全文获取类型
收费全文 | 4086篇 |
免费 | 125篇 |
国内免费 | 25篇 |
专业分类
化学 | 2857篇 |
晶体学 | 43篇 |
力学 | 105篇 |
数学 | 473篇 |
物理学 | 572篇 |
综合类 | 186篇 |
出版年
2023年 | 17篇 |
2022年 | 27篇 |
2021年 | 38篇 |
2020年 | 59篇 |
2019年 | 54篇 |
2018年 | 49篇 |
2017年 | 37篇 |
2016年 | 107篇 |
2015年 | 83篇 |
2014年 | 87篇 |
2013年 | 213篇 |
2012年 | 271篇 |
2011年 | 311篇 |
2010年 | 120篇 |
2009年 | 108篇 |
2008年 | 284篇 |
2007年 | 306篇 |
2006年 | 284篇 |
2005年 | 281篇 |
2004年 | 215篇 |
2003年 | 179篇 |
2002年 | 161篇 |
2001年 | 56篇 |
2000年 | 56篇 |
1999年 | 38篇 |
1998年 | 40篇 |
1997年 | 42篇 |
1996年 | 58篇 |
1995年 | 35篇 |
1994年 | 40篇 |
1993年 | 29篇 |
1992年 | 34篇 |
1991年 | 33篇 |
1990年 | 43篇 |
1989年 | 25篇 |
1988年 | 21篇 |
1987年 | 14篇 |
1986年 | 18篇 |
1985年 | 26篇 |
1984年 | 41篇 |
1983年 | 30篇 |
1982年 | 39篇 |
1981年 | 31篇 |
1980年 | 22篇 |
1979年 | 17篇 |
1978年 | 28篇 |
1977年 | 17篇 |
1976年 | 14篇 |
1974年 | 17篇 |
1973年 | 14篇 |
排序方式: 共有4236条查询结果,搜索用时 15 毫秒
1.
A liquid dewetting method for the determination of the viscoelastic properties of ultrathin polymer films has been extended to study thickness effects on the properties of ultrathin polycarbonate (PC) films. PC films with film thicknesses ranging from 4 to 299 nm were placed on glycerol at temperatures from below the macroscopic glass transition temperature (Tg) to above it with the dewetting responses being monitored. It is found that the isothermal creep results for films of the same thickness, but dewetted at different temperatures can be superposed into one master curve, which is consistent with the fact of PC being a thermorheologically simple material. Furthermore, the results show that the Tg of PC thin films is thickness dependent, but the dependence is weaker than the results for freely standing films and similar to literature data for PC films supported on rigid substrates. It was also found that the rubbery plateau region for the PC films stiffens dramatically, but still less than what has been observed for freely standing polycarbonate films. The rubbery stiffening is discussed in terms of a recently reported model that relates macroscopic segmental dynamics with the stiffening. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2015 , 53, 1559–1566 相似文献
2.
3.
4.
Gregory S. Constable Alan J. Lesser E. Bryan Coughlin 《Journal of Polymer Science.Polymer Physics》2003,41(12):1323-1333
An in situ ultrasonic spectroscopy technique was used to study the ring‐opening metathesis polymerization of dicyclopentadiene catalyzed by bis(tricyclohexylphosphine)benzylidene ruthenium dichloride. A reaction cell employing a flexible poly(ethylene terephthalate) window for pulse echo ultrasonic spectroscopy was used to monitor the polymerization. The changes in the density, wave speed, acoustic modulus, and attenuation were all simultaneously monitored. In comparison with Fourier transform infrared (FTIR) spectroscopy data, the changes in the density, velocity, and modulus only accurately measured the rate constant for the metathesis of the cyclopentyl unsaturation. The ultrasonic values were within 6% of the values determined by FTIR. The activation energy for metathesis of the cyclopentyl unsaturation was 84 kJ mol?1, following first‐order kinetics. Rate constants for the polymerization of the norbornyl unsaturation could not be determined by ultrasound. The gel point, vitrification, and qualitative information about the reaction rate could be determined from the change in the attenuation. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 1323–1333, 2003 相似文献
5.
Eitan Altman Konstantin Avrachenkov Richard Marquez Gregory Miller 《Mathematical Methods of Operations Research》2005,62(3):375-386
We consider a zero-sum stochastic game with side constraints for both players with a special structure. There are two independent
controlled Markov chains, one for each player. The transition probabilities of the chain associated with a player as well
as the related side constraints depend only on the actions of the corresponding player; the side constraints also depend on
the player’s controlled chain. The global cost that player 1 wishes to minimize and that player 2 wishes to maximize, depend
however on the actions and Markov chains of both players. We obtain a linear programming formulations that allows to compute
the value and saddle point policies for this problem. We illustrate the theoretical results through a zero-sum stochastic
game in wireless networks in which each player has power constraints 相似文献
6.
7.
Khaled A. Aamer Gregory N. Tew 《Journal of polymer science. Part A, Polymer chemistry》2007,45(6):1109-1121
Supramolecular block‐random copolymers containing [Ir(terpy)2]3+ in the side chain were synthesized via postfunctionalization of a P(S‐b‐ACterpy) block copolymer. Absorbance and emission spectra compared to a model compound show that the polymer backbone has a minor effect on the polymer absorbance but produces a larger shift for the phosphorescence signals to higher wavelength. Dynamic light scattering of the metal complex containing copolymer studied in various solvents showed monomodal aggregation with decreasing aggregate size as the solvent dielectric constant increased. The copolymer precursor P(S‐b‐ACterpy) shows multimodal aggregation in different solvents with the major population consisting of single chains. This difference in behavior between the two polymers is attributed to the electrolytic nature of the complex and the amphiphilicity induced by the charged metal complex. Supramolecular copolymers like these will continue to have interesting self‐organizational properties and may find applications in multicomponent systems for photoinduced charge separation processes. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 1109–1121, 2007 相似文献
8.
The Bekenstein–Hawking entropy of certain black holes can be computed microscopically in string theory by mapping the elusive
problem of counting microstates of a strongly gravitating black hole to the tractable problem of counting microstates of a
weakly coupled D-brane system, which has no event horizon, and indeed comfortably fits on the head of a pin. We show here
that, contrary to widely held beliefs, the entropy of spherically symmetric black holes can easily be dwarfed by that of stationary
multi-black-hole “molecules” of the same total charge and energy. Thus, the corresponding pin-sized D-brane systems do not
even approximately count the microstates of a single black hole, but rather those of a zoo of entropically dominant multicentered
configurations.
Fourth Award in the 2007 Essay Competition of the Gravity Research Foundation. 相似文献
9.
We utilize the unifying framework of families of convexity spaces for the treatment of various notions of planar convexity and the associated convex hulls. Our major goal is to prove the refinement and decomposition theorems for families of convexity spaces. These general theorems are then applied to two examples: restricted-oriented convex sets andNESW-convex sets. The applications demonstrate the usefulness of these general theorems, since they give rise to simple algorithms for the computation of the associated convex hulls of polygons. 相似文献
10.
The steady-state two-phase flow non-linear equation is considered in the case when one of phases has low effective permeability in some periodic set, while on the complementary set it is high; the second phase has no contrast of permeabilities in different zones. A homogenization procedure gives the homogenized model with macroscopic effective permeability of the second phase depending on the gradient and on the second order derivatives of the macroscopic pressure of the first phase. This effect cannot be obtained by classical (one small parameter) homogenization. To cite this article: G.P. Panasenko, G. Virnovsky, C. R. Mecanique 331 (2003). 相似文献