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   9709篇
  免费   1364篇
  国内免费   591篇
化学   892篇
晶体学   27篇
力学   837篇
综合类   136篇
数学   7033篇
物理学   2739篇
  2023年   81篇
  2022年   102篇
  2021年   220篇
  2020年   272篇
  2019年   242篇
  2018年   244篇
  2017年   286篇
  2016年   344篇
  2015年   216篇
  2014年   405篇
  2013年   1045篇
  2012年   480篇
  2011年   516篇
  2010年   512篇
  2009年   544篇
  2008年   572篇
  2007年   623篇
  2006年   545篇
  2005年   492篇
  2004年   386篇
  2003年   422篇
  2002年   384篇
  2001年   332篇
  2000年   318篇
  1999年   255篇
  1998年   253篇
  1997年   229篇
  1996年   154篇
  1995年   139篇
  1994年   118篇
  1993年   98篇
  1992年   91篇
  1991年   71篇
  1990年   73篇
  1989年   57篇
  1988年   65篇
  1987年   52篇
  1986年   44篇
  1985年   78篇
  1984年   55篇
  1983年   24篇
  1982年   43篇
  1981年   28篇
  1980年   19篇
  1979年   22篇
  1978年   18篇
  1977年   26篇
  1976年   20篇
  1974年   10篇
  1973年   11篇
排序方式: 共有10000条查询结果,搜索用时 312 毫秒
71.
By computing the derivatives of five classical hypergeometric summation theorems, and applying the related properties of the digamma function, we derive a large number of closed summation formulae for generalized harmonic numbers.  相似文献   
72.
73.
在ATIS和道路收费共同作用的异质性交通网络中,基于用户在信息接受程度与时间价值上的异质性,对用户进行合理分类,所有用户均按照随机方式进行择路.构建了多用户混合随机均衡等价的变分不等式模型,以及多用户随机社会最优模型.以用户感知的总出行成本作为系统性能评价的指标,当收费作为系统总成本的一部分时,分别在时间准则与费用准则下研究了多用户混合随机均衡相对于随机社会最优的绝对效率损失问题.研究结果表明,时间准则下的绝对效率损失上界与路段出行时间函数和混合随机均衡时系统的实际总出行时间有关,费用准则下的绝对效率损失上界还与出行者的社会经济特性和随机社会最优时系统的实际总出行时间有关.  相似文献   
74.
利用NA随机变量的矩不等式和截尾方法,研究了NA随机变量阵列的完全矩收敛性,给出了证明NA随机变量阵列完全矩收敛性的一些充分条件.所得结果推广了已有文献关于NA随机变量的相应结果.  相似文献   
75.
In this paper, we extend one of Erdélyi's classical integrals for the Gauss hypergeometric functions to a special class of generalized hypergeometric functions in which certain pairs of numerator and denomiator parameters differ by positive integers. Our main results are achieved by applying the fractional integration by parts and series manipulation technique. Some special cases are also pointed out which includes a new extension of a Thomae-type transformation.  相似文献   
76.
By reformulating four hypergeometric series formulae, we derive 36 Apéry-like series expressions for the Riemann zeta function, including a couple of identities conjectured by Sun [New series for some special values of L-functions. Nanjing Univ J Math. 2015;32(2): 189–218].  相似文献   
77.
78.
We study a stratified multisite cluster‐sampling panel time series approach in order to analyse and evaluate the quality and reliability of produced items, motivated by the problem to sample and analyse multisite outdoor measurements from photovoltaic systems. The specific stratified sampling in spatial clusters reduces sampling costs and allows for heterogeneity as well as for the analysis of spatial correlations due to defects and damages that tend to occur in clusters. The analysis is based on weighted least squares using data‐dependent weights. We show that this does not affect consistency and asymptotic normality of the least squares estimator under the proposed sampling design under general conditions. The estimation of the relevant variance–covariance matrices is discussed in detail for various models including nested designs and random effects. The strata corresponding to damages or manufacturers are modelled via a quality feature by means of a threshold approach. The analysis of outdoor electroluminescence images shows that spatial correlations and local clusters may arise in such photovoltaic data. Further, relevant statistics such as the mean pixel intensity cannot be assumed to follow a Gaussian law. We investigate the proposed inferential tools in detail by simulations in order to assess the influence of spatial cluster correlations and serial correlations on the test's size and power. ©2016 The Authors. Applied Stochastic Models in Business and Industry published by John Wiley & Sons, Ltd.  相似文献   
79.
In this paper, we introduce a unifying approach to option pricing under continuous‐time stochastic volatility models with jumps. For European style options, a new semi‐closed pricing formula is derived using the generalized complex Fourier transform of the corresponding partial integro‐differential equation. This approach is successfully applied to models with different volatility diffusion and jump processes. We also discuss how to price options with different payoff functions in a similar way. In particular, we focus on a log‐normal and a log‐uniform jump diffusion stochastic volatility model, originally introduced by Bates and Yan and Hanson, respectively. The comparison of existing and newly proposed option pricing formulas with respect to time efficiency and precision is discussed. We also derive a representation of an option price under a new approximative fractional jump diffusion model that differs from the aforementioned models, especially for the out‐of‐the money contracts. Copyright © 2017 John Wiley & Sons, Ltd.  相似文献   
80.
Urban rail planning is extremely complex, mainly because it is a decision problem under different uncertainties. In practice, travel demand is generally uncertain, and therefore, the timetabling decisions must be based on accurate estimation. This research addresses the optimization of train timetable at public transit terminals of an urban rail in a stochastic setting. To cope with stochastic fluctuation of arrival rates, a two‐stage stochastic programming model is developed. The objective is to construct a daily train schedule that minimizes the expected waiting time of passengers. Due to the high computational cost of evaluating the expected value objective, the sample average approximation method is applied. The method provided statistical estimations of the optimality gap as well as lower and upper bounds and the associated confidence intervals. Numerical experiments are performed to evaluate the performance of the proposed model and the solution method.  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