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121.
The primary processes involved in cyclopropanone reactivity have been investigated using a SCF-CI abinitio method. The C2C3 bond rupture has been found to be thermally favoured and the resulting oxyallyl could have a significant lifetime. By contrast, upon photonic excitation, C1C2 cleavage easily occurs, but does lead to stable intermediate. This constitutes the first step of CO extrusion. The results are discussed using simple MO and valence-state considerations, and compared with those of related compounds. 相似文献
122.
We define the complete closure number cc(G) of a graph G of order n as the greatest integer k ≤ 2n ? 3 such that the kth Bondy-Chvátal closure Clk(G) is complete, and give some necessary or sufficient conditions for a graph to have cc(G) = k. Similarly, the complete stability cs(P) of a property P defined on all the graphs of order n is the smallest integer k such that if Clk(G) is complete then G satisfies P. For some properties P, we compare cs(P) with the classical stability s(P) of P and show that cs(P) may be far smaller than s(P). © 1993 John Wiley & Sons, Inc. 相似文献
123.
Hamamelitannin Analogues that Modulate Quorum Sensing as Potentiators of Antibiotics against Staphylococcus aureus 下载免费PDF全文
Arno Vermote Dr. Gilles Brackman Dr. Martijn D. P. Risseeuw Bieke Vanhoutte Prof. Dr. Paul Cos Prof. Dr. Kristof Van Hecke Dr. Koen Breyne Prof. Dr. Evelyne Meyer Prof. Dr. Tom Coenye Prof. Dr. Serge Van Calenbergh 《Angewandte Chemie (International ed. in English)》2016,55(22):6551-6555
The modulation of bacterial communication to potentiate the effect of existing antimicrobial drugs is a promising alternative to the development of novel antibiotics. In the present study, we synthesized 58 analogues of hamamelitannin (HAM), a quorum sensing inhibitor and antimicrobial potentiator. These efforts resulted in the identification of an analogue that increases the susceptibility of Staphylococcus aureus towards antibiotics in vitro, in Caenorhabditis elegans, and in a mouse mammary gland infection model, without showing cytotoxicity. 相似文献
124.
Maftouh M Granier-Loyaux C Chavana E Marini J Pradines A Heyden YV Picard C 《Journal of chromatography. A》2005,1088(1-2):67-81
High-throughput and performance analysis and purification of enantiomers are important parts of drug discovery and provide high-quality compounds for pharmacological testing. We have previously reported two parts describing chiral chromatographic screens using normal-phase (NPLC) and reversed-phase (RPLC) liquid chromatography, in order to cope with increasing numbers of new compounds generated by chemistry programs. We present in this part the development and implementation of a third faster screen using supercritical fluid chromatography (SFC) to maximize chance in achieving rapid enantiomer resolution of large numbers of compounds in a minimum of time. The SFC screen utilizes a narrow combination of only four columns (Chirlapak AD and AS, and Chiralcel OD and OJ) and two solvent modifiers (methanol and isopropanol). A modifier and column-switching setup was employed to allow the entire screening process to be serially run in the order AD> OD > OJ > AS and methanol > isopropanol, so that the screening for a given molecule can be stopped when separation is achieved. The switching system was fully automated for unattended operation of multiple compounds. An optimization procedure was also defined, which can be performed if needed for unsuccessful separations in the screening step. The chiral SFC strategy proved its performance and robustness in resolution of hundreds proprietary chiral molecules generated by drug discovery programs, with a success rate exceeding 95%. In addition, the generic capability of the strategy was evaluated by applying the screen and optimization methodology to a test set comprising 40 marketed drugs differing from proprietary compounds in terms of chemical diversity, revealing a similar high success rate of 98%. Chiral separations developed at the analytical scale work easily and equally well at the semi-preparative level, as illustrated with an example. The SFC screen allows resolution of compounds that were partially separated by NPLC or not separated at all by RPLC, demonstrating the utility of implementing complementary chromatographic techniques. The SFC screen is currently an integral part of our analytical support to discovery chemical programs and is considered the first try for chiral separations of new compounds, because it offers a higher success rate, performance and throughput. 相似文献
125.
This work is devoted to the study of the gas pressure effect on the laser-induced breakdown spectroscopy signal intensity of carbon. Experiments are performed, using a 1064 nm Nd:YAG laser, with carbon solid samples placed inside a high pressure chamber filled with helium or nitrogen, the gas pressure varying from 1 to 80 atm. The signal intensity of the carbon line (247.86 nm) decreases with increasing pressure. As the plasma size strongly decreases with pressure, two collection optical setups are used, showing different raw results. To take into account the plasma size evolution with pressure, calculated corrections are applied to the collected light intensity. Carbon line emission is measured and corrected as a function of pressure in both gases. At 1 atm, the emission line is found to be greater in helium than in nitrogen by a factor of approximately 3, whereas the intensities in the two gases become close to each other at 80 atm. 相似文献
126.
Georges Morel Evelyne Marchand Sourisak Sinbandhit Loic Toupet 《Heteroatom Chemistry》2003,14(1):95-105
Title salts 3 were easily obtained by treatment of formimidoyl isothiocyanates 1 with a twofold excess of methanesulfenyl chloride. They showed interesting chemical behavior toward several nitrogen and carbon nucleophiles. Substitution reactions with isothioureas and acetamide in the presence of triethylamine gave the 1H, 6H‐6aλ4‐thia‐1,3,4,6‐tetraazapentalenes 7 and 6H‐6aλ4‐thia‐1‐oxa‐3,4,6‐triazapentalene 9 , respectively. Addition of p‐toluidine furnished the 5‐imino‐thiadiazole derivatives 10 , which reacted further with diverse heterocumulenes to yield the corresponding thiatriaza‐ and tetraazapentalene species 11 . The N,N′‐bis(1,2,4‐thiadiazol‐5‐ylidene)diaminobenzenes 13 were also prepared and reacted with phenyl isothiocyanate. Two stable rotational isomers were separated for the 1,2‐phenylene product 14b . Other π‐hypervalent sulfur compounds 16 were synthesized under similar conditions from salts 3 and methyl cyanoacetate or dimethyl malonate. The structural assignments were discussed on the basis of IR and NMR spectroscopic data and received additional support from X‐ray analysis of substrate 16a . © 2003 Wiley Periodicals, Inc. Heteroatom Chem 14:95–105, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/hc.10106 相似文献
127.
Gajavalli Kasi Mikaelian Georges Barrachin Marc Decreton Alexandre Fischer Evelyne Rogez Jacques Benigni Pierre 《Journal of Thermal Analysis and Calorimetry》2019,135(4):2209-2219
Journal of Thermal Analysis and Calorimetry - An Ag–Cd–In alloy is used as the control rod material in most pressurized water reactors. Despite this important application, the phase... 相似文献
128.
Simone Sbrescia Jianzhu Ju Tom Engels Evelyne Van Ruymbeke Michelle Seitz 《Journal of polymer science. Part A, Polymer chemistry》2021,59(6):477-493
Thermoplastic elastomers (TPEs) combine high elasticity with melt processability due to their structural features being based on physical associations rather than chemical crosslinking. Their mechanical properties are governed by the interplay of the different dynamics present in the system (i.e., hard block associations and soft block mobility) combined with their morphology. Irrespective of their exact chemical structure or type of association (crystals, hydrogen bonds, or glassy domains), many soft TPEs show a reduction in toughness at elevated temperatures. In this study, we investigate the high-temperature mechanical properties of a model series of industrially relevant TPEs via systematically varying composition and molecular weight. The results show an increase in temperature resistance and in large-strain stress response as chain length increases. We underline the key parameters that influence the mechanical behavior and explain the observed effect of molecular weight on both the temperature- and rate-dependent large-strain response. A physical network-based model is presented that can explain the experimental findings assuming an improved network connectivity and extended lifetime of the entangled segments with increasing molecular weight. 相似文献
129.
Miriam Khodeir He Jia Sayed Antoun Christian Friebe Ulrich S. Schubert Yan Lu Evelyne Van Ruymbeke Jean-François Gohy 《Journal of polymer science. Part A, Polymer chemistry》2020,58(11):1553-1563
Smart hydrogels containing 2,2,6,6-tetramethylpiperidinoxy methacrylate (TEMPO) and N-isopropylacrylamide (NIPAM) that undergo reversible redox behavior are prepared and investigated. Several polymer networks are first prepared by free-radical copolymerization of varying amounts of TEMPO, NIPAM, and a crosslinker (diethylene glycol diacrylate) and subsequently swelled with water to lead to hydrogels. In order to investigate the effects of the redox activity of TEMPO units and of the lower critical solution temperature of NIPAM on the hydrogel properties, a study of the swelling ratio of the polymer networks in distilled water at different temperatures is performed for the two forms of TEMPO, the reduced (TEMPO) and oxidized (TEMPO+) one. Moreover, the rheological properties are also measured for both hydrogel forms. Finally, the encapsulation abilities of the oxidized hydrogels are demonstrated via electrostatic interactions between positively charged TEMPO+ units and negatively charged guest molecules, supporting future application of our system in the biomedical and environmental fields. 相似文献
130.
Evelyne Neau Otilio Hernández-Garduza Joan Escandell Christophe Nicolas Isabelle Raspo 《Fluid Phase Equilibria》2009
A theoretical analysis of the strengths and weaknesses of the Soave, Twu and Boston–Mathias attractive terms was performed with the Redlich–Kwong EoS. Special attention was paid to the variations of the alpha functions and their first and second derivatives with respect to temperature. Contrary to the Soave function, abnormal behaviors of the derived Twu and Boston–Mathias functions were evidenced in the temperature range commonly covered by industrial applications. The unsuccessful variations of the derived alpha functions observed with these two last models strengthen the interest of the Soave equation for the modeling of derived thermodynamic properties. The accuracy of pure component data modeling by means of the cubic equation of state is discussed in a second part. 相似文献