全文获取类型
收费全文 | 963篇 |
免费 | 29篇 |
国内免费 | 4篇 |
专业分类
化学 | 641篇 |
力学 | 30篇 |
数学 | 205篇 |
物理学 | 120篇 |
出版年
2023年 | 4篇 |
2022年 | 13篇 |
2021年 | 20篇 |
2020年 | 21篇 |
2019年 | 20篇 |
2018年 | 13篇 |
2017年 | 12篇 |
2016年 | 38篇 |
2015年 | 32篇 |
2014年 | 31篇 |
2013年 | 56篇 |
2012年 | 54篇 |
2011年 | 56篇 |
2010年 | 50篇 |
2009年 | 38篇 |
2008年 | 56篇 |
2007年 | 54篇 |
2006年 | 37篇 |
2005年 | 37篇 |
2004年 | 28篇 |
2003年 | 35篇 |
2002年 | 38篇 |
2001年 | 14篇 |
2000年 | 18篇 |
1999年 | 19篇 |
1998年 | 14篇 |
1997年 | 13篇 |
1996年 | 12篇 |
1995年 | 7篇 |
1994年 | 10篇 |
1993年 | 10篇 |
1992年 | 11篇 |
1991年 | 6篇 |
1990年 | 4篇 |
1989年 | 4篇 |
1988年 | 7篇 |
1987年 | 9篇 |
1986年 | 4篇 |
1985年 | 6篇 |
1984年 | 9篇 |
1983年 | 5篇 |
1982年 | 6篇 |
1981年 | 5篇 |
1980年 | 8篇 |
1979年 | 4篇 |
1978年 | 5篇 |
1977年 | 9篇 |
1975年 | 5篇 |
1974年 | 4篇 |
1970年 | 3篇 |
排序方式: 共有996条查询结果,搜索用时 15 毫秒
81.
Solvent polarity plays an important role in electrospray ionization-mass spectrometry (ESI-MS), one of the most widely used
analytical methods for biochemistry. To have a comprehensive understanding of how solvent polarity affects ESI-MS measurements,
we systematically investigated the polarity change in the ESI plume formed from an ethanol solution using laser-induced fluorescence
(LIF) spectroscopy. Two solvatochromic dyes (i.e., dyes whose fluorescence emission is sensitive to solvent polarity), Nile
red and DCM (4-dicyanomethylene-2-methyl-6-p-dimethylaminostyryl-4H-pyran), were used as probes. The peak emission wavelengths
of these two dyes exhibited significant red shifts (8–12 nm) when the measuring spot was moved away from the spray tip and
in radial direction in the plume, indicating a dramatic polarity change during shrinking of the droplets. The emission intensities
were also measured with a polarity-insensitive dye as a reference. The results are consistent with the peak wavelength measurements.
Two key mechanisms responsible for the change of solvent polarity in the plume were considered, water entrainment from the
surrounding air and solvent evaporation. Furthermore, quantitative analysis of the solvent polarity change was performed by
using the Lippert-Mataga polarity parameter Δf. The value of Δf reached 0.305–0.307 at the periphery of the ESI plume, which means that the solvent polarity in the smaller droplet is close
to that of a mixture of 30% water and 70% ethanol (Δf = 0.307), even though the bulk solvent was ethanol containing less than 1% water as an impurity. 相似文献
82.
San Martin A Rovirosa J Carrasco A Orejarena S Soto-Delgado J Contreras R Chamy MC 《Natural product communications》2010,5(12):1859-1864
The sesquiterpene pacifenol is one of the main constituents of the red alga Laurencia claviformis. Earlier work on the semisynthetic derivatives of pacifenol afforded a series of halogenated sesquiterpenes. The aim of the present work was to obtain new hydroxylated derivatives of halogenated sesquiterpenes by means of microbial transformation using Aspergillus niger, Gibberella fujikuroi and Mucor plumbeus. The best results were obtained with M. plumbeus. The microbiological transformation by M. plumbeus of pacifenol, and two semisynthetic derivatives, is described. The structures of the new compounds obtained were determined by spectroscopic means. 相似文献
83.
84.
The radiative neutron capture on lithium-7 is calculated model independently using a low-energy halo effective field theory. The cross section is expressed in terms of scattering parameters directly related to the S-matrix elements. It depends on the poorly known p-wave effective range parameter r(1). This constitutes the largest uncertainty in traditional model calculations. It is explicitly demonstrated by comparing with potential model calculations. A single parameter fit describes the low-energy data extremely well and yields r(1)≈-1.47 fm(-1). 相似文献
85.
Renato Assunção Peter Guttorp 《Annals of the Institute of Statistical Mathematics》1999,51(4):657-678
We consider robustness for estimation of parametric inhomogeneous Poisson point processes. We propose an influence functional to measure the effect of contamination on estimates. We also propose an M-estimator as an alternative to maximum likelihood estimator, show its consistency and asymptotic normality. 相似文献
86.
Renato M. Fonseca Jorge C. Rom?o Ana M. Teixeira 《The European Physical Journal C - Particles and Fields》2012,72(11):1-16
We present a generator for single top-quark production via flavour-changing neutral currents. The MEtop event generator allows for Next-to-Leading-Order direct top production pp??t and Leading-Order production of several other single top processes. A?few packages with definite sets of dimension six operators are available. We discuss how to improve the bounds on the effective operators and how well new physics can be probed with each set of independent dimension six operators. 相似文献
87.
Alexander V. Avdeev Eldar V. Goriounov Mikhail M. Lavrentiev Jr. Renato Spigler 《Applied Mathematical Modelling》2009
A behavior-oriented diffusion model, governing the time evolution of the cross-shore position of coastal profiles, is studied. Here, two time-independent, space-varying coefficients, which embody the relevant physical properties, are identified simultaneously. Two sets of real data, the first measured over 10 years at Duck, in NC (USA), the second obtained over 39 years measurements at Delfland (Holland), have been processed numerically by a suitable “inversion algorithm”, earlier developed by the authors. This is based on the minimization of a certain cost functional in order to identify both coefficients. The numerical results, obtained by solving the diffusion equation with the so-determined coefficients, favorably agree with the real data, which fact validates and calibrates somehow the diffusion model under investigation. A short-term prediction is finally obtained for coastal profiles, using such a model. 相似文献
88.
89.
Probabilistically induced domain decomposition methods for elliptic boundary-value problems 总被引:1,自引:0,他引:1
Juan A. Acebrn Maria Pia Busico Piero Lanucara Renato Spigler 《Journal of computational physics》2005,210(2):421-438
Monte Carlo as well as quasi-Monte Carlo methods are used to generate only few interfacial values in two-dimensional domains where boundary-value elliptic problems are formulated. This allows for a domain decomposition of the domain. A continuous approximation of the solution is obtained interpolating on such interfaces, and then used as boundary data to split the original problem into fully decoupled subproblems. The numerical treatment can then be continued, implementing any deterministic algorithm on each subdomain. Both, Monte Carlo (or quasi-Monte Carlo) simulations and the domain decomposition strategy allow for exploiting parallel architectures. Scalability and natural fault tolerance are peculiarities of the present algorithm. Examples concern Helmholtz and Poisson equations, whose probabilistic treatment presents additional complications with respect to the case of homogeneous elliptic problems without any potential term and source. 相似文献
90.
Trust region affine scaling algorithms for linearly constrained convex and concave programs 总被引:4,自引:0,他引:4
We study a trust region affine scaling algorithm for solving the linearly constrained convex or concave programming problem. Under primal nondegeneracy assumption, we prove that every accumulation point of the sequence generated by the algorithm satisfies the first order necessary condition for optimality of the problem. For a special class of convex or concave functions satisfying a certain invariance condition on their Hessians, it is shown that the sequences of iterates and objective function values generated by the algorithm convergeR-linearly andQ-linearly, respectively. Moreover, under primal nondegeneracy and for this class of objective functions, it is shown that the limit point of the sequence of iterates satisfies the first and second order necessary conditions for optimality of the problem. © 1998 The Mathematical Programming Society, Inc. Published by Elsevier Science B.V.The work of these authors was based on research supported by the National Science Foundation under grant INT-9600343 and the Office of Naval Research under grants N00014-93-1-0234 and N00014-94-1-0340. 相似文献