全文获取类型
收费全文 | 1098篇 |
免费 | 244篇 |
国内免费 | 106篇 |
专业分类
化学 | 142篇 |
力学 | 166篇 |
综合类 | 6篇 |
数学 | 169篇 |
物理学 | 512篇 |
无线电 | 453篇 |
出版年
2024年 | 3篇 |
2023年 | 25篇 |
2022年 | 34篇 |
2021年 | 41篇 |
2020年 | 41篇 |
2019年 | 25篇 |
2018年 | 28篇 |
2017年 | 50篇 |
2016年 | 64篇 |
2015年 | 58篇 |
2014年 | 102篇 |
2013年 | 100篇 |
2012年 | 90篇 |
2011年 | 87篇 |
2010年 | 75篇 |
2009年 | 85篇 |
2008年 | 65篇 |
2007年 | 53篇 |
2006年 | 51篇 |
2005年 | 51篇 |
2004年 | 32篇 |
2003年 | 23篇 |
2002年 | 35篇 |
2001年 | 30篇 |
2000年 | 28篇 |
1999年 | 31篇 |
1998年 | 30篇 |
1997年 | 14篇 |
1996年 | 11篇 |
1995年 | 11篇 |
1994年 | 20篇 |
1993年 | 7篇 |
1992年 | 7篇 |
1991年 | 5篇 |
1990年 | 5篇 |
1989年 | 8篇 |
1988年 | 7篇 |
1987年 | 4篇 |
1986年 | 3篇 |
1985年 | 1篇 |
1984年 | 2篇 |
1982年 | 1篇 |
1981年 | 1篇 |
1979年 | 1篇 |
1977年 | 1篇 |
1975年 | 1篇 |
1957年 | 1篇 |
排序方式: 共有1448条查询结果,搜索用时 62 毫秒
111.
112.
113.
文中详细分析了全桥型LLC变换器在三种工作模式下的状态轨迹特征,提出了一种宽输入条件下改进的最优轨迹控制策略,并讨论了电路参数选择对控制策略适用性的影响。仿真结果证明了所提策略的有效性。 相似文献
114.
基于ELM算法的起重船摆动轨迹跟踪 总被引:1,自引:0,他引:1
起重船进行海洋作业时,难免会受到风浪的影响,船体随之发生摇摆,使得起重船无法正常作业.船舶摇摆是一个复杂的非线性运动,神经网络具有很好的在线学习预测的能力,对此本文提出一种基于极端学习机ELM算法的轨迹跟踪方法,对起重船的摆动进行实时跟踪预测,在MATLAB中仿真出跟踪效果图,并与传统的BP神经网络算法对比,得出ELM具有更快更准确的跟踪预测能力,突出了ELM算法的优越性,最后可将此方法用于吊摆控制系统中. 相似文献
115.
M.S. Child 《Contemporary Physics》2013,54(3):212-221
Monodromy (or once round) is a classical property of integrable dynamical systems in two or more degrees of freedom, which imposes a characteristic pattern on the quantum mechanical eigenvalue distribution. This article explains the connection by showing how the presence of an isolated critical point of the Hamiltonian leads to a classical action function that is multi-valued with respect to energy and angular momentum. Consequently, by the Bohr correspondence principle between actions and quantum numbers, there can be no uniquely defined global system of quantum numbers. Implications for the interpretation of highly excited molecular spectra are brought out by reference to quasi-linear molecules, which transfer one degree of freedom from rotational to vibrational motion during the excitation process. Emphasis is placed on the simplest examples, while a brief resumé of the wide scope of the quantum monodromy phenomenon is given in the final section. 相似文献
116.
采用Kinetic Monte Carlo方法对1+1维抛射沉积(BD)模型内部结构的动力学行为进行了大量的数值模拟研究.分别分析了空洞密度和内部界面的动力学行为.研究表明,空洞密度呈高斯型分布,其平均值首先随生长时间快速增长,然后达到一个与基底尺寸无关的饱和值.除表面宽度,还引入了新的极值统计方法来分析该模型内部界面的动力学行为,分析结果显示,1+1维BD模型内部界面的演化满足标准的Family-Vicsek标度规律,并且属Kardar-Parisi-Zhang方程所描述的普适类.最后对表面宽度和极值统计两种理论方法的有限尺寸效应进行了比较. 相似文献
117.
分数布朗运动和反常扩散 总被引:2,自引:0,他引:2
本文评述了分数布朗运动和反常扩散现象及描写它们的几种数学方式。报告了我们在弹道扩散的产生条件、起源和长时间效应方面的工作。 相似文献
118.
119.
Nonlinear two-point boundary-value problems (TPBVP) can be reduced to the iterative solution of a sequence of linear problems by means of quasilinearization techniques. Therefore, the efficient solution of linear problems is the key to the efficient solution of nonlinear problems.Among the techniques available for solving linear two-point boundary-value problems, the method of particular solutions (MPS) is particularly attractive in that it employs only one differential system, the original nonhomogeneous system, albeit with different initial conditions. This feature of MPS makes it ideally suitable for implementation on parallel computers in that the following requirements are met: the computational effort is subdivided into separate tasks (particular solutions) assigned to the different processors; the tasks have nearly the same size; there is little intercommunication between the tasks.For the TPBVP, the speedup achievable is ofO(n), wheren is the dimension of the state vector, hence relatively modest for the differential systems of interest in trajectory optimization and guidance. This being the case, we transform the TPBVP into a multi-point boundary-value problem (MPBVP) involvingm time subintervals, withm–1 continuity conditions imposed at the interface of contiguous subintervals. For the MPBVP, the speedup achievable is ofO(mn), hence substantially higher than that achievable for the TPBVP. It reduces toO(m) if the parallelism is implemented only in the time domain and not in the state domain.A drawback of the multi-point approach is that it requires the solution of a large linear algebraic system for the constants of the particular solutions. This drawback can be offset by exploiting the particular nature of the interface conditions: if the vector of constants for the first subinterval is known, the vector of constants for the subsequent subintervals can be obtained with linear transformations. Using decomposition techniques together with the discrete version of MPS, the size of the linear algebraic system for the multi-point case becomes the same as that for the two-point case.Numerical tests on the Intel iPSC/860 computer show that substantial speedup can be achieved via parallel algorithms vis-a-vis sequential algorithms. Therefore, the present technique has considerable interest for real-time trajectory optimization and guidance.Dedicated to the Memory of Professor Jan M. SkowronskiThis paper, based on Refs. 1–3, is a much condensed version of the material contained in these references.The technical assistance of the Research Center on Parallel Computation of Rice University, Houston, Texas is gratefully acknowledged. 相似文献
120.