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排序方式: 共有171条查询结果,搜索用时 15 毫秒
1.
A PULSED LASER AND PULSE RADIOLYSIS STUDY OF AMPHIPHILIC CHLOROPHYLL DERIVATIVES WITH PDT ACTIVITY TOWARD MALIGNANT MELANOMA 总被引:1,自引:0,他引:1
L. Fiedor A. A. Gorman I. Hamblett V. Rosenbach-Belkin Y. Salomon A. Scherz I. Tregub 《Photochemistry and photobiology》1993,58(4):506-511
Two amphiphilic derivatives of chlorophyll, which have high potential as photodynamic therapy sensitizers for malignant melanoma have been investigated by a combination of laser flash photolysis and pulse radiolysis. It is shown that direct excitation of monomeric forms of these molecules in both hydrophilic and hydrophobic environments produces significant yields of the corresponding triplet states, which have been characterized in terms of spectral and kinetic parameters. In both environments, scavenging of the triplets by oxygen produces singlet oxygen, O2 (l Δ8 ), with essentially unit efficiency as evidenced by time-resolved IR luminescence measurements. 相似文献
2.
Tyson L ChasseJoshua C Yohannan Namjin KimQun Li Zemin LiChristopher B Gorman 《Tetrahedron》2003,59(22):3853-3861
Examples of new dendrimers are presented. In the first, the effect on electron transfer rate attenuation is investigated for two dendrimer isomers that differ only in the linkage (ortho- versus meta-linked) of the phenyl ether units within one generation of the structure. Second, the effect of encapsulation on electrochemical and luminescence behavior of a new type of rhenium selenide cluster core dendrimer is illustrated. 相似文献
3.
J. M. Bruce N. J. F. Dodd A. A. Gorman I. Hamblett C. W. Kerr C. Lambert S. P. McNeeney 《Photochemistry and photobiology》1990,52(2):345-351
The singlet and triplet states of the anthralin (1,8-dihydroxy-9-anthrone) dehydrodimer have been produced selectively in benzene via pulsed laser excitation and pulse radiolysis respectively. The lifetime of S1 is less than or equal to 30 ps, that of T1 short but unspecified. Both states fragment spontaneously to yield a pair of anthralin radicals. The singlet radical pair predominantly undergoes geminate recombination within the solvent cage. In contrast, the corresponding triplet radical pair undergoes essentially exclusive cage escape to give the anthralin free radical (lambda max 370, 490 and 720 nm) which recombines under normal diffusive conditions. Both recombination processes lead, at least in part, to one or more species which have been assigned as tautomeric forms of the original dimer. The anthralin free radical in benzene is insensitive to the vitamin E model 6-hydroxy-2,2,5,7,8-pentamethylchroman and reacts only slowly with oxygen. 相似文献
4.
Petrie RJ Bailey T Gorman CB Genzer J 《Langmuir : the ACS journal of surfaces and colloids》2004,20(23):9893-9896
In this Letter, we report on the motion of water droplets on surfaces decorated with molecular gradients comprising semifluorinated (SF) organosilanes. SF molecular gradients deposited on flat silica substrates facilitate faster motion of water droplets relative to the specimens covered with an analogous hydrocarbon gradient. Further increase in the drop speed is achieved by advancing it along porous substrates coated with the SF wettability gradients. The results of our experiments are in quantitative agreement with a simple scaling theory that describes the faster liquid motion in terms of reduced friction at the liquid/substrate interface. 相似文献
5.
There is widespread acceptance that singlet oxygen is a key intermediate on one of the pathways leading to the phenomenon of photodynamic action. However, the identification of this moiety within a particular biological system and the determination of a direct link between its presence and a particular photodynamic effect is a goal which photobiologists have hitherto failed to achieve. The aim of this review is to assess the problems associated with such a goal and methods whereby they might be overcome. Initially the general photochemical and environmental factors which govern the ability of a photosensitizer to promote photodynamic action via the intermediacy of singlet oxygen are introduced and the fundamental parameters defining the formation, decay and reactivity of this species summarized. The experimental requirements for relating a particular photodynamic effect to singlet oxygen intermediacy are then analysed and the intrinsic properties of singlet oxygen which will influence this goal are discussed. Having concluded that the singlet oxygen detection method of choice for this purpose is that in which the IR emission at 1269 nm of this molecule is monitored, the advantages and disadvantages of pulsed and continuous wave photoexcitation of cellular systems are analysed. It becomes evident that, no matter what the future improvements in instrumentation are likely to be, the inherent natures of singlet oxygen and the biological system lead to a kinetic situation which will preclude a successful time-resolved solution to this problem. In contrast, experimentation with continuous wave systems holds out significant hope for the future. In particular, the use of phase modulation techniques to overcome background emission problems, the enhancement of photosensitizer optical densities as a consequence of higher extinction coefficients and/or improved photosensitizer delivery systems and the use of high power lasers and/or improved light delivery systems can, at least in principle, lead to the solution of the problem addressed herein. 相似文献
6.
Stephanie M. Hart James L. Banal Maria A. Castellanos Larysa Markova Yuliia Vyborna Jeffrey Gorman Robert Hner Adam P. Willard Mark Bathe Gabriela S. Schlau-Cohen 《Chemical science》2022,13(44):13020
Strongly-coupled multichromophoric assemblies orchestrate the absorption, transport, and conversion of photonic energy in natural and synthetic systems. Programming these functionalities involves the production of materials in which chromophore placement is precisely controlled. DNA nanomaterials have emerged as a programmable scaffold that introduces the control necessary to select desired excitonic properties. While the ability to control photophysical processes, such as energy transport, has been established, similar control over photochemical processes, such as interchromophore charge transfer, has not been demonstrated in DNA. In particular, charge transfer requires the presence of close-range interchromophoric interactions, which have a particularly steep distance dependence, but are required for eventual energy conversion. Here, we report a DNA-chromophore platform in which long-range excitonic couplings and short-range charge-transfer couplings can be tailored. Using combinatorial screening, we discovered chromophore geometries that enhance or suppress photochemistry. We combined spectroscopic and computational results to establish the presence of symmetry-breaking charge transfer in DNA-scaffolded squaraines, which had not been previously achieved in these chromophores. Our results demonstrate that the geometric control introduced through the DNA can access otherwise inaccessible processes and program the evolution of excitonic states of molecular chromophores, opening up opportunities for designer photoactive materials for light harvesting and computation.DNA scaffolds enable the activation and suppression of photochemistry between strongly-coupled synthetic chromophores. 相似文献
7.
Several reports of experimentally derived proton affinity values and gas-phase basicity values for amino acids and peptides have recently appeared in the literature. Here, we show that the thermodynamic quantity that is measured by the Fourier transform mass spectrometry proton transfer bracketing of amino acids and peptides is gas-phase basicity and not proton affinity. Both experimental and theoretical evidence supports this conclusion. The difference between the values determined by proton transfer bracketing measurements for lysine versus leucine is consistent with a difference in gas-phase basicity rather than proton affinity. The rate of proton transfer from protonated lysine to a series of reference compounds have been measured. Entropy-driven, endothermic proton transfer is found to occur at the collision rate. Recent ab initio and semi-empirical calculations of the proton affinity of lysine are found to agree with the value that is derived from bracketing studies when one assumes that gas-phase basicity is measured. While entropy-driven reactions have been observed previously in high-pressure mass spectrometers, this is the first evidence for such reactions at low pressure in a Fourier transform mass spectrometer. 相似文献
8.
A. A. Gorman I. Hamblett T. A. King M. D. Rahn 《Journal of photochemistry and photobiology. A, Chemistry》2000,130(2-3):127-132
The triplet state of pyrromethene 567, a molecule with potential as a solid state laser dye, has been characterized in benzene by pulse radiolysis in terms of its absorption spectrum, lifetime, self-quenching, electronic excitation energy, triplet–triplet extinction coefficient and oxygen quenching rate constant. The use of laser flash photolysis has then allowed determination of the triplet quantum yield, efficiency of formation of singlet oxygen (1Δg), and the rate constant for reaction of the latter species with the ground state. The affects of oxygen on the fluorescence and triplet yields demonstrate that oxygen-induced intersystem crossing is important, the sum of these parameters being unity within experimental error. The mechanism of reaction of P-567 with 1Δg in benzene is predominantly physical in character with only a small (6%) contribution from chemical reaction. 相似文献
9.
Gorman BA Francis PS Dunstan DE Barnett NW 《Chemical communications (Cambridge, England)》2007,(4):395-397
Mixtures of silver(I) and citrate that are used to produce silver nanoparticles evoke intense chemiluminescence with tris(2,2'-bipyridyl)ruthenium(II) and cerium(IV), which can be exploited for the determination of citrate ions and other analytes over a wide concentration range. 相似文献
10.
Gabriela Ionita Petre Ionita Victor EM. Sahini Constantin Luca 《Journal of inclusion phenomena and macrocyclic chemistry》2001,39(3-4):269-271
The kinetics of oxidation of amino acids (Arg, His, Lys, Phe, Thr and Tyr), a dipeptide (Gly-His), and BSA (bovine serum albumin) by two persistent water soluble free radicals of the hydrazyl type has been studied.The rate decreases in the order Arg>Lys>Tyr>Thr>HisBSAPheGly-His with bothfree radicals. Addition to the reaction mixture of - and -cyclodextrin decreases the oxidation rate, probably due to amino acidencapsulation in the cyclodextrin cavity. -Cyclodextrin protects more efficiently against oxidation than -cyclodextrin. 相似文献