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181.
182.
Laser thermal ablation 总被引:4,自引:0,他引:4
A J Welch M Motamedi S Rastegar G L LeCarpentier D Jansen 《Photochemistry and photobiology》1991,53(6):815-823
Continuous wave and pulsed laser ablation of tissue is described as an explosive event. A subsurface temperature maximum and superheated tissue produce high pressures that eject fragments from the tissue. Decreased water content due to dehydration and vaporization decreases thermal conductivity which reduces heat conduction. Also, a decrease in water content dramatically alters the local rate of heat generation of laser radiation above 1.3 microns since water is the primary absorber. In contrast, at UV wavelengths protein and DNA are the primary absorbers so destruction of tissue bonds is due to direct absorption of the laser light rather than heat transfer from water. 相似文献
183.
Shaobo Li Madushani Dharmarwardana Raymond P. Welch Yixin Ren Dr. Christina M. Thompson Prof. Ronald A. Smaldone Prof. Jeremiah J. Gassensmith 《Angewandte Chemie (International ed. in English)》2016,55(36):10691-10696
Metal–organic frameworks (MOFs) are promising high surface area coordination polymers with tunable pore structures and functionality; however, a lack of good size and morphological control over the as‐prepared MOFs has persisted as an issue in their application. Herein, we show how a robust protein template, tobacco mosaic virus (TMV), can be used to regulate the size and shape of as‐fabricated MOF materials. We were able to obtain discrete rod‐shaped TMV@MOF core–shell hybrids with good uniformity, and their diameters could be tuned by adjusting the synthetic conditions, which can also significantly impact the stability of the core–shell composite. More interestingly, the virus particle underneath the MOF shell can be chemically modified using a standard bioconjugation reaction, showing mass transportation within the MOF shell. 相似文献
184.
Identification of an anti-MRSA dihydrofolate reductase inhibitor from a diversity-oriented synthesis
Wyatt EE Galloway WR Thomas GL Welch M Loiseleur O Plowright AT Spring DR 《Chemical communications (Cambridge, England)》2008,(40):4962-4964
The screening of a diversity-oriented synthesis library followed by structure-activity relationship investigations have led to the discovery of an anti-MRSA agent which operates as an inhibitor of Staphylococcus aureus dihydrofolate reductase. 相似文献
185.
Ellis D McIntosh RD Esquirolea S Viñas C Rosair GM Teixidor F Welch AJ 《Dalton transactions (Cambridge, England : 2003)》2008,(8):1009-1017
Reduction of 1,12-closo-C2B10H12 followed by reaction with the appropriate metal halide and metathesis with either [K(18-crown-6)]Br or [BTMA]Cl ([BTMA] = [C6H5CH2N(CH3)3]+) affords isolable salts of the supraicosahedral metallacarborane sandwich anions [4,4-M-(1,10-closo-C2B10H12)2]n- in moderate to good yield. Compounds prepared are [BTMA][4,4-Co-(1,10-closo-C2B10H12)2] ( 1), [K(18-crown-6)][4,4-Co-(1,10-closo-C2B10H12)2] ( 2), [K(18-crown-6)]2[4,4-Ni-(1,10-closo-C2B10H12)2] ( 3), [K(18-crown-6)]2[4,4-Fe-(1,10-closo-C2B10H12)2] ( 4), [BTMA]2[4,4-Fe-(1,10-closo-C2B10H12)2] ( 5) and [K(18-crown-6)]2[4,4-Ti-(1,10-closo-C2B10H12)2] ( 6). Oxidation of the iron(II) species 4 and 5 with FeCl3 in THF generates the iron(III) analogues [K(18-crown-6)][4,4-Fe-(1,10-closo-C2B10H12)2] ( 7) and [BTMA][4,4-Fe-(1,10-closo-C2B10H12)2] ( 8), respectively. All diamagnetic compounds were characterised spectroscopically and the structures of 1, 3, 4, 6, 7 and 8 were established by single crystal X-ray diffraction. All anions have the anticipated cluster structures with two docosahedral 13-vertex cages joined at the central metal atom (the common degree-six vertex 4). Carbon atoms occupy the degree-four vertex 1 and the degree-five vertex 10. 11B NMR spectroscopy suggests the anions have, on the NMR timescale, C2h symmetry in solution at room temperature, consistent with free rotation, or at least substantial libration, of cage units about the long molecular axis. In the solid state the relative conformations of the two cages may be rationalised by simple bonding arguments, the single exception being the conformation of 4, in which both cages are subject to directional B-H...K+ interactions to the [K(18-crown-6)]+ counterion. The salts 3, 6 and 7 also show B-H...K+ interactions but involving one cage only. 相似文献
186.
The environmental-induced surface dynamics of the biomimetic phosphoryl choline (PC)-functionalized poly(trimethylene carbonate) ionomer has been studied and compared to its unfunctionalized counterpart using in situ second harmonic generation measurements. Whereas the nonpolar liquid n-hexane did not induce any surface dynamic processes in the ionomer under study, the presence of water initiated a Debye-type dynamic reaction at the surface of the PC ionomer, which had no equivalent in the unfunctionalized material. This first-order reaction was attributed to a surface enrichment process of the functionalized ionomer in the hydrophilic environment involving movement of the PC endgroups from aggregates in the bulk to the surface. The time constant of the process was found to be about 6 min, and the corresponding activation energy was 0.4 eV. The dehydration process of the PC-functionalized ionomer in nitrogen gas atmosphere could be described by two time constants, one slightly below 1 min and the other one just above 13 min. The results presented in this work show that SHG measurements are well suited for the study of polymer surface restructuring dynamics in response to environmental changes. Such information is very important for the successful design and implementation of biomimetic polymers intended for biomedical applications. 相似文献
187.
Karamertzanis PG Day GM Welch GW Kendrick J Leusen FJ Neumann MA Price SL 《The Journal of chemical physics》2008,128(24):244708
The predicted stability differences of the conformational polymorphs of oxalyl dihydrazide and ortho-acetamidobenzamide are unrealistically large when the modeling of intermolecular energies is solely based on the isolated-molecule charge density, neglecting charge density polarization. Ab initio calculated crystal electron densities showed qualitative differences depending on the spatial arrangement of molecules in the lattice with the greatest variations observed for polymorphs that differ in the extent of inter- and intramolecular hydrogen bonding. We show that accounting for induction dramatically alters the calculated stability order of the polymorphs and reduces their predicted stability differences to be in better agreement with experiment. Given the challenges in modeling conformational polymorphs with marked differences in hydrogen bonding geometries, we performed an extensive periodic density functional study with a range of exchange-correlation functionals using both atomic and plane wave basis sets. Although such electronic structure methods model the electrostatic and polarization contributions well, the underestimation of dispersion interactions by current exchange-correlation functionals limits their applicability. The use of an empirical dispersion-corrected density functional method consistently reduces the structural deviations between the experimental and energy minimized crystal structures and achieves plausible stability differences. Thus, we have established which types of models may give worthwhile relative energies for crystal structures and other condensed phases of flexible molecules with intra- and intermolecular hydrogen bonding capabilities, advancing the possibility of simulation studies on polymorphic pharmaceuticals. 相似文献
188.
Welch K Nederberg F Bowden T Hilborn J Strømme M 《Langmuir : the ACS journal of surfaces and colloids》2007,23(20):10209-10215
Broadband dielectric spectroscopy was used to investigate the bulk molecular dynamics of a recently developed biodegradable biomimetic ionomer potentially useful for biomedical applications. Isothermal dielectric spectra were gathered for a phosphoryl choline (PC)-functionalized poly(trimethylene carbonate) (PTMC) ionomer and unfunctionalized PTMC at temperatures ranging from 2 to 60 degrees C over a broad frequency range of 10(-3) to 10(6) Hz. Four relaxations were clearly identified, two of which were shown to stem from the PTMC polymer backbone. A detailed analysis showed that the formation of zwitterionic aggregates was responsible for the material's bulk functionality and that bulk conduction processes may provide useful information for assessing the PC ionomer as a candidate for drug delivery applications. Finally, it was concluded that absorbed water concentrates around the aggregates, resulting in an increased mobility of the PC end-groups. 相似文献
189.
Arlinghaus LR Li X Rahman AR Welch EB Xu L Gore JC Yankeelov TE 《Magnetic resonance imaging》2011,29(5):630-638
MRI techniques have been developed that can noninvasively probe the apparent diffusion coefficient (ADC) of water via diffusion-weighted MRI (DW-MRI). These methods have found much application in cancer where it is often found that the ADC within tumors is inversely correlated with tumor cell density, so that an increase in ADC in response to therapy can be interpreted as an imaging biomarker of positive treatment response. Dynamic contrast enhanced MRI (DCE-MRI) methods have also been developed and can noninvasively report on the extravascular extracellular volume fraction of tissues (denoted by ve). By conventional reasoning, the ADC should therefore also be directly proportional to ve. Here we report measurements of both ADC and ve obtained from breast cancer patients at both 1.5 and 3.0 T. The 1.5-T data were acquired as part of normal standard of care, while the 3.0-T data were obtained from a dedicated research protocol. We found no statistically significant correlation between ADC and ve for the 1.5- or 3.0-T patient sets on either a voxel-by-voxel or a region-of-interest (ROI) basis. These data, combined with similar results from other disease sites in the literature, may indicate that the conventional interpretation of either ADC, ve or their relationship is not sufficient to explain experimental findings. 相似文献
190.
Stephan DW Greenberg S Graham TW Chase P Hastie JJ Geier SJ Farrell JM Brown CC Heiden ZM Welch GC Ullrich M 《Inorganic chemistry》2011,50(24):12338-12348
In 2006, our group reported the first metal-free systems that reversibly activate hydrogen. This finding was extended to the discovery of "frustrated Lewis pair" (FLP) catalysts for hydrogenation. It is this catalysis that is the focal point of this article. The development and applications of such FLP hydrogenation catalysts are reviewed, and some previously unpublished data are reported. The scope of the substrates is expanded. Optimal conditions and functional group tolerance are considered and applied to targets of potential commercial significance. Recent developments in asymmetric FLP hydrogenations are also reviewed. The future of FLP hydrogenation catalysts is considered. 相似文献