全文获取类型
收费全文 | 229篇 |
免费 | 3篇 |
专业分类
化学 | 149篇 |
力学 | 5篇 |
数学 | 23篇 |
物理学 | 55篇 |
出版年
2016年 | 2篇 |
2015年 | 3篇 |
2014年 | 4篇 |
2013年 | 6篇 |
2012年 | 3篇 |
2011年 | 7篇 |
2010年 | 8篇 |
2009年 | 7篇 |
2008年 | 7篇 |
2007年 | 4篇 |
2006年 | 10篇 |
2005年 | 11篇 |
2004年 | 6篇 |
2003年 | 9篇 |
2002年 | 6篇 |
2001年 | 6篇 |
2000年 | 14篇 |
1999年 | 2篇 |
1998年 | 3篇 |
1995年 | 5篇 |
1993年 | 8篇 |
1992年 | 5篇 |
1990年 | 3篇 |
1989年 | 4篇 |
1988年 | 5篇 |
1987年 | 3篇 |
1986年 | 2篇 |
1985年 | 6篇 |
1984年 | 4篇 |
1983年 | 5篇 |
1982年 | 3篇 |
1981年 | 4篇 |
1980年 | 3篇 |
1979年 | 6篇 |
1978年 | 3篇 |
1976年 | 4篇 |
1975年 | 4篇 |
1973年 | 2篇 |
1972年 | 4篇 |
1969年 | 2篇 |
1967年 | 1篇 |
1966年 | 2篇 |
1962年 | 3篇 |
1942年 | 2篇 |
1941年 | 1篇 |
1938年 | 1篇 |
1937年 | 3篇 |
1935年 | 2篇 |
1920年 | 2篇 |
1912年 | 1篇 |
排序方式: 共有232条查询结果,搜索用时 15 毫秒
61.
Hubbard R.F. Sprangle P. Hafizi B. 《IEEE transactions on plasma science. IEEE Nuclear and Plasma Sciences Society》2000,28(4):1159-1169
Future wakefield accelerator (LWFA) experiments are expected to operate in the short pulse resonant regime and employ some form of laser guiding, such as a preformed plasma channel. Performance of an LWFA may be characterized by the maximum axial electric field Em, the dephasing length Ld, and the corresponding dephasing limited energy gain Wd. Dephasing is characterized by the normalized phase slippage rate Δβp, of the wakefield relative to a particle moving at the velocity of light. This paper presents analytical models for all of these quantities and compares them with results from simulations of channel-guided LWFAs. The simulations generally confirm the scaling predicted by the analytical models, agreeing within a few percent in most cases. The results show that with the proper choice of laser and channel parameters, the pulse will propagate at a nearly constant spot size rM over many Rayleigh lengths and generate large accelerating electric fields. The spot size correction to the slippage rate is shown to be important in the LWFA regime, whereas Δβp, is essentially independent of laser intensity. An example is presented of a 25-TW, 100-fs laser pulse that produces a dephasing limited energy gain in excess of 1 GeV 相似文献
62.
Abhijit Pramanick Anderson D. Prewitt Michelle A. Cottrell Wayne Lee Andrew J. Studer Ke An Camden R. Hubbard Jacob L. Jones 《Applied Physics A: Materials Science & Processing》2010,99(3):557-564
Structural changes in commercial lead zirconate titanate (PZT) ceramics (EC-65) under the application of electric fields and
mechanical stress were measured using neutron diffraction instruments at the Australian Nuclear Science and Technology Organisation
(ANSTO) and the Oak Ridge National Laboratory (ORNL). The structural changes during electric-field application were measured
on the WOMBAT beamline at ANSTO and include non-180° domain switching, lattice strains and field-induced phase transformations.
Using time-resolved data acquisition capabilities, lattice strains were measured under cyclic electric fields at times as
short as 30 μs. Structural changes including the (002) and (200) lattice strains and non-180° domain switching were measured
during uniaxial mechanical compression on the NRSF2 instrument at ORNL. Contraction of the crystallographic polarization axis,
(002), and reorientation of non-180° domains occur at lowest stresses, followed by (200) elastic strains at higher stresses. 相似文献
63.
Hart SR Lau KW Hao Z Broadhead R Portman N Hühmer A Gull K McKean PG Hubbard SJ Gaskell SJ 《Journal of the American Society for Mass Spectrometry》2009,20(2):167-175
The use of electron-transfer dissociation as an alternative peptide ion activation method for generation of protein sequence
information is examined here in comparison with the conventional method of choice, collisionally activated dissociation, using
a linear ion trapping instrument. Direct comparability between collisionally and electron-transfer-activated product ion data
were ensured by employing an activation-switching method during acquisition, sequentially activating precisely the same precursor
ion species with each fragmentation method in turn. Sequest (Thermo Fisher Scientific, San Jose, CA) searching of product
ion data generated an overlapping yet distinct pool of polypeptide identifications from the products of collisional and electron-transfer-mediated
activation products. To provide a highly confident set of protein recognitions, identification data were filtered using parameters
that achieved a peptide false discovery rate of 1%, with two or more independent peptide assignments required for each protein.
The use of electron transfer dissociation (ETD) has allowed us to identify additional peptides where the quality of product
ion data generated by collisionally activated dissociation (CAD) was insufficient to infer peptide sequence. Thus, a combined
ETD/CAD approach leads to the recognition of more peptides and proteins than are achieved using peptide analysis by CAD- or
ETD-based tandem mass spectrometry alone. 相似文献
64.
In this paper Protein A mimetic and hydrophobic charge induction chromatographic (HCIC) stationary phases are characterized in terms of their protein adsorption characteristics and their selectivity is compared with Protein A chromatography using a set of Chinese hamster ovary-derived monoclonal antibodies and Fc-fusion proteins. Linear retention experiments were employed to compare the selectivities of these resins for both non-IgG model proteins as well as antibodies and the fusion proteins. While none of the non-IgG model proteins were observed to bind to the Protein A resin, most of them did in fact bind to the alternative resins. In addition, while the elution pH was similar for the model proteins and antibodies on the HCIC resin, the mimetic resins did exhibit higher binding for the antibodies under these linear pH gradient conditions. A mixed mode preparative isotherm model previously developed for HCIC was shown to accurately describe the adsorption behavior of the mimetic materials as well. Host cell protein clearance profiles were also investigated under preparative conditions using complex biological feeds and the results indicated that while some selectivity was observed for both the HCIC and the mimetic materials, the purification factors were in general significantly less than those obtained with Protein A. It is important to note, however, that the selectivity of the mimetic and HCIC materials was also observed to be antibody specific indicating that further optimization may well result in increased selectivities for these materials. 相似文献
65.
[reaction: see text] The syntheses of five laulimalide analogues are described, incorporating modifications at the C(16)-C(17)-epoxide, the C(20)-alcohol, as well as the C(1)-C(3)-enoate of the parent natural product. The resultant analogues are active in drug-sensitive HeLa and MDA-MB-435 cell lines. Significantly, like laulimalide, these analogues are poor substrates for the drug transport protein P-glycoprotein (Pgp) and are thus effective against Taxol-resistant cell lines. 相似文献
66.
Three-component cycloadditions: the first transition metal-catalyzed [5+2+1] cycloaddition reactions
Wender PA Gamber GG Hubbard RD Zhang L 《Journal of the American Chemical Society》2002,124(12):2876-2877
Prompted by our studies of transition metal-catalyzed [4+4], [4+2], [5+2], and [6+2] cycloadditions and by the view that these two-component reactions could be intercepted by a third component of one or more atoms, a new three-component transition metal-catalyzed cycloaddition is described. This new [5+2+1] cycloaddition proceeds in good to excellent yield and with high or complete regioselectivity with a variety of carbonyl-substituted alkynes to give bicyclo[3.3.0]octenone adducts, resulting from transannular closure of the intermediate eight-membered-ring cycloadduct. Effects of concentration, temperature, pressure, and catalyst loading on the efficiency of the reaction are discussed. This process provides access to complex building blocks for synthesis based on simple, readily available components. 相似文献
67.
Grotjahn DB Lo HC Dinoso J Adkins CD Li C Nolan SP Hubbard JL 《Inorganic chemistry》2000,39(12):2493-2499
A comparative synthetic, structural, and thermochemical study on a series of chelate complexes containing the fragment (eta 5-C5Me5)Ir [(eta 5-C5Me5)Ir(TsNCH2CH2NTs) (1), (eta 5-C5Me5)Ir(TsNCH2CO2) (2), (eta 5-C5Me5)Ir(CO2CO2) (3)] was performed to clarify the roles of carboxylato and sulfonamido ligands. Whereas 1 and 2 are monomeric in solution and in the solid state, 3 appears to exist as an oligomer or polymer, (3)n, which can be broken up by addition of a ligand L such as a phosphine, CO, or 2-methoxypyridine to form (eta 5-C5Me5)Ir(L)(CO2CO2) (6). The synthesis of (3)n from [(eta 5-C5Me5)IrCl(mu-Cl)]2 required the use of silver oxalate in CH3CN, but if other solvents were used, the bridging oxalato complex (eta 5-C5Me5)IrCl(mu-eta 2-eta 2-C2O4)ClIr(eta 5-C5Me5) (7) was obtained and identified by X-ray diffraction. Enthalpies for reaction of THF-soluble monomers 1 and 2 with PMe3 were determined to be -28.7(0.5) and -28.5(0.4) kcal mol-1, respectively. The oligomerization behavior of 3 may be a result of reduced sigma- or pi-donation of carboxylato ligands compared to N-tosylamido ligands, because the values for nu CO in oxalato and bissulfonamido complexes 6-CO and (eta 5-C5Me5)Ir(CO)(TsNCH2CH2NTs) (4-CO) were 2064 and 2042 cm-1, respectively. 相似文献
68.
Burgess John Hubbard Colin D. Patel Marttand S. Radulović Stojan Thuresson Kristina> Parsons Simon A. Guardado Pilar 《Transition Metal Chemistry》2002,27(2):134-144
Solubilities are reported for the perchlorates of five iron(II)-diimine complexes in t-BuOH–H2O and one in MeOH–H2O mixtures, for three iron(III)-3-hydroxy-4-pyranonate and three iron(III)-3-hydroxy-4-pyridinonate complexes in MeOH–H2O and t-BuOH–H2O, and for two chromium(III)-3-hydroxy-4-pyranonate complexes in MeOH–H2O. Transfer chemical potentials are thence derived for the various iron(II), iron(III) and chromium(III) complexes, for transfer from H2O into the respective mixed solvents (at 298.2 K). These results are combined with values reported earlier for related complexes, and for other alcohol–H2O mixtures, to give an overall picture of solvation, expressed in the thermodynamic format of transfer chemical potentials, for iron(II)-diimine, iron(III)-3-hydroxy-4-pyridinonate and chromium(III)-3-hydroxy-4-pyranonate complexes in H2O-rich aqueous-alcohol mixtures. Some spectroscopic (1H-n.m.r.; i.r.) and kinetic (aquation rate constants at 298.2 K) data are reported for the chromium(III) complexes. 相似文献
69.
70.
W. K. Warburton D. A. Darknell B. Hubbard 《Journal of Radioanalytical and Nuclear Chemistry》1998,233(1-2):233-239
The XIA DXP-4C, a 4 channel, CAMAC based X-ray spectrometer, is based on digitally processing directly digitized preamplifier
signals. Designed for instrumenting multi-detector arrays for synchrotron radiation applications, the DXP-4C was optimized
for very high count rates at a low cost per detector channel. These design constraints coincidentally lead to an instrument
which is very compact and relatively low power (3.4 W/channel), considering its count rate and MCA capabilities, and which
therefore offers interesting possibilities for effective extension to portable applications. Further, because all functions
(gain, filter parameters, pileup inspection criteria and internal calibrations) are digitally controlled, the design can be
readily adapted to a large variety of user interfaces, including remote access interfaces. Here we present the basics of the
design and examine approaches to lowering the power to less than 300 mW/channel while retaining count rate capabilities in
excess of 50,000 cps. We then consider the engineering issues associated with portable and remote spectrometry applications,
examining in detail the three cases of a lead paint detector, a remote contamination monitor, and a space mission spectrometer. 相似文献