全文获取类型
收费全文 | 7459篇 |
免费 | 303篇 |
国内免费 | 52篇 |
专业分类
化学 | 5560篇 |
晶体学 | 71篇 |
力学 | 192篇 |
综合类 | 1篇 |
数学 | 941篇 |
物理学 | 1049篇 |
出版年
2023年 | 52篇 |
2022年 | 38篇 |
2021年 | 149篇 |
2020年 | 142篇 |
2019年 | 125篇 |
2018年 | 101篇 |
2017年 | 86篇 |
2016年 | 208篇 |
2015年 | 184篇 |
2014年 | 225篇 |
2013年 | 381篇 |
2012年 | 533篇 |
2011年 | 582篇 |
2010年 | 328篇 |
2009年 | 241篇 |
2008年 | 488篇 |
2007年 | 510篇 |
2006年 | 517篇 |
2005年 | 508篇 |
2004年 | 425篇 |
2003年 | 350篇 |
2002年 | 278篇 |
2001年 | 100篇 |
2000年 | 79篇 |
1999年 | 71篇 |
1998年 | 68篇 |
1997年 | 76篇 |
1996年 | 117篇 |
1995年 | 61篇 |
1994年 | 64篇 |
1993年 | 65篇 |
1992年 | 46篇 |
1991年 | 26篇 |
1990年 | 24篇 |
1989年 | 24篇 |
1988年 | 38篇 |
1987年 | 23篇 |
1986年 | 30篇 |
1985年 | 61篇 |
1984年 | 39篇 |
1983年 | 25篇 |
1982年 | 49篇 |
1981年 | 26篇 |
1980年 | 21篇 |
1979年 | 26篇 |
1978年 | 32篇 |
1977年 | 28篇 |
1976年 | 22篇 |
1975年 | 19篇 |
1974年 | 22篇 |
排序方式: 共有7814条查询结果,搜索用时 31 毫秒
991.
Preat J Jacquemin D Wathelet V André JM Perpète EA 《The journal of physical chemistry. A》2006,110(26):8144-8150
The UV absorption spectra of more than 80 substituted coumarins and chromones have been investigated with the PCM-TD-DFT theoretical scheme using three hybrid functionals (O3LYP, B3LYP, and PBE0) and taking into account methanol or ethanol solvation effects. For most of the studied derivatives, there are at least two allowed excited states presenting a strong oscillator strength in the UV region. The first allowed excitation is associated to a HOMO-LUMO transition whereas the second corresponds to a transition from the HOMO-1 to the LUMO. Both involve a charge transfer from the benzenic cycle to the pyranone moiety. Statistically treating the PBE0 results allows a prediction of the lambda(max) with small standard deviations: in methanol, 6 nm (0.07 eV) for the first excitation (lambda(max)(1)) and 5 nm (0.08 eV) for the second one (lambda(max)(2)), whereas in ethanol 6 nm (0.08 eV) for (lambda(max)(1)) and 6 nm (0.13 eV) for (lambda(max)(2)). 相似文献
992.
Ge N Fogel P Young SS Austin RE Wegrzyniak E Connelly JA 《Combinatorial chemistry & high throughput screening》2006,9(6):465-472
The goal of combinatorial chemistry is to simultaneously synthesize sets of compounds possessing properties that are then distinguished through screening. As the size of a compound set increases, data analysis becomes more challenging. Analysis of Variance (ANOVA) is an accepted statistical method that offers a straightforward solution to this problem. Two steps encountered by combinatorial scientists appear well suited to ANOVA: the prediction of synthetic outcomes (purity and yield) of set members and the analysis of screening data to identify combinations of reagent inputs that result in molecules with a desired property. To illustrate, a subset of a combinatorial array, referred to as a reaction rehearsal set, is evaluated to create a model predictive of the individual synthetic outcomes of the full matrix. In a second exercise, the biochemical screening data obtained from a combinatorial library is analyzed to identify reagent interactions that result in molecules possessing the sought activity. 相似文献
993.
994.
995.
Peter Kop?anský Martina Koneracká Vlasta Závišová Katalin Fodor-Csorba Anikó Vajda Eric Beaugnon 《Journal of magnetism and magnetic materials》2010,322(22):3696-3700
The studied ferronematic is a nematic liquid crystal (ZLI1695) of low negative anisotropy of the diamagnetic susceptibility (χa<0) doped with the magnetic particles Fe3O4. Structural instabilities are interpreted within Burylov and Raikher's theory. The high magnetic fields were oriented perpendicular (Freedericksz transition) or parallel to the initial director. Using capacitance measurements the Freedericksz threshold magnetic field of the ferronematic BFN, and the critical magnetic field Bmax, at which the initial parallel orientation between the director and the magnetic moment of magnetic particles breaks down, have been determined. The values of these quantities have been used to estimate the surface density of the anchoring energy W of liquid crystal molecules on the surface of the magnetic particles. The obtained values indicate a soft anchoring of the liquid crystal on the magnetic particles with a preferred parallel orientation of the magnetic moment of magnetic particles and the director. 相似文献
996.
We show that the nonequilibrium entropy production for a driven quantum system is larger than the Bures length, the geometric distance between its actual state and the corresponding equilibrium state. This universal lower bound generalizes the Clausius inequality to arbitrary nonequilibrium processes beyond linear response. We further derive a fundamental upper bound for the quantum entropy production rate and discuss its connection to the Bremermann-Bekenstein bound. 相似文献
997.
998.
A thermodynamical treatment of a massless scalar field (a photon) confined to a fractal spatial manifold leads to an equation of state relating pressure to internal energy, PV(s) = U/d(s), where d(s) is the spectral dimension and V(s) defines the "spectral volume." For regular manifolds, V(s) coincides with the usual geometric spatial volume, but on a fractal this is not necessarily the case. This is further evidence that on a fractal, momentum space can have a different dimension than position space. Our analysis also provides a natural definition of the vacuum (Casimir) energy of a fractal. We suggest ways that these unusual properties might be probed experimentally. 相似文献
999.
Lecaplain C Ortaç B Machinet G Boullet J Baumgartl M Schreiber T Cormier E Hideur A 《Optics letters》2010,35(19):3156-3158
We report the generation of high-energy high-peak power pulses in an all-normal dispersion fiber laser featuring large-mode-area photonic crystal fibers. The self-starting chirped-pulse fiber oscillator delivers 11 W of average power at 15.5 MHz repetition rate, resulting in 710 nJ of pulse energy. The output pulses are dechirped outside the cavity from 7 ps to nearly transform-limited duration of 300 fs, leading to pulse peak powers as high as 1.9 MW. Numerical simulations reveal that pulse shaping is dominated by the amplitude modulation and spectral filtering provided by a resonant semiconductor saturable absorber. 相似文献
1000.
We consider a strongly heterogeneous medium saturated by an incompressible viscous fluid as it appears in geomechanical modeling.This poroelasticity problem suffers from rapidly oscillating material parameters,which calls for a thorough numerical treatment.In this paper,we propose a method based on the local orthogonal decomposition technique and motivated by a similar approach used for linear thermoelasticity.Therein,local corrector problems are constructed in line with the static equations,whereas we propose to consider the full system.This allows to benefit from the given saddle point structure and results in two decoupled corrector problems for the displacement and the pressure.We prove the optimal first-order convergence of this method and verify the result by numerical experiments. 相似文献