全文获取类型
收费全文 | 5990篇 |
免费 | 554篇 |
国内免费 | 463篇 |
专业分类
化学 | 232篇 |
晶体学 | 1篇 |
力学 | 968篇 |
综合类 | 136篇 |
数学 | 4692篇 |
物理学 | 978篇 |
出版年
2024年 | 9篇 |
2023年 | 52篇 |
2022年 | 55篇 |
2021年 | 63篇 |
2020年 | 138篇 |
2019年 | 116篇 |
2018年 | 133篇 |
2017年 | 176篇 |
2016年 | 145篇 |
2015年 | 122篇 |
2014年 | 279篇 |
2013年 | 462篇 |
2012年 | 228篇 |
2011年 | 433篇 |
2010年 | 305篇 |
2009年 | 357篇 |
2008年 | 412篇 |
2007年 | 371篇 |
2006年 | 357篇 |
2005年 | 323篇 |
2004年 | 266篇 |
2003年 | 286篇 |
2002年 | 252篇 |
2001年 | 197篇 |
2000年 | 187篇 |
1999年 | 188篇 |
1998年 | 196篇 |
1997年 | 161篇 |
1996年 | 111篇 |
1995年 | 92篇 |
1994年 | 90篇 |
1993年 | 61篇 |
1992年 | 49篇 |
1991年 | 34篇 |
1990年 | 39篇 |
1989年 | 21篇 |
1988年 | 24篇 |
1987年 | 25篇 |
1986年 | 22篇 |
1985年 | 17篇 |
1984年 | 28篇 |
1983年 | 11篇 |
1982年 | 25篇 |
1981年 | 21篇 |
1980年 | 14篇 |
1979年 | 7篇 |
1978年 | 12篇 |
1977年 | 7篇 |
1976年 | 6篇 |
1973年 | 6篇 |
排序方式: 共有7007条查询结果,搜索用时 15 毫秒
81.
An approximate method is developed to solve the full nonlinear equations governing two-dimensional irrotational flow in a free waterfall, falling under the influence of gravity, at high Froude number based on conditions far upstream. Schwarz—Christoffel transformation is used to map the region, in the complex potential-plane, onto the upper half-plane. The Hilbert transformation as well as the perturbation technique, for large Froude number, are used as a basis for the approximate solution of the problem. A complete solution, up to second-order approximation, for the downstream free-surfaces profiles, for different Froude number, is discussed and illustrated. The obtained approximate solutions are compared with those of other authors. Favourable agreement with other results suggests that this method is effective in dealing with flow problems strongly influenced by gravity and high Froude number. The results obtained by this method are sufficiently accurate for practical purposes. 相似文献
82.
In this article, by introducing characteristic singular integral operator and associate singular integral equations (SIEs), the authors discuss the direct method of solution for a class of singular integral equations with certain analytic inputs. They obtain both the conditions of solvability and the solutions in closed form. It is noteworthy that the method is different from the classical one that is due to Lu. 相似文献
83.
The problem treated in this paper concerns calculating the evolution of the pressure in a single-phase, slightly compressible fluid in a porous medium consisting of communicating layers. The fluid is produced through a point sink located on the side of an otherwise sealed cylindrical wellbore. This location of the sink causes the flow around the wellbore to be azimuthally asymmetric.The problem is solved through successive application of Laplace, finite Fourier and finite Hankel transforms. Although apparently straightforward, this approach leads to serious numerical difficulties. The published form of the inversion formula for the finite Hankel transform leads to inaccurate computation for the higher azimuthal modes even with 128 bit arithmetic. An alternative form is developed which enables accurate evaluation of the solution with the more practical 64 bit arithmetic. The technique for two-layer solution presented here can be directly extended to a problem with a larger number of communicating layers. This is the first instance of successful application of the finite Hankel transform to an azimuthally asymmetric diffusion problem. 相似文献
84.
Gary Sampson 《应用数学学报(英文版)》2002,(3)
In this paper, the authors prove that some oscillatory singular integral operators of non-convolution type with non-polynomial phases are bounded from the Herz-type Hardy spaces to the Herz spaces and from the Hardy spaces associated with the Beurling algebras to the Beurling algebras in higher dimensions, even though it is well-known that these operators are not bounded from the Hardy space H1(Rn) into the Lebesgue spaceL1(Rn). 相似文献
85.
86.
应用一个新的积分不等式,得到了具阻尼的非线性耦合方程组的衰减估计,以及精确的估计常数. 相似文献
87.
应用导数的定义,为分段函数的分界点提供了一种行之有效的求导方法,利用微分的定义判断函数在分界点及其他特殊点的可微性,运用定和分的定义求一类特殊类型的极限. 相似文献
88.
Models are developed for decision making about monitoring andmaintenance of systems whose performance through time is describedby a general stochastic process. The system is monitored andpreventive and corrective maintenance actions are carried outin response to the observed system state. The decision processis simplified by using the maximum process as a decision variable.The models developed generalize age replacement models and othersimple maintenance strategies. The approach can deal with failuresthat prevent the system functioning further, and also failuresthat are defined by regulation or economic considerations. Attentionis restricted to perfect repair and inspection, but the structureprovides the framework for further developments. 相似文献
89.
Starting from the vectorial Rayleigh diffraction integral formula and without using the far-field approximation, a solution of the wave equation beyond the paraxial approximation is found, which represents vectorial non-paraxial elliptical Gaussian beams in free space. The far-field expressions for non-paraxial Gaussian beams and elliptical Gaussian beams can be regarded as special cases treated in this paper. Some basic propagation properties of vectorial non-paraxial elliptical Gaussian beams, including the irradiance distribution, phase term, beam widths and divergence angles are studied. Numerical results are given and illustrated. 相似文献
90.
B.J. Stoyanov R.A. Farrell J.F. Bird 《Journal of Computational and Applied Mathematics》1994,50(1-3):533-543
Asymptotic expansions of certain finite and infinite integrals involving products of two Bessel functions of the first kind are obtained by using the generalized hypergeometric and Meijer functions. The Bessel functions involved are of arbitrary (generally different) orders, but of the same argument containing a parameter which tends to infinity. These types of integrals arise in various contexts, including wave scattering and crystallography, and are of general mathematical interest being related to the Riemann—Liouville and Hankel integrals. The results complete the asymptotic expansions derived previously by two different methods — a straightforward approach and the Mellin-transform technique. These asymptotic expansions supply practical algorithms for computing the integrals. The leading terms explicitly provide valuable analytical insight into the high-frequency behavior of the solutions to the wave-scattering problems. 相似文献