全文获取类型
收费全文 | 132篇 |
免费 | 4篇 |
国内免费 | 1篇 |
专业分类
化学 | 48篇 |
力学 | 27篇 |
数学 | 22篇 |
物理学 | 40篇 |
出版年
2021年 | 2篇 |
2020年 | 2篇 |
2019年 | 1篇 |
2018年 | 2篇 |
2017年 | 1篇 |
2016年 | 7篇 |
2015年 | 2篇 |
2014年 | 2篇 |
2013年 | 6篇 |
2012年 | 5篇 |
2011年 | 13篇 |
2010年 | 6篇 |
2009年 | 7篇 |
2008年 | 9篇 |
2007年 | 6篇 |
2006年 | 10篇 |
2005年 | 2篇 |
2004年 | 2篇 |
2003年 | 4篇 |
2002年 | 4篇 |
2001年 | 3篇 |
2000年 | 3篇 |
1999年 | 2篇 |
1998年 | 4篇 |
1997年 | 1篇 |
1996年 | 2篇 |
1995年 | 3篇 |
1994年 | 11篇 |
1993年 | 5篇 |
1992年 | 1篇 |
1991年 | 3篇 |
1989年 | 1篇 |
1988年 | 2篇 |
1985年 | 1篇 |
1982年 | 1篇 |
1940年 | 1篇 |
排序方式: 共有137条查询结果,搜索用时 15 毫秒
41.
[Structure: see text]. Three universal solid supports exhibiting an hydroxyl function were prepared. The introduction of a first H-phosphonate diester linkage which was kept throughout the elongation allowed the release of 3'-hydroxyl oligonucleotides by a transesterification mechanism. The transesterification was performed in a few minutes with either amino alcohols or K2CO3/methanol. Starting from a hydroxyl solid support, tandem oligonucleotides were synthesized and the solid support was easily recyclable. This strategy was extended to the release of an oligonucleotide from the solid support by a nonbasic treatment opening the way to the synthesis of base-sensitive oligonucleotides thanks to the selective deprotection of a hydroxyl in beta of the H-phosphonate diester linkage. 相似文献
42.
This paper presents a method for modeling microgeometric structures of porous media with a predominant using successive cross-sections. The proposed model takes into account the properties of diffusive flow in capillaries. In order to characterize uncertainty and imprecision occurring in geometric features of cross-sections, we introduce the concept of connection degrees as well as tracking degrees based on fuzzy theory. The proposed model can be used for classifying different types of media and finding the relationship between the geometric structure of a porous medium and its physical properties. This model has been successfully applied to polyester yarn structure. 相似文献
43.
44.
B. Djafari Rouhani Y. Pennec E. H. El Boudouti J. O. Vasseur Y. El Hassouani C. Li A. Akjouj D. Bria 《Applied Physics A: Materials Science & Processing》2011,103(3):735-739
We discuss the simultaneous existence of phononic and photonic band gaps in two types of phononic crystals slabs, namely periodic
arrays of nanoholes in a Si membrane and of Si nanodots on a SiO2 membrane. In the former geometry, we investigate in detail both the boron nitride lattice and the square lattice with two
atoms per unit cell (these include the square, triangular and honeycomb lattices as particular cases). In the latter geometry,
some preliminary results are reported for a square lattice. 相似文献
45.
The stability of a conducting fluid saturating a porous medium, in the presence of a uniform magnetic field, is investigated using the Brinkman model. In the first part of the paper constant-flux thermal boundary conditions are considered for which the onset of convection is known to correspond to a vanishingly small wave number. The external magnetic field is assumed to be aligned with gravity. Closed form solutions are obtained, based on a parallel flow assumption, for a porous layer with either rigid-rigid, rigid-free or free-free boundaries. In the second part of the paper, the linear stability of a porous layer, heated isothermally from below, is investigated using the normal mode technique. The external magnetic field is applied either vertically or horizontally. Solutions are obtained for the case of a porous layer with free boundaries. Results for a pure viscous fluid and a Darcy (densely packed) porous medium emerge from the present analysis as limiting cases. 相似文献
46.
The transient natural convection in a fluid contained in a rectangular enclosure, the wall of which is maintained at a uniform temperature which changes at a steady rate, is approached by a numerical method. Numerical solutions are obtained forPr=0.73, 7.3 and 73 and a range of Rayleigh numbersRa=102 ~ 108. At relatively low Rayleigh numbers the flow is characterized by the development of double cells with flow up the center and down the sidewalk However it was found that an increase of the Rayleigh number leads to the development of strong secondary circulation on the axis of symmetry of the cavity near the top wall. Thus, as the Rayleigh number is increased the secondary cells grow in size. The effects of the secondary cells on the temperature field and heat transfer coefficients are discussed. Most results are obtained for the case of a square cavity (E=2) but the influence of the aspect ratio of the cavity is also studied forE=1 and 4. 相似文献
47.
Lombard L Azarian A Cadoret K Bourdon P Goular D Canat G Jolivet V Jaouën Y Vasseur O 《Optics letters》2011,36(4):523-525
We report what we believe to be the first experimental demonstration of coherent beam combining of two fiber amplifiers in a 100 ns pulse regime using a signal leak between the pulses. Pulses of ~100 W stimulated-Brillouin-scattering limited peak power are combined with 95% efficiency, a residual phase error of λ/27, and no significant beam quality degradation. 相似文献
48.
Small libraries of di-, tri-, and tetragalactosyl clusters were efficiently synthesized using combinatorial methodology, on solid support, by click chemistry assisted by microwaves, starting from different poly alkyne DNA-based scaffolds and two galactosyl azide derivatives. The scaffold was synthesized by standard DNA solid-supported phosphoramidite chemistry using a novel alkyne phosphoramidite and an alkyne solid support. The proportion of each glycocluster in a library was modulated using different molar ratios of both galactose azides. 相似文献
49.
In this paper we consider bounded weak solutions u of scalar conservation laws, not necessarily of class BV, defined in a subset . We define a strong notion of trace at the boundary of reached by L
1 convergence for a large class of functionals of u, G(u). The functionals G depend on the flux function of the conservation law and on the boundary of . The result holds for a general flux function and a general subset. 相似文献
50.
In this article we present a Ladyženskaja–Prodi–Serrin Criteria for regularity of solutions for the Navier–Stokes equation
in three dimensions which incorporates weak L
p
norms in the space variables and log improvement in the time variable. 相似文献