全文获取类型
收费全文 | 18036篇 |
免费 | 1841篇 |
国内免费 | 858篇 |
专业分类
化学 | 607篇 |
晶体学 | 18篇 |
力学 | 2334篇 |
综合类 | 123篇 |
数学 | 12794篇 |
物理学 | 4859篇 |
出版年
2024年 | 37篇 |
2023年 | 194篇 |
2022年 | 177篇 |
2021年 | 294篇 |
2020年 | 517篇 |
2019年 | 484篇 |
2018年 | 493篇 |
2017年 | 506篇 |
2016年 | 497篇 |
2015年 | 450篇 |
2014年 | 826篇 |
2013年 | 1908篇 |
2012年 | 757篇 |
2011年 | 1076篇 |
2010年 | 864篇 |
2009年 | 1175篇 |
2008年 | 1166篇 |
2007年 | 1092篇 |
2006年 | 1009篇 |
2005年 | 766篇 |
2004年 | 714篇 |
2003年 | 673篇 |
2002年 | 664篇 |
2001年 | 552篇 |
2000年 | 557篇 |
1999年 | 489篇 |
1998年 | 422篇 |
1997年 | 388篇 |
1996年 | 293篇 |
1995年 | 205篇 |
1994年 | 182篇 |
1993年 | 152篇 |
1992年 | 124篇 |
1991年 | 101篇 |
1990年 | 92篇 |
1989年 | 66篇 |
1988年 | 57篇 |
1987年 | 55篇 |
1986年 | 39篇 |
1985年 | 64篇 |
1984年 | 101篇 |
1983年 | 51篇 |
1982年 | 66篇 |
1981年 | 66篇 |
1980年 | 58篇 |
1979年 | 57篇 |
1978年 | 54篇 |
1977年 | 34篇 |
1976年 | 27篇 |
1973年 | 7篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
971.
Shape reconstruction of an inverse boundary value problem of two‐dimensional Navier–Stokes equations
This paper is concerned with the problem of the shape reconstruction of two‐dimensional flows governed by the Navier–Stokes equations. Our objective is to derive a regularized Gauss–Newton method using the corresponding operator equation in which the unknown is the geometric domain. The theoretical foundation for the Gauss–Newton method is given by establishing the differentiability of the initial boundary value problem with respect to the boundary curve in the sense of a domain derivative. The numerical examples show that our theory is useful for practical purpose and the proposed algorithm is feasible. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
972.
Alberto Damiano Daniele Struppa Adrian Vajiac Mihaela Vajiac 《Journal of Geometric Analysis》2009,19(2):288-300
We introduce the notion of antisyzygies, which studies the inverse problem of finding a system of PDEs, given compatibility
conditions. The system obtained possesses the property of removability of compact singularities. We write explicit computations
in the cases of the Cauchy-Fueter system and Maxwell’s system for electromagnetism, and we conclude with a study of systems
of non-maximal rank.
相似文献
973.
Shear banding occurs in the flow of complex fluids: various types of shear thinning and shear thickening micelle solutions
and liquid crystals. In order to cope with the strongly inhomogeneous interface between the bands, constitutive models used
in standard rheology must be supplemented by non-local terms. This leads rather generally to non-linear partial differential
equations of the reaction-diffusion type. We use this formalism in order to explain some observed experimental features and
as a guide for future research in this field.
Received: 17 May 1999/Accepted: 3 August 1999 相似文献
974.
Hong-jiong Tian 《计算数学(英文版)》2001,(2)
1. IntroductionFor a large class of electrical ~ks containing IOssless transmission lines the describingequations can be reduced to a system of neutral differential equations.This paper deals with the numerical solution of initial value problems for syste… 相似文献
975.
《中国化学快报》2021,32(8):2415-2418
Supramolecular transformations of coordination cage or capsule have received much attention recently,which help elucidate this natural self-assembly behavior in biological systems.The current study describes the first supramolecular transformation of titanium-o rganic coordination capsule triggered by phenol(and H_3 PO_3).The structural alterations are accompanied by the reconstruction of 5-coordinated Ti centers to 6-coordinated ones.Meanwhile,different amounts of encapsulated phenol guest molecules can be identified,dependent on the sizes of the obtained cavities.In addition,they display much better visible light absorption and air stability than the isopropanol stabilized ones. 相似文献
976.
Serge Nicaise 《Mathematical Methods in the Applied Sciences》2013,36(7):794-813
We deal with the well‐posedness of the transient Maxwell equations in a particular class of heterogeneous isotropic chiral material modeled by the Drude–Born–Fedorov constitutive relations with different boundary conditions. A new formulation of the underlying evolution problems allows us to establish existence and uniqueness results. The selfadjointness of the curl operator multiplied by a piecewise smooth function in an appropriated Hilbert space is also proved. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
977.
978.
A new mathematical algorithm is proposed to address the essential details of vertical distributions of horizontal velocity for one‐dimensional steady open‐channel flow. This new algorithm comprises a system of weighted averaged equations developed from corresponding Reynolds equations by performing weighted average operations instead of conventional depth average operations. It is the system of weighted averaged equations, instead of the vertical grids, that allows for more hydraulic coefficients identifiable. It can be thought of as an extension of the St. Venant equations to address the vertical distributions of horizontal velocities, as well as the water surface profiles. To avoid the difficult expansion of governing partial differential equations in high order, an indirect scheme is proposed to solve hydraulic variables through their weighted average values. The governing partial differential equations are generated by using a variety of weight functions, and the weighted averages of relevant hydraulic variables are taken as the unknown independent variables to be solved first. Then, on the basis of the values and polynomial expansions of these weighted averaged velocities, a system of linear algebraic equations is generated and the unknown hydraulic variables or their coefficients are easily solved. Note that the new model is not proposed to compete with any three‐dimensional models in modeling accuracy or accommodation ability to all conditions. It just provides a valuable option to study the vertical structure of flow in open channels where only essential detail and reasonable accuracy of vertical distributions are required, and the data availability and other conditions limit the application of fully three‐dimensional models. The performance of the model is evaluated with experimental data of flows in two different flumes. It is shown that the model well predicted the velocity profiles of sections along the centerlines of these flumes with reasonable accuracy and essential details of vertical distributions of horizontal velocity. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
979.
Viorica Mariela Ungureanu 《Journal of Mathematical Analysis and Applications》2008,343(1):446-463
The aim of this paper is to give a deterministic characterization of the uniform observability property of linear differential equations with multiplicative white noise in infinite dimensions. We also investigate the properties of a class of perturbed evolution operators and we used these properties to give a new representation of the covariance operators associated to the mild solutions of the investigated stochastic differential equations. The obtained results play an important role in obtaining necessary and sufficient conditions for the stochastic uniform observability property. 相似文献
980.
Stephen Pankavich 《Mathematical Methods in the Applied Sciences》2008,31(4):375-389
A collisionless plasma is modelled by the Vlasov–Poisson system in one dimension. A fixed background of positive charge, dependent only upon velocity, is assumed and the situation in which the mobile negative ions balance the positive charge as |x| → ∞ is considered. Thus, the total positive charge and the total negative charge are infinite. In this paper, the charge density of the system is shown to be compactly supported. More importantly, both the electric field and the number density are determined explicitly for large values of |x|. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献