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   3742篇
  免费   471篇
  国内免费   156篇
化学   285篇
晶体学   2篇
力学   352篇
综合类   96篇
数学   2674篇
物理学   960篇
  2024年   7篇
  2023年   48篇
  2022年   71篇
  2021年   118篇
  2020年   94篇
  2019年   89篇
  2018年   74篇
  2017年   147篇
  2016年   169篇
  2015年   91篇
  2014年   247篇
  2013年   340篇
  2012年   180篇
  2011年   195篇
  2010年   181篇
  2009年   215篇
  2008年   234篇
  2007年   214篇
  2006年   178篇
  2005年   181篇
  2004年   137篇
  2003年   109篇
  2002年   108篇
  2001年   113篇
  2000年   103篇
  1999年   94篇
  1998年   95篇
  1997年   66篇
  1996年   65篇
  1995年   57篇
  1994年   35篇
  1993年   35篇
  1992年   22篇
  1991年   22篇
  1990年   35篇
  1989年   19篇
  1988年   12篇
  1987年   25篇
  1986年   11篇
  1985年   38篇
  1984年   11篇
  1983年   12篇
  1982年   12篇
  1981年   12篇
  1980年   9篇
  1979年   14篇
  1978年   4篇
  1976年   4篇
  1974年   3篇
  1973年   4篇
排序方式: 共有4369条查询结果,搜索用时 15 毫秒
211.
熵损失函数下两参数指数威布尔分布尺度参数的Bayes估计   总被引:1,自引:0,他引:1  
本文给定一截尾样本,在熵损失函数下,研究了两参数指数威布尔分布尺度参数在先验伽玛分布下的Bayes估计,并给出了该参数的Bayes区间估计。  相似文献   
212.
In this note we propose a nonstandard technique for constructing global a posteriori error estimates for the stationary convection–reaction–diffusion equation. In order to estimate the approximation error in appropriate weighted energy norms, which measures the overall quality of the approximations, the underlying bilinear form is decomposed into several terms which can be directly computed or easily estimated from above using elementary tools of functional analysis. Several auxiliary parameters are introduced to construct such a splitting and tune the resulting upper error bound. It is demonstrated how these parameters can be chosen in some natural and convenient way for computations so that the weighted energy norm of the error is almost recovered, which shows that the estimates proposed are, in fact, quasi-sharp. The presented methodology is completely independent of numerical techniques used to compute approximate solutions. In particular, it is applicable to approximations which fail to satisfy the Galerkin orthogonality, e.g., due to an inconsistent stabilization, flux limiting, low-order quadrature rules, round-off and iteration errors etc. Moreover, the only constant that appears in the proposed error estimates is of global nature and comes from the Friedrichs–Poincaré inequality.  相似文献   
213.
For neural networks with all the parameters unknown, we focus on the global robust synchronization between two coupled neural networks with time-varying delay that are linearly and unidirectionally coupled. First, we use Lyapunov functionals to establish general theoretical conditions for designing the coupling matrix. Neither symmetry nor negative (positive) definiteness of the coupling matrix are required; under less restrictive conditions, the two coupled chaotic neural networks can achieve global robust synchronization regardless of their initial states. Second, by employing the invariance principle of functional differential equations, a simple, analytical, and rigorous adaptive feedback scheme is proposed for the robust synchronization of almost all kinds of coupled neural networks with time-varying delay based on the parameter identification of uncertain delayed neural networks. Finally, numerical simulations validate the effectiveness and feasibility of the proposed technique.  相似文献   
214.
The effects of absolute energy calibration on BESⅢ physics are discussed in detail,which mainly involve the effects on τ mass measurement,cross section scan measurement,and generic error determination in other measurements.  相似文献   
215.
本文讨论半线性Klein—Gordon方程Cauchy问题。对初值φ(x)、ψ(x),对空间维数n及半线性项加以适当限制,在Sobolev空间框架下、用不动点原理得到了整体解的存在唯一性。  相似文献   
216.
本文给出一种双扰动随机化回答模型.理论上扰动变量的引入会降低随机化调查的效率,本文使用两个设计参数设计了一种合理的双扰动变量随机化问答技术,在不降低装置对个体保护度的情况下,得出的结论表明,使用两个扰动变量可以提高调查装置的效率.通过数值模拟验证了本文模型的效率优于Bar-Lev,Bobovitch和Boukai 2004年单扰动回答模型的效率.  相似文献   
217.
Revenue management (RM) enhances the revenues of a company by means of demand-management decisions. An RM system must take into account the possibility that a booking may be canceled, or that a booked customer may fail to show up at the time of service (no-show). We review the Passenger Name Record data mining based cancellation rate forecasting models proposed in the literature, which mainly address the no-show case. Using a real-world dataset, we illustrate how the set of relevant variables to describe cancellation behavior is very different in different stages of the booking horizon, which not only confirms the dynamic aspect of this problem, but will also help revenue managers better understand the drivers of cancellation. Finally, we examine the performance of the state-of-the-art data mining methods when applied to Passenger Name Record based cancellation rate forecasting.  相似文献   
218.
The Monte Carlo study evaluates the relative accuracy of Warm's (1989) weighted likelihood estimate (WLE) compared to the maximum likelihood estimate (MLE) using the nominal response model. And the results indicate that WLE was more accurate than MLE.  相似文献   
219.
We propose the test statistic to check whether the nonparametric func-tions in two partially linear models are equality or not in this paper. We estimate the nonparametric function both in null hypothesis and the alternative by the local linear method, where we ignore the parametric components, and then estimate the parameters by the two stage method. The test statistic is derived, and it is shown to be asymptotically normal under the null hypothesis.  相似文献   
220.
In this article, based on a set of upper record values from a Rayleigh distribution, Bayesian and non-Bayesian approaches have been used to obtain the estimators of the parameter, and some lifetime parameters such as the reliability and hazard functions. Bayes estimators have been developed under symmetric (squared error) and asymmetric (LINEX and general entropy (GE)) loss functions. These estimators are derived using the informative and non-informative prior distributions for σ. We compare the performance of the presented Bayes estimators with known, non-Bayesian, estimators such as the maximum likelihood (ML) and the best linear unbiased (BLU) estimators. We show that Bayes estimators under the asymmetric loss functions are superior to both the ML and BLU estimators. The highest posterior density (HPD) intervals for the Rayleigh parameter and its reliability and hazard functions are presented. Also, Bayesian prediction intervals of the future record values are obtained and discussed. Finally, practical examples using real record values are given to illustrate the application of the results.  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