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排序方式: 共有260条查询结果,搜索用时 31 毫秒
51.
Three new pyridylindolizine derivatives, 1, 2, 3-tricarbometoxi-7-(4-pyridyl)-pyrrolo[1, 2-a]pyridine (I), 1,2-dicarboethoxy-3-(4-bromobenzoyl)-7-(4-pyridyl)-pyrrolo[1,2-a]pyridine (II) and its isomer 1,2-dicarboethoxy-3- (4-bromobenzoyl) -5- (2-pyridyl) -pyrrolo[1, 2-a]pyridine (III) have been investigated in different solutions by UV-VIS absorption, steady-state, and time-resolved fluorescence methods. The effects of the substituent and solvent on the spectroscopic properties have been demonstrated. The fluorescence decay data could be fitted to a single-exponential function. The lifetime values are higher in protic polar than in aprotic apolar solvents for compound I. In the case of compounds II and III the fluorescence intensities and lifetimes are very low, with the exception of III in aprotic solvents. The absorption and fluorescence properties of the compounds showed a solvent dependence. 相似文献
52.
Marilena Meira Cristina M. Quintella Iuri M. Pepe Pedro R. da Costa Neto Alessandra dos Santos Tanajura Humbervania Reis Gon?alves da Silva 《Central European Journal of Chemistry》2012,10(4):1328-1337
Regressions based on fluorescence spectroscopy were developed to provide relatively inexpensive and rapid measurements of the concentration, viscosity, and specific gravity of biodiesel-diesel blends. The methods involved obtaining a mathematical model from spectrofluorimetric data and data from a given property (concentration, dynamic viscosity, or specific gravity) using partial least squares (PLS) regression, which was then applied as a model for predicting properties of interest. The predicted concentrations, dynamic viscosities, and specific gravities of the biodiesel-diesel blends were compared with actual values and agreed reasonably well with the obtained results. The models showed high correlation between real and predicted values. The R-square values near 1 indicated excellent model accuracy for predicting concentrations, specific gravities, and dynamic viscosities of biodiesel-diesel blends. The residual distribution did not follow a trend with respect to the predicted variables, indicating an excellent fit to the data. 相似文献
53.
Orian L Carlotto S Di Valentin M Polimeno A 《The journal of physical chemistry. A》2012,116(15):3926-3933
We present a computational study based on accurate DFT and TD-DFT methods on model bioinspired donor-acceptor dyads, formed by a carotenoid covalently linked to a tetraphenylporphyrin (TPP) at the ortho position of one of the TPP phenyl rings. Dyadic systems can be used in the construction of organic solar cells and development of efficient photocatalytic systems for the solar energy conversion, due to the unique advantages they offer in terms of synthetic feasibility. This study aims to describe the influence of chemical modifications on the absorption spectra, in particular on the lowest energy charge transfer bands. Effects of different metals of biological interest, i.e., Mg, Fe, Ni, and Zn, and of H(2)O and histidine molecules coordinated to the metals in different axial positions are rationalized. 相似文献
54.
Cristina Stere Mihaela‐Corina Iovu Horia Iovu Adrian Boborodea Dan Sorin Vasilescu Simon James Read 《先进技术聚合物》2001,12(5):300-305
The polymerization of ?‐caprolactone initiated by two catalyst systems was studied: (1) carbazole‐potassium in the presence of 18‐crown‐6 ether and (2) NdCl3/TBP/TIBA (neodymiumtrichloride/tri‐n‐butyl‐phosphate/triisobutylaluminium) at the molar ratio 1/3/1. For both initiator systems conversion/time plots were determined and the polymers were characterized by IR, GPC and by 1H‐ and 13C?NMR spectroscopy. Polyesters with the highest molecular weight (M n?44 000 g/mol) were obtained for the polymerizations initiated by the carbazole‐potassium/18‐crown‐6 ether system. The features of the polymerization initiated by the carbazole‐potassium/18‐crown‐6 ether system are discussed on the basis of a simple scheme. The nature of this polymerization is non‐living. Copyright © 2000 John Wiley & Sons, Ltd. 相似文献
55.
Polymerisation of vinyl acetate in microemulsions with methanol 总被引:1,自引:0,他引:1
D. Donescu L. Fusulan C. Petcu A.-G. Boborodea D.-S. Vasilescu 《Colloid and polymer science》2000,278(10):927-935
The homogeneity domains for the system vinyl acetate – methanol – monomaleate of nonylphenol ethoxylated with 25 mol ethylene
oxide as an aqueous solution (MEMNPEO25) (33%) have been studied; it has been shown that, due to the shorter chain of methanol,
these domains are more reduced than in the case of ethanol. The changes in refractive indexes and electrical conductivities
have shown the formation of microemulsions with different structures (water-in-oil, bicontinuous or oil-in-water). Ammonium
persulphate is soluble only in oil-in-water or in bicontinuous microemulsions. The initial polymerisation rates as well as
the decomposition rates for the initiator are apparently affected when the microemulsion structure is modified. The polymerisation
rate of vinyl acetate is higher in the presence of methanol than in the presence of ethanol for similar compositions; this
fact may be attributed to a higher degree of ionisation of the initiator in the presence of methanol. Also, in polymerisations
initiated by benzoyl peroxide, the conversions are influenced by the microstructure; thus, the maximum corresponds to water-in-oil
microemulsions. By measuring the amount of unreacted MEMNPEO25 (gel permeation chromatography) we were able to show that the
copolymer formed consisted of vinyl acetate and reactive surfactant.
Received: 9 March 1999/Accepted: 13 March 2000 相似文献
56.
The purpose of this paper is to examine the potential of three binary borate glasses; namely PbOB2O3, K2OB2O3 and Li2OB2O3 as candidates for fabrication of low optical loss and low cost fiber-glass wave-guides.The importance of ultrasonic measurements as the first step in a systematic search for a glass with low optical loss, is discussed. Results of ultrasonic measurements of PbOB2O3 system are then presented. Using these results and the published results for the K2OB2O3 and Li2OB2O3 systems, estimates of the magnitude of density fluctuations as a function of composition have been made for each system. Comparison with the previously published results on the K2OSiO2 system suggests that out of the three systems chosen, only 50 mole % Li2O50 mole % B2O3 glass is a likely candidate for the production of low optical loss glass fibers. 相似文献
57.
58.
Polese Pierluigi Tolazzi Marilena Melchior Andrea 《Journal of Thermal Analysis and Calorimetry》2018,132(2):1317-1323
Journal of Thermal Analysis and Calorimetry - The pyrolysis characteristics and kinetics of lignocellulosic biomass (cotton stalk) and seaweed (Gracilaria lemaneiformis) were studied comparatively.... 相似文献
59.
Melchior Andrea Lanas Sara Gràcia Valiente Manuel Tolazzi Marilena 《Journal of Thermal Analysis and Calorimetry》2018,134(2):1261-1266
Journal of Thermal Analysis and Calorimetry - The adsorption of Pt(IV) by iron oxide (Fe3O4) superparamagnetic nanoparticles (SPION) functionalized with 3-mercaptopropionic acid (3-MPA) is... 相似文献
60.
Bioremediation of toluene and naphthalene in liquid cultures of bacteria grown in the presence of these aromatic compounds as unique sources of carbon was investigated by gas chromatography (GC). For this purpose, a method based on the use of GC with flame ionization detection was developed and validated. Validation was carried out in terms of limit of detection (LOD), limit of quantitation (LOQ), linearity, precision and trueness. In the case of naphthalene, LOD and LOQ values of 0.43 and 0.72 mg kg(-1) were achieved. Linearity was established over one order of magnitude in the range of interest, i.e. 10-100 mg kg(-1). Excellent precision was obtained both in terms of intra-day repeatability and between-day precision on two concentration levels (RSD% lower than 0.5%). A recovery of 97.9 +/- 0.2% (n=3) was calculated by addition of 640 mg kg(-1) of naphthalene to the Bushnell & Haas mineral salts basal solution containing the micro-organisms. Findings clearly showed a reduction of the naphthalene content equal to 50% and 75% after two and four weeks of contact with the micro-organisms, whereas a lower degradation was shown in the case of toluene. Finally bioremediation activity was ascribed to two different microbial populations, Bordetella Petrii and Bacillus Sphericus, which survived in the polluted medium. 相似文献