全文获取类型
收费全文 | 729篇 |
免费 | 25篇 |
专业分类
化学 | 383篇 |
晶体学 | 9篇 |
力学 | 15篇 |
数学 | 225篇 |
物理学 | 122篇 |
出版年
2023年 | 4篇 |
2022年 | 7篇 |
2021年 | 14篇 |
2020年 | 11篇 |
2019年 | 19篇 |
2018年 | 20篇 |
2017年 | 21篇 |
2016年 | 31篇 |
2015年 | 25篇 |
2014年 | 33篇 |
2013年 | 66篇 |
2012年 | 60篇 |
2011年 | 50篇 |
2010年 | 28篇 |
2009年 | 20篇 |
2008年 | 44篇 |
2007年 | 49篇 |
2006年 | 47篇 |
2005年 | 17篇 |
2004年 | 24篇 |
2003年 | 19篇 |
2002年 | 19篇 |
2001年 | 7篇 |
2000年 | 8篇 |
1999年 | 9篇 |
1998年 | 10篇 |
1997年 | 5篇 |
1996年 | 10篇 |
1995年 | 8篇 |
1994年 | 8篇 |
1993年 | 3篇 |
1992年 | 2篇 |
1991年 | 5篇 |
1990年 | 5篇 |
1989年 | 2篇 |
1988年 | 2篇 |
1987年 | 3篇 |
1986年 | 2篇 |
1985年 | 5篇 |
1984年 | 4篇 |
1983年 | 2篇 |
1982年 | 4篇 |
1981年 | 3篇 |
1980年 | 5篇 |
1979年 | 2篇 |
1976年 | 3篇 |
1975年 | 2篇 |
1967年 | 1篇 |
1963年 | 1篇 |
1930年 | 1篇 |
排序方式: 共有754条查询结果,搜索用时 15 毫秒
91.
Beleaga A Bojan VR Pöllnitz A Raţ CI Silvestru C 《Dalton transactions (Cambridge, England : 2003)》2011,40(35):8830-8838
The reaction of RH (1) with Hg(OAc)(2), in EtOH, gave the acetate RHgOAc (2) [R = 2,6-[O(CH(2)CH(2))(2)NCH(2)](2)C(6)H(3)]. The corresponding RHgCl (3) was obtained from 2 and LiCl. The reaction of 3 with TeCl(4) (1:1 molar ratio), in anhydrous 1,4-dioxane, resulted in the transfer of the organic ligand from mercury to tellurium and the isolation of the unexpected ionic compounds [RTe](2)[Hg(2)Cl(6)] (4) and [RH(3)][HgCl(4)] (5). The molecular structures of 1-4 and 5·H(2)O were established by single-crystal X-ray diffraction. The acetate 2 and the chloride 3 are monomeric in solid state. In both mercury and tellurium organometallic compounds the organic group acts as an (N,C,N) "pincer" ligand. This coordination pattern provided stability for the rare [RTe](+) cation. Weak cation-anion interactions [Te···Cl 3.869(3) ?] are present between [RTe](+) and the dinuclear anion [Hg(2)Cl(6)](2-) in the crystal of 4. Theoretical calculations with DFT methods were performed for models of 3 and 4. The results show that in the cation of 4 the coordination of the nitrogen atoms play an important role for the stabilization of the structure found in the crystal whereas in 3 the coordination of the nitrogen atoms to the metal centre stabilizes to a less extent the structure found in solid state. 相似文献
92.
Osman Ra?it I?ikMehmet Sezer Zekeriya Güney 《Applied mathematics and computation》2011,217(22):9438-9450
We introduce a new method to solve high order linear differential equations with initial and boundary conditions numerically. In this method, the approximate solution is based on rational interpolation and collocation method. Since controlling the occurrence of poles in rational interpolation is difficult, a construction which is found by Floater and Hormann [1] is used with no poles in real numbers. We use the Bernstein series solution instead of the interpolation polynomials in their construction. We find that our approximate solution has better convergence rate than the one found by using collocation method. The error of the approximate solution is given in the case of the exact solution f ∈ Cd+2[a, b]. 相似文献
93.
Montero R Conde AP Ovejas V Martínez R Castaño F Longarte A 《The Journal of chemical physics》2011,135(5):054308
The ultrafast relaxation of jet-cooled aniline was followed by time-resolved ionization, after excitation in the 294-234 interval. The studied range of energy covers the absorption of the two bright ππ? excitations, S(1) and S(3), and the almost dark S(2) (πσ?) state. The employed probe wavelengths permit to identify different ultrafast time constants related with the coupling of the involved electronic surfaces. A τ(1) = 165 ± 30 fs lifetime is attributed to dynamics along the S(2) (πσ?) repulsive surface. Other relaxation channels as the S(1)→S(0) and S(3)→S(1) internal conversion are also identified and characterized. The work provides a general view of the photophysics of aniline, particularly regarding the role of the πσ? state. This state appears as minor dissipation process due to the ineffective coupling with the bright S(1) and S(3) states, being the S(1)→S(0) internal conversion the main non-radiative process in the full studied energy range. Additionally, the influence of the off-resonance adiabatic excitation of higher energy electronic states, particularly S(3), is also observed and discussed. 相似文献
94.
Raúl Ferreira 《Israel Journal of Mathematics》2011,184(1):387-402
In this paper we study the quenching problem for the non-local diffusion equation
ut(x,t) = òW J(x - y)u(y,t)dy + ò\mathbbRN\W J(x - y)dy - u(x,t) - lu - p(x,t) {u_t}(x,t) = \int\limits_\Omega {J(x - y)u(y,t)dy + \int\limits_{{\mathbb{R}^N}\backslash \Omega } {J(x - y)dy - u(x,t) - \lambda {u^{ - p}}(x,t)} } 相似文献
95.
A systematic study of the rotational activation free energy around the Caromatic-Cethylenic bond of para-substituted styrene systems is carried out in the present work from a quantum chemistry point of view. Calculations of the rotational potential barriers in the AM1 approach are developed as function of the electron-donor groups localized on the aromatic ring. Based on these calculations and thermodynamical data, we predict changes in the activation free energy barriers due to the long distance electronic effects of the substituents in acetophenones, cinnamaldehydes and benzalketones according to the following equation: Our results agree the experimental measurements registered up to date and the standard deviations are similar to experimental determinations. 相似文献
96.
97.
G. Račiukaitis S. Grubinskas P. Gečys M. Gedvilas 《Applied Physics A: Materials Science & Processing》2013,110(1):93-98
Selectiveness of the laser processing is the top-most important for applications of the processing technology in thin-film electronics, including photovoltaics. Coupling of laser energy in multilayered thin-film structures, depending on photo-physical properties of the layers and laser wavelength was investigated experimentally and theoretically. Energy coupling within thin films highly depends on the film structure. The finite element and two-temperature models were applied to simulate the energy and temperature distributions inside the stack of different layers of a thin-film solar cell during a picosecond laser irradiation. Reaction of the films to the laser irradiation was conditioned by optical properties of the layers at the wavelength of laser radiation. Simulation results are consistent with the experimental data achieved in laser scribing of copper-indium-gallium diselenide (CIGS) solar cells on a flexible polymer substrate using picosecond-pulsed lasers. Selection of the right laser wavelength (1064 nm or 1572 nm) enabled keeping the energy coupling in a well-defined volume at the interlayer interface. High absorption at inner interface of the layers triggered localized temperature increase. Transient stress caused by the rapid temperature rise facilitating peeling of the films rather than evaporation. Ultra-short pulses ensured high energy input rate into absorbing material permitting peeling of the layers with no influence on the remaining material. 相似文献
98.
99.
In this paper, we extend the Hölderian invariance principle of Lamperti [6] to the case of partial-sum processes based on a triangular array of row-wise independent random variables. As an application, we obtain necessary and sufficient conditions for the almost sure (resp. in probability) weak Hölder convergence of partial-sum processes based on bootstrapped samples. 相似文献
100.
Raúl Ferreira Arturo de Pablo Fernando Quirós Julio D. Rossi 《Zeitschrift für Angewandte Mathematik und Physik (ZAMP)》2006,57(4):586-594
We study the solutions of a parabolic system of heat equations coupled at the boundary through a nonlinear flux. We characterize
in terms of the parameters involved when non-simultaneous quenching may appear. Moreover, if quenching is non-simultaneous
we find the quenching rate, which surprisingly depends on the flux associated to the other component.
Partially supported by project BFM2002-04572 (Spain).
Partially supported by UBA grant EX046, CONICET and Fundación Antorchas (Argentina).
Received: February 17, 2004; revised: July 5, 2004 相似文献
|