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   430篇
  免费   16篇
  国内免费   2篇
化学   297篇
晶体学   1篇
力学   3篇
数学   59篇
物理学   61篇
无线电   27篇
  2023年   5篇
  2022年   15篇
  2021年   10篇
  2020年   13篇
  2019年   11篇
  2018年   8篇
  2017年   3篇
  2016年   13篇
  2015年   16篇
  2014年   22篇
  2013年   42篇
  2012年   49篇
  2011年   52篇
  2010年   18篇
  2009年   19篇
  2008年   23篇
  2007年   20篇
  2006年   25篇
  2005年   15篇
  2004年   13篇
  2003年   3篇
  2002年   18篇
  2000年   1篇
  1997年   4篇
  1996年   1篇
  1995年   3篇
  1994年   2篇
  1992年   1篇
  1990年   2篇
  1989年   1篇
  1988年   2篇
  1987年   1篇
  1986年   1篇
  1985年   1篇
  1984年   1篇
  1983年   1篇
  1982年   1篇
  1981年   1篇
  1980年   1篇
  1979年   1篇
  1978年   2篇
  1977年   1篇
  1974年   1篇
  1973年   2篇
  1971年   1篇
  1956年   1篇
  1935年   1篇
排序方式: 共有448条查询结果,搜索用时 15 毫秒
41.
This paper deals with the dielectric barrier discharge (DBD) ion source composed of the outer cylindrical dielectric tube and the inner grounded metallic tube electrode. The sample gas is supplied through the inner ceramic tube. In this ion source, the DBD plasma is localized in the DBD tube so that the sample gases can be ionized just outside of the ceramic tube by the DBD excited helium gas without being exposed in the plasma jet. Besides, ambient air does not take part in the ionization of the sample vapor because ionization takes place inside the DBD ion source. Thus, this method is totally free from contaminants in ambient air. It was found that this ion source is capable of soft, high-sensitivity, and reproducible ionization. Application of this technique to the analysis of methamphetamine, carbaryl and basil leaf was given.  相似文献   
42.
In a coded self‐assembly, a simple code is written in the molecule, which self‐assembles the molecules into a fractal like structure, which acts as a seed for the next step. As the molecule turns into a complex seed, the code transforms into another form and several seeds self‐assemble into another structure, which acts as a seed for the next step. Until now, this technology was considered as a prerogative of nature. Here, a dendritic network is used to write a basic code by synthetically attaching 32 molecular rotors and doping two controller molecules in its cavity. The code live, which is an energy transmission path in the molecule, is imaged. When the energy transmission path or code is triggered, a series of products generate one after another spontaneously. Two examples are: i) dendritic seed (5–6 nm)→paired nanowire (≈12 nm)→nanowire (≈200 nm)→microwire (500 nm)→wire like rod (1–2 μm)→jelly→rectangular sheet (5 μm). ii) dendritic seed→nano‐sphere (20 nm)→micro‐sphere (500 nm)→large balls(1 μm)→oval shape rod (5–10 μm)→Y, L or T shaped rod assembly. The energy level interactions are tracked using spectroscopy how exactly a directed energy transfer code generates multi‐step synthesis from nano to the visible scale.  相似文献   
43.
We study a zero sum differential game of fixed duration in a separable Hilbert space. We prove a minimax principle and establish the equivalence between the dynamic programming principle and the existence of a saddle point equilibrium. We also prove sufficient conditions for optimality.  相似文献   
44.
A base free one-pot conversion of azides to N,N-dialkylamine is described. A two-step reaction pathway has been postulated invoking the intermediacy of stannaimine. This new carbon-nitrogen bond formation strategy adds to the repertoire of tin(II) chemistry.  相似文献   
45.
46.
The commutativity degree of a finite group is the probability that two arbitrarily chosen group elements commute. This notion has been generalized in a number of ways. The object of this article is to study yet another generalization of the same notion, which further extends some of the existing generalizations.  相似文献   
47.
The problem of ergodic control of a reflecting diffusion in a compact domain is analysed under the condition of partial degeneracy, i.e. when its transition kernel after some time is absolutely continuous with respect to the Lebesgue measure on a part of the state space. Existence of a value function and a “martingale dynamic programming principle” are established by mapping the problem to a discrete time control problem. Implications for existence of optimal controls are derived.  相似文献   
48.
In this article, we address stochastic differential games of mixed type with both control and stopping times. Under standard assumptions, we show that the value of the game can be characterized as the unique viscosity solution of corresponding Hamilton-Jacobi-Isaacs (HJI) variational inequalities.  相似文献   
49.
We address risk minimizing option pricing in a regime switching market where the floating interest rate depends on a finite state Markov process. The growth rate and the volatility of the stock also depend on the Markov process. Using the minimal martingale measure, we show that the locally risk minimizing prices for certain exotic options satisfy a system of Black-Scholes partial differential equations with appropriate boundary conditions. We find the corresponding hedging strategies and the residual risk. We develop suitable numerical methods to compute option prices.  相似文献   
50.
In this article, a genetic evolutionary algorithm is proposed for efficient allocation of wavelength converters in WDM optical networks. Since wavelength converters are expensive, it is desirable that each node in WDM optical networks uses a minimum number of wavelength converters to achieve a near-ideal performance. The searching capability of genetic evolutionary algorithm has been exploited for this purpose. The distinguished feature of the proposed approach lies in handling the conflicting circumstances during allocation of wavelength converters considering various practical aspects (e.g., spatial problem, connectivity of a node with other nodes) rather than arbitrarily to possibly improve the overall blocking performance of WDM optical networks. The proposed algorithm is compared with a previous approach to establish its effectiveness and the results demonstrate the ability of the proposed algorithm to efficiently solve the problem of Optimal Wavelength Converters Allocation (OWCA) in practical WDM optical networks.
Mrinal K. NaskarEmail:
  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