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51.
52.
Michael L. Jones Lee F. Kuyper Virgil L. Styles J. Marc Caddell 《Journal of heterocyclic chemistry》1994,31(6):1681-1683
The mild preparation of N-cyano-N-(1-H-indol-5-yl)guanidine and its cyclization to 1,3-diamino-7H-pyrrolo[3,2-f]quinazoline is described. Whereas previously reported methods of cyclization employed high temperatures to effect ring closure, we found that certain Lewis acids, such as boron trifluoride etherate, induce cyclization at moderate temperatures. 相似文献
53.
J. Kuyper L.G. Hubert-Pfalzgraf P.C. Keijzer K. Vrieze 《Journal of organometallic chemistry》1976,108(2):271-280
The preparation and properties are described of trans-[(Ph3P)2(CO)M(RNSNR)] [ClO4] (M RhI, IrI; R Me, Et, i-Pr, t-Bu) and of cis- or trans-[L2Pt(RNSNR)X] [ClO4] (X Cl?, L Et2S, PhMe2As, PhMe2P, R Me, t-Bu; X CH3, L PhMe2P, R Me).1H and 13C NMR data show the existence of various isomers in solution which may interconvert via intra- and inter-molecular exchange processes. A general reaction scheme for the intramolecular exchange processes is discussed. 相似文献
54.
Fabrication of thermoset polyester microfluidic devices and embossing masters using rapid prototyped polydimethylsiloxane molds 总被引:3,自引:0,他引:3
Plastics are increasingly being used for the fabrication of Lab-on-a-Chip devices due to the variety of beneficial material properties, affordable cost, and straightforward fabrication methods available from a range of different types of plastics. Rapid prototyping of polydimethylsiloxane (PDMS) devices has become a well-known process for the quick and easy fabrication of microfluidic devices in the research laboratory; however, PDMS is not always an appropriate material for every application. This paper describes the fabrication of thermoset polyester microfluidic devices and masters for hot embossing using replica molding techniques. Rapid prototyped PDMS molds are convienently used for the production of non-PDMS polymeric devices. The recessed features in the cast polyester can be bonded to a second polyester piece to form an enclosed microchannel. Thermoset polyester can withstand moderate amounts of pressure and elevated temperature; therefore, the cast polyester piece also can be used as a master for embossing polymethylmethacrylate (PMMA) microfluidic systems. Examples of enclosed polyester and PMMA microchannels are presented, and we discuss the electroosmotic properties of both types of channels, which are important for analytical applications such as capillary electrophoresis. 相似文献
55.
Li Y Xia H Fan F Feng Z van Santen RA Hensen EJ Li C 《Chemical communications (Cambridge, England)》2008,(6):774-776
For the first time an ordered mesoporous silica (Fe-Al-SBA-15) with catalytically active isolated Fe surface species for the hydroxylation of benzene with nitrous oxide is prepared by introduction of Fe3+ in the synthesis gel of Al-SBA-15. 相似文献
56.
The preparation, structure and some properties of compounds (M = Mo, W; R = aryl and R′ = aryl or alkyl) are reported. Temperature dependent 13C NMR spectra show that for R ≠ R′ = aryl the complexes are fluxional, but not when one of the R groups is an alkyl group. The fluxional mechanism involves an interchange of the two CO groups via Berry type pseudorotations.Mass spectrometric measurements show the formation of nitrene type species [(η5-C5H5)(CO)nM=NR]+ with n = 0, 1, 2. 相似文献
57.
58.
Kuyper CL Fujimoto BS Zhao Y Schiro PG Chiu DT 《The journal of physical chemistry. B》2006,110(48):24433-24441
The ability to accurately size low concentrations of nanoscale particles in small volumes is useful for a broad range of disciplines. Here, we characterize confocal correlation spectroscopy (CCS), which is capable of measuring the sizes of both fluorescent and nonfluorescent particles, such as quantum dots, gold colloids, latex spheres, and fluorescent beads. We accurately measured particles ranging in diameter from 11 to 300 nm, a size range that had been difficult to probe, owing to a phenomenon coined biased diffusion that causes diffusion times, or particle size, to deviate as a function of laser power. At low powers, artifacts mimicking biased diffusion are caused by saturation of the detector, which is especially problematic when probing highly fluorescent or highly scattering nanoparticles. However, at higher powers (>1 mW), autocorrelation curves in both resonant and nonresonant conditions show a structure indicative of an increased contribution from longer correlation times coupled with a decrease in shorter correlation times. We propose that this change in the autocorrelation curve is due to the partial trapping of the particles as they transit the probe volume. Furthermore, we found only a slight difference in the effect of biased diffusion when comparing resonant and nonresonant conditions. Simulations suggest the depth of trapping potential necessary for biased diffusion is > 1 k(B)T. Overcoming artifacts from detector saturation and biased diffusion, CCS is particularly advantageous due to its ability to size particles in the small volumes characteristic of microfluidic channels and aqueous microdroplets. We believe the method will find increasing use in a wide range of applications in measuring nanoparticles and macromolecular systems. 相似文献
59.
Pidko EA Xu J Mojet BL Lefferts L Subbotina IR Kazansky VB van Santen RA 《The journal of physical chemistry. B》2006,110(45):22618-22627
A FT-IR spectroscopic study of methane, ethane, and propane adsorption on magnesium and calcium forms of zeolite Y reveals different vibrational properties of the adsorbed molecules depending on the exchanged cation. This is attributed to different adsorption conformations of the hydrocarbons. Two-fold eta(2) coordination of light alkanes is realized for MgY, whereas in case of CaY zeolite quite different adsorption modes are found, involving more C-H bonds in the interaction with the cation. The topological analysis of the electron density distribution function of the adsorption complexes shows that when a hydrocarbon coordinates to the exchanged Mg(2+) ions, van der Waals bonds between H atoms of the alkane and basic zeolitic oxygens significantly contribute to the overall adsorption energy, whereas in case of CaY zeolite such interactions play only an indirect role. It is found that, due to the much smaller ionic radius of the Mg(2+) ion as compared to that of Ca(2+), the former ions are significantly shielded with the surrounding oxygens of the zeolitic cation site. This results in a small electrostatic contribution to the stabilization of the adsorbed molecules. In contrast, for CaY zeolite the stabilization of alkanes in the electrostatic field of the partially shielded Ca(2+) cation significantly contributes to the adsorption energy. This is in agreement with the experimentally observed lower overall absorption of C-H stretching vibrations of alkanes loaded to MgY as compared to those for CaY zeolite. The preferred conformation of the adsorbed alkanes is controlled by the bonding within the adsorption complexes that, in turn, strongly depends on the size and location of the cations in the zeolite cavity. 相似文献
60.
Ligthart DA van Santen RA Hensen EJ 《Angewandte Chemie (International ed. in English)》2011,50(23):5306-5310