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   762篇
  免费   137篇
  国内免费   29篇
化学   119篇
晶体学   1篇
力学   33篇
综合类   33篇
数学   318篇
物理学   424篇
  2023年   5篇
  2022年   25篇
  2021年   19篇
  2020年   24篇
  2019年   19篇
  2018年   21篇
  2017年   33篇
  2016年   35篇
  2015年   26篇
  2014年   39篇
  2013年   61篇
  2012年   42篇
  2011年   50篇
  2010年   63篇
  2009年   38篇
  2008年   57篇
  2007年   43篇
  2006年   40篇
  2005年   39篇
  2004年   26篇
  2003年   26篇
  2002年   28篇
  2001年   16篇
  2000年   22篇
  1999年   17篇
  1998年   23篇
  1997年   14篇
  1996年   12篇
  1995年   14篇
  1994年   5篇
  1993年   3篇
  1992年   8篇
  1991年   3篇
  1990年   2篇
  1989年   1篇
  1988年   4篇
  1987年   4篇
  1986年   1篇
  1985年   2篇
  1984年   5篇
  1982年   2篇
  1981年   1篇
  1980年   1篇
  1979年   5篇
  1974年   1篇
  1973年   1篇
  1957年   2篇
排序方式: 共有928条查询结果,搜索用时 234 毫秒
61.
In this paper, we present some relations between generalized distributivity of quotient algebras and Mahlo operations, and show that the distributivity implies some variants of stationary relections.

  相似文献   

62.
It is common to schedule project activities first, then the utilization of equipment and its operating crew is planned based on such schedule. Real world experiences indicate that activity scheduling can be heavily impacted by the resources needed. In particular, if a project requires highly specialized and expensive equipment type, then one needs to take into account the schedule and cost of such resources in developing the project schedule.  相似文献   
63.
Summary In the paper [5], several operations on generalized topologies are considered. They are not monotone in general, but an old result on monotonicity may be sharpened.  相似文献   
64.
Designs of cavities for fundamental and high harmonic operation in Large Orbit Gyrotron (LOG) are discussed. The fundamental operation allows one to use beam currents in the range from 200 A to 300 A achieve output power of the order of 9–10 MW at frequency 143.6 GHz. Mode competition calculations show that stable oscillations in the TE1,4 mode using high beam currents are possible even with the pitch factor 1.3 which is significantly lower than the design value 1.55. For the second harmonic operation, the maximum current used for excitation of the TE2,4 mode is 60 A and the optimum magnetic field is 7.6 T. A cavity design for fourth harmonic operation using the TE4,4 mode is also presented.  相似文献   
65.
The axioms of iteration 2-theories capture, up to isomorphism, the equational properties of iteration in conjunction with horizontal and vertical composition in all algebraically complete categories. We give a concrete representation of the free iteration 2-theory generated by a 2-signature.  相似文献   
66.
A scheduling model for a production system including machining, setup and assembly operations is considered. Production of a number of single-item products is ordered. Each product is made by assembling a set of several different parts. First, the parts are manufactured in a flow-shop consisting of multiple machines. Then, they are assembled into products on a single assembly stage. Setup operation and setup time are needed when a machine starts processing the parts or it changes items. The operations are partitioned into several blocks. Each block consists of the machining operations, the setup operations, and the assembly operation(s) for one or several products. The parts of the same item in a block are processed successively. The objective function is the mean completion time for all products. We consider a problem to partition the operations into blocks and sequence the parts in each block so as to minimize the objective function. Solution procedures using pseudo-dynamic programming and a branch-and-bound method are proposed. Computational experiments are carried out to evaluate the performance of the solution procedures. It has been found that a good near-optimal schedule is obtained efficiently by the proposed solution procedures.  相似文献   
67.
1IntroductionAconsiderableresearcheforthasbeenmadeduringthepastfewyearstodevelopopticallogicoperationsbasedonphotorefractivem...  相似文献   
68.
A simple approach for photonic generation of a tunable microwave signal is proposed and successfully demonstrated. By mixing the output from a single-longitudinal-mode Brillouin fiber ring laser with the reflected laser pump at photodetector, a microwave signal at the Brillouin shift can be obtained. Since the Brillouin shift can be changed by tuning the pump wavelength, tunable microwave can be generated. As a result a microwave signal tunable from 10.39 to 10.67 GHz has been achieved, with linewidth less than 600 KHz.  相似文献   
69.
A novel algorithm for branch cut phase unwrapping   总被引:1,自引:0,他引:1  
Branch cut method is a powerful noise-immune algorithm for correct phase unwrapping of noisy phase maps. The shortest branch cut length promises the optimal unwrapping result of the wrapped phase maps. A new algorithm is proposed to search for the shortest branch cut length by simple exchange operation. Although the algorithm is on the basis of stochastic search techniques, it has a high probability of finding the shortest branch cut length or an approximation of it. Compared with the traditional algorithms, the algorithm is fast and competitive.  相似文献   
70.
浅析相关系数的显著性检验   总被引:2,自引:0,他引:2  
本文用最小二乘法作直线拟合,给出相关系数显著性检验的判断方法,指出了用概率理论判断线性相关的必要性。  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