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   1911篇
  免费   446篇
  国内免费   149篇
化学   418篇
晶体学   6篇
力学   59篇
综合类   171篇
数学   796篇
物理学   1056篇
  2024年   4篇
  2023年   44篇
  2022年   65篇
  2021年   81篇
  2020年   77篇
  2019年   81篇
  2018年   51篇
  2017年   62篇
  2016年   75篇
  2015年   63篇
  2014年   122篇
  2013年   134篇
  2012年   102篇
  2011年   111篇
  2010年   104篇
  2009年   138篇
  2008年   130篇
  2007年   122篇
  2006年   122篇
  2005年   102篇
  2004年   77篇
  2003年   85篇
  2002年   77篇
  2001年   56篇
  2000年   47篇
  1999年   47篇
  1998年   41篇
  1997年   35篇
  1996年   33篇
  1995年   52篇
  1994年   27篇
  1993年   27篇
  1992年   18篇
  1991年   9篇
  1990年   14篇
  1989年   13篇
  1988年   8篇
  1987年   8篇
  1986年   5篇
  1985年   8篇
  1984年   3篇
  1983年   5篇
  1982年   2篇
  1981年   2篇
  1980年   5篇
  1979年   2篇
  1976年   2篇
  1975年   2篇
  1974年   3篇
  1972年   1篇
排序方式: 共有2506条查询结果,搜索用时 15 毫秒
111.
Chunzao Wang 《中国物理 B》2022,31(4):47304-047304
A lateral insulated gate bipolar transistor (LIGBT) based on silicon-on-insulator (SOI) structure is proposed and investigated. This device features a compound dielectric buried layer (CDBL) and an assistant-depletion trench (ADT). The CDBL is employed to introduce two high electric field peaks that optimize the electric field distributions and that, under the same breakdown voltage (BV) condition, allow the CDBL to acquire a drift region of shorter length and a smaller number of stored carriers. Reducing their numbers helps in fast-switching. Furthermore, the ADT contributes to the rapid extraction of the stored carriers from the drift region as well as the formation of an additional heat-flow channel. The simulation results show that the BV of the proposed LIGBT is increased by 113% compared with the conventional SOI LIGBT of the same length LD. Contrastingly, the length of the drift region of the proposed device (11.2 μ) is about one third that of a traditional device (33 μ) with the same BV of 141 V. Therefore, the turn-off loss (EOFF) of the CDBL SOI LIGBT is decreased by 88.7% compared with a conventional SOI LIGBT when the forward voltage drop (VF) is 1.64 V. Moreover, the short-circuit failure time of the proposed device is 45% longer than that of the conventional SOI LIGBT. Therefor, the proposed CDBL SOI LIGBT exhibits a better VF-EOFF tradeoff and an improved short-circuit robustness.  相似文献   
112.
Interval logics are very expressive temporal formalisms, but reasoning with them is often undecidable or has high computational complexity. As a result, a vast number of approaches limiting their expressive power—in order to obtain better computational behaviour—have been introduced. Unfortunately, due to such restrictions, interval logics often lose referentiality, that is, the capacity to refer to specific time intervals, which is crucial for temporal representation and reasoning. The computational price that needs to be paid in order to regain referentiality is not well studied and our research aims to fill this gap. In particular we study the main interval temporal logic, called the Halpern-Shoham logic, and its low complexity modifications. To regain referentiality in these modifications, we extend the language with the hybrid machinery—nominals and satisfaction operators—and classify the obtained logics according to their computational complexity. We show that such a hybridisation often makes tractable logics intractable but not undecidable. This allows us to construct hybrid interval temporal logics which are referential as well as maintain a good compromise between expressiveness and complexity; it makes them valuable formalisms for temporal knowledge representation. We also introduce a class of models which, due to a specific interplay between the interpretation of modal operators and a structure of time, makes reasoning in interval logics computationally hard even in the absence of the hybrid machinery.  相似文献   
113.
提出一种生成模糊蕴涵的新方法,即通过一个或多个选定的模糊蕴涵作多重迭代生成新的模糊蕴涵,称为多重模糊蕴涵.从选定的模糊蕴涵出发,根据不同的迭代次数,分别证明迭代结果仍为模糊蕴涵.进一步,分析当选定的模糊蕴涵具有某种性质时,所生成的多重模糊蕴涵是否仍保持这些性质.还对选定的模糊蕴涵分别为(S,N)-蕴涵和R-蕴涵这两种重要情形,进行更深入的分析.这些结果将为模糊蕴涵在控制及决策等领域的应用提供支持.  相似文献   
114.
郭静波  徐新智  史启航  胡铁华 《物理学报》2013,62(11):110508-110508
提出了基于现场可编程门阵列 (FPGA) 技术的混沌直接序列扩频信号盲解调的硬件电路实现方法. 设计了混沌直接序列扩频信号发射机与接收机. 发射机可产生10种不同的混沌直接序列扩频信号. 为方便接收机的硬件电路实现, 对无先导卡尔曼滤波混沌拟合盲解调算法进行了简化, 在简化模型的基础上设计了接收机硬件结构. 提出了一种动态调整偏移因子的新方法, 使接收机能实时适应混沌映射的变化. 通过高斯白噪声信道及多径信道条件下的盲解调实验, 验证了盲解调算法硬件实现的抗噪声与抗多径性能, 以及对10种不同的混沌直接序列扩频信号的自适应破译效果. 关键词: FPGA 混沌直接序列扩频通信 盲解调  相似文献   
115.
王斌  张鹤鸣  胡辉勇  张玉明  宋建军  周春宇  李妤晨 《物理学报》2013,62(21):218502-218502
结合了“栅极工程”和“应变工程”二者的优点, 异质多晶SiGe栅应变Si MOSFET, 通过沿沟道方向使用不同功函数的多晶SiGe材料, 在应变的基础上进一步提高了MOSFET的性能. 本文结合其结构模型, 以应变Si NMOSFET为例, 建立了强反型时的准二维表面势模型, 并进一步获得了其阈值电压模型以及沟道电流的物理模型. 应用MATLAB对该器件模型进行了分析, 讨论了异质多晶SiGe栅功函数及栅长度、衬底SiGe中Ge组分等参数对器件阈值电压、沟道电流的影响, 获得了最优化的异质栅结构. 模型所得结果与仿真结果及相关文献给出的结论一致, 证明了该模型的正确性. 该研究为异质多晶SiGe栅应变Si MOSFET的设计制造提供了有价值的参考. 关键词: 异质多晶SiGe栅 应变Si NMOSFET 表面势 沟道电流  相似文献   
116.
Pedestrian speed in a transfer station corridor is faster than usual and sometimes running can be found among some of them. In this paper, pedestrians are divided into two categories. The first one is aggressive, and the other is conservative. Aggressive pedestrians weaving their way through crowd in the corridor are the study object of this paper. During recent decades, much attention has been paid to the pedestrians’ behavior, such as overtaking (also deceleration) and collision avoidance, and that continues in this paper. After sufficiently analyzing the characteristics of pedestrian flow in transfer station corridor, a cell-based model is presented in this paper, including the acceleration (also deceleration) and overtaking analysis. Acceleration (also deceleration) in a corridor is fixed according to Newton’s Law and then speed calculated with a kinematic formula is discretized into cells based on the fuzzy logic. After the speed is updated, overtaking is analyzed based on updated speed and force explicitly, compared to rule-based models, which herein we call implicit ones. During the analysis of overtaking, a threshold value to determine the overtaking direction is introduced. Actually, model in this paper is a two-step one. The first step is to update speed, which is the cells the pedestrian can move in one time interval and the other is to analyze the overtaking. Finally, a comparison between the rule-based cellular automata, the model in this paper and data in HCM 2000 is made to demonstrate our model can be used to achieve reasonable simulation of acceleration (also deceleration) and overtaking among pedestrians.  相似文献   
117.
陈小鹏  李斌 《发光学报》2013,34(9):1108-1112
利用次氯酸根(ClO-)的氧化性质和Cu+与Cu2+不同的配位性质,一种高效的可用于探测ClO-的铜离子化合物CS1被合成出来。通过吸收和发射光谱系统地研究了CS1对ClO-的传感性能。结果表明,在Cu+存在条件下,CS1的光谱强烈受到OCl-影响:最大吸收峰从396 nm红移到545 nm(Δλ=149 nm);520nm处的荧光强度降低近25倍。以Cu+和ClO-为输入信号,以470 nm和396 nm吸收峰比值(A470/A396)为输出信号,构建了一个基于CS1的AND逻辑门,并且可以用乙二胺四乙酸二钠盐(EDTA)对其进行简单重置。  相似文献   
118.
The current form of Web provides numerous product resources available to users. Users can rely on intelligent agents for purchase actions. These actions are taken in specific environments such as Electronic Markets (EMs). In this paper, we study the interaction process between buyers and sellers and focus on the buyer side. Each buyer has the opportunity to interact with a number of sellers trying to buy the most appropriate products. This interaction can be modeled as a finite horizon Bargaining Game (BG). In this game, players have opposite goals concerning the product price. We adopt a number of techniques in the buyer side trying to give the appropriate level of efficiency in the buyer decision process. The buyer uses a prediction mechanism in combination with the use of Fuzzy Logic (FL) theory in order to be able to predict the upcoming seller proposal and, thus, understand the seller pricing policy. Based on this, he/she can adapt his/her behavior when trying to purchase products. The buyer adaptation mechanism produces the belief that the buyer has about the seller pricing policy and a parameter that indicates his/her own pricing policy which yields the buyer offers in the upcoming rounds. Moreover, the buyer is based on FL system that derives the appropriate actions at every round of the BG. Our results show that the combination of Fuzzy Logic (FL) with the above-mentioned techniques provides an efficient decision mechanism in the buyer side that in specific scenarios outperforms an optimal stopping model.  相似文献   
119.
Pr值逻辑函数相关免疫的等价判别条件   总被引:2,自引:0,他引:2  
杨锐  曾本胜  李世取 《应用数学》2006,19(1):139-144
本文首先基于环Zpr中的元的padic分解并结合概率论的思想,给出了pr值随机变量的分解性质及pr值随机变量独立性的等价描述,然后在对pr值逻辑函数及其变元都进行padic分解的基础上,直接通过p值逻辑函数的Chrestenson谱给出了padic分解意义下pr值逻辑函数k阶相关免疫的线性组合引理和谱判别定理.  相似文献   
120.
This paper proposes a scheme for realization of a three-qubit Toffoli gate operation using three four-level atoms by a selective atom--field interaction in a cavity quantum electrodynamics system. In the proposed protocol, the quantum information is encoded on the stable ground states of atoms, and atomic spontaneous emission is negligible as the large atom--cavity detuning effectively suppresses the spontaneous decay of the atoms. The influence of the dissipation on fidelity and success probability of the three-qubit Toffoli gate is also discussed. The scheme can also be applied to realize an N-qubit Toffoli gate and the interaction time required does not rise with increasing the number of qubits.  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