首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   433篇
  免费   38篇
  国内免费   22篇
化学   295篇
晶体学   2篇
力学   25篇
综合类   14篇
数学   49篇
物理学   108篇
  2023年   3篇
  2022年   17篇
  2021年   25篇
  2020年   27篇
  2019年   22篇
  2018年   24篇
  2017年   27篇
  2016年   40篇
  2015年   10篇
  2014年   30篇
  2013年   44篇
  2012年   24篇
  2011年   22篇
  2010年   27篇
  2009年   19篇
  2008年   18篇
  2007年   14篇
  2006年   7篇
  2005年   14篇
  2004年   9篇
  2003年   8篇
  2002年   8篇
  2001年   9篇
  2000年   9篇
  1999年   6篇
  1998年   2篇
  1997年   2篇
  1996年   5篇
  1994年   3篇
  1993年   1篇
  1991年   3篇
  1986年   1篇
  1984年   1篇
  1983年   1篇
  1980年   3篇
  1979年   1篇
  1978年   1篇
  1976年   5篇
  1969年   1篇
排序方式: 共有493条查询结果,搜索用时 15 毫秒
481.
Journal of Radioanalytical and Nuclear Chemistry - The effect of natural gas use on indoor radon concentrations was studied in the dwelling of two cities in Cyprus using an AlphaGUARD radon...  相似文献   
482.
483.
Gibberellic acid (GA3) is reported to have diverse effects on hairy root cultures of many plant species; therefore, the effects of GA3 on the growth, secondary metabolite production (caffeic acid derivatives and lignin), phenylalanine ammonia lyase (PAL) activity, and free radical scavenging activity of light-grown Echinacea purpurea L. hairy roots were investigated. Eight concentrations of GA3, ranging from 0.005 to 1.0 μM, were added to shake flask cultures. The moderate GA3 concentration, 0.025 μM, resulted in the highest concentrations of cichoric acid, caftaric acid, and chlorogenic acid, as well as increased PAL activity, cell viability, and free radical scavenging activity, while higher and lower GA3 concentrations resulted in reduced levels compared to the control (lacking GA3). The moderate GA3 concentration also affected root morphogenesis; supplementation with 0.025 μM GA3 resulted in the development of thick, dense, purple-colored roots, while roots exposed to the higher and lower concentrations of GA3 were thin and off-white. This study demonstrates that supplementation with GA3 may be an excellent strategy to optimize the production of secondary metabolites from E. purpurea hairy root cultures; however, the GA3 concentration is a critical factor.  相似文献   
484.
A theoretical model is presented to study the characteristics of dust acoustic shock in a viscous, magnetized, rotating dusty plasma at both fast and slow time scales. By employing the reductive perturbation technique, the non-linear Zakharov–Kuznetsov–Burger (ZKB) equation is derived for both cases when the dust is inactive and dynamic (fast and slow time scales). Both electrons and ions are considered to follow the kappa/Cairns distribution. It is observed that in both cases, i.e. when dust is in the background and active, viscosity plays a key role in dissipation for the propagation of acoustic shock. Magnetic field and rotation are responsible for the dispersive term. Superthermality is found to affect significantly the formation of the shock wave along with viscous nature of plasma, whereas the dust charge affects the non-linear coefficient of the ZKB equation. The present investigation may be beneficial to the understanding of the rotating plasma, in particular the experiments being carried out.  相似文献   
485.
针对移动信道的特点,分析了移动通信中信源与信道独立编码的局限性和联合编码研究的必要性,列举了几种常用的联合编码技术,对联合编码技术研究现状和发展进行了详细的评述,结合Turbo码技术指出了联合编码方法是进一步优化多媒体移动通信系统性能的出路之一。  相似文献   
486.
A generalized formulation of non-commutative geometry for the Bargmann–Fock space of quantum field theory is presented. The analysis is related to the symmetry of the simplistic space and a minimal length uncertainty.  相似文献   
487.
We find the eigenfunctions of a generalized Frankl problem with the use of Bessel functions. We prove that these eigenfunctions form a Riesz basis in the space L 2(D +), where D + is the elliptic part of the domain. In addition, we prove the Riesz basis property of a trigonometric function system and the completeness of this system in the space L 2(0, π/2).  相似文献   
488.
This paper continues the research implemented in previous work of (Schreider et al. in Environ. Model. Assess. 15(4):223–238, 2010) where a game theoretic model for optimal fertilizer application in the Hopkins River catchment was formulated, implemented and solved for its optimal strategies. In that work, the authors considered farmers from this catchment as individual players whose objective is to maximize their objective functions which are constituted from two components: economic gain associated with the application of fertilizers which contain phosphorus to the soil and environmental harms associated with this application. The environmental losses are associated with the blue-green algae blooming of the coastal waterways due to phosphorus exported from upstream areas of the catchment. In the previous paper, all agents are considered as rational players and two types of equilibria were considered: fully non-cooperative Nash equilibrium and cooperative Pareto optimum solutions. Among the plethora of Pareto optima, the solution corresponding to the equally weighted individual objective functions were selected. In this paper, the cooperative game approach involving the formation of coalitions and modeling of characteristic value function will be applied and Shapley values for the players obtained. A significant contribution of this approach is the construction of a characteristic function which incorporates both the Nash and Pareto equilibria, showing that it is superadditive. It will be shown that this approach will allow each players to obtain payoffs which strictly dominate their payoffs obtained from their Nash equilibria.  相似文献   
489.
In this article, the Multiple Scales Method is used to analyze the chaotic behavior and different types of fixed points in ferroresonance of voltage transformers considering core loss. This phenomenon has nonlinear chaotic dynamics and includes subharmonic, quasi‐periodic, and also chaotic oscillations. In this article, the chaotic behavior and various ferroresonant oscillations modes of the voltage transformer is studied. This phenomenon consists of different types of bifurcations such as Period Doubling Bifurcation (PDB), Saddle Node Bifurcation (SNB), Hopf Bifurcation (HB) and chaos. The dynamic analysis of ferroresonant circuit is based on bifurcation theory. The bifurcation and phase plane diagrams are illustrated using a continuous method and linear and nonlinear models of core loss. To analyze ferroresonance phenomenon, the Lyapunov exponents are calculated via Multiple Scales Method obtaining Feigenbaum numbers. The bifurcation diagrams illustrate the variation of the control parameter. Therefore, the chaos is created and increased in the system. © 2013 Wiley Periodicals, Inc. Complexity 18: 34‐45, 2013  相似文献   
490.
设计了一种利用红外遥控进行远距离音视频切换的系统,阐述了该系统的工作原理及其实现方法.实用表明,该系统在各种监控领域中采用光耦技术,增大了抗干扰能力,减少了施工难度,具有很好的实用价值  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号