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361.
B. Bakowski G. Hancock R. Peverall G.A.D. Ritchie 《Applied physics. B, Lasers and optics》2006,82(1):123-131
The absolute concentration and translational temperature of the 2p10 and 2p7 excited states of argon have been measured in an inductively coupled plasma chamber under a variety of operating conditions
using both calibrated diode laser frequency modulation spectroscopy and cavity enhanced absorption spectroscopy. Accurate
lineshape analysis of frequency modulation signals has been employed to extract the desired information, and is corroborated
by cavity enhanced measurements. Temperatures are found to vary linearly with pressure from ∼400 K at 20 mTorr (2.7 Pa) to
∼510 K at 90 mTorr (12 Pa) in a 200 W discharge while concentrations peak at 3.25×108 cm-3 at 30 mTorr (4 Pa) (also in a 200 W discharge). The uncertainty in the recovered temperature is 7%, dominated by uncertainties
in the calibration of the frequency scale.
PACS 42.62Fi; 52.70kz 相似文献
362.
363.
364.
Simmons MY Hamilton AR Pepper M Linfield EH Rose PD Ritchie DA 《Physical review letters》2000,84(11):2489-2492
A detailed investigation of the metallic behavior in high-quality GaAs-AlGaAs two-dimensional hole systems reveals the presence of quantum corrections to the resistivity at low temperatures. Despite the low density ( r(s)>10) and high quality of these systems, both weak localization (observed via negative magnetoresistance) and weak hole-hole interactions (giving a correction to the Hall constant) are present in the so-called metallic phase where the resistivity decreases with decreasing temperature. If these quantum corrections persist down to T = 0, the results suggest that even at high r(s) there is no metallic phase in two dimensions. 相似文献
365.
A preservation study of carbon nanotubes in alumina-based nanocomposites via Raman spectroscopy and nuclear magnetic resonance 总被引:1,自引:0,他引:1
K.E. Thomson Dongtao Jiang R.O. Ritchie A.K. Mukherjee 《Applied Physics A: Materials Science & Processing》2007,89(3):651-654
Raman spectroscopy was used to study the preservation of the carbon nanotube structure in nanotube-reinforced alumina nanocomposites
consolidated via spark plasma sintering (SPS). A series of Raman spectroscopy experiments was used to identify the thermal
breakdown temperature of single-walled carbon nanotubes (SWCNTs) embedded in nanocrystalline alumina. It was found that the
carbon nanotube structure remains intact after sintering at 1150 °C, but almost completely breaks down by 1350 °C after only
5 min. Also, 27Al nuclear magnetic resonance (NMR) was used to study the chemical and structural effects of high-energy ball milling (HEBM)
and SPS consolidation on pure alumina and SWCNT-alumina nanocomposites. HEBM does not change the mixed coordination number
of the as-received alumina, but slight peak shifts indicate residual stresses. No Al4C3 was detected in any of the consolidated samples – even up to 1550 °C for 10 min. Thus, it is concluded that consolidation
of carbon nanotube-reinforced composites should be completed at temperatures below ∼1250 °C in order to preserve the carbon
nanotube structure.
PACS 61.18.Fs; 61.46.Fg; 61.82.Rx; 62.25.+g; 76.60.-k 相似文献
366.
W. Denzer G. Hancock A. Hutchinson M. Munday R. Peverall G.A.D. Ritchie 《Applied physics. B, Lasers and optics》2007,86(3):437-441
We have utilised a periodically poled LiNbO3 crystal with a waveguide structure to produce up to 146 μW of mid-IR radiation around 2976 cm-1 by difference frequency mixing of 1064 nm pump radiation with 1558 nm signal radiation. A conversion efficiency of 45% W-1 is achieved within a crystal of length 50 mm, and temperature tuning curves are reported. The resultant idler radiation is
exploited for high resolution absorption studies of both methane and methanethiol. The absorption cross-sections for methanethiol
in the region of 2979 cm-1 are measured and found to be ∼10-19 cm2, the relevance of these results to breath and headspace analysis of clinical samples containing volatile sulphur compounds
is briefly discussed.
PACS 42.62.Fi; 42.65.Ky 相似文献
367.
Billen J Guillarme D Rudaz S Veuthey JL Ritchie H Grady B Desmet G 《Journal of chromatography. A》2007,1161(1-2):224-233
To study the influence of the particle size distribution (PSD), we measured the chromatographic performance of a series of sub-2 microm particle high performance liquid chromatography (HPLC) columns packed with four different particle mixtures having a purposely imposed different size distribution. Using the reduced kinetic plot representation by plotting the separation impedance (E(0)) versus the plate number ratio (N(opt)/N), the different columns could be classified according to their chromatographic performance without the need to specify a mean particle diameter or a molecular diffusion coefficient, as is needed in the classical reduced plate height and flow resistance analysis. The present analysis shows that it is not so much the width or span of the particle size distribution, but rather the presence of fines that greatly determines the chromatographic performance of particulate columns. 相似文献
368.
Cooper GJ Boulay AG Kitson PJ Ritchie C Richmond CJ Thiel J Gabb D Eadie R Long DL Cronin L 《Journal of the American Chemical Society》2011,133(15):5947-5954
The process of osmotically driven crystal morphogenesis of polyoxometalate (POM)-based crystals is investigated, whereby the transformation results in the growth of micrometer-scale tubes 10-100 μm in diameter and many thousands of micrometers long. This process initiates when the crystals are immersed in aqueous solutions containing large cations and is governed by the solubility of the parent POM crystal. Evidence is presented that indicates the process is general to all types of POMs, with solubility of the parent crystal being the deciding parameter. A modular approach is adopted since different POM precursor crystals can form tubular architectures with a range of large cationic species, producing an ion-exchanged material that combines the large added cations and the large POM-based anions. It is also shown that the process of morphogenesis is electrostatically driven by the aggregation of anionic metal oxides with the dissolved cations. This leads to the formation of a semi-permeable membrane around the crystal. The osmotically driven ingress of water leads to an increase in pressure, and ultimately rupture of the membrane occurs, allowing a saturated solution of the POM to escape and leading to the formation of a "self-growing" microtube in the presence of the cation. It is demonstrated that the growth process is sustained by the osmotic pressure within the membrane surrounding the parent crystal, as tube growth ceases whenever this pressure is relieved. Not only is the potential of the modular approach revealed by the fact that the microtubes retain the properties of their component parts, but it is also possible to control the direction of growth and tube diameter. In addition, the solubility limits of tube growth are explored and translated into a predictive methodology for the fabrication of tubular architectures with predefined physical properties, opening the way for real applications. 相似文献
369.
Ligand-based shape matching approaches have become established as important and popular virtual screening (VS) techniques. However, despite their relative success, many authors have discussed how best to choose the initial query compounds and which of their conformations should be used. Furthermore, it is increasingly the case that pharmaceutical companies have multiple ligands for a given target and these may bind in different ways to the same pocket. Conversely, a given ligand can sometimes bind to multiple targets, and this is clearly of great importance when considering drug side-effects. We recently introduced the notion of spherical harmonic-based "consensus shapes" to help deal with these questions. Here, we apply a consensus shape clustering approach to the 40 protein-ligand targets in the DUD data set using PARASURF/PARAFIT. Results from clustering show that in some cases the ligands for a given target are split into two subgroups which could suggest they bind to different subsites of the same target. In other cases, our clustering approach sometimes groups together ligands from different targets, and this suggests that those ligands could bind to the same targets. Hence spherical harmonic-based clustering can rapidly give cross-docking information while avoiding the expense of performing all-against-all docking calculations. We also report on the effect of the query conformation on the performance of shape-based screening of the DUD data set and the potential gain in screening performance by using consensus shapes calculated in different ways. We provide details of our analysis of shape-based screening using both PARASURF/PARAFIT and ROCS, and we compare the results obtained with shape-based and conventional docking approaches using MSSH/SHEF and GOLD. The utility of each type of query is analyzed using commonly reported statistics such as enrichment factors (EF) and receiver-operator-characteristic (ROC) plots as well as other early performance metrics. 相似文献
370.
Ritchie C Miller CE Boskovic C 《Dalton transactions (Cambridge, England : 2003)》2011,40(45):12037-12039
A new polyoxometalate-based 3D framework K(5)Na[K(2){Dy(H(2)O)(3)}(2){As(2)W(19)O(68)}{WO(2)(pic)}(2)] (1) (pic = 2-picolinate), composed of picolinate-functionalised dysprosium-containing tungstoarsenates and distorted potassium-picolinate cubane units, has been synthesised from the polyoxometalate precursor [As(2)W(19)O(67)(H(2)O)](14-). 相似文献