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61.
Statistical control charts are presented for the evaluation of time series radiation counter data from flow cells used for
monitoring of low levels of 99TcO4− in environmental solutions. Control chart methods consisted of the 3-sigma (3σ) chart, the cumulative sum (CUSUM) chart, and the exponentially weighted moving average (EWMA) chart. Each method involves
a control limit based on the detector background which constitutes the detection limit. Both the CUSUM and EWMA charts are
suitable to detect and estimate sample concentration requiring less solution volume than when using a 3σ control chart. Data presented here indicate that the overall accuracy and precision of the CUSUM method is the best. 相似文献
62.
63.
Zhaohui Li David Hughes Jill P.G. Urban Zhanfeng Cui 《Journal of membrane science》2008,310(1-2):237-245
There is a growing interest in using large pore size probes for microdialysis of macromolecular markers to monitor cell and tissue functions. Fluid balance could be an important issue when using large pore size microdialysis probes, which are affected by the mode of operation. In this study, the effect of pumping systems, push, pull, push-and-pull, and the resulting transmembrane pressure on the fluid balance, as well as, the relative recovery of small molecular nutrients and metabolites and macromolecules (proteins) were examined. The validity of the internal reference in situ calibration was examined in detail. It is concluded that a push-and-pull system is the only effective method of eliminating fluid loss or gain. The relative recovery of small solutes is not affected much by the applied pumping methods; however, the relative recovery of macromolecules is significantly influenced by them. The in situ calibration technique using Phenol Red can provide reliable results for small molecules including glucose and lactic acid. Using 10 and 70-kDa fluorescent dextrans as the internal standard for large molecules in situ calibration of similar size does not work for the pull pump system, but does work well when using a push-and-pull pumping method. 相似文献
64.
Miller AK Hughes CC Kennedy-Smith JJ Gradl SN Trauner D 《Journal of the American Chemical Society》2006,128(51):17057-17062
A concise, stereoselective, and convergent total synthesis of the unnatural enantiomer of the neodolastane diterpenoid heptemerone B has been completed. Saponification of (-)-heptemerone afforded (-)-guanacastepene E. The absolute stereochemistry of (-)-heptemerone B was thus established as 5-(S), the same as (-)-guanacastepene E. The longest linear sequence of the synthesis comprises 17 (18) steps from simple known starting materials. Our general synthetic approach integrates a diverse set of reactions, including an intramolecular Heck reaction to create one quaternary stereocenter and a cuprate conjugate addition for the establishment of the other. The central seven-membered ring was closed with an uncommon electrochemical oxidation, whereas the five-membered ring was formed through ring-closing metathesis. The absolute configuration of the two key building blocks was established through an asymmetric reduction and an asymmetric ene reaction. 相似文献
65.
Application of a triple-pulse waveform is described for the anodic detection of methanol, ethanol, and ethylene glycol. The execution of the waveform incorporates the cleaning and reactivation of the platinum electrode, by alternate anodic and cathodic polarization, with measurement of the faradaic signal for the analyte at the reduced electrode surface. Some results for formic acid are also presented. The waveform is completed within approximately 2 s and the faradaic signal exhibits no decay with time as would be the case for amperometric detection at a constant applied potential. Calibration curves made by plotting —1/I vs. 1/C are linear. This is consistent with a reaction mechanism in which the analyte is adsorbed prior to anodic detection. The technique is applicable for detection in chromatographic and flow-injection systems. 相似文献
66.
Dr. Luke A. Clifton Dr. Stephen A. Holt Dr. Arwel V. Hughes Dr. Emma L. Daulton Dr. Wanatchaporn Arunmanee Dr. Frank Heinrich Dr. Syma Khalid Damien Jefferies Dr. Timothy R. Charlton Dr. John R. P. Webster Dr. Christian J. Kinane Prof. Jeremy H. Lakey 《Angewandte Chemie (International ed. in English)》2015,54(41):11952-11955
Gram‐negative bacteria are an increasingly serious source of antibiotic‐resistant infections, partly owing to their characteristic protective envelope. This complex, 20 nm thick barrier includes a highly impermeable, asymmetric bilayer outer membrane (OM), which plays a pivotal role in resisting antibacterial chemotherapy. Nevertheless, the OM molecular structure and its dynamics are poorly understood because the structure is difficult to recreate or study in vitro. The successful formation and characterization of a fully asymmetric model envelope using Langmuir–Blodgett and Langmuir–Schaefer methods is now reported. Neutron reflectivity and isotopic labeling confirmed the expected structure and asymmetry and showed that experiments with antibacterial proteins reproduced published in vivo behavior. By closely recreating natural OM behavior, this model provides a much needed robust system for antibiotic development. 相似文献
67.
The spectroscopic, electronic, and DNA-binding characteristics of two novel ruthenium complexes based on the dialkynyl ligands 2,3-bis(phenylethynyl)-1,4,8,9-tetraaza-triphenylene (bptt, 1) and 2,3-bis(4-tert-butyl-phenylethynyl)-1,4,8,9-tetraaza-triphenylene (tbptt, 2) have been investigated. Electronic structure calculations of bptt reveal that the frontier molecular orbitals are localized on the pyrazine-dialkynyl portion of the free ligand, a property that is reflected in a red shift of the lowest energy electronic transition (1: λ(max) = 393 nm) upon substitution at the terminal phenyl groups (2: λ(max) = 398 nm). Upon coordination to ruthenium, the low-energy ligand-centered transitions of 1 and 2 are retained, and metal-to-ligand charge transfer transitions (MLCT) centered at λ(max) = 450 nm are observed for [Ru(phen)(2)bptt](2+)(3) and [Ru(phen)(2)tbptt](2+)(4). The photophysical characteristics of 3 and 4 in ethanol closely parallel those observed for [Ru(bpy)(3)](2+) and [Ru(phen)(3)](2+), indicating that the MLCT excited state is primarily localized within the [Ru(phen)(3)](2+) manifold of 3 and 4, and is only sparingly affected by the extended conjugation of the bptt framework. In an aqueous environment, 3 and 4 possess notably small luminescence quantum yields (3: ?(H(2)O) = 0.005, 4: ?(H(2)O) = 0.011) and biexponential decay kinetics (3: τ(1) = 40 ns, τ(2) = 230 ns; 4: τ(1) ~ 26 ns, τ(2) = 150 ns). Addition of CT-DNA to an aqueous solution of 3 causes a significant increase in the luminescence quantum yield (?(DNA) = 0.045), while the quantum yield of 4 is relatively unaffected (?(DNA) = 0.013). The differential behavior demonstrates that tert-butyl substitution on the terminal phenyl groups inhibits the ability of 4 to intercalate with DNA. Such changes in intrinsic luminescence demonstrate that 3 binds to DNA via intercalation (K(b) = 3.3 × 10(4) M(-1)). The origin of this light switch behavior involves two competing (3)MLCT states similar to that of the extensively studied light switch molecule [Ru(phen)(2)dppz](2+). The solvent- and temperature-dependence of the luminescence of 3 reveal that the extended ligand aromaticity lowers the energy of the (3)ππ* excited state into competition with the emitting (3)MLCT state. Interconversion between these two states plays a significant role in the observed photophysics and is responsible for the dual emission in aqueous environments. 相似文献
68.
Lewis M. Broomfield David Boschert Joseph A. Wright David L. Hughes Manfred Bochmann 《Journal of organometallic chemistry》2009,694(25):4084-4089
Potassium salts of the new 2-phosphinomethyl-1H-pyrroles, K[R2PCH2C4H3N] (R = Ph, Cy) react with (η3-allyl)nickel bromide to give the chelate complexes (R2PCH2C4H3N)Ni(allyl), whereas the sterically hindered 2-diphenylphosphinomethyl-5-t-butyl-1H-pyrrole and (η3-allyl)nickel bromide afford a phosphine adduct (HNC4H2-5-But-2-CH2PPh2)Ni(allyl)Br which is stabilized by an intramolecular NHBr hydrogen bond. The addition of B(C6F5)3 to (R2PCH2C4H3N)Ni(allyl) leads to an electrophilic attack in 5-position of the pyrrole ring, to give the thermally unstable zwitterions (η3-C3H5)Ni[NC4H3(2-CH2PR2)-5-B(C6F5)3] which catalyse the isomerisation of 1-hexene. The addition of B(C6F5)3 is reversible, and slow ligand rearrangement to Ni(N-P)2 products appears to be the major catalyst deactivation pathway. 相似文献
69.
Simon Maher Sarfaraz U. Syed David M. Hughes John R. Gibson Stephen Taylor 《Journal of the American Society for Mass Spectrometry》2013,24(8):1307-1314
Previous experimental and theoretical work identified that the application of a static magnetic (B) field can improve the resolution of a quadrupole mass spectrometer (QMS) and this simple method of performance enhancement offers advantages for field deployment. Presented here are further data showing the effect of the transverse magnetic field upon the QMS performance. For the first time, the asymmetry in QMS operation with B x and B y is considered and explained in terms of operation in the fourth quadrant of the stability diagram. The results may be explained by considering the additional Lorentz force (v x B) experienced by the ion trajectories in each case. Using our numerical approach, we model not only the individual ion trajectories for a transverse B field applied in x and y but also the mass spectra and the effect of the magnetic field upon the stability diagram. Our theoretical findings, confirmed by experiment, show an improvement in resolution and ion transmission by application of magnetic field for certain operating conditions. Figure
? 相似文献
70.