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61.
C.G. Olson J.H. Sexton D.W. Lynch A.J. Bevolo H.R. Shanks B.N. Harmon W.Y. Ching D.M. Wieliczka 《Solid State Communications》1985,56(1):35-37
The valence bands of epitaxial layers of A1N were studied by ultraviolet photoelectron spectroscopy and electron energy loss spectroscopy. A self-consistent band structure was calculated and the resultant density of states compared with the UPS spectra. Qualitative agreement was good, with discrepancies arising primarily from the neglect of dipole matrix elements. 相似文献
62.
Robert A. Shanks 《高分子科学》2002,(6):497-508
The effect of time-temperature treatment on morphology of polyethylene-polypropylene (PE-PP) blends wasstudied to establish a relationship between thermal history, morphology and mechanical properties. Polypropylene (PP)homopolymers were used to blend with various polyethylenes (PE), including high density polyethylene (HDPE), lowdensity polyethylene (LDPE), linear low density polyethylene (LLDPE), and very and ultra low density polyethylene(VLDPE and ULDPE). The majority of the blends were prepared at a ratio of PE:PP = 80:20, while blends of PP and LLDPEwere prepared at various compositions. Thermal treatment was carried out at temperatures between the crystallizationtemperatures of PP and PEs to allow PP to crystallize first from the blends. On cooling further, PE crystallized too. A verydiffuse PP spherulite morphology in the PE matrix was formed in some partially miscible blends when PP was less than 20%by mass. Droplet-matrix structures were developed in other blends with either PP or PE as dispersed domains in a continuousmatrix, depending on the composition ratio. The scanning electron microscopy (SEM) images displayed a fibrillar structureof PP spherulite in the LLDPE-PP (80:20) and large droplets of PP in the HDPE-PP (80:20) blend, providing larger surfacearea and better bonding in the LLDPE-PP (80:20) blends. This explains why the blends with diffuse spherulite morphologyshowed greater improvement in tensile properties than droplet-matrix morphology blends after time-temperature treatment. 相似文献
63.
Lin VS Radu DR Han MK Deng W Kuroki S Shanks BH Pruski M 《Journal of the American Chemical Society》2002,124(31):9040-9041
A polyalkynylene-based conducting polymer (molecular wire) has been synthesized within the Cu-functionalized mesoporous MCM-41 silica catalyst. Fluorescence and 13C solid-state NMR provided spectroscopic evidence that the synthesis of extended polymeric chains with a high degree of alignment requires homogeneously distributed catalytic sites throughout the entire MCM matrix. This type of homogeneity has been achieved via co-condensation of the catalytic groups in narrow pores. In addition, our results indicated that proper adjustment of the pore diameter is vital to prevent clogging of the pores with aggregated or cross-linked polymers or both. 相似文献
64.
The crystallisation kinetics, melting behaviour and
morphology, of bacterial poly(3-hydoxybutyrate) (PHB) have been investigated
by using differential scanning calorimetry (DSC), step-scan DSC (SDSC), wide
angle X-ray diffraction (WAXRD) and hot stage polarised optical microscopy
(HSPOM). DSC imparted isothermal crystallisation thermal history. The subsequent
melting behaviour revealed that all PHB materials experienced secondary crystallisation
during heating and the extent of secondary crystallisation varied depending
on the crystallisation temperature. PHB samples were found to exhibit double
melting behaviour due to melting of SDSC scan-induced secondary crystals,
while considerable secondary crystallisation or annealing took place under
the modulated heating conditions. The overall melting behaviour was rationalised
in terms of recrystallisation and/or annealing of crystals. Interestingly,
the PHB materials analysed by SDSC showed a broad exotherm before the melting
peak in the non-reversing curve and a multiple melting peak reversing curve,
verifying that the melting-recrystallisation and remelting process was operative.
HSOM studies supported the conclusions from DSC that the radial growth rate
of the PHB spherulites was significantly varied upon the crystallisation conditions.
One form of crystals was shown by WAXRD from isothermally crystallised PHB. 相似文献
65.
Corn stover has potential as a resource for both fiber and chemical needs if separation strategies can be developed to deal
with its heterogeneity. Relative hydrolysis characteristics were assessed for pith (sclerenchyma and parenchyma) and fiber
(collenchyma) tissue fractions derived from mechanical separation of corn stover to determine whether classification by tissue
type resulted in fractions with different hydrolysis response. The physical characteristics of the tissue fractions were analyzed.
The hydrolysis behavior of the fractions was evaluated under both acidic and basic conditions. The results from the hydrolysis
experiments are compared with previously reported compositional analysis for the tissue fractions. 相似文献
66.
Gary M. Hieftje David S. Hanselman Patrick P. Mahoney Norman N. Sesi Kathryn E. Shanks Steven E. Hobbs Daniel L. Burden 《Mikrochimica acta》1995,120(1-4):3-19
In chemical measurement and characterization, lasers are playing a unique role in improving sensitivity, enhancing spatial and spectral resolution, and enabling time resolution on the fastest time scales that are chemically significant. Furthermore, lasers have permitted entirely new classes of measurements to be undertaken that would not be possible without the high radiant power, directionality, and coherence of a laser beam. In this paper, a number of these capabilities are illustrated with examples from the authors' laboratory. Prominent among these examples is the use of a high-power pulsed laser for producing scattering and fluorescence from species in an inductively coupled plasma (ICP). With the appropriate laser and photometric equipment, such measurements enable the determination of time-resolved and spatially resolved values for electron concentration, electron energy distribution, gas-kinetic temperature, and the concentrations of important sample and intrinsic species that the plasma contains. Another example shows how either a continuous wave (CW) or repetitively pulsed laser can be coupled with relatively simple electronic instrumentation to permit measurements to be obtained on a sub-nanosecond time scale. Interestingly, a recent development might obviate the need for a sophisticated laser in such schemes. Lastly, a relatively simple experimental configuration can be used to determine as few as 106 molecules in a real sample. In this arrangement, a single aliquot of the sample is dispensed in a volume as small as 6 nL. This aliquot, in droplet from, then constitutes the sample cell itself. As the droplet falls through the focused laser beam, its contents can be determined with extraordinarily high sensitivity. Methods to improve even this detection capability will be outlined. 相似文献
67.
The high-resolution infrared absorption spectra of eight2H or13C substituted isotopomers of diacetylene have been recorded, and the bands corresponding to thev
4 fundamental andv
6 combination of the major isotopomer have been analyzed using a Loomis-Wood-type program. Effective ground-state rotational constants have been obtained from ground-state combination differences. A number ofr
0,r
s,r
m
, and (r
m
)corr structures have been calculated from the available data and are compared to those obtained by ab initio methods. The (r
m
)corr structure, which is a reliable near-equilibrium structure of diacetylene, isr
C–H=106.131(13) pm;r
C–C=137.081(16) pm;r
C-C=120.964(14). (r
m
)corr structures of the related molecules cyanogen, cyanoacetylene, and cyanodiacetylene have been calculated, and near-equilibrium structures of triacetylene and dicyanoacetylene have been predicted. 相似文献
68.
69.
Hunt NT Kattner L Shanks RP Wynne K 《Journal of the American Chemical Society》2007,129(11):3168-3172
Changes in the ultrafast dynamics and terahertz Raman spectrum accompanying a helix-to-coil transition of a homo-polypeptide have been observed for the first time. Formation of the alpha-helix is associated with a shift to lower frequency of a broad Raman band attributable to solvent-peptide intermolecular hydrogen bonding. This band facilitates direct spectroscopic observation of so-called hydration water near a peptide and yields the first quantitative estimate of the time scale of the ultrafast dynamics in the solvation shell, which range from 0.18 to 0.33 ps (185-100 cm(-1)) depending on the secondary structure of the peptide. Such fast motions of solvent molecules have been referred to as the "lubricant of life" and are thought to play key roles in determining structure and activity of proteins. 相似文献
70.
Gazi E Dwyer J Lockyer NP Gardner P Shanks JH Roulson J Hart CA Clarke NW Brown MD 《Analytical and bioanalytical chemistry》2007,387(5):1621-1631
Prostate cancer (CaP) cells preferentially metastasise to the bone marrow, a microenvironment that plays a substantial role
in the sustenance and progression of the CaP tumour. Here we use a combination of FTIR microspectroscopy and histological
stains to increase molecular specificity and probe the biochemistry of metastatic CaP cells in bone marrow tissue derived
from a limited source of paraffin-embedded biopsies of different patients. This provides distinction between the following
dominant metabolic processes driving the proliferation of the metastatic cells in each of these biopsies: glycerophospholipid
synthesis from triacylglyceride, available from surrounding adipocytes, in specimen 1, through significantly high (p ≤ 0.05) carbohydrate (8.23 ± 1.44 cm−1), phosphate (6.13 ± 1.5 cm−1) and lipid hydrocarbon (24.14 ± 5.9 cm−1) signals compared with the organ-confined CaP control (OC CaP), together with vacuolation of cell cytoplasm; glycolipid synthesis
in specimen 2, through significantly high (p ≤ 0.05) carbohydrate (5.51 ± 0.04 cm−1) and high lipid hydrocarbon (17.91 ± 2.3 cm−1) compared with OC CaP, together with positive diastase-digested periodic acid Schiff staining in the majority of metastatic
CaP cells; glycolysis in specimen 3, though significantly high (p ≤ 0.05) carbohydrate (8.86 ± 1.78 cm−1) and significantly lower (p ≤ 0.05) lipid hydrocarbon (11.67 ± 0.4 cm−1) than OC CaP, together with negative diastase-digested periodic acid Schiff staining in the majority of metastatic CaP cells.
Detailed understanding of the biochemistry underpinning the proliferation of tumour cells at metastatic sites may help towards
refining chemotherapeutic treatment. 相似文献