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   23918篇
  免费   2032篇
  国内免费   1735篇
化学   759篇
晶体学   14篇
力学   1032篇
综合类   324篇
数学   5486篇
物理学   2833篇
综合类   17237篇
  2024年   140篇
  2023年   309篇
  2022年   577篇
  2021年   629篇
  2020年   519篇
  2019年   542篇
  2018年   554篇
  2017年   737篇
  2016年   793篇
  2015年   808篇
  2014年   1289篇
  2013年   1263篇
  2012年   1380篇
  2011年   1531篇
  2010年   1153篇
  2009年   1447篇
  2008年   1480篇
  2007年   1905篇
  2006年   1703篇
  2005年   1375篇
  2004年   1213篇
  2003年   989篇
  2002年   873篇
  2001年   720篇
  2000年   596篇
  1999年   536篇
  1998年   465篇
  1997年   398篇
  1996年   321篇
  1995年   262篇
  1994年   193篇
  1993年   186篇
  1992年   158篇
  1991年   112篇
  1990年   121篇
  1989年   88篇
  1988年   79篇
  1987年   59篇
  1986年   40篇
  1985年   37篇
  1984年   28篇
  1983年   9篇
  1982年   18篇
  1981年   5篇
  1980年   5篇
  1979年   5篇
  1978年   3篇
  1977年   5篇
  1959年   5篇
  1955年   13篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
951.
产品拆卸过程中零部件之间会相互干扰影响任务作业时间,基于该情形构建了多目标U型SDDLBP优化模型,并提出一种自适应ABC算法。所提算法设计了自适应动态邻域搜索方法,以提高局部开发能力;采用了轮盘赌与锦标赛法结合的分段选择法,以有效评价并选择蜜源进行深度开发;建立了基于当前最优解的变异操作,以提高全局探索能力快速跳出局部最优。最后,通过算例测试和实例分析验证算法的高效性。  相似文献   
952.
We consider a coefficient identification problem for a mathematical model with free boundary related to ductal carcinoma in situ (DCIS). This inverse problem aims to determine the nutrient consumption rate from additional measurement data at a boundary point. We first obtain a global‐in‐time uniqueness of our inverse problem. Then based on the optimization method, we present a regularization algorithm to recover the nutrient consumption rate. Finally, our numerical experiment shows the effectiveness of the proposed numerical method.  相似文献   
953.
954.
分析了古巴比伦人求算术平方根的算法,证明了其正确性。然后将其算法推广到求n次算术根,并证明了其正确性。  相似文献   
955.
A new decoupled two-gird algorithm with the Newton iteration is proposed for solving the coupled Navier-Stokes/Darcy model which describes a fluid flow filtrating through porous media. Moreover the err...  相似文献   
956.
957.
We present a generalization of the transition state search using chemical dynamics simulations (TSSCDS) methodology (discussed in a previous study) which allows the topographical characterization of intermolecular potential energy surfaces (IPES) for non-covalently bound complexes (vdW-TSSCDS). Starting from a single random input geometry, we show that vdW-TSSCDS is able to globally and automatically locate stationary points of an IPES, even in limiting cases such as extremely flat regions or nontrivial topologies (eg, bifurcation points). The basic idea is the expression of the connectivity matrix in block structure, where diagonal blocks correspond to the isolated fragments and off-diagonal blocks provide the intermolecular connectivity. To this end, we introduce a new definition of bound or not, in a non-covalent sense, utilizing an extra set of van der Waals distances, which encompasses all kinds of non-covalent distances. To discuss the use of the vdW-TSSCDS method, we present a series of 2-body van der Waals systems, namely, Ar-Benzene (3D), N2-Benzene (6D) and H2O-Benzene (9D). Finally, we further illustrate its capabilities by presenting some applications for n-body problems (n > 2), (H2O)2-Benzene (12D) and (H2O)3-Benzene (21D), as well as to a reactive, fully-flexible, system (Benzene-NO2)+ (39D) in which the simultaneous breaking/formation of both covalent and non-covalent interactions takes place.  相似文献   
958.
Distance weighted discrimination (DWD) is an appealing classification method that is capable of overcoming data piling problems in high-dimensional settings. Especially when various sparsity structures are assumed in these settings, variable selection in multicategory classification poses great challenges. In this paper, we propose a multicategory generalized DWD (MgDWD) method that maintains intrinsic variable group structures during selection using a sparse group lasso penalty. Theoretically, we derive minimizer uniqueness for the penalized MgDWD loss function and consistency properties for the proposed classifier. We further develop an efficient algorithm based on the proximal operator to solve the optimization problem. The performance of MgDWD is evaluated using finite sample simulations and miRNA data from an HIV study.  相似文献   
959.
针对列车通信在越区切换过程中切换触发率和切换成功率均较低的问题, 提出一种基于改进遗传算法的自适应联合判决切换算法. 首先, 以遗传算法为基础, 在高速特性下对切换判决过程中的相关参数进行优化, 针对列车的不同运行速度动态选择出满足快速切换需求的迟滞容限值; 其次, 引入满意通信概率(SCP), 当列车在小区之间移动时, SCP值达不到要求的将不能接入下一个小区, 以保障通信质量的优良. 仿真结果表明, 与传统切换方案相比, 该方案可实现提高切换触发率和切换成功率的目标, 具有较高的满意通信概率.  相似文献   
960.
This work proposes an extended version of the well-known tree-augmented naive Bayes (TAN) classifier where the structure learning step is performed without requiring features to be connected to the class. Based on a modification of Edmonds' algorithm, our structure learning procedure explores a superset of the structures that are considered by TAN, yet achieves global optimality of the learning score function in a very efficient way (quadratic in the number of features, the same complexity as learning TANs). We enhance our procedure with a new score function that only takes into account arcs that are relevant to predict the class, as well as an optimization over the equivalent sample size during learning. These ideas may be useful for structure learning of Bayesian networks in general. A range of experiments shows that we obtain models with better prediction accuracy than naive Bayes and TAN, and comparable to the accuracy of the state-of-the-art classifier averaged one-dependence estimator (AODE). We release our implementation of ETAN so that it can be easily installed and run within Weka.  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