全文获取类型
收费全文 | 149篇 |
免费 | 1篇 |
国内免费 | 11篇 |
专业分类
化学 | 64篇 |
力学 | 2篇 |
数学 | 68篇 |
物理学 | 27篇 |
出版年
2022年 | 1篇 |
2021年 | 5篇 |
2020年 | 5篇 |
2019年 | 2篇 |
2018年 | 4篇 |
2017年 | 3篇 |
2016年 | 3篇 |
2015年 | 4篇 |
2014年 | 4篇 |
2013年 | 11篇 |
2012年 | 6篇 |
2011年 | 4篇 |
2010年 | 6篇 |
2009年 | 9篇 |
2008年 | 10篇 |
2007年 | 7篇 |
2006年 | 3篇 |
2005年 | 9篇 |
2004年 | 6篇 |
2003年 | 9篇 |
2002年 | 5篇 |
2001年 | 3篇 |
2000年 | 3篇 |
1999年 | 1篇 |
1998年 | 4篇 |
1997年 | 2篇 |
1996年 | 2篇 |
1995年 | 1篇 |
1994年 | 1篇 |
1993年 | 2篇 |
1992年 | 4篇 |
1991年 | 1篇 |
1990年 | 1篇 |
1989年 | 1篇 |
1988年 | 1篇 |
1987年 | 3篇 |
1986年 | 1篇 |
1984年 | 1篇 |
1982年 | 1篇 |
1978年 | 2篇 |
1976年 | 1篇 |
1975年 | 1篇 |
1974年 | 1篇 |
1973年 | 3篇 |
1972年 | 2篇 |
1968年 | 2篇 |
排序方式: 共有161条查询结果,搜索用时 15 毫秒
61.
The proximal point mapping is the basis of many optimization techniques for convex functions. By means of variational analysis, the concept of proximal mapping was recently extended to nonconvex functions that are prox-regular and prox-bounded. In such a setting, the proximal point mapping is locally Lipschitz continuous and its set of fixed points coincide with the critical points of the original function. This suggests that the many uses of proximal points, and their corresponding proximal envelopes (Moreau envelopes), will have a natural extension from convex optimization to nonconvex optimization. For example, the inexact proximal point methods for convex optimization might be redesigned to work for nonconvex functions. In order to begin the practical implementation of proximal points in a nonconvex setting, a first crucial step would be to design efficient methods of approximating nonconvex proximal points. This would provide a solid foundation on which future design and analysis for nonconvex proximal point methods could flourish. In this paper we present a methodology based on the computation of proximal points of piecewise affine models of the nonconvex function. These models can be built with only the knowledge obtained from a black box providing, for each point, the function value and one subgradient. Convergence of the method is proved for the class of nonconvex functions that are prox-bounded and lower- ${\mathcal{C}}^2$ and encouraging preliminary numerical testing is reported. 相似文献
62.
Bernie OHare Alan J. Benesi Scott A. Showalter 《Journal of magnetic resonance (San Diego, Calif. : 1997)》2009,200(2):354-358
Exclusively heteronuclear 13C-detected NMR spectroscopy of proteins in solution has seen resurgence in the past several years. For disordered or unfolded proteins, which tend to have poor 1H-amide chemical shift dispersion, these experiments offer enhanced resolution and the possibility of complete heteronuclear resonance assignment at the cost of leaving the 1H resonances unassigned. Here we report two novel 13C-detected NMR experiments which incorporate a 1H chemical shift evolution period followed by 13C-TOCSY mixing for aliphatic 1H resonance assignment without reliance on 1H detection. 相似文献
63.
Bennett GW Bousquet B Brown HN Bunce G Carey RM Cushman P Danby GT Debevec PT Deile M Deng H Deninger W Dhawan SK Druzhinin VP Duong L Efstathiadis E Farley FJ Fedotovich GV Giron S Gray FE Grigoriev D Grosse-Perdekamp M Grossmann A Hare MF Hertzog DW Huang X Hughes VW Iwasaki M Jungmann K Kawall D Kawamura M Khazin BI Kindem J Krienen F Kronkvist I Lam A Larsen R Lee YY Logashenko I McNabb R Meng W Mi J Miller JP Mizumachi Y Morse WM Nikas D Onderwater CJ Orlov Y Ozben CS Paley JM Peng Q 《Physical review letters》2008,100(9):091602
The spin precession frequency of muons stored in the (g-2) storage ring has been analyzed for evidence of Lorentz and CPT violation. Two Lorentz and CPT violation signatures were searched for a nonzero delta omega a(=omega a mu+ - omega a mu-) and a sidereal variation of omega a mu+/-). No significant effect is found, and the following limits on the standard-model extension parameters are obtained: bZ = -(1.0+/-1.1) x 10(-23) GeV; (m mu dZ0 + HXY)=(1.8+/-6.0) x 10(-23) GeV; and the 95% confidence level limits b perpendicular mu+ <1.4 x 10(-24) GeV and b perpendicular mu- <2.6 x 10(-24) GeV. 相似文献
64.
Abstract. Exposure of dilute solutions of L-tryptophan in balanced salt mixtures to near-ultraviolet light (ca. 320–390nm) yield several photoproducts capable of inhibiting the growth of cultured mouse embryonic fibroblasts. Recent literature suggested a need to test the possibility that the major toxic photoproduct is hydrogen peroxide, and therefore several lines of experimentation were pursued. On the basis of chemical and morphological studies and an analysis of the uptake of 3H-thymidine by these cells and its incorporation into their DNA, it is concluded that sufficient hydrogen peroxide could not be generated without the addition of high concentrations of oxygen to influence the growth or DNA synthesis of mouse embryonic fibroblasts. 相似文献
65.
We show that the minimalk such that μκ ∈L
1(SU(n)) for all central, continuous measures μ on SU(n) isk=n. We do this by exhibiting an elementg∈SU(n) for which the (n−1)-fold product of its conjugacy class has zero Haar measure. This ensures that if μ
g
is the corresponding orbital measure supported on the conjugacy class, then μ
g
n-1
is singular toL
1.
This research is supported in part by NSERC. The hospitality of the University of Waterloo is gratefully acknowledged. 相似文献
66.
Prosser AJ Retter U Lunkenheimer K 《Langmuir : the ACS journal of surfaces and colloids》2004,20(7):2720-2725
The dynamic surface tension data for n-dodecanoic acid in 0.005 M hydrochloric acid, for as-received as well as for surface-chemically pure solutions, show the presence of a prolonged induction period, clearly indicating that the adsorption of this nonionic surfactant is not simply diffusion-controlled. A kinetic model for the reversible formation of monolayer islands, long known in the field of electrochemistry, is shown to also apply to the adsorption of n-dodecanoic acid at the air/water interface. The rate constant increases linearly with increasing bulk concentration, while the induction time decreases exponentially. The phenomenon of nucleation at the air/water interface is consistent with the direct experimental observation of the formation of solid-like patches as the interfacial region is drastically compressed. 相似文献
67.
Sian Genoud Michael W. M. Jones Benjamin Guy Trist Junjing Deng Si Chen Dominic James Hare Kay L. Double 《Chemical science》2020,11(33):8919
Examining chemical and structural characteristics of micro-features in complex tissue matrices is essential for understanding biological systems. Advances in multimodal chemical and structural imaging using synchrotron radiation have overcome many issues in correlative imaging, enabling the characterization of distinct microfeatures at nanoscale resolution in ex vivo tissues. We present a nanoscale imaging method that pairs X-ray ptychography and X-ray fluorescence microscopy (XFM) to simultaneously examine structural features and quantify elemental content of microfeatures in complex ex vivo tissues. We examined the neuropathological microfeatures Lewy bodies, aggregations of superoxide dismutase 1 (SOD1) and neuromelanin in human post-mortem Parkinson''s disease tissue. Although biometals play essential roles in normal neuronal biochemistry, their dyshomeostasis is implicated in Parkinson''s disease aetiology. Here we show that Lewy bodies and SOD1 aggregates have distinct elemental fingerprints yet are similar in structure, whilst neuromelanin exhibits different elemental composition and a distinct, disordered structure. The unique approach we describe is applicable to the structural and chemical characterization of a wide range of complex biological tissues at previously unprecedented levels of detail.Structural and chemical characterisation of microfeatures in unadulterated Parkinson''s disease brain tissue using synchrotron nanoscale XFM and ptychography. 相似文献
68.
69.
70.
Patrick M. Hare Chris T. Middleton Kristin I. Mertel John M. Herbert Bern Kohler 《Chemical physics》2008,347(1-3):383-392
Vibrational spectra of the lowest energy triplet states of thymine and its 2′-deoxyribonucleoside, thymidine, are reported for the first time. Time-resolved infrared (TRIR) difference spectra were recorded over seven decades of time from 300 fs to 3 μs using femtosecond and nanosecond pump-probe techniques. The carbonyl stretch bands in the triplet state are seen at 1603 and 1700 cm−1 in room-temperature acetonitrile-d3 solution. These bands and additional ones observed between 1300 and 1450 cm−1 are quenched by dissolved oxygen on a nanosecond time scale. Density-functional calculations accurately predict the difference spectrum between triplet and singlet IR absorption cross sections, confirming the peak assignments and elucidating the nature of the vibrational modes. In the triplet state, the C4O carbonyl exhibits substantial single-bond character, explaining the large (70 cm−1) red shift in this vibration, relative to the singlet ground state. Femtosecond TRIR measurements unambiguously demonstrate that the triplet state is fully formed within the first 10 ps after excitation, ruling out a relaxed 1nπ* state as the triplet precursor. 相似文献