全文获取类型
收费全文 | 431122篇 |
免费 | 3863篇 |
国内免费 | 1705篇 |
专业分类
化学 | 216479篇 |
晶体学 | 6008篇 |
力学 | 20865篇 |
综合类 | 66篇 |
数学 | 60780篇 |
物理学 | 132492篇 |
出版年
2019年 | 2877篇 |
2018年 | 11445篇 |
2017年 | 12215篇 |
2016年 | 9265篇 |
2015年 | 4421篇 |
2014年 | 5619篇 |
2013年 | 14330篇 |
2012年 | 15352篇 |
2011年 | 25044篇 |
2010年 | 16129篇 |
2009年 | 16132篇 |
2008年 | 22530篇 |
2007年 | 25622篇 |
2006年 | 12923篇 |
2005年 | 17429篇 |
2004年 | 13309篇 |
2003年 | 12146篇 |
2002年 | 10317篇 |
2001年 | 10192篇 |
2000年 | 7989篇 |
1999年 | 5817篇 |
1998年 | 4934篇 |
1997年 | 4875篇 |
1996年 | 4817篇 |
1995年 | 4310篇 |
1994年 | 4340篇 |
1993年 | 4114篇 |
1992年 | 4532篇 |
1991年 | 4703篇 |
1990年 | 4364篇 |
1989年 | 4260篇 |
1988年 | 4175篇 |
1987年 | 4064篇 |
1986年 | 3988篇 |
1985年 | 5212篇 |
1984年 | 5400篇 |
1983年 | 4506篇 |
1982年 | 4852篇 |
1981年 | 4550篇 |
1980年 | 4293篇 |
1979年 | 4604篇 |
1978年 | 4941篇 |
1977年 | 4787篇 |
1976年 | 4913篇 |
1975年 | 4548篇 |
1974年 | 4684篇 |
1973年 | 4773篇 |
1972年 | 3517篇 |
1971年 | 2883篇 |
1968年 | 2690篇 |
排序方式: 共有10000条查询结果,搜索用时 18 毫秒
991.
Ch. Tsitouras 《Numerical Algorithms》2007,44(3):291-307
Runge–Kutta (RK) pairs furnish approximations of the solution of an initial value problem at discrete points in the interval
of integration. Many techniques for enriching these methods with continuous approximations have been proposed. Here we construct
C
1 continuous, eighth and ninth order interpolation methods for a recently appeared RK pair of orders 9(8). These interpolants
share a very small leading truncation error making them suitable for use at quadruple precision, i.e. 32–33 decimal digits
of accuracy. Extended numerical results justify our effort. 相似文献
992.
The photogyrotropic properties of several mordant yellow azo dyes in gelatin and polymer matrices that are in the normal state or exposed to circularly polarized light are investigated. A model explanation for the experimental data is given. 相似文献
993.
994.
In this context, we introduce and investigate the properties of the nonlinear negative binomial state (the state which interpolates between the nonlinear coherent and the number states). Mainly we concentrate on the statistical properties for such state where we have discussed two different cases of squeezing phenomenon. The first case is the normal squeezing while the second is the amplitude squared squeezing, further the second order correlation function is also considered. Our discussion have been extended to include the quasi-probability distribution functions (W-Wigner and Q-functions). The quadrature distribution and the phase properties in Pegg-Barnett formalism besides the phase variances are considered. Examination of the resonance fluorescence against the present state is given (single atom and thermodynamic limit). It has been shown that the atomic inversion is sensitive to any variation in the nonlinear negative binomial number m. 相似文献
995.
Hydrogels of N‐vinylimidazole (VI) and sodium styrenesulfonate (SSS) were synthesized in aqueous solution by radical crosslinking copolymerization with N,N′‐methylene‐bis(acrylamide) as crosslinker. Swelling in several saline solutions was measured for hydrogel samples synthesized with different comonomer concentrations (CT = 10, 25, or 40%) and with SSS mole fractions covering a broad range (fSSS = 0–0.7), while the crosslinker ratio was 2 wt % in all cases. The degree of swelling in aqueous solution with a specific ionic strength (μ), plotted versus the SSS composition of the feed, shows a minimum for any set of samples synthesized with a fixed CT. The dependence of swelling on μ shows both polyelectrolyte (fSSS beyond the minimum) and antipolyelectrolyte behaviors (in the low fSSS limit). It was found that the nonGaussian factor of the crosslinking density and the polymer‐solvent interaction parameter increase with fSSS for any CT. Moreover, in the low fSSS limit, the osmotic swelling pressure is governed not only by the ionic contribution, but also by the polymer‐solvent mixing and, the concentration of mobile counterions inside the gel is not proportional to the net fixed charge but to the addition of cationic and anionic side groups, what discards the formation of ionic pairs. The antipolyelectrolyte effect is interpreted as due to the increasing protonation of VI as μ goes up. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 1683–1693, 2007 相似文献
996.
997.
I. P. Raevskii L. A. Reznichenko M. P. Ivliev V. G. Smotrakov V. V. Eremkin M. A. Malitskaya L. A. Shilkina S. I. Shevtsova A. V. Borodin 《Crystallography Reports》2003,48(3):486-490
(Na, K)NbO3 crystals with a perovskite structure and a KNbO3 content up to 40 mol % were grown from flux with the use of the solvent NaBO2. The dielectric measurements of the crystals grown revealed phase transitions that had never been observed before in ceramic samples. 相似文献
998.
Controllability of Functional Integro-Differential Inclusions with an Unbounded Delay 总被引:1,自引:0,他引:1
In this paper, a sufficient condition is established for the controllability of neutral functional integro-differential inclusions
with an unbounded delay in Banach spaces. The approach used is a fixed-point theorem for condensing maps due to Martelli and
the theory of analytic semigroup of linear operators.
Communicated by F. Zirilli
Research supported by NNSF of China, by the Teaching and Research Award Program for Outstanding Young Teachers in Higher Education
Institutions of the Ministry of Education of China, and by the Qing Lan Talent Engineering Fund QL-05-164 of Lanzhou Jiaotong
University. The authors are grateful to Professor F. Zirilli and two anonymous referees for valuable suggestions improving
this paper. 相似文献
999.
1000.
A. V. Gavrilov 《Siberian Mathematical Journal》2007,48(1):56-61
We study the double exponential map which is a composition of a special form of two exponential maps on a manifold with connection. We relate this map and the composition of covariant derivations as well as the composition of pseudodifferential operators on these manifolds. 相似文献