全文获取类型
收费全文 | 502篇 |
免费 | 14篇 |
专业分类
化学 | 387篇 |
晶体学 | 4篇 |
力学 | 2篇 |
数学 | 41篇 |
物理学 | 82篇 |
出版年
2023年 | 8篇 |
2022年 | 18篇 |
2021年 | 23篇 |
2020年 | 10篇 |
2019年 | 13篇 |
2018年 | 15篇 |
2017年 | 10篇 |
2016年 | 21篇 |
2015年 | 17篇 |
2014年 | 28篇 |
2013年 | 26篇 |
2012年 | 38篇 |
2011年 | 61篇 |
2010年 | 24篇 |
2009年 | 20篇 |
2008年 | 27篇 |
2007年 | 28篇 |
2006年 | 20篇 |
2005年 | 12篇 |
2004年 | 17篇 |
2003年 | 17篇 |
2002年 | 11篇 |
2001年 | 1篇 |
2000年 | 2篇 |
1999年 | 3篇 |
1998年 | 4篇 |
1997年 | 5篇 |
1996年 | 2篇 |
1995年 | 1篇 |
1993年 | 1篇 |
1992年 | 1篇 |
1990年 | 3篇 |
1989年 | 1篇 |
1988年 | 2篇 |
1986年 | 1篇 |
1985年 | 3篇 |
1984年 | 1篇 |
1983年 | 2篇 |
1982年 | 2篇 |
1981年 | 1篇 |
1979年 | 1篇 |
1977年 | 1篇 |
1976年 | 4篇 |
1975年 | 4篇 |
1974年 | 2篇 |
1973年 | 2篇 |
1972年 | 1篇 |
1937年 | 1篇 |
排序方式: 共有516条查询结果,搜索用时 39 毫秒
151.
Sandra Babić Dragana Mutavdžić Pavlović Danijela Ašperger Martina Periša Mirta Zrnčić Alka J. M. Horvat Marija Kaštelan-Macan 《Analytical and bioanalytical chemistry》2010,398(3):1185-1194
An analytical method for multi-class pharmaceuticals determination in wastewater has been developed and validated. Target
compounds were: sulfonamides (sulfadiazine, sulfaguanidine, sulfamethazine, sulfamethoxazole), fluoroquinolones (ciprofloxacin,
enrofloxacin, norfloxacin), diaminopyrimidine (trimethoprim), anaesthetic (procaine), anthelmintic (praziquantel and febantel),
and macrolide (roxithromycin). The method involves pre-concentration and clean-up by solid-phase extraction (SPE) using Strata-X
extraction cartridges at pH 4.0. Target analytes were identified and quantitatively determined by liquid chromatography–tandem
mass spectrometry using multiple reaction monitoring (MRM). Recoveries were higher than 50% with relative standard deviation
(RSD) below 18.3% for three concentrations. Only for sulfaguanidine was low recovery obtained. Matrix effect was evaluated
using matrix-matched standards. The method detection limit (MDL) was between 0.5 and 5 ng L−1 in spiked water samples. The precision of the method, calculated as relative standard deviation, ranged from 0.5 to 2.0%
and from 1.4 to 8.3 for intra-day and inter-day analysis, respectively. The described analytical method was used for determination
of pharmaceuticals in effluent wastewaters from the pharmaceutical industry. 相似文献
152.
Marija Aleškovi? Kata Mlinari?-Majerski Krešimir Mol?anov Manoj K. Kesharwani 《Tetrahedron》2010,66(9):1689-8746
Adamantane-dipyrromethane (AdD) receptors [di(pyrrole-2-yl)methyladamantane (1), 2,2-di(pyrrole-2-yl)adamantane (2), 1,3-bis[di(pyrrole-2-yl)methyl]adamantane (3), 2,2,6,6-tetra(pyrrole-2-yl)adamantane (4)] form complexes with F−, Cl−, Br−, AcO−, NO3−, HSO4−, and H2PO4−. The association constants of the complexes were determined by 1H NMR titrations, whereas the geometries of complexes 1·F− (2:1), 2·F− (2:1), 2·Cl− (2:1), 2·AcO− (2:1), and 4·F− (1:1) were determined by X-ray structural analysis. The most stable complexes are of 2:1 stoichiometry with F− and AcO−. The stability constants are in accordance with the anion basicity and the ability of AdD receptors to place the hydrogen bonding donor groups in a tetrahedral fashion around anions. The binding energies of the complexes between receptors 1-4 and F− anion are calculated using quantum chemical methods. The calculated results show that the solvent polarity is important for the complexation of fluoride ion with AdD receptors 1-4. 相似文献
153.
Stilbeneylsydnone derivatives were synthesized by a sequence of reactions in good yields. Irradiation of 3-stilbeneyl-4-methylsydnone 4 gives 1H-1,2-benzodiazepine derivative 7 as the main product along with 2-methylquinoline derivative 20. Irradiation of 3-stilbeneyl-4-phenylsydnone 5 afforded only 1H-1,2-benzodiazepine derivative 8 whereas on irradiation of 4-unsubstituted 3-stilbeneylsydnone 3 no benzodiazepine derivative was detected. An efficient novel photochemical approach to 1H-1,2-benzodiazepines has been found from the new 3-(o-stilbeneyl)-4-substituted-sydnones via intramolecular 1,7-electrocyclization reaction of the photogenerated nitrile imines. 相似文献
154.
Marija Slavec SamoB. Hocevar Lucie Baldrianova Eva Tesarova Ivan Svancara Bozidar Ogorevc Karel Vytras 《Electroanalysis》2010,22(14):1617-1622
The antimony film microelectrode (SbFME) is presented for measuring trace heavy metal ions in combination with anodic stripping voltammetry. The SbFME was tested in model solutions of 0.01 M HCl containing Cd(II) and Pb(II) in the presence of dissolved oxygen. The microsensor exhibited good linear behavior in the examined concentration range 20 μg L−1 to 100 μg L−1 and LoD of 1.9 and 3.1 μg L−1 for Cd(II) and Pb(II), respectively. The suitability of SbFME for measuring trace levels of Cu(II) was demonstrated using the standard reference material of natural water exploiting the sensor's specific characteristic of low re‐oxidation signal for antimony. 相似文献
155.
156.
Škorić I Pavošević F Vazdar M Marinić Ž Šindler-Kulyk M Eckert-Maksić M Margetić D 《Organic & biomolecular chemistry》2011,9(19):6771-6778
The first example of thermal (8π,6π)-electrocyclisation of 1,3,5,7-octatetraene with one double bond embedded in an aromatic moiety is described. By this process, [3,4]-benzo-8-substituted octatetraene derivatives, the cis,trans-1-(o-vinylphenyl)-4-(R = Me, Ph, 2-furyl)buta-1,3-dienes were transformed to a new endo-7-(R = Me, Ph, 2-furyl) and exo-7-(R = Me)-2,3-benzobicyclo[4.2.0]octa-2,4-dienes. Mechanism of reaction was also studied by DFT quantum-chemical calculations. The M06/6-311+G(d,p)//M06/6-31+G(d,p) calculations indicate that formation of the single endo-isomer in the case of phenyl and 2-furyl substituents is determined by higher activation barriers for exo-6π-electrocyclisation than for 8π-cycloreversion. 相似文献
157.
Ziprasidone is known as a novel "atypical" or "second-generation" antipsychotic drug. A sensitive and reproducible method was developed and validated for determination of ziprasidone and its major impurities, which are significantly different in polarity. The separation is performed on a Waters Spherisorb octadecylsilyl 1 column (5.0 microm particle size, 250 x 4.6 mm id) using a gradient with mobile phase A [buffer-acetonitrile (80+20, v/v)] and mobile phase B [buffer-acetonitrile (10+90, v/v)] at a working temperature of 25 degrees C. The buffer was 0.05 M KH2PO4 solution with an addition of 10 mL triethylamine/L solution, adjusted to pH 2.5 with orthophosphoric acid. The flow rate was 1.5 mL/min, and the eluate was monitored at 250 nm using a diode array detector. Optimization of the experimental conditions was performed using partial least squares regression, for which four factors were selected for optimization: buffer concentration, buffer pH, triethylamine concentration, and temperature. The proposed validated method is convenient and reliable for the assay and purity control in both raw materials and dosage forms. 相似文献
158.
Direct oxidation of enolizable ketones to α-hydroxy derivatives, vicinal dicarbonyls or tricarbonyl compounds has been achieved by a catalytic amount of 2-alkylidene-4-oxothiazolidine vinyl bromide in DMSO as a solvent. The yields range from moderate to good. 相似文献
159.
160.
For the first time hexaaquaaluminium(III) tetrafluoroborate has been used as a mild acid catalyst in organic synthesis. A simple method of its preparation based on the reaction of aluminium triisopropoxide and tetrafluoroboric acid in isopropanol afforded catalyst of high purity and activity. The three-component Biginelli condensation of acetoacetate esters, urea and aldehydes catalyzed by 10 mol % of [Al(H2O)6](BF4)3 in refluxing acetonitrile afforded 3,4-dihydropyrimidonones in good to high yields on multigram scales. The tolerance to acid sensitive reactants such as thienyl and furyl carbaldehydes, applicability to sterically hindered β-ketoesters and simple recyclability without losing catalytic activity make this catalyst as good replacement to literature methods. The mechanism of the reaction includes formation of the so called ‘ureido-crotonate’ rather than corresponding acylimino intermediate as found with Brønsted type catalysts. 相似文献