全文获取类型
收费全文 | 92244篇 |
免费 | 7082篇 |
国内免费 | 5416篇 |
专业分类
化学 | 23507篇 |
晶体学 | 1758篇 |
力学 | 5511篇 |
综合类 | 403篇 |
数学 | 28575篇 |
物理学 | 44988篇 |
出版年
2023年 | 307篇 |
2022年 | 241篇 |
2021年 | 469篇 |
2020年 | 1000篇 |
2019年 | 1312篇 |
2018年 | 1248篇 |
2017年 | 959篇 |
2016年 | 704篇 |
2015年 | 651篇 |
2014年 | 1527篇 |
2013年 | 3162篇 |
2012年 | 1555篇 |
2011年 | 2425篇 |
2010年 | 2925篇 |
2009年 | 7665篇 |
2008年 | 8748篇 |
2007年 | 7165篇 |
2006年 | 6535篇 |
2005年 | 4498篇 |
2004年 | 4206篇 |
2003年 | 4472篇 |
2002年 | 5165篇 |
2001年 | 3986篇 |
2000年 | 3825篇 |
1999年 | 3602篇 |
1998年 | 2980篇 |
1997年 | 2150篇 |
1996年 | 1913篇 |
1995年 | 2334篇 |
1994年 | 2264篇 |
1993年 | 1712篇 |
1992年 | 1188篇 |
1991年 | 906篇 |
1990年 | 739篇 |
1989年 | 655篇 |
1988年 | 599篇 |
1987年 | 443篇 |
1985年 | 997篇 |
1984年 | 713篇 |
1983年 | 535篇 |
1982年 | 697篇 |
1981年 | 851篇 |
1980年 | 776篇 |
1979年 | 612篇 |
1978年 | 635篇 |
1977年 | 571篇 |
1976年 | 567篇 |
1975年 | 324篇 |
1974年 | 361篇 |
1973年 | 468篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
利用hirota双线性法,得到(3+1)维孤子方程、(3+1)维KP-Boussinesq方程、(2+1)维修正Caudrey-Dodd-Gibbon-Kotera-S awada方程、Hirota-Satsuma浅水波方程的精确解,并做出一部分解的图形,进一步研究解的结构和性质. 相似文献
2.
On Regularization of a Source Identification Problem in a Parabolic PDE and its Finite Dimensional Analysis 下载免费PDF全文
Subhankar Mondal & M. Thamban Nair 《偏微分方程(英文版)》2021,34(3):240-257
We consider the inverse problem of identifying a general source term, which is a function of both time variable and the spatial variable, in a parabolic PDE from the knowledge of boundary measurements of the solution on some portion of the lateral boundary. We transform this inverse problem into a problem of solving a compact linear operator equation. For the regularization of the operator equation with noisy data, we employ the standard Tikhonov regularization, and its finite dimensional realization is done using a discretization procedure involving the space $L^2(0,\tau;L^2(Ω))$. For illustrating the specification of an a priori source condition, we have explicitly obtained the range space of the adjoint of the operator involved in the operator equation. 相似文献
3.
We address the problem of telegraphic transport in several dimensions. We review the derivation of two and three dimensional telegrapher’s equations—as well as their fractional generalizations—from microscopic random walk models for transport (normal and anomalous). We also present new results on solutions of the higher dimensional fractional equations. 相似文献
4.
《Annales de l'Institut Henri Poincaré (C) Analyse Non Linéaire》2021,38(6):1681-1702
We prove the existence of a -normalized solitary wave solution for the Maxwell-Dirac equations in (3+1)-Minkowski space. In addition, for the Coulomb-Dirac model, describing fermions with attractive Coulomb interactions in the mean-field limit, we prove the existence of the (positive) energy minimizer. 相似文献
5.
We present a model for the silicosis disease mechanism following the original proposal by Tran et al. (1995), as modified recently by da Costa et al. (2020). The model consists in an infinite ordinary differential equation system of coagulation–fragmentation–death type. Results of existence, uniqueness, continuous dependence on the initial data and differentiability of solutions are proved for the initial value problem. 相似文献
6.
Hacer Bilgin Ellidokuzoğlu & Serkan Demiriz 《分析论及其应用》2021,37(4):557-571
Başar and Braha [1], introduced the sequence spaces $\breve{\ell}_\infty$, $\breve{c}$ and $\breve{c}_0$ of Euler-Cesáro bounded, convergent and null difference sequences and studied their some properties. Then, in [2], we introduced the sequence spaces ${[\ell_\infty]}_{e.r}, {[c]}_{e.r}$ and ${[c_0]}_{e.r}$ of Euler-Riesz bounded, convergent and null difference sequences by using the composition of the Euler mean $E_1$ and Riesz mean $R_q$ with backward difference operator $\Delta$. The main purpose of this study is to introduce the sequence space ${[\ell_p]}_{e.r}$ of Euler-Riesz $p-$absolutely convergent series, where $1 \leq p <\infty$, difference sequences by using the composition of the Euler mean $E_1$ and Riesz mean $R_q$ with backward difference operator $\Delta$. Furthermore, the inclusion $\ell_p\subset{[\ell_p]}_{e.r}$ hold, the basis of the sequence space ${[\ell_p]}_{e.r}$ is constructed and $\alpha-$, $\beta-$ and $\gamma-$duals of the space are determined. Finally, the classes of matrix transformations from the ${[\ell_p]}_{e.r}$ Euler-Riesz difference sequence space to the spaces $\ell_\infty, c$ and $c_0$ are characterized. We devote the final section of the paper to examine some geometric properties of the space ${[\ell_p]}_{e.r}$. 相似文献
7.
Presenting the devices invented by Toepler, Holtz, Wimshurst, and Wommelsdorf, the history of the influence machines, the progress made, and the remaining deficits are discussed. The theoretical considerations published in the literature lack generalizable statements on the efficiency. Based on R. W. Pohl's model (1927), an elementary analysis is made, with the result that the upper limit of the theoretically achievable efficiency of influence machines is only 50%. 相似文献
8.
We investigate and concentrate on new infinitesimal generators of Lie symmetries for an extended (2+ 1)-dimensional Calogero-Bogoyavlenskii-Schif (eCBS) equation using the commutator table which results in a system of nonlinear ordinary differential equations (ODEs) which can be manually solved. Through two stages of Lie symmetry reductions, the eCBS equation is reduced to non-solvable nonlinear ODEs using different combinations of optimal Lie vectors. Using the integration method and the Riccati and Bernoulli equation methods, we investigate new analytical solutions to those ODEs. Back substituting to the original variables generates new solutions to the eCBS equation. These results are simulated through three- and two-dimensional plots. 相似文献
9.
M. Amar D. Andreucci R. Gianni C. Timofte 《Journal of Mathematical Analysis and Applications》2021,493(2):124533
We prove a well-posedness result for two pseudo-parabolic problems, which can be seen as two models for the same electrical conduction phenomenon in heterogeneous media, neglecting the magnetic field. One of the problems is the concentration limit of the other one, when the thickness of the dielectric inclusions goes to zero. The concentrated problem involves a transmission condition through interfaces, which is mediated by a suitable Laplace-Beltrami type equation. 相似文献
10.
Youpei Zhang Limin Zhang Lixi Wen 《Journal of Mathematical Analysis and Applications》2021,493(2):124535
We are concerned with qualitative analysis of weak solutions for a class of magnetic Laplace equations with lack of compactness. By variational arguments, we establish related nonexistence, existence and multiplicity results. 相似文献