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71.
72.
Bernadette A. Higgins Duane L. Simonson Eric J. Houser James G. Kohl R. Andrew Mcgill 《Journal of polymer science. Part A, Polymer chemistry》2010,48(14):3000-3009
Sorbent polymers can be designed to target molecular interactions with a variety of hazardous chemicals including explosives, chemical agents, narcotics, and toxic industrial chemicals. Applications of functionalized sorbent polymers include preconcentrator devices, SPME fibers, membrane introduction systems, chromatographic stationary phases and coatings for chemical sensors. One common feature of a wide range of hazardous chemicals is their hydrogen bond (h‐b) basicity. In this work, we report on the synthesis and characterization of a h‐b acidic hyperbranched carbosilane fluoroalcohol based sorbent polymer (poly(methyldi(1,1,1‐trifluoro‐2‐trifluoromethyl‐2‐hydroxypent‐4‐enyl)silane; HCSFA2), which is suitable for sorbing these hazardous h‐b basic analytes. Multiple batches of HCSFA2 were characterized with routine composition, spectroscopic, thermal analysis, and inverse gas chromatography (iGC) to evaluate polymer physicochemical properties. In comparison with previously developed h‐b acidic polymers (e.g., FPOL and SXFA), HCSFA2 exhibits a sorption improvement of 10–15 fold for h‐b basic analytes. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 3000–3009, 2010 相似文献
73.
Methods are described for making reproducible and robust vanadate-glass threshold switches both by a bulk and a thick-film technique; the latter method lendsitself to the large-scale production of the devices. The electrical characteristics obtained using dc, sine-wave and square-wave inputs are described and the various electrical parameters such as: threshold voltage, holding current, delay time, etc. are given. The results of a statistical analysis involving 30 alumina substrates with 12 switches on each are described, the population being analysed in terms of the standard deviation and mean deviation of the dc threshold voltage and the resistance of the off-state. An attempt is made to correlate the variation in parameters from device to device with variables involved in the furnace-firing schedule as well as the printing. 相似文献
74.
Functions belonging to various Paley-Wiener spaces have representations in sampling series. When a function does not belong
to such a space, the sampling series may converge, not to the object function but to an "alias" of it, and an aliasing error
is said to occur. Aliasing error bounds are derived for one- and two-channel sampling series analogous to the Whittaker-Kotel’nikov-Shannon
series, and for the multi-band sampling series, and a "derivative" extension of it, due to Dodson, Beaty, et al. The Poisson
summation formula is a basic tool throughout. Aliasing in the one-channel case is shown to arise from a transformation with
similarities to a projection. Where possible, the sharpness of the error bounds is discussed. 相似文献
75.
Robert H. Higgins Monique R. Watson William J. Faircloth Quentin L. Eaton Harvey Jenkins 《Journal of heterocyclic chemistry》1988,25(2):383-387
Preparation of the trimethylsilyl ethers of 1-alkyl-3-azetidinols from non-hindered primary amines and epichlorohydrin by conversion of the intermediate 1-(alkylamino)-3-chloro-2-propanols to their trimethylsilyl ethers by either N-(trimethylsilyl)acetamide or by 1-(trimethylsilyl)imidazole followed by ring closure in acetonitrile is described. This sequence of reactions fails for aromatic amines, but appears to be general for all primary aliphatic amines, although the condensation of hindered amines with epichlorohydrin occurs slowly. Several novel azetidinols, in which the N-alkyl substituent itself contains a second heterocyclic system, are reported. In addition, the pKA's of several m. and p-substituted 1-benzylazetidinols correlates well with the Hammett equation. 相似文献
76.
77.
F. Stienkemeier J. Higgins C. Callegari S. I. Kanorsky W. E. Ernst G. Scoles 《Zeitschrift für Physik D Atoms, Molecules and Clusters》1996,38(3):253-263
Large liquid helium clusters (Hen, n ≈ 104) produced in a supersonic jet are doped with alkali atoms (Li, Na, K) and characterized by means of laser induced fluorescence. Each cluster contains, on average, less than one dopant atom. Both excitation and emission spectra have been recorded. The observed excitation spectra are analyzed, calculating the transitions within an approach based on the hypothesis that the chromophores are trapped in a dimple on the cluster’s surface as predicted by the theoretical calculations of Ancilotto et al. [9]. The results of the model calculations are in good qualitative agreement with the experimental findings. In spite of the very weak binding energy (a few cm?1), some of the excited atoms remain bound to the surface, provided the excitation occurs at frequencies not too far from the alkali’s gas phase absorptions. These bound-bound excitations produce very broad, red shifted emission spectra. At other, blue shifted frequencies, the excited atoms desorb from the cluster’s surface, giving rise to unshifted, free atom, emission spectra. The heavier alkali metals (Na, K) show, compared to the calculations, an additional broadening which is attributed to surface excitations on the helium droplet. 相似文献
78.
Identification of nolR-regulated proteins in Sinorhizobium meliloti using proteome analysis 总被引:2,自引:0,他引:2
Chen H Higgins J Kondorosi E Kondorosi A Djordjevic MA Weinman JJ Rolfe BG 《Electrophoresis》2000,21(17):3823-3832
Extractable proteins from Sinorhizobium meliloti strains AK631 and EK698 (a Tn5-induced noIR-deficient mutant of AK631), grown in tryptone agar (TA) medium with or without the addition of the plant signal luteolin, were separated by two-dimensional gel electrophoresis and compared. Analysis of silver-stained gels showed that the noIR mutant had 189 proteins that were significantly altered in their levels (101 protein spots up- and 88 downregulated). Coomassie-stained preparative two-dimensional (2-D) gels or polyvinylidene difluoride (PVDF) membranes blotted from preparative gels showed that at least 52 of the altered proteins could be reproducibly detected and isolated from the noIR mutant. These 52 altered protein spots were classified into five groups based on an assessment of protein abundance by computer analysis and the effect of the presence or absence of luteolin addition to the growth medium. N-terminal microsequencing of 38 proteins revealed that the most striking feature of the consequence of the noIR mutation is the number and broad spectrum of cellular functions that are affected by the loss of the NoIR function. These include proteins involved in the tricarboxylic acid (TCA) cycle, heat shock and cold shock proteins, protein synthesis, a translation elongation factor, oxidative stress and cell growth and maintenance functions. We propose that the NoIR repressor is a global regulatory protein which responds to environmental factors to fine-tune intracellular metabolism. 相似文献
79.
Sara H. Sohail John P. Otto Paul D. Cunningham Young C. Kim Ryan E. Wood Marco A. Allodi Jacob S. Higgins Joseph S. Melinger Gregory S. Engel 《Chemical science》2020,11(32):8546
Vibronic coupling between pigment molecules is believed to prolong coherences in photosynthetic pigment–protein complexes. Reproducing long-lived coherences using vibronically coupled chromophores in synthetic DNA constructs presents a biomimetic route to efficient artificial light harvesting. Here, we present two-dimensional (2D) electronic spectra of one monomeric Cy5 construct and two dimeric Cy5 constructs (0 bp and 1 bp between dyes) on a DNA scaffold and perform beating frequency analysis to interpret observed coherences. Power spectra of quantum beating signals of the dimers reveal high frequency oscillations that correspond to coherences between vibronic exciton states. Beating frequency maps confirm that these oscillations, 1270 cm−1 and 1545 cm−1 for the 0-bp dimer and 1100 cm−1 for the 1-bp dimer, are coherences between vibronic exciton states and that these coherences persist for ∼300 fs. Our observations are well described by a vibronic exciton model, which predicts the excitonic coupling strength in the dimers and the resulting molecular exciton states. The energy spacing between those states closely corresponds to the observed beat frequencies. MD simulations indicate that the dyes in our constructs lie largely internal to the DNA base stacking region, similar to the native design of biological light harvesting complexes. Observed coherences persist on the timescale of photosynthetic energy transfer yielding further parallels to observed biological coherences, establishing DNA as an attractive scaffold for synthetic light harvesting applications.Dyes coupled to DNA display distance-dependent vibronic couplings that prolongs quantum coherences detected with 2D spectroscopy. 相似文献
80.
The conformational potential energy surface as a function of the two internal torsion angles in C-nitrosomethanol has been obtained using the semiempirical AM1 method. Optimized geometries are reported for the local minima on this surface and also for the corresponding points on the HF/6-31G, 6-31G*, and 6-31G** surfaces. All methods predict cis and trans minima which occur in degenerate pairs, each pair being connected by a transition state of Cs symmetry. The AM1 structures are found to compare well with the corresponding ab initio structures. Ab initio HF/6-31G and HF/6-31G* harmonic vibrational frequencies are reported for the cis and trans forms of nitrosomethanol. When scaled appropriately the calculated frequencies are found to compare well with experimental frequencies. The ab initio calculations predict the energy barrier for cis → trans isomerization to be between 5.8 and 6.5 kcal/mol with the trans → cis isomerization barrier lying between 2.3 and 6.5 kcal/mol. The corresponding AM1 energy barriers are around 1 kcal/mol lower in energy. The ab initio calculations predict the barrier to conversion between the two cis rotamers to be very small with the AM1 value being around 1 kcal/mol. Both AM1 and ab initio calculations predict interconversion between trans rotamers to require between 1.2 and 1.4 kcal/mol. 相似文献