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91.
Ali EM Edwards HG Hargreaves MD Scowen IJ 《Analytical and bioanalytical chemistry》2008,390(4):1159-1166
This study describes the application of Raman spectroscopy to the detection of drugs of abuse and noncontrolled substances
used in the adulteration of drugs of abuse on human nail. Contamination of the nail may result from handling or abusing these
substances. Raman spectra of pure cocaine hydrochloride, a seized street sample of cocaine hydrochloride (77%), and paracetamol
could be acquired from drug crystals on the surface of the nail. An added difficulty in the analytical procedure is afforded
by the presence of a nail varnish coating the nail fragment. By using confocal Raman spectroscopy, spectra of the drugs under
nail varnish could be acquired. Spectra of the drugs could be readily obtained nondestructively within three minutes with
little or no sample preparation. Raman spectra could be acquired from drug particles with an average size of 5–20 μm. Acquisition
of Raman point maps of crystals from both pure and street samples of cocaine hydrochloride under nail varnish is also reported.
Figure Raman spectrum and point Raman map of cocaine HCI 相似文献
92.
The unique reactivity of 2-methyleneoxetanes and 1,5-dioxaspiro[3.2]hexanes has been exploited for the synthesis of epi-oxetin (26), an oxetane-containing beta-amino acid. While the preparation of the natural product oxetin (1) was the original goal, the unexpected diastereoselectivity of an precedented reduction provided the epi-oxetin framework. The methodology described herein should be amenable for the preparation of oxetin with a change in nitrogen protection. 相似文献
93.
Rhudy KL Su S Howell HR Urban MW 《Langmuir : the ACS journal of surfaces and colloids》2008,24(5):1808-1813
These studies focus on the role of poly(vinyl alcohol) (pVOH) during colloidal synthesis of poly(methyl methacrylate/n-butyl acrylate) (pMMA/nBA) and its effect on particle coalescence. Using 2D photoacoustic FT-IR spectroscopy and internal reflection IR imaging, we showed that the presence of pVOH creates competing environments between the copolymer particle surfaces, aqueous phases, and dispersing agents which results in migration and self-induced stratification occurring during coalescence. pMMA/nBA/pVOH films stratify to form sodium dodecyl sulfate rich film-air interfaces, and the -SO3- moieties exhibit preferential parallel orientation with respect to the surface. At the same time, the bulk of the film is dominated by intramolecular hydrogen bonding between the pVOH phase and the copolymer matrix. This behavior is attributed to significant interactions between pVOH and pMMA/nBA, resulting in limited mobility of pVOH. 相似文献
94.
This study describes the application of confocal Raman microscopy to the detection and identification of drugs-of-abuse in situ on undyed natural synthetic fibres, and coloured textile specimens. Raman spectra were obtained from drug particles trapped between the fibres of the specimens. Pure samples of cocaine hydrochloride and N-methyl-3,4-methylenedioxy-amphetamine HCl (MDMA-HCl) were used in this study. Raman spectra were collected from drug particles of an average size in the range 5-15 μm. Despite the presence of spectral bands arising from the natural and synthetic polymer and dyed textiles, the drugs could be identified by their characteristic Raman bands. If necessary, interfering bands could be successfully removed by spectral subtraction. Furthermore, Raman spectra were recorded from drug particles trapped between the fibres of highly fluorescent specimens. Interference from the fibres, including background fluorescence, was overcome by careful focusing of the confocal beam and the resulting spectra allow ready differentiation from interference from the fibres substrate bands. Spectra of several drugs-of-abuse on dyed and undyed clothing substrates were readily obtained within 3 min with little or no sample preparation and with no alteration of the evidential material. 相似文献
95.
[reaction: see text] The cross metathesis reactivities of alpha-methylene-gamma-butyrolactone and an alpha-methylene-delta-lactone have been investigated. alpha-Methylene-gamma-butyrolactone undergoes rapid and efficient olefin isomerization in the presence of second-generation metathesis catalysts. However, cross metathesis can be achieved with the additive 2,6-dichlorobenzoquinone. In contrast, the alpha-methylene-delta-lactone neither isomerizes nor couples under similar conditions. 相似文献
96.
Pandey D Zemlyanov DY Bevan K Reifenberger RG Dirk SM Howell SW Wheeler DR 《Langmuir : the ACS journal of surfaces and colloids》2007,23(9):4700-4708
Molecular layers formed from 4-trifluoromethylbenzenediazonium tetrafluoroborate and 4-Methylbenzenediazonium tetrafluoroborate have been assembled on H-passivated Si(111) and studied by UHV STM and XPS. STM imaging shows well-developed Si(111) step edges and terraces both on Si(111):H and Si(111) substrates covered with a molecular layer. STM I(V) data acquired at different tip-substrate separations reveals a factor of approximately 10 enhancement in current for positive bias voltage when current flows through the 4-trifluoromethyl molecule when compared to the 4-methyl variant. The observed current enhancement in I(V) can be understood by comparing the projected density of states of the two molecule-Si systems calculated using a density functional theory local density approximation after geometry optimization was performed via the conjugate gradient method. XPS data independently confirm that H-passivated Si(111) remains oxygen free for short exposures to ambient conditions and provide evidence that the molecules chemically react with the silicon surface. 相似文献
97.
Flood C Cosgrove T Qiu D Espidel Y Howell I Revell P 《Langmuir : the ACS journal of surfaces and colloids》2007,23(5):2408-2413
Solvent relaxation NMR and small-angle neutron scattering have been used to characterize adsorbed poly(ethylene oxide) (PEO) layers on silica at a range of surfactant and electrolyte concentrations. Below the critical aggregation concentration (cac), the results suggest that sodium dodecyl sulfate (SDS) interacts relatively weakly, perhaps analogously to a simple salt reducing the solvency of PEO. This is evidenced by a decrease in the adsorbed layer thickness combined with an increase in the bound fraction, although the total adsorbed amount is not greatly affected. The layer thickness goes through a minimum at the cac, after which further SDS addition results in the formation of PEO/SDS aggregates that repel each other and, hence, tend to desorb. The adsorbed amount therefore decreases, from 0.7 mg m(-2) initially to 0.2 mg m(-2) with 32 mM SDS. The aggregates that remain adsorbed also repel, and hence, there is an increase in the layer thickness and the persistence length, while the bound fraction is reduced. In comparison, the effects of electrolyte at the ionic strength studied are relatively minimal. There is, however, evidence that the repulsions between adsorbed PEO/SDS aggregates are partially screened, allowing them to approach each other more readily. This leads to a contraction of the adsorbed layer when the SDS concentration is sufficiently high. 相似文献
98.
Howell JA 《Dalton transactions (Cambridge, England : 2003)》2007,(11):1104-1114
The mechanism of Rh(ii)-catalysed cyclopropanation has been investigated computationally using Rh(2)(formate)(4) as a model precatalyst, with the model organic substrates CH(2)N(2) and C(2)H(4) and MeCl as a model for coordinating solvent. Three potential carriers of catalysis have been identified, one retaining the Rh(2)(formate)(4) framework and two others resulting from ligand insertion of Rh-CH(2) into an Rh-O bond. Both 2 + 1 and 2 + 2 pathways have been identified for the cyclopropanation step depending on the catalytic carrier involved. Complexes resulting from CH(2) insertion into the Rh-O bond are more efficient at lowering the activation enthalpy for CH(2)-N(2) scission in the rate determining step. 相似文献
99.
100.
General purpose poly(styrene) prepared by conventional radical techniques contains a head-to-head unit as a consequence of
polymerization termination by radical coupling. As has been previously demonstrated, thermal stress promotes homolysis of
the bond linking the head-to-head components. The macroradicals generated depolymerize rapidly to generate styrene monomer.
This decomposition during processing can lead to finished articles containing objectionable levels of styrene monomer, particularly
for food packaging applications in which even low levels of monomer can promote objectionable taste and aroma. Polymer containing
no head-to-head units should not be prone to this facile decomposition. In this instance, poly(styrene) has been prepared
by nitroxyl-mediated polymerization of styrene monomer followed by reductive removal of nitroxyl end groups. Polymer prepared
in this manner contains no head-to-head units and displays thermal stability much greater than that observed for conventional
poly(styrene). A direct comparison of the stability for the two polymers is readily available by thermogravimetric techniques.
A quantitative reflection of the difference in stability is available from the rate constants for the respective decomposition. 相似文献