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   445篇
  免费   10篇
  国内免费   2篇
化学   210篇
晶体学   3篇
力学   34篇
数学   71篇
物理学   139篇
  2022年   23篇
  2021年   22篇
  2020年   9篇
  2019年   15篇
  2018年   18篇
  2017年   13篇
  2016年   14篇
  2015年   16篇
  2014年   17篇
  2013年   32篇
  2012年   32篇
  2011年   22篇
  2010年   21篇
  2009年   11篇
  2008年   13篇
  2007年   17篇
  2006年   19篇
  2005年   15篇
  2004年   5篇
  2003年   9篇
  2002年   24篇
  2001年   5篇
  2000年   6篇
  1999年   1篇
  1997年   2篇
  1996年   4篇
  1995年   7篇
  1994年   3篇
  1993年   8篇
  1992年   7篇
  1991年   7篇
  1990年   10篇
  1989年   2篇
  1988年   1篇
  1987年   3篇
  1986年   5篇
  1985年   2篇
  1984年   4篇
  1982年   4篇
  1981年   1篇
  1980年   1篇
  1975年   2篇
  1974年   1篇
  1972年   1篇
  1967年   1篇
  1939年   2篇
排序方式: 共有457条查询结果,搜索用时 15 毫秒
411.
This paper presents a co-evolutionary particle swarm optimization (PSO) algorithm, hybridized with noising metaheuristics, for solving the delay constrained least cost (DCLC) path problem, i.e., shortest-path problem with a delay constraint on the total “cost” of the optimal path. The proposed algorithm uses the principle of Lagrange relaxation based aggregated cost. It essentially consists of two concurrent PSOs for solving the resulting minimization-maximization problem. The main PSO is designed as a hybrid PSO-noising metaheuristics algorithm for efficient global search to solve the minimization part of the DCLC-Lagrangian relaxation by finding multiple shortest paths between a source-destination pair. The auxiliary/second PSO is a co-evolutionary PSO to obtain the optimal Lagrangian multiplier for solving the maximization part of the Lagrangian relaxation problem. For the main PSO, a novel heuristics-based path encoding/decoding scheme has been devised for representation of network paths as particles. The simulation results on several networks with random topologies illustrate the efficiency of the proposed hybrid algorithm for the constrained shortest path computation problems.  相似文献   
412.
We present a direct method for finding particular solutions of equations of sine-Gordon type, including single sinh-Gordon equation, single sine-Gordon equation, double sinh-Gordon and double sine-Gordon equations.  相似文献   
413.
414.
The reaction of 2-amino- and 2,4-diamino-sym-triazines with nitrourea and phenyl isocyanate was studied; it gives N-mono- and N,N-disubstituted ureas that contain sym-triazine segments. General features were established for the decomposition of carbamide derivatives of sym-triazine under electron impact.For communication 4, see [1].Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 3, pp. 356–362, March, 1987.  相似文献   
415.
In this paper the optimal control of a single-channel bulk service queueing system with random server capacity is investigated. Given an accumulation level r, the server stops processing new customers whenever the queue falls below r and resumes service when the queue reaches level r again. Server capacity becomes random following an idle period. A quick search procedure is designed to determine the value of r that yields the minimum expected total cost per unit of time. The effect of the server capacity distribution on the optimal control is then studied. Finally, a sensitivity analysis is conducted in order to assess the extent to which our results are valid.  相似文献   
416.
Thicknesses of gold and silver thin films have been determined by NAA technique. Reasonable agreement with conventional optical method has been obtained, but the lower detection limit in the case of NAA is far better than in the optical method.

Es wurde die Dicke von Gold- und Silberfilmen mittels NAA-Technik bestimmt. Dabei konnte eine vernünftige Übereinstimmung mit der konventionellen optischen Methode erzielt werden, wobei im Falle der NAA die untere Nachweis grenze wescntlich besser war als vergleichsweise die optische Methode.  相似文献   
417.
This paper explores the relations between the matrix Riccati equation and the standard matrix eigenvalue methods. It is demonstrated that the mathematics of the analysis of the two objects is essentially the same; consisting of the analysis of flows on the homogeneous spaces of various Lie groups.Supported in part by DOE Contract DE-ACOL-80RA-5256.Supported in part by DOE Contract DE-ACOL-80RA-5256 and by NASA Grant DAG2-82.  相似文献   
418.
Six gel-type functional resins, that is, three poly-DMAA-co-TMPTP (DMAA = N,N-dimethylacrylamide, TMPTP = trimethylolpropyltrimethacrylate) samples with different degrees of cross-linking (0.6, 1.2, 1.7 % mol) and three poly-DMAA-co-MA-co-TMPTP (MA = methacrylic acid, ca. 5.5 % mol) samples with 1.7, 3.5, and 7 % mol cross-linking were investigated with ISEC (inverse steric exclusion chromatography), and ESR and CP-MAS (cross polarization magic angle spinning) 13C NMR spectroscopy after swelling in water and other solvents. This unprecedented combination of conceptually independent physicochemical techniques provides a thorough overall consistent picture of the morphology of the resins on the nanometer scale and of the molecular accessibility of the swollen polymer framework to the paramagnetic probe TEMPONE (2,2,6,6-tetramethyl-4-oxo-1-oxypiperidine) and to selected solvents.  相似文献   
419.
    
The absorptions of RuO4 coincident with12C16O2 and14N2 16O laser lines have been observed with sub-Doppler resolution and their frequency distances from the laser line-centers have been measured. These preliminary results suggest a possible extension of the absolute reference frequency grid up to the 10.9 m region, based on transitions of hyperfine-structure free heavy molecules.  相似文献   
420.
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