全文获取类型
收费全文 | 7426篇 |
免费 | 647篇 |
国内免费 | 598篇 |
专业分类
化学 | 390篇 |
晶体学 | 5篇 |
力学 | 705篇 |
综合类 | 123篇 |
数学 | 6176篇 |
物理学 | 1272篇 |
出版年
2023年 | 59篇 |
2022年 | 92篇 |
2021年 | 144篇 |
2020年 | 165篇 |
2019年 | 167篇 |
2018年 | 161篇 |
2017年 | 176篇 |
2016年 | 205篇 |
2015年 | 98篇 |
2014年 | 239篇 |
2013年 | 633篇 |
2012年 | 273篇 |
2011年 | 343篇 |
2010年 | 320篇 |
2009年 | 433篇 |
2008年 | 480篇 |
2007年 | 490篇 |
2006年 | 448篇 |
2005年 | 391篇 |
2004年 | 325篇 |
2003年 | 365篇 |
2002年 | 360篇 |
2001年 | 281篇 |
2000年 | 249篇 |
1999年 | 250篇 |
1998年 | 230篇 |
1997年 | 212篇 |
1996年 | 152篇 |
1995年 | 105篇 |
1994年 | 99篇 |
1993年 | 67篇 |
1992年 | 67篇 |
1991年 | 72篇 |
1990年 | 56篇 |
1989年 | 39篇 |
1988年 | 47篇 |
1987年 | 48篇 |
1986年 | 33篇 |
1985年 | 53篇 |
1984年 | 33篇 |
1983年 | 24篇 |
1982年 | 31篇 |
1981年 | 26篇 |
1980年 | 21篇 |
1979年 | 20篇 |
1978年 | 19篇 |
1977年 | 16篇 |
1976年 | 14篇 |
1974年 | 9篇 |
1973年 | 13篇 |
排序方式: 共有8671条查询结果,搜索用时 17 毫秒
1.
Tomoyuki Nakatsuka 《Mathematische Nachrichten》2021,294(1):98-117
We study the existence of a time‐periodic solution with pointwise decay properties to the Navier–Stokes equation in the whole space. We show that if the time‐periodic external force is sufficiently small in an appropriate sense, then there exists a time‐periodic solution of the Navier–Stokes equation such that and uniformly in as . Our solution decays faster than the time‐periodic Stokes fundamental solution and the faster decay of its spatial derivatives of higher order is also described. 相似文献
2.
《Studies in Applied Mathematics》2018,141(3):399-417
We extend our previous results characterizing the loading properties of a diffusing passive scalar advected by a laminar shear flow in ducts and channels to more general cross‐sectional shapes, including regular polygons and smoothed corner ducts originating from deformations of ellipses. For the case of the triangle and localized, cross‐wise uniform initial distributions, short‐time skewness is calculated exactly to be positive, while long‐time asymptotics shows it to be negative. Monte Carlo simulations confirm these predictions, and document the timescale for sign change. The equilateral triangle appears to be the only regular polygon with this property—all others possess positive skewness at all times. Alternatively, closed‐form flow solutions can be constructed for smooth deformations of ellipses, and illustrate how both nonzero short‐time skewness and the possibility of multiple sign switching in time is unrelated to domain corners. Exact conditions relating the median and the skewness to the mean are developed which guarantee when the sign for the skewness implies front (more mass to the right of the mean) or back (more mass to the left of the mean) “loading” properties of the evolving tracer distribution along the pipe. Short‐ and long‐time asymptotics confirm this condition, and Monte Carlo simulations verify this at all times. The simulations are also used to examine the role of corners and boundaries on the distribution for short‐time evolution of point source , as opposed to cross‐wise uniform, initial data. 相似文献
4.
A fundamental question in random matrix theory is to quantify the optimal rate of convergence to universal laws. We take up this problem for the Laguerre β ensemble, characterized by the Dyson parameter β, and the Laguerre weight , in the hard edge limit. The latter relates to the eigenvalues in the vicinity of the origin in the scaled variable . Previous work has established the corresponding functional form of various statistical quantities—for example, the distribution of the smallest eigenvalue, provided that . We show, using the theory of multidimensional hypergeometric functions based on Jack polynomials, that with the modified hard edge scaling , the rate of convergence to the limiting distribution is , which is optimal. In the case , general the explicit functional form of the distribution of the smallest eigenvalue at this order can be computed, as it can for and general . An iterative scheme is presented to numerically approximate the functional form for general . 相似文献
5.
In a previous paper (Ref. 1), an exact solution of the optimal planar interception with fixed end conditions was derived in closed form. The optimal control was expressed as an explicit function of the state variables and two fixed parameters, obtained by solving a set of nonlinear algebraic equations involving elliptic integrals. In order to facilitate the optimal control implementation, the present paper derives a highly accurate simplified solution assuming that the ratio of the pursuer turning radius to the initial range is small. An asymptotic expansion further reduces the computational workload. Construction of a near-optimal open-loop control, based on the approximations, completes the present paper. 相似文献
6.
Lisa Lorentzen 《Numerical Algorithms》1995,10(1):69-111
Over the last 20 years a large number of algorithms has been published to improve the speed and domain of convergence of continued fractions. In this survey we show that these algorithms are strongly related. Actually, they essentially boil down to two main principles.We also prove some results on asymptotic expansions of tail values of limit periodic continued fractions.Dedicated to Luigi Gatteschi on his seventieth birthdayThis research was partially supported by The Norwegian Research Council and by the HMC project ROLLS, under contract CHRX-CT93-0416. 相似文献
7.
K. Y. Lin 《Journal of statistical physics》1987,49(1-2):269-279
The spontaneous magnetization of the Ising model on a 4–8 lattice with six different coupling constants and two different magnetic moments is studied. A formula for the spontaneous magnetization is proposed. The result agrees with the exact low-temperature series expansions up to the 12th order. 相似文献
8.
采用Cundari和Stevens等推导的有效芯势对镧系金属一氢化物进行了理论计算,以探讨镧系金属元素与氢的相互作用。结果表明所有镧系金属一氢化物基态时理论上是稳定的,最稳定的是SmH,最不稳定的是DyH;键长计算结果显示,基态时镧系金属一招兵买马花物有独立王国 收缩现象发生;红外振动频率理论计算值与实验结果一致;成键轨道中,金属原子轨道的贡献主要是s轨道和d轨道:从CeH至ErH(GdH)例外)随着外层电子的增加s轨道成分逐渐增大d轨道成分逐渐减小;从TmH和LuH(包括GdH),成键轨道中金属原子轨道的贡献主要是d轨道,约为90%;约大多数镧系金属一氧化物的成键轨道中金属原子轨道f成分小于1%。 相似文献
9.
LIU Jixue ZHANG Sanguo & CHEN Xiru Department of Statistics Finance University of Science Technology of China Hefei China Department of Mathematics Graduate School of Chinese Academy of Sciences Beijing China 《中国科学A辑(英文版)》2006,49(6):752-769
This paper studies the linear EV model when replicate observations are made only on independent variables. We construct the estimates of regression coefficients and prove the consistency and asymptotic normality under some proper conditions. Results obtained reveal the difference between the case where the independent and dependent variables are observed repeatedly and simultaneously and the case studied in this article. 相似文献
10.
Lance Nielsen 《Acta Appl Math》2002,74(3):265-292
Stability properties of Feynman's operational calculus are addressed in the setting of exponential functions of noncommuting operators. Applications of some of the stability results are presented. In particular, the time-dependent perturbation theory of nonrelativistic quantum mechanics is presented in the setting of the operational calculus and application of the stability results of this paper to the perturbation theory are discussed. 相似文献