全文获取类型
收费全文 | 8127篇 |
免费 | 868篇 |
国内免费 | 505篇 |
专业分类
化学 | 655篇 |
晶体学 | 14篇 |
力学 | 1178篇 |
综合类 | 135篇 |
数学 | 5731篇 |
物理学 | 1787篇 |
出版年
2024年 | 6篇 |
2023年 | 86篇 |
2022年 | 87篇 |
2021年 | 123篇 |
2020年 | 233篇 |
2019年 | 244篇 |
2018年 | 224篇 |
2017年 | 271篇 |
2016年 | 266篇 |
2015年 | 182篇 |
2014年 | 353篇 |
2013年 | 997篇 |
2012年 | 341篇 |
2011年 | 460篇 |
2010年 | 388篇 |
2009年 | 481篇 |
2008年 | 492篇 |
2007年 | 533篇 |
2006年 | 447篇 |
2005年 | 440篇 |
2004年 | 371篇 |
2003年 | 377篇 |
2002年 | 326篇 |
2001年 | 258篇 |
2000年 | 225篇 |
1999年 | 203篇 |
1998年 | 184篇 |
1997年 | 148篇 |
1996年 | 135篇 |
1995年 | 101篇 |
1994年 | 92篇 |
1993年 | 66篇 |
1992年 | 59篇 |
1991年 | 59篇 |
1990年 | 33篇 |
1989年 | 23篇 |
1988年 | 25篇 |
1987年 | 15篇 |
1986年 | 6篇 |
1985年 | 28篇 |
1984年 | 15篇 |
1983年 | 9篇 |
1982年 | 12篇 |
1981年 | 16篇 |
1980年 | 9篇 |
1979年 | 10篇 |
1978年 | 13篇 |
1977年 | 13篇 |
1976年 | 6篇 |
1974年 | 4篇 |
排序方式: 共有9500条查询结果,搜索用时 78 毫秒
1.
Dr. Kyung-Seok Kang Dr. Krishnan A. Iyer Prof. Dr. Jeffrey Pyun 《Chemistry (Weinheim an der Bergstrasse, Germany)》2022,28(35):e202200115
In this concept review, the fundamental and polymerization chemistry of inverse vulcanization for the preparation of statistical and segmented sulfur copolymers, which have been actively developed and advanced in various applications over the past decade is discussed. This concept review delves into a discussion of step-growth polymerization constructs to describe the inverse vulcanization process and discuss prepolymer approaches for the synthesis of segmented sulfur polyurethanes. Furthermore, this concept review discusses the advantages of inverse vulcanization in conjunction with dynamic covalent polymerization and post-polymerization modifications to prepare segmented block copolymers with enhanced thermomechanical and flame retardant properties of these materials. 相似文献
2.
3.
《Discrete Mathematics》2021,344(12):112589
Let be the set of positive integers. For a nonempty set A of integers and every integer u, denote by the number of with such that . For a sequence S of positive integers, let be the counting function of S. The set is called a perfect difference set if for every positive integer u. In 2008, Cilleruelo and Nathanson (2008) [4] constructed dense perfect difference sets from dense Sidon sets. In this paper, as a main result, we prove that: let be an increasing function satisfying for any positive integer n, then for every Sidon set B and every function , there exists a set such that for every positive integer u and for all . 相似文献
4.
5.
In this article, we have developed an overlapping Schwarz method for a weakly coupled system of convection-diffusion equations. The method splits the original domain into two overlapping subdomains. A hybrid difference scheme is proposed in which on the boundary layer region, we use the central finite difference scheme on a uniform mesh, whereas on the nonlayer region, we use the mid-point difference scheme on a uniform mesh. It is shown that the numerical approximations converge in the maximum norm to the exact solution. We have proved that, when appropriate subdomains are used, the method produces almost second-order convergence. Furthermore, it is shown that two iterations are sufficient to achieve the expected accuracy. Numerical examples are presented to support the theoretical results. The main advantage of this method used with the proposed scheme is that it reduces iteration counts very much and easily identifies in which iteration the Schwarz iterate terminates. 相似文献
6.
Yuhua Long 《Journal of Difference Equations and Applications》2020,26(7):966-986
In the present paper, we apply the method of invariant sets of descending flow to establish a series of criteria to ensure that a second-order nonlinear functional difference equation with periodic boundary conditions possesses at least one trivial solution and three nontrivial solutions. These nontrivial solutions consist of sign-changing solutions, positive solutions and negative solutions. Moreover, as an application of our theoretical results, an example is elaborated. Our results generalize and improve some existing ones. 相似文献
7.
8.
Samala
Rathan 《国际流体数值方法杂志》2020,92(12):1927-1947
This article presents an improved fifth-order finite difference weighted essentially nonoscillatory (WENO) scheme to solve Hamilton-Jacobi equations. A new type of nonlinear weights is introduced with the construction of local smoothness indicators on each local stencil that are measured with the help of generalized undivided differences in L1-norm. A novel global smoothness measurement is also constructed with the help of local measurements from its linear combination. Numerical experiments are conducted in one- and two-dimensions to demonstrate the performance enhancement, resolution power, numerical accuracy for the proposed scheme, and compared it with the classical WENO scheme. 相似文献
9.
目前,针对空间电磁场作用有耗介质层上传输线的电磁耦合,仍缺乏有效的数值分析方法.因此,本文提出一种高效的时域混合算法,很好地解决了有耗介质层上传输线电磁耦合建模难的问题.首先,对经典传输线方程进行改进,推导了适用于有耗介质层上多导体传输线电磁耦合分析的修正传输线方程.然后,结合时域有限差分方法和相应插值技术,求解修正传输线方程,获得多导线及其端接负载上的电压和电流响应,并实现空间电磁场辐射与多导线瞬态响应的同步计算.最后,通过相应计算实例的数值模拟,与CST软件的仿真结果进行对比,验证了时域混合算法的正确性和高效性. 相似文献