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141.
142.
Compound specific isotope analysis of hexachlorocyclohexane isomers: a method for source fingerprinting and field investigation of in situ biodegradation 下载免费PDF全文
143.
Thomas O. Schrader Xiuwen Zhu Michelle Kasem Sufang Li Chunyan Liu Albert Ren Chunrui Wu Graeme Semple 《Tetrahedron letters》2018,59(21):2030-2033
Asymmetric syntheses of N-protected (R)-4-halo-6,6a,7,8,9,10-hexahydro-5H-pyrazino[1,2-a][1,n]naphthyridines, advanced intermediates for the synthesis of highly potent and selective 5-HT2C agonists, are described. The key transformation involves ring opening of N-protected bicyclic sulfamidate (R)-hexahydro-3H-pyrazino[1,2-c][1,2,3]oxathiazine 1,1-dioxide with (4-halo-2-fluoropyridin-3-yl)lithiums or (3-bromo-5-fluoropyridin-4-yl)lithium. In situ hydrolyses of the resultant sulfamic acids and subsequent intramolecular nucleophilic aromatic substitutions (SNAr) produce the enantiopure tricycles. The two step procedure represents new methodology for the stereoselective syntheses of tetrahydronaphthyridines. 相似文献
144.
Michelle Guy Sally Freeman John F. Alder Simon D. Brandt 《Central European Journal of Chemistry》2008,6(4):526-534
A clandestine two-step route to psychoactive racemic phenylalkylamines utilises the Henry reaction. In the first step an aromatic
aldehyde reacts with a nitroalkane to give the nitrostyrene intermediate. In the second step the nitrostyrene is reduced to
the phenylalkylamine. An impurity profile of both steps was evaluated through the synthesis and analysis of common street
derivatives. The formation of nitrile impurities in the nitroaldol reaction and hydroxylamine impurities in the reduction
step were shown by NMR spectroscopy and GC-MS. A selection of reducing agents has been used to give the phenylalkylamines,
together with variable quantities of the partially reduced hydroxylamine product. GC-MS analysis of the hydroxylamines showed
heat-induced disproportionation which led to the detection of the corresponding oximes.
相似文献
145.
146.
Polarizing microscopy, X-ray scattering, and absorption spectroscopy are used to investigate the aggregation process and chromonic liquid crystal of the anionic compound Bordeaux dye, a product of the sulfonation of the dibenzimidazole derivative of naphthalenetetracarboxylic acid. Polarizing microscopy reveals that the liquid crystal phase forms at room temperature when the concentration is only about 6 wt%, a value lower than what is found in many aggregating systems. The X-ray results indicate that the aggregation is via columns, with a cross-sectional area about 2.5 times larger than the individual molecule. Absorption spectroscopy shows a significant change in the absorption spectrum due to aggregation, which is nicely explained by a simple theory of isodesmic aggregation and excitonic coupling between the molecules in an aggregate. The "stacking free energy change" for a molecule in an aggregate relative to a molecule in solution is estimated to be about 9 kBT, a larger value than that found in the one other system where it has been estimated. 相似文献
147.
A sequential injection analysis procedure with dual-reagent chemiluminescence detection was applied to the screening of street drug seizure samples for the presence of heroin. The chemiluminescence reagents (acidic potassium permanganate and tris(2,2'-bipyridine)ruthenium(III)) were aspirated from either side of a sample aliquot that was sufficiently large to prevent interdispersion of the reagent zones, and therefore two different chemical reactions could be performed simultaneously at either end of the sample zone. The presence of heroin in seizure samples was indicated by a strong response with the tris(2,2'-bipyridine)ruthenium(III) reagent and confirmed by a significant increase in the response with the permanganate reagent when the sample was treated with sodium hydroxide to hydrolyse the heroin to morphine. Nicomorphine (a morphine-derived pharmaceutical) was synthesised and tested under the same conditions. The responses with the permanganate reagent were similar to those for heroin, which supports the proposed chemical basis for the test. However, the responses with tris(2,2'-bipyridine)ruthenium(III) were far lower for nicomorphine than heroin (approximately 5-fold for the samples that had not been hydrolysed). 相似文献
148.
Dimethyl methylphosphonate (DMMP), an important flame retardant in lithium-ion batteries, has been studied theoretically. The energy, enthalpy, and Gibbs free energy of DMMP and its protonated form (DMMP-H+) have been calculated using the high-level ab initio methods G3(MP2), G3(MP2)//B3LYP, G3, G3//B3-LYP, and CBS-QB3. All calculated proton affinities showed good agreement with experiment (within 1.5%), with the best values being obtained with G3MP2. At this level of theory, the calculated proton affinity of DMMP is 895 kJ · mol?1. The ionization potential (9.94 eV) was calculated using the related procedure G3(MP2)-RAD, and also showed excellent with experiment (0.6%). Hydrogen bonding in DMMP-H+ has also been studied. 相似文献
149.
Hydroxyproline quantification for the estimation of collagen in tissue using multiple reaction monitoring mass spectrometry 总被引:1,自引:0,他引:1
Collagens are highly abundant mammalian proteins that contain a high content of hydroxylated amino acids such as hydroxyproline. We have exploited the high hydroxyproline content of collagen and developed a method for hydroxyproline quantification as a measure of collagen content in muscle samples. The novel method utilizes a highly selective and sensitive method of multiple reaction monitoring (MRM) by mass spectrometry. The analytical method is simple, rapid (5min), convenient (no derivatization), precise (<17% RSD), accurate (90-108%), sensitive (4.88nmol/L) and linear (R(2)>0.999) over three orders of magnitude (5-5000nmol/L). 相似文献
150.
Jiang H Li Y Pelzer M Cannon MJ Randlett C Junga H Jiang X Ji QC 《Journal of chromatography. A》2008,1192(2):230-238
A sensitive and selective bioanalytical assay was developed and validated for the determination of enantiomeric molindone in human plasma using high-performance liquid chromatography-tandem mass spectrometry along with supported liquid extraction procedures. The chiral separation was evaluated and optimized on macrocyclic antibiotic type chiral stationary phases (CSPs) based on teicoplanin aglycone (Chirobiotic TAG) in polar organic, polar ionic, and reversed-phase mode chromatography, respectively. Complete baseline separation was achieved on a Chirobiotic TAG column under isocratic condition in reversed-phase chromatography. The method validation was conducted using a Chirobiotic TAG column (100 mm x 2.1 mm) over the curve range 0.100-100 ng/ml for each molindone enantiomer using 0.0500 ml of plasma sample. The flow rate was 0.8 ml/min and the total run time was 9 min. Supported liquid extraction in a 96-well plate format was used for sample preparation. Parameters including recovery, matrix effect, linearity, sensitivity, specificity, carryover, precision, accuracy, dilution integrity, and stability were evaluated. The intra- and inter-day precision and accuracy of the quality control samples at low, medium, and high concentration levels were RSD 相似文献