration in its surface. The structure of the protective film was studied by XPS and AES measurements. It was characterized to be a complex of Cu(I)BTA. The antitarnish effect is certified by the formation of the protective Cu(I)BTA film. Molybdate does not participate in the formation of the protective film. The presence of molybdate promotes the passivation of copper. This facilitates the stabilization of the cuprous oxide film, and strengthens the adsorption of BTAH. Copyright © 2008 John Wiley & Sons, Ltd. 相似文献
219.
Recent progress on the bismuth molybdate catalysts for oxidative dehydrogenation of n-butene to 1,3-butadiene was reported in this review. A number of bismuth molybdate catalysts, including pure bismuth molybdates
(α-Bi2Mo3O12, β-Bi2Mo2O9, and γ-Bi2MoO6) and multicomponent bismuth molybdates, were prepared by a co-precipitation method for use in the production of 1,3-butadiene
from C4 raffinate-3 through oxidative dehydrogenation of n-butene. It was observed that multicomponent bismuth molybdate catalyst was more efficient than pure bismuth molybdate catalyst
in the oxidative dehydrogenation of n-butene. Various experimental measurements such as temperature-programmed reoxidation, X-ray photoelectron spectroscopy, and
O2-temperature-programmed desorption analyses were carried out to elucidate the different catalytic activity of bismuth molybdate
catalysts. It was revealed that a bismuth molybdate catalyst with a higher oxygen mobility showed a better catalytic performance
in terms of conversion of n-butene and yield for 1,3-butadiene. We have successfully demonstrated from experimental findings that oxygen mobility of
bismuth molybdate catalyst played a key role in determining the catalytic performance in the oxidative dehydrogenation of
n-butene to 1,3-butadiene. 相似文献
220.