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41.
Flávia Pereira Duta Francisca Pessôa De França Eliana Flávia Camporese Sérvulo Léa Maria De Almeida Lopes Antonio Carlos Augusto Da Costa Ana Barros 《Applied biochemistry and biotechnology》2004,114(1-3):639-652
The production of biopolymers by a Rhizobium strain was studied under batch and bioreactor conditions. The best viscosity levels were obtained under low mannitol concentrations as well as low agitation and aeration conditions. Infrared spectra indicated the presence of chemical groups characteristic of microbially produced biopolymers, including C=O and O-acetyl groups. Thermogravimetric analysis showed the characteristic degradation profiles of the exopolysaccharide produced (T onset=290°C). The experimental design showed that a low substrate concentration (10.0 g/L), and low aeration (0.2 vvm) and agitation (200 rpm) levels should be used. The maximum yield of the process was a Yp/s (g/g) of 0.19±0.1, obtained under optimized conditions. 相似文献
42.
Acidity of Ni-modified alumina and silica-alumina catalysts was determined using n-butylamine titration and pyridine adsorption methods. Strong influence of Ni2+ ions on the Brönsted acidity of silicaalumina was observed. Improved Brönsted acidity of such system was confirmed by the results of the test reaction. 相似文献
43.
Maria M. Orive Blanca Gallo Rosa M. Alonso Francisca Vicente Jean C. Viré Gaston J. Patriarche 《Mikrochimica acta》1989,97(3-4):181-190
The acid-base behaviour of midazolam, a psychotropic drug derived from imidazobenzodiazepine family, has been studied spectro-photometrically. This compound hydrolyzes at pH values lower than 4. Reversible cleavage of the azomethine bond takes place and the open-ring compound is in equilibrium with the closed-ring compound (protonated form of the parent drug). Absorbance-time data (measured at 225 nm and for different pH values) have been evaluated by a pseudo-first order logarithmic approach, leading to different apparent kinetic constants, depending on pH and temperature. A simple mechanism of hydrolysis, corresponding to fast protonation and slow hydrolysis with opening of the ring is in good agreement with the kinetic results. From data obtained at pH values greater than 4, the deprotonation constant of the nitrogen atom at position 2 of the imidazole ring has been calculated and a pKa value of 5.50 ± 0.05 obtained. In addition, a Spectrophotometric method has been developed which allows the determination of midazolam at concentrations from 1.23 × 10–6
M to 3.38 × 10–5
M. This method has been applied to a pharmaceutical formulation midazolam; the Dormicum error, in terms of relative standard deviation, was lower than 1.5%. 相似文献
44.
A solid-liquid extraction procedure followed by reversed-phase high-performance liquid chromatography (RP-HPLC) coupled with a photodiode array detector (DAD) for the determination of polyphenols in freeze-dried apple peel and pulp is reported. The extraction step consists in sonicating 0.5 g of freeze-dried apple tissue with 30 mL of methanol-water-acetic acid (30:69:1, v/v/v) containing 2 g of ascorbic acid/L, for 10 min in an ultrasonic bath. The whole method was validated, concluding that it is a robust method that presents high extraction efficiencies (peel: >91%, pulp: >95%) and appropriate precisions (within day: R.S.D. (n = 5) <5%, and between days: R.S.D. (n = 5) <7%) at the different concentration levels of polyphenols that can be found in apple samples. The method was compared with one previously published, consisting in a pressurized liquid extraction (PLE) followed by RP-HPLC-DAD determination. The advantages and disadvantages of both methods are discussed. 相似文献
45.
Francisca Cánovas Orvay 《代数通讯》2013,41(11):3953-3962
For a family of cyclic cubic fields, we give a system of fundamental units, we obtain conditions sufficient to force the evenness of the classnumber hK, and we prove asymptotic results for the classnumbers of those fields. 相似文献
46.
47.
M. A. Rebolledo 《光谱学快报》2013,46(8):537-541
The application of fluorescence correlation spectroscopy to the measurement of diffusion coefficients of atoms is proposed. After a theoretical analysis of the problem the experimental viability of this technique is studied in the particular case of Tl. Finally applications to other experiments such as ground state level-crossing are proposed. 相似文献
48.
Alfonso G. Rubia Mateo M. Salgado Carlos T. Nieto Alejandro Manchado David Díez Francisca Sanz Narciso M. Garrido 《Tetrahedron: Asymmetry》2017,28(10):1394-1400
The asymmetric synthesis of methyl (E)-4-((1R,2S,3R)-3-amino-2-((E)-2-methoxycarbonyl-eten-1-yl)cyclohexyl)but-2-enoate 14 has been achieved from dimethyl (2E,7E)-nona-2,7-dienedioate 2. A key step is the asymmetric synthesis of 1-hydroxyoctahydro-1H-isochromene derivative 5 whose X-ray analysis corroborated the stereochemistry of the new stereocenters. The asymmetric synthesis of the isochromenyl acetate derivative 11 shows the potential of this methodology for fused cyclohexanic system heterocyclic synthesis. 相似文献
49.
Christoph Bremberger Francisca Bremberger Mikulas Luptacik Stephan Schmitt 《The Journal of the Operational Research Society》2015,66(3):421-433
In this paper, we propose an approach to implement environmental standards into Data Envelopment Analysis (DEA) and in this way to measure their regulatory impact on eco-efficiency of firms. One standard feature of basic DEA models lies in the exogeneity of inputs, desirable and undesirable outputs. Taking into account the environmental constraints, we therefore apply the bounded variable DEA model. The regulatory impact is assessed as difference in eco-efficiency scores before and after fictive introduction of an environmental standard. Furthermore, we distinguish between weak and strong disposability of undesirable outputs and develop corresponding models. Assessing the regulatory impact of environmental standards in advance provides support for environmental policymakers in choosing appropriate instruments and in adjusting the intensity of regulation. 相似文献
50.
Francisca M. Albertí Juan J. Fiol Angel García-Raso Marta Torres A. Terrón Miquel Barceló-Oliver María J. Prieto Virtudes Moreno Elies Molins 《Polyhedron》2010
A new chloride-dimethylsulfoxide-ruthenium(III) complex with nicotine trans-[RuIIICl4(DMSO)[H-(Nicotine)]] (1) and three related iridium(III) complexes; [H-(Nicotine)]trans-[IrIIICl4(DMSO)2] (2), trans-[IrIIICl4(DMSO)[H-(Nicotine)]] (3) and mer-[IrIIICl3(DMSO)(Nicotine)2] (4) have been synthesized and characterized by spectroscopic techniques and by single crystal X-ray diffraction (1, 2, and 4). Protonated nicotine at pyrrolidine nitrogen is present in complexes 1 and 3 while two neutral nicotine ligands are observed in 4. In these three inner-sphere complexes coordination occurs through the pyridine nitrogen. Moreover, in the outer-sphere complex 2, an electrostatic interaction is observed between a cationic protonated nicotine at the pyrrolidine nitrogen and the anionic trans-[IrIIICl4(DMSO)2]¯ complex. 相似文献