全文获取类型
收费全文 | 165篇 |
免费 | 0篇 |
国内免费 | 1篇 |
专业分类
化学 | 68篇 |
力学 | 5篇 |
数学 | 18篇 |
物理学 | 75篇 |
出版年
2021年 | 3篇 |
2019年 | 1篇 |
2017年 | 1篇 |
2016年 | 3篇 |
2014年 | 2篇 |
2013年 | 6篇 |
2012年 | 5篇 |
2011年 | 4篇 |
2010年 | 3篇 |
2009年 | 1篇 |
2008年 | 6篇 |
2007年 | 5篇 |
2006年 | 7篇 |
2005年 | 3篇 |
2004年 | 4篇 |
2003年 | 4篇 |
2002年 | 3篇 |
2001年 | 1篇 |
2000年 | 2篇 |
1999年 | 3篇 |
1998年 | 2篇 |
1997年 | 1篇 |
1996年 | 4篇 |
1995年 | 2篇 |
1994年 | 7篇 |
1993年 | 8篇 |
1992年 | 13篇 |
1991年 | 2篇 |
1990年 | 2篇 |
1989年 | 2篇 |
1988年 | 1篇 |
1987年 | 2篇 |
1986年 | 2篇 |
1985年 | 5篇 |
1984年 | 4篇 |
1983年 | 6篇 |
1982年 | 2篇 |
1981年 | 5篇 |
1980年 | 2篇 |
1979年 | 3篇 |
1978年 | 4篇 |
1977年 | 6篇 |
1976年 | 3篇 |
1974年 | 4篇 |
1973年 | 2篇 |
1971年 | 3篇 |
1933年 | 1篇 |
1912年 | 1篇 |
排序方式: 共有166条查询结果,搜索用时 31 毫秒
141.
Pfeifer CS Shelton ZR Braga RR Windmoller D Machado JC Stansbury JW 《European Polymer Journal》2011,47(2):162-170
The resin phase of dental composites is mainly composed of combinations of dimethacrylate comonomers, with final polymeric network structure defined by monomer type/reactivity and degree of conversion. This fundamental study evaluates how increasing concentrations of the flexible triethylene glycol dimethacrylate (TEGDMA) influences void formation in bisphenol A diglycidyl dimethacrylate (BisGMA) co-polymerizations and correlates this aspect of network structure with reaction kinetic parameters and macroscopic volumetric shrinkage. Photopolymerization kinetics was followed in real-time by a near-infrared (NIR) spectroscopic technique, viscosity was assessed with a viscometer, volumetric shrinkage was followed with a linometer, free volume formation was determined by positron annihilation lifetime spectroscopy (PALS) and the sol–gel composition was determined by extraction with dichloromethane followed by 1H NMR analysis. Results show that, as expected, volumetric shrinkage increases with TEGDMA concentration and monomer conversion. Extraction/1H NMR studies show increasing participation of the more flexible TEGDMA towards the limiting stages of conversion/crosslinking development. As the conversion progresses, either based on longer irradiation times or greater TEGDMA concentrations, the network becomes more dense, which is evidenced by the decrease in free volume and weight loss after extraction in these situations. For the same composition (BisGMA/TEGDMA 60–40 mol%) light-cured for increasing periods of time (from 10 to 600 s), free volume decreased and volumetric shrinkage increased, in a linear relationship with conversion. However, the correlation between free volume and macroscopic volumetric shrinkage was shown to be rather complex for variable compositions exposed for the same time (600 s). The addition of TEGDMA decreases free-volume up to 40 mol% (due to increased conversion), but above that concentration, in spite of the increase in conversion/crosslinking, free volume pore size increases due to the high concentration of the more flexible monomer. In those cases, the increase in volumetric shrinkage was due to higher functional group concentration, in spite of the greater free volume. Therefore, through the application of the PALS model, this study elucidates the network formation in dimethacrylates commonly used in dental materials. 相似文献
142.
Pan D Caruthers SD Senpan A Yalaz C Stacy AJ Hu G Marsh JN Gaffney PJ Wickline SA Lanza GM 《Journal of the American Chemical Society》2011,133(24):9168-9171
A new site-targeted molecular imaging contrast agent based on a nanocolloidal suspension of lipid-encapsulated, organically soluble divalent copper has been developed. Concentrating a high payload of divalent copper ions per nanoparticle, this agent provides a high per-particle r1 relaxivity, allowing sensitive detection in T1-weighted magnetic resonance imaging when targeted to fibrin clots in vitro. The particle also exhibits a defined clearance and safety profile in vivo. 相似文献
143.
Shelton AH Sazanovich IV Weinstein JA Ward MD 《Chemical communications (Cambridge, England)》2012,48(22):2749-2751
A macrocycle-appended naphthalimide derivative and its Eu(III) complex show triple luminescence from isolated naphthalimide (blue), aggregated naphthalimide excimers (green) and Eu centres (red) with the balance being sensitive to the degree of aggregation, allowing white light emission to be obtained from a single molecule. 相似文献
144.
De-Hao Tsai Melanie P. Shelton Frank W. DelRio Sherrie Elzey Suvajyoti Guha Michael R. Zachariah Vincent A. Hackley 《Analytical and bioanalytical chemistry》2012,404(10):3015-3023
Dithiothreitol (DTT)-based displacement is widely utilized for separating ligands from their gold nanoparticle (AuNP) conjugates, a critical step for differentiating and quantifying surface-bound functional ligands and therefore the effective surface density of these species on nanoparticle-based therapeutics and other functional constructs. The underlying assumption is that DTT is smaller and much more reactive toward gold compared with most ligands of interest, and as a result will reactively displace the ligands from surface sites thereby enabling their quantification. In this study, we use complementary dimensional and spectroscopic methods to characterize the efficiency of DTT displacement. Thiolated methoxypolyethylene glycol (SH-PEG) and bovine serum albumin (BSA) were chosen as representative ligands. Results clearly show that (1) DTT does not completely displace bound SH-PEG or BSA from AuNPs, and (2) the displacement efficiency is dependent on the binding affinity between the ligands and the AuNP surface. Additionally, the displacement efficiency for conjugated SH-PEG is moderately dependent on the molecular mass (yielding efficiencies ranging from 60 to 80?% measured by ATR-FTIR and ≈90?% by ES-DMA), indicating that the displacement efficiency for SH-PEG is predominantly determined by the S–Au bond. BSA is particularly difficult to displace with DTT (i.e., the displacement efficiency is nearly zero) when it is in the so-called normal form. The displacement efficiency for BSA improves to 80?% when it undergoes a conformational change to the expanded form through a process of pH change or treatment with a surfactant. An analysis of the three-component system (SH-PEG?+?BSA?+?AuNP) indicates that the presence of SH-PEG decreases the displacement efficiency for BSA, whereas the displacement efficiency for SH-PEG is less impacted by the presence of BSA. Figure
Schematic displacement of ligands from a AuNP by DTT 相似文献
145.
Shelton DP 《The Journal of chemical physics》2010,133(23):234507
Hyper-Rayleigh scattering (HRS) from liquid nitrobenzene-benzene solutions with nitrobenzene mole fraction in the range 0.001 < x(NB) < 1 was measured for several combinations of linear polarized incident and scattered light, for scattering angles near 90°. Polar collective modes are identified by their distinctive HRS polarization dependence. At all concentrations the nitrobenzene HRS intensity is dominated by the transverse polar collective mode contribution and the longitudinal collective mode contribution is near zero. The transverse polar mode HRS is due to long range dipole-dipole orientation correlations between the nitrobenzene molecules, such that the molecular dipoles are oriented transverse to the wave vector for each spatial Fourier component of the orientation distribution. 相似文献
146.
Upper critical fields, Hc2(T), for superconducting LaMo6Se8, La0.8Eu0.2Mo6Se8, La0.8Ce0.2Mo6Se8 and PrMo6Se8 were measured. For the best material, LaMo6Se8, Tc = 11.3 K, (dHc2/dT)T=Tc=70 kG/K and and Hc2 (4.2 K) = 370 kG. These selenide compounds show promise as very high field superconductors. 相似文献
147.
K.S. Athreya L.S. Hausermann-Berg R.N. Shelton S.K. Malik A.M. Umarji G.K. Shenoy 《Physics letters. A》1985,113(6):330-334
The compounds CeOs3B2 and CeRu3B2 show superconductivity with Tc's of 3.5 and 1.1 K respectively. The magnetic susceptibility of both these compounds may be described as the sum of a Curie-Weiss term dominating at low temperature and a large temperature independent term. The heat capacity measurements yield the value of electronic specific heat coefficient γ of 40.1 and 15.6 mJ/mol K2 for Os and Ru compounds, respectively. These compounds appear to be conventional bulk superconductors in which Ce is in a strongly mixed valent state. 相似文献
148.
The superconducting transition temperature and its dependence on hydrostatic pressure to 22 kbar have been determined for a series of (La, Ce)Ru2 alloys. The variations of these quantities with composition are found to be generally related; however, specific irregularities in the curve of dTc/dp versus composition are not reflected in the smooth variation of the transition temperature Tc. Some features of dTc/dp may be correlated with the occurrence of a cubic-tetragonal transformation at low temperatures. 相似文献
149.
The pseudoternary orthorhombic system TbxLu1?xRuB2) (0 ? x ? 0.1 andx = 1.0) has been investigated by static magnetization, ac susceptibility and resistivity measurements down to 1.5 K. Superconductivity occurs for 0 ? x ? 0.1, while ferromagnetic order occurs for x = 1.0. For each sample studied, the Tb ion maintains a configurationally stable trivalent state. The initial linear depression of the superconducting transition temperature yields a coupling constant value N(0)Γ2 between conduction electrons and magnetic Tb3+ moments of 3.5 x 10-4 ev-atom-states/spin-direction. 相似文献
150.
The electrical resistivity of LaAg has been measured from 1–300 K at hydrostatic pressures to 12.4 kbar and the superconducting transition temperature Tc determined inductively to 23 kbar. For P ? 6.2 kbar a lattice transformation is observed at a temperature TM which increases rapidly with pressure. Tc shows an oscillatory pressure dependence, increasing initially from Tc (0) = 1.062 K. There is no obvious correlation between the pressure dependence of TM and Tc. 相似文献