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   731篇
  免费   31篇
  国内免费   18篇
化学   376篇
晶体学   1篇
力学   50篇
综合类   3篇
数学   184篇
物理学   166篇
  2024年   3篇
  2023年   50篇
  2022年   19篇
  2021年   10篇
  2020年   16篇
  2019年   19篇
  2018年   10篇
  2017年   25篇
  2016年   18篇
  2015年   20篇
  2014年   24篇
  2013年   60篇
  2012年   45篇
  2011年   43篇
  2010年   32篇
  2009年   33篇
  2008年   43篇
  2007年   35篇
  2006年   28篇
  2005年   38篇
  2004年   43篇
  2003年   26篇
  2002年   11篇
  2001年   10篇
  2000年   16篇
  1999年   11篇
  1998年   10篇
  1997年   13篇
  1996年   12篇
  1995年   8篇
  1994年   8篇
  1993年   3篇
  1992年   3篇
  1991年   3篇
  1990年   7篇
  1989年   4篇
  1988年   4篇
  1987年   2篇
  1986年   4篇
  1985年   2篇
  1984年   1篇
  1982年   3篇
  1979年   3篇
  1978年   2篇
排序方式: 共有780条查询结果,搜索用时 296 毫秒
1.
Optimization of the Heck reaction of 4-bromoacetophenone with styrene by a polymer supported, sulfur-containing palladacycle, varying 6 factors at a total of 28 different levels, corresponding to 5760 different possibilities was undertaken. Conversion improved from 34%, with large observable leaching to 88% with no leaching. This was accomplished using a Design of Experiments approach facilitated by the Statistical Design Package, MODDE 7.0TM.  相似文献   
2.
衍/折射光学元件消二级光谱的设计   总被引:1,自引:0,他引:1       下载免费PDF全文
 采用衍/折射光学元件结合的方法,使用两种玻璃设计了星载用长焦距望远物镜,对其二级光谱进行了校正。具体介绍了衍/折透镜望远透镜消二级光谱方法、步骤。计算机模拟结果表明:校正后的望远物镜轴上位置色差小于0.08mm,满足使用要求,并且设计方法步骤简单。  相似文献   
3.
混合位级正交试验设计的极差分析方法   总被引:3,自引:0,他引:3  
本文指出,在混合位级的正交试验设计中,以往的极差分析方法存在着不足。本文给出了极差的修正方法,并用大量实例做了数值验证,说明这个修正确实很有效  相似文献   
4.
We consider the problem of scheduling orders for multiple different product types in an environment with m dedicated machines in parallel. The objective is to minimize the total weighted completion time. Each product type is produced by one and only one of the m dedicated machines; that is, each machine is dedicated to a specific product type. Each order has a weight and may also have a release date. Each order asks for certain amounts of various different product types. The different products for an order can be produced concurrently. Preemptions are not allowed. Even when all orders are available at time 0, the problem has been shown to be strongly NP-hard for any fixed number (?2) of machines. This paper focuses on the design and analysis of efficient heuristics for the case without release dates. Occasionally, however, we extend our results to the case with release dates. The heuristics considered include some that have already been proposed in the literature as well as several new ones. They include various static and dynamic priority rules as well as two more sophisticated LP-based algorithms. We analyze the performance bounds of the priority rules and of the algorithms and present also an in-depth comparative analysis of the various rules and algorithms. The conclusions from this empirical analysis provide insights into the trade-offs with regard to solution quality, speed, and memory space.  相似文献   
5.
The system design must be started from the concept with low cost and high performance. In this point, the topological shape of the structure is very important in the view of the structural rigidities and light-weight design.In this paper, the optimization methodology is presented in the design stage of the large optical mirror. We obtain the optimal layout through the topology optimization and then design the details through the size or shape optimization for structural rigidity.  相似文献   
6.
7.
Transpiration is a technique in which extra non-physical normal flows are created on an aerofoil surface in order to form a new streamline pattern such that the surface streamlines no longer follow the aerofoil surface under inviscid flow. The transpiration model is an important technique adopted in aerofoil design either to avoid mesh regeneration when aerofoil profile co-ordinates are adjusted or to find shape corrections in inverse design methods. A first-order approximation (with respect to the normal streamline displacement) to the transpiration model is commonly adopted; it is shown that this can be a poor approximation especially in regions of high curvature. In this paper more accurate approximations are developed to address this problem and improve the accuracy.  相似文献   
8.
电子电路的计算机辅助设计方法是促进电子技术发展的一种有效工具。本文介绍如何将行之有效的正交优化法与国际盛行的模拟电子电路的分析程序SPICE相结合,形成了ACOD软件,将CAA扩展为CAD。  相似文献   
9.
本文就回归估计量回归系数已知和未知两种情况,给出确定样本容量的方法.  相似文献   
10.
研究了四元体系CsCl-LaCl3-HCl-H2O(25℃、「HCl」=13%(wt),23%(wt)和CsCl-LaCl3-HAc-H2O(30℃,「HAc」=42%(wt))的平衡态的溶度数据,并给出制了相应的溶度图,共得到了CsCl.LaCl3.4H2O、2CsCl.LaCl3.2H2O和3CsCl.LaCl3.3H2O3种化合物。对得到的新相进行了热分析,X射线粉末衍射及偏光性质的测定,依  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