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991.
Making use of the maximum entropy method, we study the most probable source function in heavy ion collisions. An anisotropic Gaussian source is deduced by simply assuming that the particles are emitted within a finite proper-time. The general relations between the most probable source function and the minimal assumptions are discussed, which are instructive in constructing a self-consistent source function from observed Hanbury-Brown/Twiss(HBT) correlations. 相似文献
992.
一种改进的GPS/DR组合位置自适应滤波算法 总被引:3,自引:2,他引:1
为解决自适应滤波算法中观测误差与状态误差估计的关键问题,在分析GPS/DR组合导航系统测量信息性质的基础上,提出了GPS光滑度计算方法,并在其基础上给出了GPS位置误差估计算法及状态误差协方差阵和观测误差协方差阵自适应调节算法。算法仿真实现了观测误差的直接测量,较好地解决了Sage-Husa自适应滤波算法中对误差特性估计不准确的问题。仿真结果表明:位置滤波输出的精度相比Sage-Husa算法有明显的提高。 相似文献
993.
一种求解有限元问题结点平衡方程的快速方法 总被引:1,自引:0,他引:1
目前随着工程实际问题复杂程度的增加及分析的要求,特别是材料非线性分析的引入,尽管计算机的运算速度、内存、外存容量等不断提高,但并不能完全满足大规模计算的需要,更快、更节省存贮空间的算法一直是有限元法分析过程中的一项核心技术要求。本文针对一些结点及单元均规律化地排列的有限元问题,提出可以透过其相邻结点的关系记录结点平衡方程中系数矩阵的非零元素,无需再像等带宽存贮那样去记录带宽内大量的零元素。此方法可以大大地减少系数矩阵元素的存贮量,从而可以提高计算机读取数据的速度及改善利用迭代法求解的效率。 相似文献
994.
Min Chan Kim Do-Young Yoon Joo Hyung Moon Chang Kyun Choi 《Transport in Porous Media》2008,74(3):369-380
When porous media saturated with initially stagnant cold water around the density maximum temperature are cooled from above,
convection may be induced in an unstable lower layer. In this study, the onset of buoyancy-driven convection during time-dependent
cooling is investigated using the propagation theory, which transforms disturbance equations similarly, and also considering
the density inversion effect. The critical Darcy–Rayleigh number Ra
D,c is found as a function of the dimensionless density maximum temperature θ
max. For Ra
D > Ra
D,c the dimensionless critical time τ
c to mark the onset of instability is presented as a function of Ra
D and θ
max. These critical conditions are compared with previous theoretical results. 相似文献
995.
In the theory of classical mechanics, the two-body central forcing problem is formulated as a system of the coupled nonlinear
second-order deterministic differential equations. The uncertainty introduced by the small, unmodeled stochastic acceleration
is not assumed in the particle dynamics. The small, unmodeled stochastic acceleration produces an additional random force
on a particle. Estimation algorithms for a two-body dynamics, without introducing the stochastic perturbation, may cause inaccurate
estimation of a particle trajectory. Specifically, this paper examines the effect of the stochastic acceleration on the motion
of the orbiting particle, and subsequently, the stochastic estimation algorithm is developed by deriving the evolutions of
conditional means and conditional variances for estimating the states of the particle-earth system. The theory of the nonlinear
filter of this paper is developed using the Kolmogorov forward equation “between the observations" and a functional difference
equation for the conditional probability density “at the observation." The effectiveness of the nonlinear filter is examined
on the basis of its ability to preserve perturbation effect felt by the orbiting particle and the signal-to-noise ratio. The Kolmogorov forward equation, however, is not appropriate for the numerical simulations, since it is the equation for
the evolution of “the conditional probability density." Instead of the Kolmogorov equation, one derives the evolutions for
the moments of the state vector, which in our case consists of positions and velocities of the orbiting body. Even these equations
are not appropriate for the numerical implementations, since they are not closed in the sense that computing the evolution
of a given moment involves the knowledge of higher order moments. Hence, we consider the approximations to these moment evolution
equations. This paper makes a connection between classical mechanics, statistical mechanics and the theory of the nonlinear
stochastic filtering. The results of this paper will be of use to astrophysicists, engineers and applied mathematicians, who
are interested in applications of the nonlinear filtering theory to the problems of celestial and satellite mechanics. Simulation
results are introduced to demonstrate the usefulness of an analytic theory developed, in this paper. 相似文献
996.
997.
Estimating the values of the parameter estimates of econometric functions (maximum likelihood functions or nonlinear least squares functions) are often challenging global optimization problems. Determining the global optimum for these functions is necessary to understand economic behavior and to develop effective economic policies. These functions often have flat surfaces or surfaces characterized by many local optima. Classical deterministic optimization methods often do not yield successful results. For that reason, stochastic optimization methods are becoming widely used in econometrics. Selected stochastic methods are applied to two difficult econometric functions to determine if they might be useful in estimating the parameters of these functions. 相似文献
998.
Consider the Bayes problem in which one has to discriminate if the random unknown initial state of a stochastic process is distributed according to either of two preassigned distributions, on the base of the observation of the first‐passage time of the process through 0. For processes whose first‐passage times to state 0 are increasing in the initial state according to the likelihood ratio order, such problem is solved by determining the Bayes decision function and the corresponding Bayes error. The special case of fixed initial values including a family of first‐passage times with proportional reversed hazard functions is then studied. Finally, various applications to birth‐and‐death and to diffusion processes are discussed. Copyright © 2001 John Wiley & Sons, Ltd. 相似文献
999.
1000.
薄膜厚度测控技术中的物理原理 总被引:6,自引:0,他引:6
针对当前应用较为广泛的各种薄膜厚度测控技术,简明介绍了光电极值法,干涉法,石英晶体振荡法及椭偏仪法的物理原理及其应用。 相似文献