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   466391篇
  免费   3424篇
  国内免费   1318篇
化学   206798篇
晶体学   6873篇
力学   26329篇
综合类   7篇
数学   85666篇
物理学   145460篇
  2021年   3188篇
  2020年   3374篇
  2019年   3819篇
  2018年   19815篇
  2017年   20221篇
  2016年   15127篇
  2015年   5508篇
  2014年   7451篇
  2013年   16335篇
  2012年   18451篇
  2011年   32132篇
  2010年   20899篇
  2009年   21251篇
  2008年   26469篇
  2007年   30680篇
  2006年   12547篇
  2005年   16866篇
  2004年   13714篇
  2003年   12998篇
  2002年   10691篇
  2001年   10725篇
  2000年   8182篇
  1999年   6154篇
  1998年   5172篇
  1997年   4955篇
  1996年   4786篇
  1995年   4065篇
  1994年   3971篇
  1993年   3870篇
  1992年   4217篇
  1991年   4439篇
  1990年   4210篇
  1989年   4140篇
  1988年   3914篇
  1987年   4043篇
  1986年   3807篇
  1985年   4756篇
  1984年   4821篇
  1983年   4016篇
  1982年   4103篇
  1981年   3819篇
  1980年   3777篇
  1979年   4065篇
  1978年   4055篇
  1977年   3964篇
  1976年   3968篇
  1975年   3753篇
  1974年   3679篇
  1973年   3742篇
  1972年   2656篇
排序方式: 共有10000条查询结果,搜索用时 10 毫秒
61.
62.
The quantitative rainbow schlieren deflectometry (RSD) technique was applied to measure temperature and oxygen concentration in an axisymmetric hydrogen gas-jet diffusion flame burning in quiescent air at fuel jet exit Reynolds number of 70. Schlieren measurements were compared with conventional measurements using a thermocouple and a gas-sampling probe. Good agreement between the two measurement techniques was achieved on the fuel-lean side of the flame.  相似文献   
63.
A successful application of ultrasound Doppler velocimetry in liquid sodium flows is described. To obtain sufficient Doppler signals, different problems had to be solved: the transmission of the ultrasonic beam through the channel wall made of stainless steel, the acoustic coupling between the transducer and the channel wall, and the wetting of the inner surface of the wall by the liquid metal, respectively. A sodium flow in a square duct exposed to a transverse magnetic field is investigated. In accordance with the existing knowledge about MHD channel flows, we found that the velocity profiles modified to a M-shape owing to the effect of an inhomogeneous magnetic field. Received: 12 June 2001/Accepted: 27 October 2001  相似文献   
64.
65.
Balaganskii  V. S. 《Mathematical Notes》2002,72(5-6):752-756
Necessary conditions for the Gâteaux differentiability of the distance function to a set are considered. A series of characterizing results is obtained.  相似文献   
66.
67.
The variational problem of contact equilibrium of a punch and an elastic body is considered. An equivalent formulation of the problem is given in variational inequality form. Existence and uniqueness of the solution is investigated in a particular case. A penalty method is proposed for approximate solution of the problem.Translated from Vychislitel'naya i Prikladnaya Matematika, No. 56, pp. 97–103, 1985.  相似文献   
68.
A convenient method of synthesis of 2-(methoxycarbonylmethylene)-substituted imidazolidines and imidazolidinium bromides, and also of bicyclic diazo compounds has been developed starting from methyl bromopropiolate and ethylenediamine and its derivatives.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 9, pp. 1205–1208, September, 1991.  相似文献   
69.
70.
A firm's logistics cost, including shipping and inventory-carrying, is a substantial percentage of its sales. Nevertheless, typical inventory-control methods ignore or insufficiently represent the shipping cost. This paper describes a recursive algorithm that determines the reorder cycle-time that minimizes total logistics cost. It allows for a realistic accounting of shipping cost, which is modelled here as a function of shipping distance and weight. The algorithm uses a relaxation procedure to identify a suitable initial approximation to the optimal order cycle-time and then, through a series of recursive steps, moves to the optimal result. We demonstrate the algorithm with a single item, with a group of items that share a common order cycle, and with multi-items when item demands are random variables. Experience with this algorithm indicates that it converges to the optimal result in a very few steps.  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