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排序方式: 共有196条查询结果,搜索用时 171 毫秒
141.
Rolf H. Prager Mehdi M. Baradarani Jabbar Khalafy 《Journal of heterocyclic chemistry》2000,37(3):631-637
A comparative study of the flash vacuum pyrolysis of a number of N‐alkyl and N‐acyl benzotriazoles and benzisoxazolones has confirmed that carbene derived pathways predominate at lower temperatures, and radical pathways at highter temperatures. Two new general unimolecular thermal reactions are also highlighted. 相似文献
142.
A convenient synthesis of various biscoumarins by condensing a series of aldehydes with 4-hydroxycoumarin under microwave irradiation is reported for the first time along with a comparative account of the syntheses under conventional conditions. The reaction times have been reduced considerably with improvement in yields in comparison to thermal conditions. The reactions have been carried out in solvent as well as under solvent-free conditions, and the adopted procedure provides an energy-and time-saving protocol. 相似文献
143.
Syed Ghulam Musharraf Shumaila Mazhar Amna Jabbar Siddiqui M. Iqbal Choudhary Atta-ur-Rahman 《Analytica chimica acta》2013
For the comprehensive metabolite profiling of human plasma, sample preparation is a crucial step. In this investigation, we have compared 10 different extraction techniques for metabolite profiling by GC–MS. Six one-dimensional (1D) and four two-dimensional (2D) extraction techniques involving solvent precipitation, molecular weight cut off tube (MWCOT) and solid phase extraction (SPE) by using silica, RP C18, cation and anion were investigated. Pooled samples of 50 Healthy Male Plasma (HMP), 50 Healthy Female Plasma (HFP) and 100 Healthy Pakistani Plasma (HPP) were subjected to these extraction methods for comparison purposes. Metabolites obtained were identified through NIST mass spectral (Wiley registry), METLIN and Fiehn RTL libraries. XCMS Software was used for the detection of metabolic features, retention time correction, alignment, annotation and statistical analysis in each method. 116–34 peaks were detected by various methods and approx 33% of the peaks were characterized in each method. Hierarchical clustering of the 10 extraction methods showed a low similarity index (50.1%) which indicated different chemical nature of metabolites, resulting from different methods. Venn diagram highlights the GC–MS peaks (33–77%) common in various methods. Metabolites which were different in male and female groups were detected using a threshold value of p ≤ 0.0001, q ≤ 0.001 and fold change ≥3 by employing Welch's t-test and identified through METLIN. Results indicated that 2D-C18 and 2D-silica offers a comprehensive metabolite profile in term of reproducibility, number of peaks and difference in metabolite pattern of male and female. 相似文献
144.
Mehdi Rimaz Nader Noroozi Pesyan Jabbar Khalafy 《Magnetic resonance in chemistry : MRC》2010,48(4):276-285
The tautomerism of the synthesized 3‐arylpyrimido[4,5‐c]pyridazine‐5,7(6H,8H)‐diones ( 1a–d ) and 3‐aryl‐7‐thioxo‐7,8‐dihydro‐6H‐pyrimido[4,5‐c]pyridazine‐5‐ones ( 2a–d ) was studied in dimethyl sulfoxide (DMSO)‐d6. 1H NMR spectra of 1a–d showed a clustered water molecule in the structure backbone that is attached by strong intermolecular H bonding. The relation between the temperature and H bonding of the clustered water molecule with 1a was also studied as representative. The relation between the electronegativity (χ) of the substituent on phenyl ring and the chemical shifts of clustered water protons in 1a–d was also studied. All of 1a–d and also 2d compounds existed in lactam ( I ) form, whereas 2a–c compounds have two distinguished tautomers in DMSO‐d6 [lactam ( I ) and lactim ( II ) forms]. The solvent‐substrate proton exchange was examined in compounds 1a–d and 2a–d by adding one drop of D2O. All compounds (except 1d ) showed proton/deuterium exchange of the clustered water protons in DMSO by adding one drop of D2O. Some compounds (but not all of them) that are easily soluble in DMSO‐d6 containing D2O showed isotopic splitting (β‐isotope effect) in their 13C NMR spectra. Among them, compound 1a was the best evidence to help the spectral assignments and structure determination of predominant tautomer by carbon‐13 splitting (β‐isotope effect). Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
145.
Ali N. Siyal Saima Q. Memon Abdullah Akdoğan Aysen Hol Aslihan Arslan Kartal 《International journal of environmental analytical chemistry》2013,93(8):743-755
Expanded polystyrene (EPS) foam waste (white pollutant) was utilised for the synthesis of novel chelating resin i.e. EPS-N = N-α-Benzoin oxime (EPS-N = N-Box). The synthesised resin was characterised by FT-IR spectroscopy, elemental analysis, and thermogravimetric analysis. A selective method for the preconcentration of Pb(II) ions on EPS-N = N-Box resin packed in mini-column was developed. The sorbed Pb(II) ions were eluted with 5.0 mL of 2.0 mol L?1 HCl and determined by microsample injection system coupled flame atomic absorption spectrometry (MIS-FAAS). The average recovery of Pb(II) ions was achieved 95.5% at optimum parameters such as pH 7, resin amount 400 mg, flow rates 1.0 mL min?1 (of eluent) and3.0 mL min?1 (of sample solution). The total saturation capacity of the resin, limit of detection (LOD) and limit of quantification (LOQ) of Pb(II) ions were found to be 30 mg g?1, 0.033 μg L?1 and 0.107 μg L?1, respectively with preconcentration factor of 300. The accuracy, selectivity and validation of the method was checked by analysis of sea water (BCR-403), wastewater (BCR-715) and Tibet soil (NCS DC-78302) as certified reference materials (CRMs). The proposed method was applied successfully for the trace determination of Pb(II) ions in aqueous samples. 相似文献
146.
Hussain S Ahmed E Malik A Jabbar A Ashraf M Lodhi MA Choudhary MI 《Chemical & pharmaceutical bulletin》2006,54(5):623-625
Two new sterols, halosterols A (1) and B (2), have been isolated from the CHCl(3) soluble fraction of Haloxylon recurvum, and their structures were elucidated by spectroscopic techniques including two dimensional-NMR. Both the compounds displayed chymotrypsin enzyme inhibitory potential. 相似文献
147.
Saima Jabeen Trevor J. Dines Stephen A. Leharne Robert Withnall Babur Z. Chowdhry 《Journal of Raman spectroscopy : JRS》2010,41(10):1306-1317
Raman and infrared spectra are reported for rhodanine, 3‐aminorhodanine and 3‐methylrhodanine in the solid state. Comparisons of the spectra of non‐deuterated/deuterated species facilitate discrimination of the bands associated with N H, NH2, CH2 and CH3 vibrations. DFT calculations of structures and vibrational spectra of isolated gas‐phase molecules, at the B3‐LYP/cc‐pVTZ and B3‐PW91/cc‐pVTZ level, enable normal coordinate analyses in terms of potential energy distributions for each vibrational normal mode. The cis amide I mode of rhodanine is associated with bands at ∼1713 and 1779 cm−1, whereas a Raman and IR band at ∼1457 cm−1 is assigned to the amide II mode. The thioamide II and III modes of rhodanine, 3‐aminorhodanine and 3‐methylrhodanine are observed at 1176 and 1066/1078; 1158 and 1044; 1107 and 984 cm−1 in the Raman and at 1187 and 1083; 1179 and 1074; 1116 and 983 cm−1 in the IR spectra, respectively. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
148.
Saima Jabeen Rex A. Palmer Brian S. Potter Madeleine Helliwell Trevor J. Dines Babur Z. Chowdhry 《Journal of chemical crystallography》2009,39(2):151-156
Abstract Rhodanines (2-thio-4-oxothiazolidines) are synthetic small molecular weight organic molecules with diverse applications in
biochemistry, medicinal chemistry, photochemistry, coordination chemistry and industry. The X-ray crystal structure determination
of two rhodanine derivatives, namely (I), 3-aminorhodanine [3-amino-2-thio-4-oxothiazolidine], C3H4N2OS2, and (II) 3-methylrhodanine [3-methyl-2-thio-4-oxothiazolidine], C4H5NOS2, have been conducted at 100 K. I crystallizes in the monoclinic space group P21/n with unit cell parameters a = 9.662(2), b = 9.234(2), c = 13.384(2) ?, β = 105.425(3)°, V = 1151.1(3) ?3, Z = 8 (2 independent molecules per asymmetric unit), density (calculated) = 1.710 mg/m3, absorption coefficient = 0.815 mm−1. II crystallizes in the orthorhombic space group Iba2 with unit cell a = 20.117(4), b = 23.449(5), c = 7.852(2) ?, V = 3703.9(12)
?3, Z = 24 (three independent molecules per asymmetric unit), density (calculated) = 1.584 mg/m3, absorption coefficient 0.755 mm−1. For I in the final refinement cycle the data/restraints /parameter ratios were 2639/0/161, goodness-of-fit on F2 = 0.934, final R indices [I > 2sigma(I)] were R1 = 0.0299, wR2 = 0.0545 and R indices (all data) R1 = 0.0399, wR2 = 0.0568.
The largest difference peak and hole were 0.402 and −0.259 e ?−3. For II in the final refinement cycle the data/restraints/parameter ratios were 3372/1/221, goodness-of-fit on F2 = 0.950, final R indices [I > 2sigma(I)] were R1 = 0.0407, wR2 = 0.1048 and R indices (all data) R1 = 0.0450, wR2 = 0.1088.
The absolute structure parameter = 0.19(9) and largest difference peak and hole 0.934 and −0.301 e ?−3. Details of the geometry of the five molecules (two for I and three for II) and the crystal structures are fully discussed. Corresponding features of the molecular geometry are highly consistent and
firmly establish the geometry of the rhodanine ring.
Index Abstract Low temperature X-ray structures of (I) 3-aminorhodanine [3-amino-2-thio-4-oxothiazolidine] and (II) 3-methylrhodanine3-methyl-2-thio-4-oxothiazolidine are presented. Crystals of I are monoclinic and occupy space group P21/n with eight molecules (2 per asymmetric unit cell) and (II) is orthorhombic in space group Iba2 with 24 molecules (3 per asymmetric unit). This study has provided five highly consistent
copies of the rhodanine ring at high resolution thus enabling its geometry to be established with confidence.
The two independent molecules in the asymmetric unit of 3-aminorhodanine (left) and the three independent molecules in the
asymmetric unit of 3-methylrhodanine (right) showing space filling and van der Waals contacts (drawn with MERCURY [Bruno et al.
Acta Cryst B58:389, 2002]). 相似文献
149.
Mahmood Akhtar Abdul Jabbar Shaukat Mahmood Zeshan Adeel Umar Rizwan Ahmed 《Analytical letters》2019,52(14):2312-2328
The qualitative and quantitative analysis of soil samples collected from Sialkot, Pakistan (which contains leather industrial plants), has been performed using laser-induced breakdown spectroscopy (LIBS) and laser ablation time of flight mass spectrometry (LA-TOF-MS). The focused beam of a Q-switched Nd: YAG laser (532?nm) was used to ablate the soil samples in air at atmospheric pressure. The optical emission spectra demonstrate the presence of the spectral lines of Si, Fe, Al, Ca, Ti, K, Cr, Mg, Na, Ba, and Li in all of the samples. The emission lines intensities, electron number densities, and excitation temperatures were significantly enhanced in the presence of an external 0.3 T magnetic field applied perpendicular to the plasma plume. A maximum enhancement factor of approximately 8 was observed in the emission intensity. The emergence of several additional lines has also been detected using the magnetic field-assisted LIBS approach. The elemental composition determined using calibration-free laser-induced breakdown spectroscopy (CF-LIBS), with and without magnetic field, reveals that the external magnetic field only adjusts the laser-generated plasma dynamics without affecting the quantitative analysis of the samples. Importantly, the toxic and heavy elements such as chromium and barium were detected and quantified in all of the soil samples by both of these techniques. The variations in the compositional analysis using CF-LIBS with and without the applied magnetic field and LA-TOF-MS were less than 10%. 相似文献
150.
3‐Arylamino‐4‐ethoxycarbonylisoxazol‐5(2H)‐ones, substituted on nitrogen with a benzothiazole group, reacts with triethylamine in ethanol under reflux conditions to provide a convenient synthesis of ethyl 2‐aryl‐aminoimidazo[2,1‐b]benzothiazole‐3‐carboxylates. 相似文献