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   247篇
  免费   11篇
  国内免费   15篇
化学   68篇
力学   16篇
数学   98篇
物理学   91篇
  2024年   2篇
  2023年   10篇
  2022年   16篇
  2021年   9篇
  2020年   10篇
  2019年   3篇
  2018年   11篇
  2017年   10篇
  2016年   8篇
  2015年   9篇
  2014年   12篇
  2013年   34篇
  2012年   12篇
  2011年   20篇
  2010年   14篇
  2009年   15篇
  2008年   7篇
  2007年   16篇
  2006年   5篇
  2005年   7篇
  2004年   4篇
  2003年   2篇
  2002年   6篇
  2001年   2篇
  2000年   5篇
  1999年   2篇
  1998年   3篇
  1997年   2篇
  1996年   1篇
  1995年   1篇
  1994年   3篇
  1993年   4篇
  1990年   2篇
  1989年   1篇
  1988年   3篇
  1987年   1篇
  1986年   1篇
排序方式: 共有273条查询结果,搜索用时 31 毫秒
91.
采用分子动力学方法研究了三种水溶剂环境(即介电常数模型、部分溶剂化模型和全溶剂化模型)中牛胰蛋白酶抑制剂(BPTI)在金表面上的吸附效应. 结果表明BPTI在介电常数模型中会发生快而强的吸附作用并导致蛋白质结构发生大的结构偏差、明显的沿金表面的平铺展开、二级结构的快速消失、更多的原子出现在与金表面强相互作用的区域. 与介电常数模型相比,部分溶剂化模型中蛋白质与金表面间的显含水分子削弱了金的吸附作用,使得吸附速度和结构的变化程度减弱,但金吸附导致的蛋白质紧密水化层的损失仍然使得它的结构发生明显的变化. 蛋白质在全溶剂化的体系中吸附速度和程度是最慢最弱的,结构变化最小并能发生一定程度的旋转来寻找合适的吸附  相似文献   
92.
A new hardware-friendly mathematical method for realizing low-complexity universal Adder cells as well as its efficient hardware implementations is proposed in this paper. This method can be used in binary logic, Multiple-Valued Logic (MVL) and specifically digital fuzzy systems. The proposed mathematical method can be implemented in both voltage and current modes. The voltage-mode hardware implementation is very simple and is based on input capacitors and MVL or analog inverters and buffers. In addition, the current-mode hardware implementation leads to simple and efficient structures for digital fuzzy systems. Simulations are carried out for ternary logic as well as for digital fuzzy logic with high precision by using 180 nm standard CMOS technology and at 1.8 V supply voltage. Simulation results demonstrate that the proposed designs have excellent functionality and are very suitable for implementing MVL and fuzzy arithmetic circuits.  相似文献   
93.
对全光谱原子发射光谱法的特点和应用以及其基本原理作了较详细的介绍,引用文献24篇。  相似文献   
94.
This paper considers an unmanned aerial vehicle (UAV)-assisted mobile edge computing (MEC) system, in which the intelligent reflecting surface (IRS) is applied to enhance the performance of the wireless transmission. The role of the UAV is twofold: (1) It is equipped with a MEC server and receives computing tasks from ground users and IRS at the same time; (2) It sends interference signals to counter the potential eavesdropper. Here, the UAV is working as a full duplex equipment, i.e., sending and receiving meanwhile. We comprehensively considered the flight speed constraint of the UAV, the total mission data constraint and the minimum security rate constraint of multiple users on the ground. The phase matrix constraints of IRS are also considered. Our system is dedicated to maximizing the efficiency of secure computing. The formulated problem is highly non-convex, we consider to propose an alternative optimization algorithm. The simulation results show that the proposed scheme not only achieves higher safe computing efficiency, but also has better performance in terms of energy consumption and security rate.  相似文献   
95.
In this article, a joint resource allocation of power, time, and sub-channels that minimizes the total energy consumption of users for Hybrid NOMA MEC Offloading is proposed. By formulating and solving the joint optimization problem, first we propose a novel optimal Hybrid NOMA scheme referred to as Switched Hybrid NOMA (SH-NOMA) for power and time allocation. Subsequently, we address sub-channel allocation as a three-dimensional assignment problem, and propose the Total-Reward Exchange Stable (TES) algorithm to solve it. Analytically, we show that SH-NOMA is more energy efficient than the Hybrid NOMA scheme in the literature and that the TES algorithm converges to a solution with less energy consumption than the widely used two-sided exchange stable algorithm. Finally, via simulations we demonstrate that the proposed methods outperform the results in the literature.  相似文献   
96.
Computation offloading in mobile edge computing (MEC) systems emerges as a novel paradigm of supporting various resource-intensive applications. However, the potential capabilities of MEC cannot be fully unleashed when the communication links are blocked by obstacles. This paper investigates a double-reconfigurable-intelligent-surfaces (RISs) assisted MEC system. To efficiently utilize the limited frequency resource, the users can partially offload their computational tasks to the MEC server deployed at base station (BS) by adopting non-orthogonal multiple access (NOMA) protocol. We aim to minimize the energy consumption of users with limited resource by jointly optimizing the transmit power of users, the offloading fraction of users and the phase-shifts of RISs. Since the problem is non-convex with highly coupled variables, the block coordinate descent (BCD) method is leveraged to alternatively optimize the decomposed four subproblems. Specifically, we invoke successive convex approximation for low complexity (SCALE) and Dinkelbach technique to tackle the fractional programming of power optimization. Then the offloading fraction is obtained by closed-form solution. Further, we leverage semidefinite relaxation (SDR) and bisection method to address the phase-shifts design of double RISs. Finally, numerical results illustrate that the proposed double-RIS assisted NOMA scheme is capable of efficiently reducing the energy consumption and achieves significant performance gain over the benchmark schemes.  相似文献   
97.
98.
Let P n and T n be the partial transformation and the full transformation semigroups on the set {1,…, n}, respectively. In this paper we find necessary and sufficient conditions for any set of partial transformations of height r in the subsemigroup PK(n, r) = {α ∈P n : |im (α)| ≤r} of P n to be a (minimal) generating set of PK(n, r); and similarly, for any set of full transformations of height r in the subsemigroup K(n, r) = {α ∈T n : |im (α)| ≤r} of T n to be a (minimal) generating set of K(n, r) for 2 ≤ r ≤ n ? 1.  相似文献   
99.
100.
Penalized splines, or P-splines, are regression splines fit by least-squares with a roughness penalty.P-splines have much in common with smoothing splines, but the type of penalty used with a P-spline is somewhat more general than for a smoothing spline. Also, the number and location of the knots of a P-spline is not fixed as with a smoothing spline. Generally, the knots of a P-spline are at fixed quantiles of the independent variable and the only tuning parameters to choose are the number of knots and the penalty parameter. In this article, the effects of the number of knots on the performance of P-splines are studied. Two algorithms are proposed for the automatic selection of the number of knots. The myopic algorithm stops when no improvement in the generalized cross-validation statistic (GCV) is noticed with the last increase in the number of knots. The full search examines all candidates in a fixed sequence of possible numbers of knots and chooses the candidate that minimizes GCV.The myopic algorithm works well in many cases but can stop prematurely. The full-search algorithm worked well in all examples examined. A Demmler–Reinsch type diagonalization for computing univariate and additive P-splines is described. The Demmler–Reinsch basis is not effective for smoothing splines because smoothing splines have too many knots. For P-splines, however, the Demmler–Reinsch basis is very useful for super-fast generalized cross-validation.  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