全文获取类型
收费全文 | 162篇 |
免费 | 9篇 |
国内免费 | 3篇 |
专业分类
化学 | 126篇 |
晶体学 | 2篇 |
力学 | 2篇 |
数学 | 12篇 |
物理学 | 32篇 |
出版年
2024年 | 1篇 |
2023年 | 1篇 |
2022年 | 12篇 |
2021年 | 5篇 |
2020年 | 5篇 |
2019年 | 7篇 |
2018年 | 9篇 |
2017年 | 11篇 |
2016年 | 16篇 |
2015年 | 15篇 |
2014年 | 3篇 |
2013年 | 13篇 |
2012年 | 10篇 |
2011年 | 7篇 |
2010年 | 6篇 |
2009年 | 6篇 |
2008年 | 5篇 |
2007年 | 7篇 |
2006年 | 6篇 |
2005年 | 4篇 |
2004年 | 2篇 |
2003年 | 2篇 |
2002年 | 3篇 |
2001年 | 3篇 |
2000年 | 6篇 |
1996年 | 1篇 |
1992年 | 1篇 |
1991年 | 1篇 |
1986年 | 1篇 |
1981年 | 1篇 |
1973年 | 3篇 |
1971年 | 1篇 |
排序方式: 共有174条查询结果,搜索用时 15 毫秒
1.
Saira Shahzadi Moazzam H. Bhatti Khadija Shahid Saqib Ali Saadia R. Tariq Mohammad Mazhar Khalid M. Khan 《Monatshefte für Chemie / Chemical Monthly》2002,133(8):1089-1096
Summary. Tributyltin(IV) derivatives of six different pharmaceutically active carboxylates were synthesized. The complexes were characterized
by different analytical techniques (elemental analysis; infrared, NMR, and mass spectroscopy). 119Sn NMR data were also recorded in six different coordinating and non-coordinating solvents. The antibacterial activities of
the compounds were tested using ten different bacteria relative to the reference drugs ampicillin and cephalexin.
Received September 20, 2001. Accepted (revised) December 6, 2001 相似文献
2.
Solid phase crystallization of plasma-enhanced chemical-vapor-deposited (PECVD) amorphous silicon (alpha-Si:H) in alpha-Si:H/Al and Al/alpha-Si:H structures has been investigated using transmission electron microscopy (TEM) and X-ray diffraction (XRD). Radiative heating has been used to anneal films deposited on carbon-coated nickel (Ni) grids at temperatures between 200 and 400 degrees C for TEM studies. alpha-Si:H films were deposited on c-Si substrates using high vacuum (HV) PECVD for the XRD studies. TEM studies show that crystallization of alpha-Si:H occurs at 200 degrees C when Al film is deposited on top of the alpha-Si:H film. Similar behavior was observed in the XRD studies. In the case of alpha-Si:H deposited on top of Al films, the crystallization could not be observed at 400 degrees C by TEM and even up to 500 degrees C as seen by XRD. 相似文献
3.
A simple, rapid and sensitive spectrophotometric method is described for the quantitative determination ofN-substituted phenothiazines. The method depends on the formation of a stable phenothiazine free radical cation by the use ofN-bromophthalimide as oxidising agent in a strong acid medium (methanol/ sulphuric acid 1 1 v/v). The produced red or violet color possesses absorption maximum range from 500 to 530 nm. A linear relationship exists between the absorbance at (max) and concentration in the range 5 to 40 g ml–1 with apparent molar absorptivities range from 6 × 103 to 12 × 1031 mol–1 cm–1. The color is developed instantaneously for all the studied phenothiazines except for thioproperazine mesylate, trifluoperazine dihydrochloride and prochlorperazine mesylate that require 25, 15 and 25 min, respectively, for complete reaction. The developed colors are stable over 24 h. The average % recovery is 99.85±0.61 to 100.28±0.95. The method was applied successfully to the microdetermination of chlorpromazine HCl, promethazine HCl, pericyazine, thioproperazine mesylate, perphenazine, prochlorperazine mesylate, trimeprazine tartrate and trifluoperazine 2HCl either in pure form or incorporated in their pharmaceutical preparations. The results of analysis are in good agreement with those of the official B.P. 1988 and USP XXII. 相似文献
4.
Rapid direct and induced difference spectrophotometric methods for determination of pyrithioxin in single dosage forms (tablets and syrups) are reported. The direct methods depend upon measurement of the absorbance of pyrithioxin in different media at λmax i-e at 296 nm in 0.1 M hydrochloric acid, at 328 nm in citric acid-phosphate buffer of pH 7 and at 314 nm in 0.1 M sodium hydroxide. The mean percentage recovery of the authentic samples were 100.55±0.43, 101.21±0.58 and 100.29±0.64 respectively (P=0.05). The absorbance difference methods are based upon either measurement of the difference between the acid and the alkaline solutions i-e. Δ A (Alk-Acid) at 318 nm with an accuracy of 100.72±0.88 or the absorbance difference between the acid and neutral solutions i-e Δ A (pH 7-acid) at 328 nm with an accuracy of 100.31±0.68. 相似文献
5.
Giacomo Luigi Petretto Carlo Ignazio G. Tuberoso Gina Vlahopoulou Alessandro Atzei Alberto Mannu Saadia Zrira 《Natural product research》2016,30(3):286-292
Seven commercial Moroccan honeys were considered for chemical characterisation. Volatile fraction, total polyphenols content, antioxidant and antiradical activities were evaluated by employing different analytical methodologies. Several physical parameters such as refractive index, pH, water content, solids content and colour were measured. Volatile fraction revealed an abundant presence of cis- and trans-linalool oxide in the seven studied samples. The presence of high levels of compounds related to the Maillard reaction, like furfural and hydroxymethylfurfural, could be the result of thermal treatments used to liquefy commercial honeys or of long storage times. The CIE L*a*b*Cab*hab° chromatic coordinates confirmed the advanced stage of the Maillard reaction, showing L* values lower than the common values found for honey of similar typologies. 相似文献
6.
Richard Cremlyn Naseem Akhtar 《Phosphorus, sulfur, and silicon and the related elements》2013,188(3):247-255
Abstract Pyrrolidine, morpholine, and β-hydroxyethylmorpholine have been phosphorylated with phosphorus oxychloride, phenylphosphorodichloridate, p-chlorophenylphosphorodichloridate and thiophosphoryl chloride. The resultant phosphorodichloridates have been condensed with a wied range of nucleophilic reagents, e.g. amines, hydrazines, phenols and isobutanol. Piperazine with phosphorus oxychloride (2 mols) gave the N(1) N(4)-diphosphorotetrachloridate, which was characterized as the tetracyclohexylamidate. β-Hydroxyethylpiperazine was similarly phosphorylated to the N,O-diphosphorotetrachloridate which was characterized as the tetraphenylhydrazidate. Condensation of pyrrolidine (2 mols) with phosphorus oxychloride (1 mol) afforded N,N′-dipyrrolidinophosphorochloridate which was reacted with phenylhydrazide and sodium azide. The phosphoroazide with triphenylphosphine afforded the corresponding triphenylphosphinimine. N-Phenyl N′-pyrrolidinophosphorochloridate with aqueous pyridine gave the corresponding pyrophosphoramide and the stability of the pyrophosphoramide towards hydrolysis was examined. 1,2-Cyclohexanediol was phosphorylated with phenylphosphorodichloridate and thiophosphorylchloride. Trans-4-t-Butylcyclohexyl N,N′-diphenylhydrazinophosphorothioate by reaction with formaldehyde gave a tetra-azaphosphorine P-sulfide. Trans-4-t-Butylcyclohexyl N-phenyl N′-phenylphosphorodiamidic hydrazide reacted with 1,4-dibromobut-2-ene to give a 1,2-diazahex-4-ene. 相似文献
7.
We have reported the reductive cleavage of azlactones1 and phenylhydrazones2 of carbonyl compounds in the presence of a suitable catalyst. In this paper a general method involving a one step synthesis of β-amino acid3,4, in good yield, through catalytic reduction of oximes of α-β-unsaturated acid is reported. This method involves the reaction of α, β-unsaturated acid with hydroxylamine hydrochloride in the presence of sodium acetate. Markovnikov's rule is followed in the synthesis of oximes of α, β-unsaturated acids. 相似文献
8.
Sn(IV)Cl4 catalyst provided a rapid and efficient deprotection method for the phenolic THP and MOM ethers and sequel intramolecular Friedel–Crafts alkylation reaction of THP and MOM protected chalcone epoxides under mild conditions. The reaction took 2–3 min to give the products in excellent yield (90–98%) at 0 °C without affecting the other functional groups. 相似文献
9.
Dr. Mégane Muschi Anusha Lalitha Dr. Saad Sene Dr. Damien Aureau Dr. Mathieu Fregnaux Dr. Imène Esteve Dr. Lucie Rivier Dr. Naseem Ramsahye Dr. Sabine Devautour-Vinot Dr. Clémence Sicard Prof. Nicolas Menguy Dr. Christian Serre Prof. Guillaume Maurin Prof. Nathalie Steunou 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(26):10439-10444
An innovative strategy is proposed to synthesize single-crystal nanowires (NWs) of the Al3+ dicarboxylate MIL-69(Al) MOF by using graphene oxide nanoscrolls as structure-directing agents. MIL-69(Al) NWs with an average diameter of 70±20 nm and lengths up to 2 μm were found to preferentially grow along the [001] crystallographic direction. Advanced characterization methods (electron diffraction, TEM, STEM-HAADF, SEM, XPS) and molecular modeling revealed the mechanism of formation of MIL-69(Al) NWs involving size-confinement and templating effects. The formation of MIL-69(Al) seeds and the self-scroll of GO sheets followed by the anisotropic growth of MIL-69(Al) crystals are mediated by specific GO sheets/MOF interactions. This study delivers an unprecedented approach to control the design of 1D MOF nanostructures and superstructures. 相似文献
10.
Kulsoom Zahara Yamin Bibi Saadia Masood Sobia Nisa Ahmad Sher Naushad Ali Sunjeet Kumar Abdul Qayyum Waseem Ahmed Rokayya Sami Amina A. M. Al-Mushhin Amani H. Aljahani 《Molecules (Basel, Switzerland)》2022,27(6)
The genus Bidens a member of family Compositae, is widely documented as an ethno-medicinally important genus of plants. In the present study, anticancer potential of three ethno-medicinally important species i.e., B. bipinnata, B. biternata and B. pilosa were tested. For in-vitro evaluation, an MTT (Thiazolyl blue tetrazolium bromide) assay was performed against cervical cancer cells (HeLa), hepatocellular carcinoma (HepG), and adenocarcinoma human alveolar basal epithelial cells (A549). For in vivo evaluation, Artemia salina, Danio rerio, and Caenorhabditis elegans were used. Among all the tested extracts, the ethanol extract of B. biternata appeared to have highest anticancer activity, and the compounds responsible for this activity were identified to be Tris (2,4-di-tert-butylphenyl), 4-hydroxy-2,4′-dimethoxychalcone, and 2,4-di-tert-butylphenol. This is the first report of the isolation of Tris (2,4-di-tert-butylphenyl) phosphate from the genus Bidens and the first report of 4-hydroxy-2,4′-dimethoxychalcone and 2,4-di-tert-butylphenol from B. biternata. Among the isolated compounds, 4-hydroxy-2,4′-dimethoxychalcone showed the highest anticancer activity with an LD50 value of 236.7 µg/mL. Therefore, this compound carries promising potential for being established as a pharmaceutical for chemoprevention and chemotherapy. 相似文献