全文获取类型
收费全文 | 385篇 |
免费 | 16篇 |
国内免费 | 5篇 |
专业分类
化学 | 244篇 |
晶体学 | 1篇 |
力学 | 11篇 |
数学 | 90篇 |
物理学 | 60篇 |
出版年
2023年 | 2篇 |
2022年 | 4篇 |
2021年 | 8篇 |
2020年 | 2篇 |
2019年 | 8篇 |
2018年 | 5篇 |
2017年 | 8篇 |
2016年 | 11篇 |
2015年 | 5篇 |
2014年 | 15篇 |
2013年 | 15篇 |
2012年 | 29篇 |
2011年 | 26篇 |
2010年 | 18篇 |
2009年 | 13篇 |
2008年 | 25篇 |
2007年 | 21篇 |
2006年 | 24篇 |
2005年 | 22篇 |
2004年 | 18篇 |
2003年 | 25篇 |
2002年 | 10篇 |
2001年 | 9篇 |
2000年 | 11篇 |
1999年 | 4篇 |
1998年 | 2篇 |
1997年 | 1篇 |
1996年 | 4篇 |
1995年 | 1篇 |
1993年 | 3篇 |
1992年 | 2篇 |
1991年 | 3篇 |
1990年 | 3篇 |
1989年 | 3篇 |
1988年 | 2篇 |
1987年 | 4篇 |
1986年 | 1篇 |
1985年 | 10篇 |
1984年 | 3篇 |
1983年 | 6篇 |
1982年 | 3篇 |
1981年 | 1篇 |
1980年 | 5篇 |
1978年 | 4篇 |
1977年 | 1篇 |
1976年 | 1篇 |
1975年 | 1篇 |
1974年 | 2篇 |
1972年 | 1篇 |
1969年 | 1篇 |
排序方式: 共有406条查询结果,搜索用时 15 毫秒
101.
A DFT study of the mechanism and selectivities of the [3 + 2] cycloaddition reaction between 3‐(benzylideneamino)oxindole and trans‐β‐nitrostyrene 下载免费PDF全文
Chafia Sobhi Abdelmalek Khorief Nacereddine Abdelhafid Djerourou Mar Ríos‐ Gutiérrez Luis R. Domingo 《Journal of Physical Organic Chemistry》2017,30(6)
The mechanism and regioselectivities and stereoselectivities of the [3 + 2] cycloaddition (32CA) reaction of 3‐(benzylideneamino) oxindole (AY) and trans‐β‐nitrostyrene have been studied using both B3LYP and ωB97XD density functional theory methods together with the standard 6‐31G(d) basis set. Four reactive pathways associated with the ortho and meta regioselective channels and endo and exo stereoselective approaches modes have been explored and characterized. While the B3LYP functional fails to predict the experimental regioselectivity, the ωB97XD one succeeds to predict the experimentally observed meta regioselectivity favoring the formation of meta/endo cycloadduct as the major isomer. Inclusion of solvent effects increases the regioselectivity and decreases the experimentally observed stereoselectivity. Analysis of the density functional theory global reactivity indices and the Parr functions of the reagents in its ground state allows explaining the reactivity and the meta regioselectivity of this zwitterionic‐type 32CA reaction, which account for the high polar character of this reaction. Non‐covalent interaction analysis of the most favorable meta/endo transition state structure reveals that the formation of a hydrogen‐bond between 1 nitro oxygen and the AY N–H hydrogen is responsible for the selectivity experimentally found in this polar zwitterionic‐type 32CA reaction. 相似文献
102.
103.
María D. Acosta Julio Becerra Guerrero Domingo García Sun Kwang Kim Manuel Maestre 《Journal of Mathematical Analysis and Applications》2014
We characterize the Banach spaces Y for which certain subspaces of operators from L1(μ) into Y have the Bishop–Phelps–Bollobás property in terms of a geometric property of Y, namely AHSP. This characterization applies to the spaces of compact and weakly compact operators. New examples of Banach spaces Y with AHSP are provided. We also obtain that certain ideals of Asplund operators satisfy the Bishop–Phelps–Bollobás property. 相似文献
104.
Prediction of near field overpressure from quarry blasting 总被引:1,自引:0,他引:1
This paper investigates the propagation of airblast or pressure waves in air produced by bench blasting (i.e. detonation of the explosive in a row of blastholes, breaking the burden of rock towards the free vertical face of the block). Peak overpressure is calculated as a function of blasting parameters (explosive mass per delay and velocity at which the detonation sequence proceeds along the bench) and the polar coordinates of the position of interest (distance to the source and azimuth with respect to the free face). The model has been fitted to empirical data using linear least squares. The data set is composed of 122 airblast records monitored at distances less than 400 m in 41 production blasts carried out in two quarries. The model is statistically significant and has a determination coefficient of 0.87. The formula is validated from 12 airblast measurements gathered in five additional blasts. 相似文献
105.
106.
107.
Domingo Alberto Tarzia 《Numerical Methods for Partial Differential Equations》1999,15(3):355-369
We consider a material that occupies a convex polygonal bounded domain Ω ⊂ ℝn, with regular boundary Γ = Γ1 ∪ Γ2 (with Γ ∩ Γ = ∅︁) with meas (Γ1) = |Γ1| > 0 and |Γ2| > 0. We assume, without loss of generality, that the melting temperature is 0°C. We consider the following steady‐state heat conduction problem in Ω: with α, q, B = Const > 0, and q and α represent the heat flux on Γ2 and the heat transfer coefficient on Γ1, respectively. In a previous article (Tabacman‐ Tarzia, J Diff Eq 77 (1989), 16– 37) sufficient and/or necessary conditions on data α, q, B, Ω, Γ1, Γ2 to obtain a temperature u of nonconstant sign in Ω (that is, a multidimensional steady‐state, two‐phase, Stefan problem) were studied. In this article, we consider a regular triangulation by finite element method of the domain Ω with Lagrange triangles of the type 1, with h > 0 the parameter of the discretization. We study sufficient (and/or necessary) conditions on data α, q, B, Ω, Γ1, and Γ2 to obtain a change of phase (steady‐state, two‐phase, discretized Stefan problem) in corresponding discretized domain, that is, a discrete temperature of nonconstant sign in Ω. Moreover, error bounds as a function of the parameter h, are also obtained. © 1999 John Wiley & Sons, Inc. Numer Methods Partial Differential Eq. 15: 355–369, 1999 相似文献
108.
An experimental study has been carried out in an inhabited single-family house. Radon concentration in the different rooms of the house and in its garden soil has been measured with Nuclear Track Detectors. No high differences of radon concentration have been observed between the different rooms of the house, so that the proximity of the room level to the soil seems not to affect the radon concentration. The annual radon concentration obtained indoors and in the soil has been respectively 35 Bq m−3 and 24 kBq m−3. Since radon generation in the source, entry into indoor air and accumulation indoors depend on several parameters, the effect of a specific parameter on indoor radon concentration is difficult to explain from the radon measurements only. The RAGENA (RAdon Generation, ENtry and Accumulation indoors) model has been adapted to the room in the basement of the house. The mean radon concentration values obtained with the model are compared to experimental results derived from measurements using Nuclear Track Detectors. The use of the model, together with the experimental study, has allowed characterising radon sources, levels and entry mechanisms in the house. The concrete walls have been found to be the most relevant radon source, while the contribution of the soil is negligible in this case. The indoor radon level is given by the balance of the permanent exhalation from concrete and the removal due to ventilation. The indoor radon levels are close to the average value for the Barcelona area which, in turn, is close to the world averaged value. 相似文献
109.
David Duarte-Correa Alberto Pastrana-Palma Carlos A. Olvera-Olvera Sergio R. Ramírez-Rodríguez Daniel Alaniz-Lumbreras Domingo Gómez-Meléndez Ismael de la Rosa Salvador Noriega Vianey Torres Victor M. Castaño 《Optik》2013
The computational efficiency of 14 optical detectors over six types of transformations, namely: blur, illumination, rotation, viewpoint, zoom, and zoom-rotation changes, was analyzed. Images with the same resolution (750 × 500 pixels) were studied, in terms of correspondences, repeatability and computing time, and the correspondence was measured by using homographies i.e. projective transformations, to obtain the best efficiency for imaging applications. Results show that the multi-scale Harris Hessian detector is the most efficient for blur, illumination, and zoom-rotation changes. Meanwhile, multi-scale Hessian and Hessian Laplace are the best methods for rotation, viewpoint, and zoom changes. 相似文献
110.
Richard Aron Antonia Cardwell Domingo Garcí a Ignacio Zalduendo 《Proceedings of the American Mathematical Society》2007,135(8):2549-2554
We prove a multilinear version of Phelps' Lemma: if the zero sets of multilinear forms of norm one are `close', then so are the multilinear forms.