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   3733篇
  免费   468篇
  国内免费   389篇
化学   246篇
晶体学   2篇
力学   217篇
综合类   111篇
数学   3257篇
物理学   757篇
  2024年   2篇
  2023年   55篇
  2022年   70篇
  2021年   86篇
  2020年   119篇
  2019年   92篇
  2018年   119篇
  2017年   115篇
  2016年   131篇
  2015年   68篇
  2014年   170篇
  2013年   320篇
  2012年   155篇
  2011年   208篇
  2010年   193篇
  2009年   241篇
  2008年   234篇
  2007年   267篇
  2006年   257篇
  2005年   222篇
  2004年   180篇
  2003年   169篇
  2002年   173篇
  2001年   136篇
  2000年   125篇
  1999年   115篇
  1998年   103篇
  1997年   80篇
  1996年   67篇
  1995年   57篇
  1994年   49篇
  1993年   29篇
  1992年   25篇
  1991年   15篇
  1990年   17篇
  1989年   9篇
  1988年   10篇
  1987年   10篇
  1986年   18篇
  1985年   19篇
  1984年   9篇
  1983年   12篇
  1982年   12篇
  1981年   7篇
  1980年   3篇
  1978年   6篇
  1977年   3篇
  1974年   1篇
  1973年   1篇
  1957年   3篇
排序方式: 共有4590条查询结果,搜索用时 234 毫秒
11.
In this article, a new framework to design high-order approximations in the context of node-centered finite volumes on simplicial meshes is proposed. The major novelty of this method is that it relies on very simple and compact differential operators, which is a critical point to achieve good performances in the High-performance computing context. This method is based on deconvolution between nodal and volume-average values, which can be conducted to any order. The interest of the new method is illustrated through three different applications: mesh-to-mesh interpolation, levelset curvature computation, and numerical scheme for convection. Higher order can also be achieved within the present framework by introducing high-rank tensors. Although these tensors feature much symmetries, their manipulation can quickly become an overwhelming task. For this reason and without loss of generality, the present articles are limited to third-order expansion. This method, although tightly connected to the k-exact schemes theory, does not rely on successive corrections: the high-order property is obtained in a single operation, which makes them more attractive in terms of performances.  相似文献   
12.
基于一种新颖高效气体发生装置,设计了以氯气为氧化剂,理论产率接近100%的将锰酸钾高效转化为高锰酸钾的实验方案。实验结果表明:使用本设计制备高纯度高锰酸钾,既可保证高锰酸钾的理论转化率,减少歧化反应副产物对纯度的影响,同时得到的副产品次氯酸钠及氯水可用做无机教学实验的基础试剂,符合“循环经济”指导思想。  相似文献   
13.
14.
15.
We consider the problem of sending a message from a sender s to a receiver r through an unreliable network by specifying in a protocol what each vertex is supposed to do if it receives the message from one of its neighbors. A protocol for routing a message in such a graph is finite if it never floods r with an infinite number of copies of the message. The expected reliability of a given protocol is the probability that a message sent from s reaches r when the edges of the network fail independently with probability 1?p.We discuss, for given networks, the properties of finite protocols with maximum expected reliability in the case when p is close to 0 or 1, and we describe networks for which no one protocol is optimal for all values of p. In general, finding an optimal protocol for a given network and fixed probability is challenging and many open problems remain.  相似文献   
16.
A novel microfluidic droplet generator is proposed, which can control the droplet size through turning an integrated micrometer head with ease, and the size of the produced micro-droplet can be automatically and real-time monitored by an open-sourced software and off-the-shelf hardware.  相似文献   
17.
We generalize Nagel’s formula for the Szegö kernel and use it to compute the Szegö kernel on a class of non-compact CR manifolds whose tangent space decomposes into one complex direction and several totally real directions. We also discuss the control metric on these manifolds and relate it to the size of the Szegö kernel.  相似文献   
18.
19.
In this paper, we study the approximation properties of bivariate summation‐integral–type operators with two parameters . The present work deals within the polynomial weight space. The rate of convergence is obtained while the function belonging to the set of all continuous and bounded function defined on ([0],)(×[0],) and function belonging to the polynomial weight space with two parameters, also convergence properties, are studied. To know the asymptotic behavior of the proposed bivariate operators, we prove the Voronovskaya type theorem and show the graphical representation for the convergence of the bivariate operators, which is illustrated by graphics using Mathematica. Also with the help of Mathematica, we discuss the comparison by means of the convergence of the proposed bivariate summation‐integral–type operators and Szász‐Mirakjan‐Kantorovich operators for function of two variables with two parameters to the function. In the same direction, we compute the absolute numerical error for the bivariate operators by using Mathematica and is illustrated by tables and also the comparison takes place of the proposed bivariate operators with the bivariate Szász‐Mirakjan operators in the sense of absolute error, which is represented by table. At last, we study the simultaneous approximation for the first‐order partial derivative of the function.  相似文献   
20.
Smooth backfitting has been shown to have better theoretical properties than classical backfitting for fitting additive models based on local linear regression. In this article, we show that the smooth backfitting procedure in the local linear case can be alternatively performed as a classical backfitting procedure with a different type of smoother matrices. These smoother matrices are symmetric and shrinking and some established results in the literature are readily applicable. The connections allow the smooth backfitting algorithm to be implemented in a much simplified way, give new insights on the differences between the two approaches in the literature, and provide an extension to local polynomial regression. The connections also give rise to a new estimator at data points. Asymptotic properties of general local polynomial smooth backfitting estimates are investigated, allowing for different orders of local polynomials and different bandwidths. Cases of oracle efficiency are discussed. Computer-generated simulations are conducted to demonstrate finite sample behaviors of the methodology and a real data example is given for illustration. Supplementary materials for this article are available online.  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