全文获取类型
收费全文 | 2558篇 |
免费 | 489篇 |
国内免费 | 185篇 |
专业分类
化学 | 145篇 |
晶体学 | 3篇 |
力学 | 153篇 |
综合类 | 28篇 |
数学 | 2025篇 |
物理学 | 878篇 |
出版年
2024年 | 3篇 |
2023年 | 38篇 |
2022年 | 52篇 |
2021年 | 60篇 |
2020年 | 39篇 |
2019年 | 62篇 |
2018年 | 54篇 |
2017年 | 66篇 |
2016年 | 90篇 |
2015年 | 64篇 |
2014年 | 132篇 |
2013年 | 230篇 |
2012年 | 120篇 |
2011年 | 173篇 |
2010年 | 151篇 |
2009年 | 197篇 |
2008年 | 205篇 |
2007年 | 215篇 |
2006年 | 190篇 |
2005年 | 135篇 |
2004年 | 130篇 |
2003年 | 139篇 |
2002年 | 78篇 |
2001年 | 91篇 |
2000年 | 84篇 |
1999年 | 58篇 |
1998年 | 52篇 |
1997年 | 52篇 |
1996年 | 50篇 |
1995年 | 30篇 |
1994年 | 39篇 |
1993年 | 18篇 |
1992年 | 15篇 |
1991年 | 15篇 |
1990年 | 10篇 |
1989年 | 9篇 |
1988年 | 14篇 |
1987年 | 8篇 |
1986年 | 7篇 |
1985年 | 6篇 |
1984年 | 9篇 |
1983年 | 7篇 |
1982年 | 7篇 |
1981年 | 2篇 |
1980年 | 6篇 |
1979年 | 6篇 |
1978年 | 2篇 |
1977年 | 5篇 |
1976年 | 3篇 |
1972年 | 1篇 |
排序方式: 共有3232条查询结果,搜索用时 15 毫秒
141.
In this paper, a chemostat model with variable yield and impulsive state feedback control is considered. We obtain sufficient conditions of the globally asymptotical stability of the system without impulsive state feedback control. We also obtain that the system with impulsive state feedback control has periodic solution of order one. Sufficient conditions for existence and stability of periodic solution of order one are given. In some cases, it is possible that the system exists periodic solution of order two. Our results show that the control measure is effective and reliable. 相似文献
142.
《Journal of computational and graphical statistics》2013,22(2):185-205
The use of Gibbs samplers driven by improper posteriors has been a controversial issue in the statistics literature over the last few years. It has recently been demonstrated that it is possible to make valid statistical inferences through such Gibbs samplers. Furthermore, theoretical and empirical evidence has been given to support the idea that there are actually computational advantages to using these nonpositive recurrent Markov chains rather than more standard positive recurrent chains. These results provide motivation for a general study of the behavior of the Gibbs Markov chain when it is not positive recurrent. This article concerns stability relationships among the two-variable Gibbs sampler and its subchains. We show that these three Markov chains always share the same stability; that is, they are either all positive recurrent, all null recurrent, or all transient. In addition, we establish general results concerning the ways in which positive recurrent Markov chains can arise from null recurrent and transient Gibbs chains. Six examples of varying complexity are used to illustrate the results. 相似文献
143.
144.
State tomography on qubit pairs is routinely carried out by measuring the two qubits separately, while one expects a higher efficiency from tomography with highly symmetric joint measurements of both qubits. Our numerical study of simulated experiments does not support such expectations. 相似文献
145.
We present an improved immersed boundary method for simulating incompressible viscous flow around an arbitrarily moving body on a fixed computational grid. To achieve a large Courant–Friedrichs–Lewy number and to transfer quantities between Eulerian and Lagrangian domains effectively, we combined the feedback forcing scheme of the virtual boundary method with Peskin's regularized delta function approach. Stability analysis of the proposed method was carried out for various types of regularized delta functions. The stability regime of the 4‐point regularized delta function was much wider than that of the 2‐point delta function. An optimum regime of the feedback forcing is suggested on the basis of the analysis of stability limits and feedback forcing gains. The proposed method was implemented in a finite‐difference and fractional‐step context. The proposed method was tested on several flow problems, including the flow past a stationary cylinder, inline oscillation of a cylinder in a quiescent fluid, and transverse oscillation of a circular cylinder in a free‐stream. The findings were in excellent agreement with previous numerical and experimental results. Copyright © 2008 John Wiley & Sons, Ltd. 相似文献
146.
In this paper, we consider the general nonautonomous single-species Kolmogorov type system with delay and feedback controls. Sufficient conditions for the permanence of species are established. Our results generalize some known results. 相似文献
147.
We report on a result of upper-lower solutions for nonlinear elliptic systems without the assumption of quasi-monotonicity. An application is described involving the existence of positive steady states of a certain interaction system arising in biology and medical sciences. 相似文献
148.
Biju PhilipK. Sreekumar 《European Polymer Journal》2002,38(12):2441-2447
A polyamic acid containing 2,2′-dinitrodiphenylmethane segments in the main chain was synthesized from 4,4′-diamino-2,2′-dinitrodiphenylmethane and pyrromellitic dianhydride. Irradiation of the polyamic acid was done in solution (in a protic solvent, isopropanol, in isopropanol in the presence of a triplet exciter, benzophenone and in acidified isopropanol) and as thin film. The irradiations were done in an immersion type photoreactor using a 125 W high-pressure mercury vapour lamp. The average molecular weights of the polymers were determined by gel permeation chromatography. The polydispersity index of the polyamic acid and the photoproduct showed the absence of photodegradation. The photoproducts were identified by comparing the spectra of polymer photoproducts with that of low molecular weight 2,2′-dinitrodiphenylmethane derivatives under identical conditions. A possible mechanism for the phototransformations is suggested. Evaluation of photoresist behaviour of the polyamic acid was also done. 相似文献
149.
带有Bernoulli反馈的多级适应性休假的Geo/G/1排队系统分析 总被引:2,自引:0,他引:2
考虑带有Bernoulli反馈的多级适应性休假的Geo/G/1离散时间排队系统.通过引入服务员忙期和使用一种简洁的分解方法,讨论了队长的瞬时分布,得到了在任意时刻n队长为j的概率关于时刻n的z-变换的递推式,及队长平稳分布的递推式,且证明了稳态队长的随机分解性质.最后,给出了在特殊情形下相应的一些结果和数值计算实例. 相似文献
150.
Christian Gottlieb 《代数通讯》2013,41(8):3087-3097
Abstract Although it is well known that the growth of Thompson's group F is exponential, the exact growth function is still unknown. Elements of its submonoid of positive words can be described using a binary rooted tree, whose norm can be computed assigning weights to each caret. Combining this fact with a combinatorial argument, the growth function of the submonoid is computed and thus providing a first step in the computation of the growth function of the group, as well as a lower bound for the growth rate for the group. 相似文献