全文获取类型
收费全文 | 1546篇 |
免费 | 80篇 |
专业分类
化学 | 1343篇 |
晶体学 | 3篇 |
力学 | 11篇 |
数学 | 101篇 |
物理学 | 168篇 |
出版年
2023年 | 7篇 |
2022年 | 17篇 |
2021年 | 24篇 |
2020年 | 36篇 |
2019年 | 31篇 |
2018年 | 18篇 |
2017年 | 5篇 |
2016年 | 55篇 |
2015年 | 52篇 |
2014年 | 47篇 |
2013年 | 68篇 |
2012年 | 92篇 |
2011年 | 134篇 |
2010年 | 71篇 |
2009年 | 79篇 |
2008年 | 88篇 |
2007年 | 91篇 |
2006年 | 84篇 |
2005年 | 71篇 |
2004年 | 74篇 |
2003年 | 61篇 |
2002年 | 60篇 |
2001年 | 27篇 |
2000年 | 19篇 |
1999年 | 24篇 |
1998年 | 24篇 |
1997年 | 27篇 |
1996年 | 29篇 |
1995年 | 19篇 |
1994年 | 16篇 |
1993年 | 14篇 |
1992年 | 18篇 |
1991年 | 14篇 |
1990年 | 12篇 |
1989年 | 10篇 |
1988年 | 12篇 |
1987年 | 7篇 |
1985年 | 9篇 |
1984年 | 6篇 |
1983年 | 3篇 |
1982年 | 11篇 |
1981年 | 9篇 |
1980年 | 5篇 |
1979年 | 8篇 |
1978年 | 9篇 |
1977年 | 6篇 |
1974年 | 3篇 |
1973年 | 4篇 |
1932年 | 2篇 |
1891年 | 2篇 |
排序方式: 共有1626条查询结果,搜索用时 843 毫秒
181.
Aggregation behaviors of gemini nucleotide at the air-water interface and in solutions induced by adenine-uracil interaction 总被引:2,自引:0,他引:2
Wang Y Desbat B Manet S Aimé C Labrot T Oda R 《Journal of colloid and interface science》2005,283(2):555-564
Cationic gemini surfactants having nucleotides as counterions (called nucleo-gemini hereafter) were synthesized and their aggregation behavior at air-water surfaces as well as in bulk solutions were studied. Fluid solutions of these nucleo-gemini surfactants show transitions to hydrogels upon addition of complementary nucleoside bases or other nucleo-gemini surfactants having complementary bases as counterions. The FTIR-ATR measurements show that the carboxylate groups of uridine form hydrogen bonds with the amine groups of adenosine. The aggregation behavior was also confirmed at the air-water interface by Brewster angle microscopy as well as surface pressure measurements; the monolayer of a gemini nucleotide was observed to undergo a transition to multilayers when nucleosides with complementary bases were added into the subphase. Isotherm curves of surface pressure monitored in parallel show a decrease in molecular area upon addition of such nucleosides. 相似文献
182.
Chiesa M Giamello E Di Valentin C Pacchioni G Sojka Z Van Doorslaer S 《Journal of the American Chemical Society》2005,127(48):16935-16944
We have studied the interaction of K atoms with the surface of polycrystalline alkaline-earth metal oxides (MgO, CaO, SrO) by means of CW- and Pulsed-EPR, UV-Vis-NIR spectroscopies and DFT cluster model calculations. The K adsorption site is proposed to be an anionic reverse corner formed at the intersection of two steps, where K binds by more than 1 eV, resulting in thermally stable species up to about 400 K. The bonding has small covalent and large polarization contributions, and the K atom remains neutral, with one unpaired electron in the valence shell. The interaction results in strong modifications of the K electronic wave function which are directly reflected by the hyperfine coupling constant, (K)a(iso). This is found to be a very efficient "probe" to measure the degree of metal-oxide interaction which directly depends on the substrate basicity. These results provide an original and general model of the early stages of the metal-support interaction in the case of ionic oxides. 相似文献
183.
184.
185.
It is known that the classical capillary pressure-saturation relationship may be deficient under non-equilibrium conditions when large saturation changes may occur. An extended relationship has been proposed in the literature which correlates the rate of change of saturation to the difference between the phase pressures and the equilibrium capillary pressure. This linear relationship contains a damping coefficient, \tau, that may be a function of saturation. The extended relationship is examined at the macro-scale through simulations using the two-phase simulator MUFTE-UG. In these simulations, it is assumed that the traditional equilibrium relationship between the water saturation and the difference in fluid pressures holds locally. Steady-state and dynamic numerical experiments are performed where a non-wetting phase displaces a wetting phase in homogeneous and heterogeneous domains with varying boundary conditions, domain size, and soil parameters. From these simulations the damping coefficient can be identified as a (non-linear) function of the water saturation. It is shown that the value of increases with an increased domain size and/or with decreased intrinsic permeability. Also, the value of for a domain with a spatially correlated random distribution of intrinsic permeability is compared to a homogeneous domain with equivalent permeability; they are shown to be almost equal. 相似文献
186.
Sabine Dieter 《Calculus of Variations and Partial Differential Equations》2005,22(2):229-251
We study the evolution of closed, weakly convex hypersurfaces in
in direction of their normal vector, where the speed equals a quotient of successive elementary symmetric polynomials of the principal curvatures. We show that there exists a solution for these weakly convex surfaces at least for some short time if the elementary symmetric polynomial in the denominator of the quotient is positive. The results for this nonlinear, degenerate flow are obtained by a cylindrically symmetric barrier construction.Received: 10 November 2003, Accepted: 5 April 2004, Published online: 16 July 2004 相似文献
187.
Electron scattering sum rules for 3He are derived with a realistic ground-state wave function. The theoretical results are compared with the experimentally measured integrated cross sections. 相似文献
188.
V. Tornow P. -G. Reinhard D. Drechsel 《Zeitschrift für Physik A Hadrons and Nuclei》1977,280(3):253-257
The two-center-oscillator-basis, which is constructed from harmonic oscillator wave functions developing about two different centers, suffers from numerical problems at small center separations due to the overcompleteness of the set. In order to overcome these problems we admix higher oscillator wave functions before the orthogonalization, or antisymmetrization resp. This yields a numerically stable basis set at each center separation. The results obtained for the potential energy surface are comparable with the results of more elaborate models. 相似文献
189.
N-Arylglycolohydroxamic acids 1A are converted by in situ prepared 2,2′-dipyridyl sulfite to 1,2,3-oxathiazolidin-4-one 2,2-dioxides 5 , the formation of which can be rationalized via a radical pair mechanism. The alkylating potential of the heterocyclic system 5 is demonstrated by the alkaline ethanolysis giving rise to the open chained 2-ethoxypropionanilide 6 . 相似文献
190.