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161.
Kim MY Vankayalapati H Shin-Ya K Wierzba K Hurley LH 《Journal of the American Chemical Society》2002,124(10):2098-2099
Telomestatin is a natural product isolated from Streptomyces anulatus 3533-SV4 and has been shown to be a very potent telomerase inhibitor. The structural similarity between telomestatin and a G-tetrad suggested to us that the telomerase inhibition might be due to its ability either to facilitate the formation of or trap out preformed G-quadruplex structures, and thereby sequester single-stranded d[T(2)AG(3)](n) primer molecules required for telomerase activity. Significantly, telomestatin appears to be a more potent inhibitor of telomerase (5 nM) than any of the previously described G-quadruplex-interactive molecules. In this communication we provide the first experimental evidence that telomestatin selectively facilitates the formation of or stabilizes intramolecular G-quadruplexes, in particular, that produced from the human telomeric sequence d[T(2)AG(3)](4). A simulated annealing (SA) docking approach was used to study the binding interactions of telomestatin with the intramolecular antiparallel G-quadruplex structure. Each intramolecular G-quadruplex molecule was found to bind two telomestatin molecules (unpublished results). A 2:1 model for the telomestatin bound in the external stacking mode in an energy minimized complex with the human telomeric basket-type G-quadruplex was constructed. Our observation that a G-quadruplex-interactive molecule without significant groove interactions is able to reorient in a G-quadruplex structure proints to the importance of core interaction with an asymmetric G-quadruplex structure in producing selective binding. Furthermore, the G-quadruplex interactions of telomestatin are more selective for the intramolecular structure in contrast to other G-quadruplex-interactive agents, such as TMPyP4. 相似文献
162.
Joseph C. Lodmell William C. Anderson Michael F. Hurley James Q. Chambers 《Analytica chimica acta》1981
High-performance liquid chromatographic (h.p.l.c.) and mass spectral studies of CS2/N,N-dimethylformamide/tetrabutylammonium iodide electrolysis solutions have shown that trithiocarbonate is not formed initially in the electrochemical reduction of CS2. The h.p.l.c. separation on a Partisil 10-ODS column indicated the presence of at least six products or intermediates in this electrode process. A major chromatographic peak is assigned to the tetrathiooxalate dianion (C2S42-) which demonstrates the importance of this species as an intermediate in the CS2 reduction process. 相似文献
163.
Symmetrical dinucleoside 5'-pyrophosphates have been synthesized from the corresponding nucleoside 5'-phosphate free acid in high yield. The one-pot procedure is carried out in DMF or DMSO using triphenylphosphine and 2,2'-dipyridyldisulfide as the coupling agents, and 1-methylimidazole as the catalyst. 相似文献
164.
R. J. McDonald A. R. Smith D. L. Hurley E. B. Norman 《Journal of Radioanalytical and Nuclear Chemistry》1998,234(1-2):33-36
Instrumental Neutron Activation Analysis (INAA) is a common method of trace element analysis whose sensitivity is limited
either by interference from other trace elements in the sample or by interference from ambient background radiation in the
detection system. In at least two cases, a true low-background facility, such as that at Lawrence Berkeley National Laboratory,
substantially enhances senitivity: (1) Ultra-pure silicon, such as that used in semiconductor fabrication. Even after prolonged
exposure within a nuclear reactor, minimal observable gamma-ray emitting activities are produced in the silicon. Extrapolated
from our 7 gram sample size experiments, parts-per-quadrillion (1.E-15) sensitivity to 23 elements should be obtainable for
400 gram sample sizes. (2) Similarly, the life elements H, C, N, O are effectively inert within the reactor, and this enhances
sensitivity to trace elements in, for example, bacteria. Data will be presented for these two cases. 相似文献
165.
The fate of excitation energy and electron transfer to quinones within Chl-a-containing phosphatidyl choline liposomes has been investigated. The bilayer membrane of the liposome stabilizes the Chl triplet state, as evidenced by a three-fold increase in the lifetime over that observed in ethanol solution. The relative triplet yield follows the relative fluorescence yield, indicative of quenching at the singlet level. Triplet state lifetimes are markedly shortened as the Chl concentration is increased, demonstrating that quenching occurs at the triplet level as well. This process is shown to be due to a collisional de-excitation. In the presence of quinones, the Chl triplet reduces the quinone resulting in production of long-lived electron transfer products. The percent conversion of Chl triplet to cation radical when benzoquinone is employed as acceptor is approximately 60 ± 10%, which is slightly less than in ethanol solution (70 ± 10%). The lifetime of the radical, however, can be as much as 1900 times longer. With respect to potentially useful photochemical energy conversion, the magnitude of this increased lifetime is far more significant than is the decreased radical yield. 相似文献
166.
Jens Sehested Thomas Ellermann Ole John Nielsen Timothy J. Wallington Michael D. Hurley 《国际化学动力学杂志》1993,25(9):701-717
The ultraviolet absorption spectrum, kinetics, and mechanism of the self reaction of CF3CF2O2 radicals have been studied in the gas phase at 295 K. Two techniques were used; pulse radiolysis UV absorption to measure the spectrum and kinetics, and long-path length FTIR spectroscopy to identify and quantify the reaction products. Absorption cross sections were quantified over the wavelength range 220–270 nm. At 230 nm, σ = (2.74 ± 0.46) ×10?18 cm2 molecule?1. This absorption cross section was used to derive the observed self reaction rate constant for reaction (1), defined as, ?d[CF3CF2O2]/dt = 2k1obs[CF3CF2O2]2: k1obs = (2.10 ± 0.38) ×10?12 cm3 molecule?1 s?1 (2σ). The observed products following the self reaction of CF3CF2O2 radicals were COF2, CF3O3CF3, CF3O3C2F5, and CF3OH. CF3O2CF3 was tentatively identified as a product. The carbon balance was 90–100%. The self reaction of CF3CF2O2 radicals was found to proceed via one channel to produce CF3CF2O radicals which then decompose to give CF3 radicals and COF2. In the presence of O2, CF3 radicals are converted into CF3O radicals. CF3O radicals have several fates; self reaction to give CF3O2CF3; reaction with CF3O2 radicals to give CF3O3CF3; reaction with C2F5O2 radicals to give CF3O3C2F5; or reaction with CF3CF2H to give CF3OH. As part of this work a rate constant of (2.5 ± 0.6) ×10?16 cm3 molecule?s?1 was measured for the reaction of Cl atoms with CF3CHF2 using a relative rate technique. Results are discussed with respect to the atmospheric chemistry of CF3CF2H (HFC-125). © 1993 John Wiley & Sons, Inc. 相似文献
167.
Relative rate techniques were used to study the kinetics of the reaction of OH radicals with acetylene at 296 K in 25–8000 Torr of air, N2/O2, or O2 diluent. Results obtained at total pressures of 25–750 Torr were in good agreement with the literature data. At pressures >3000 Torr, our results were substantially (~35%) lower than that reported previously. The kinetic data obtained over the pressure range 25–8000 Torr are well described (within 15%) by the Troe expression using ko = (2.92 ± 0.55) × 10?30 cm6 molecule?2 s?1, k∞ = (9.69 ± 0.30) × 10?13 cm3 molecule?1 s?1, and Fc = 0.60. At 760 Torr total pressure, this expression gives k = 8.49 × 10?13 cm molecule?1 s?1. © 2003 Wiley Periodicals, Inc. Int J Chem Kinet 35: 191–197, 2003 相似文献
168.
Abstract— The extinction coefficient εT , of triplet benzophenone in benzene has been directly determined by absolute measurements of absorbed energy and triplet absorbance, Δ D 0 T , under demonstrably linear conditions where incident excitation energy, E 0 , and ground state absorbance, A 0 , are both extrapolated to zero. The result, 7220 ± 320 M -1 cm-1 at 530 nm, validates and slightly corrects many measurements relative to benzophenone of triplet extinction coefficients made by the energy transfer technique, and of triplet yields obtained by the comparative method.
As E0 and A 0 both decrease, Δ D 0 T becomes proportional to their product. In this situation, the ratio R = (1/ A 0 )(dΔ D 0 T /d E 0 ) = (εT - εG )φT . Measurements of R , referred to benzophenone, give (εT - εG )φT for any substance, without necessity for absolute energy calibration.
Both absolute and relative laser flash measurements on zinc tetraphenyl porphyrin (εT - εG at 470 nm = 7.3 × 104 M -1 cm-1 ) give φT = 0.83 ± 0.04. 相似文献
As E
Both absolute and relative laser flash measurements on zinc tetraphenyl porphyrin (ε
169.
Thurston DE Bose DS Thompson AS Howard PW Leoni A Croker SJ Jenkins TC Neidle S Hartley JA Hurley LH 《The Journal of organic chemistry》1996,61(23):8141-8147
An efficient convergent synthesis of a homologous series of C8-linked pyrrolobenzodiazepine dimers with remarkable DNA interstrand cross-linking activity and potent in vitro cytotoxicity is reported. The "amino thioacetal" cyclization procedure was used to produce the electrophilic DNA-interactive N10-C11 imine moiety during the final synthetic step. In order to construct the key A-ring fragments (9a-d), a versatile convergent approach has been developed to join two units of vanillic acid with alpha,omega-dihaloalkanes of varying length to provide the required bis(4-carboxy-2-methoxyphenoxy)alkanes while avoiding the formation of mixtures of monoalkylated and bisalkylated products. 相似文献
170.
Mike Hurley 《Proceedings of the American Mathematical Society》1998,126(1):245-256
We prove two theorems concerning Lyapunov functions on metric spaces. The new element in these theorems is the lack of a hypothesis of compactness or local compactness. The first theorem applies to a discrete dynamical system on any metric space; the result is that if is an attractor for a continuous map of a metric space to itself, then there is a Lyapunov function for . The second theorem applies only to separable metric spaces; the theorem is that there is a complete Lyapunov function for any continuously-generated discrete dynamical system on a separable metric space. (A complete Lyapunov function is a real-valued function that is constant on orbits in the chain recurrent set, is strictly decreasing along all other orbits, and separates different components of the chain recurrent set.)