全文获取类型
收费全文 | 7461篇 |
免费 | 303篇 |
国内免费 | 52篇 |
专业分类
化学 | 5562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 | 37篇 |
2021年 | 149篇 |
2020年 | 143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 | 380篇 |
2012年 | 532篇 |
2011年 | 582篇 |
2010年 | 328篇 |
2009年 | 244篇 |
2008年 | 489篇 |
2007年 | 509篇 |
2006年 | 516篇 |
2005年 | 505篇 |
2004年 | 426篇 |
2003年 | 352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 | 118篇 |
1995年 | 61篇 |
1994年 | 64篇 |
1993年 | 66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7816条查询结果,搜索用时 15 毫秒
991.
992.
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
993.
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
994.
995.
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
996.
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
997.
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
998.
The notion of broken k-diamond partitions was introduced by Andrews and Paule in 2007. For a fixed positive integer k, let \(\Delta _k(n)\) denote the number of broken k-diamond partitions of n. Recently, Paule and Radu conjectured two relations on \(\Delta _5(n)\) which were proved by Xiong and Jameson, respectively. In this paper, employing these relations, we prove that, for any prime p with \(p\equiv 1\ (\mathrm{mod}\ 4)\), there exists an integer \(\lambda (p)\in \{2,\ 3,\ 5,\ 6,\ 11\}\) such that, for \(n, \alpha \ge 0\), if \(p\not \mid (2n+1)\), then Moreover, some non-standard congruences modulo 11 for \(\Delta _5(n)\) are deduced. For example, we prove that, for \(\alpha \ge 0\), \(\Delta _5\left( \frac{11\times 5^{5\alpha }+1}{2}\right) \equiv 7\ (\mathrm{mod}\ 11)\).
相似文献
$$\begin{aligned} \Delta _5\left( 11p^{\lambda (p)(\alpha +1)-1} n+\frac{11p^{\lambda (p)(\alpha +1)-1}+1}{2}\right) \equiv 0\ (\mathrm{mod}\ 11). \end{aligned}$$
999.
Tiphaine Wong Lorette Brault Eric Gasparotto Romuald Valle Pierre-Yves Morvan Vincent Ferrires Caroline Nugier-Chauvin 《Molecules (Basel, Switzerland)》2021,26(15)
Marine polysaccharides are part of the huge seaweeds resources and present many applications for several industries. In order to widen their potential as additives or bioactive compounds, some structural modifications have been studied. Among them, simple hydrophobization reactions have been developed in order to yield to grafted polysaccharides bearing acyl-, aryl-, alkyl-, and alkenyl-groups or fatty acid chains. The resulting polymers are able to present modified physicochemical and/or biological properties of interest in the current pharmaceutical, cosmetics, or food fields. This review covers the chemical structures of the main marine polysaccharides, and then focuses on their structural modifications, and especially on hydrophobization reactions mainly esterification, acylation, alkylation, amidation, or even cross-linking reaction on native hydroxyl-, amine, or carboxylic acid functions. Finally, the question of the necessary requirement for more sustainable processes around these structural modulations of marine polysaccharides is addressed, considering the development of greener technologies applied to traditional polysaccharides. 相似文献
1000.
Stefanie Scholtyssek Rameshwar Adhikari Volker Seydewitz Goerg Hannes Michler Eric Baer Anne Hiltner 《Macromolecular Symposia》2010,294(1):33-44
Nanostructured polymers and ultra-thin polymer layers are used more and more in technical applications like nanotechnology and microelectronics. Therefore, it is really important to understand the size-scale dependent properties as bulk polymers become thinner and more two-dimensional. Here the morphology as well as the macroscopic and the microscopic deformation behaviour of multilayered films of polypropylene (PP) and polystyrene (PS) have been investigated. For investigation different microscopic techniques and tensile testing were used. The films were prepared by multilayer coextrusion, whereas the composition of PP and PS and the film thickness – and therefore the thickness of each layer – varied. The thinnest calculated thickness of a single layer was about 5 nm. It is shown that the PP/PS films consist usually of homogeneous layers with only few defects. As the composition of PP/PS deviates strongly from 50/50 or the films get thinner the number of defects increases and the layered system turns to irregular lamellar system. In macroscopic tensile tests the small PS layers affect the elongation at break enormously: Most of the samples are brittle. For the films with a composition of PP/PS 90/10 and the film PP/PS 70/30 with a film thickness of 25 µm an elongation at break of 66% and higher could be reached. Transmission electron microscopy on these samples shows that the layers are characterized by plastic yielding in local deformation zones. 相似文献