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   700293篇
  免费   19600篇
  国内免费   1943篇
化学   397930篇
晶体学   9489篇
力学   30711篇
综合类   25篇
数学   85776篇
物理学   197905篇
  2021年   7135篇
  2020年   9615篇
  2019年   8157篇
  2018年   10242篇
  2017年   8712篇
  2016年   17227篇
  2015年   12548篇
  2014年   16196篇
  2013年   33933篇
  2012年   25415篇
  2011年   28662篇
  2010年   22145篇
  2009年   21432篇
  2008年   26549篇
  2007年   26292篇
  2006年   23900篇
  2005年   21492篇
  2004年   19770篇
  2003年   17508篇
  2002年   17249篇
  2001年   18692篇
  2000年   14449篇
  1999年   11358篇
  1998年   9631篇
  1997年   9421篇
  1996年   9240篇
  1995年   8447篇
  1994年   8455篇
  1993年   8190篇
  1992年   9120篇
  1991年   8890篇
  1990年   8591篇
  1989年   8259篇
  1988年   8431篇
  1987年   8205篇
  1986年   7782篇
  1985年   10230篇
  1984年   10541篇
  1983年   8644篇
  1982年   8807篇
  1981年   8738篇
  1980年   8375篇
  1979年   8701篇
  1978年   9114篇
  1977年   9023篇
  1976年   9047篇
  1975年   8437篇
  1974年   8489篇
  1973年   8514篇
  1972年   6098篇
排序方式: 共有10000条查询结果,搜索用时 11 毫秒
961.
Novosibirsk. Translated fromSibirskiî Matematicheskiî Zhurnal, Vol. 34, No. 3, pp. 3–18, May–June, 1993.  相似文献   
962.
963.
964.
965.
966.
Management of moisture penetration and hydrolytic degradation of polylactide (PLA) is extremely important during the manufacturing, shipping, storage, and end-use of PLA products. Moisture transport, crystallization, and degradation, in PLA have been measured through a variety of experimental techniques including size-exclusion chromatography, differential scanning calorimetry, and X-ray diffraction. Quartz crystal microbalance and dynamic vapor sorption experiments have also been used to measure moisture sorption isotherms in PLA films with varying crystallinity. A surprising result is that, within the accuracy of the experiments, crystalline and amorphous PLA films exhibit identical sorption isotherms.  相似文献   
967.
The problem of transforming a linear dynamical system in the neighbourhood of a state of equilibrium [1,2] is solved using the special problem of the damping of the system by controls of minimum intensity after a finite time interval. The possibility of using other problems of optimal control is discussed. The main attention is devoted to constructing algorithms of the operation of a device (a stabilizer) which is able, in real time, to generate a stabilizing control circulating in the closed optimal system when unknown perturbations operate constantly [3, 4]. The proposed method is based on the constructive theory of optimal control [5, 6]. Another form of this theory for solving the problem of stabilization is presented in [7](see also [8]).  相似文献   
968.
Using the relations of the improved model of layered anisotropic shells based on the straight line assumption taking account of the thermal compression over the thickness we obtain a resolvent system of equations for shells whose properties depend on temperature. We carry out a study of the stresses in a two-layer cylindrical shell formed by winding as a function of the winding angle. Translated fromMatematicheskie Metody i Fiziko-Mekhanicheskie Polya, Issue 35, 1992, pp. 82–85.  相似文献   
969.
Liquid crystals incorporating in their molecular framework a seven-membered ring are still relatively rare [1]. Recently the synthesis and thermal behaviour of a series of liquid crystal materials having a tropone moiety in their mesogenic core have been reported [2-4]. These mesogens, based on a 2-(acyloxy)tropone core structure, show intramolecular migration of the acyl substituents between the two oxygen atoms at C-1 and C-2, an effect already known for simple 2-(acyloxy)tropones in their isotropic solutions [5]. This migration involves a concerted [1, 9]-sigmatropic rearrangement [2]. This rearrangement could play a major role in determining the properties of the mesophases: it has been suggested in fact that, because of this rearrangement, the mesogenic molecules acquire a mean rod-like shape which can sustain the mesophase formation [2].  相似文献   
970.
We consider a method of obtaining an approximate system of equations of elasticity theory for shells, based on representing the components of the stress tensor and the displacement vector as a sum of products of moment characteristics depending on the coordinates of the base surface of the shell and functions of the normal coordinate to the base surface.Translated fromMatematicheskie Metody i Fiziko-Mekhanicheskie Polya, Issue 33, 1991, pp. 56–59.  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