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   600534篇
  免费   4480篇
  国内免费   1659篇
化学   290705篇
晶体学   8309篇
力学   32274篇
综合类   17篇
数学   98083篇
物理学   177285篇
  2021年   5043篇
  2020年   5485篇
  2019年   6226篇
  2018年   18178篇
  2017年   18066篇
  2016年   17276篇
  2015年   6945篇
  2014年   10693篇
  2013年   23733篇
  2012年   21782篇
  2011年   31436篇
  2010年   21615篇
  2009年   21902篇
  2008年   26709篇
  2007年   28524篇
  2006年   18807篇
  2005年   17797篇
  2004年   16857篇
  2003年   15808篇
  2002年   14781篇
  2001年   14923篇
  2000年   11586篇
  1999年   8875篇
  1998年   7755篇
  1997年   7588篇
  1996年   7111篇
  1995年   6369篇
  1994年   6338篇
  1993年   6109篇
  1992年   6428篇
  1991年   6924篇
  1990年   6630篇
  1989年   6542篇
  1988年   6378篇
  1987年   6184篇
  1986年   5927篇
  1985年   7453篇
  1984年   7811篇
  1983年   6567篇
  1982年   6857篇
  1981年   6364篇
  1980年   6047篇
  1979年   6546篇
  1978年   6775篇
  1977年   6648篇
  1976年   6602篇
  1975年   6316篇
  1974年   6138篇
  1973年   6448篇
  1972年   4724篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
We investigated the laser-induced fluorescence spectra (LIF) of porcine cardiac tissues with different degrees of viability. The data obtained are compared with the results of routine histological investigations and also with the experiments performed with the use of fluorescent probes. It has been found with a high degree of reliability that the loss of the viability of the myocardium tissue leads to the alteration of its LIF spectra. This can be used for low-invasive rapid control of transplant viability in the process of its preparation and during surgery.  相似文献   
992.
 We prove that for any simple theory which is constructed via Fr?issé-Hrushovski method, if the forking independence is the same as the d-independence then the stable forking property holds. Received: 22 January 2001 / Published online: 19 December 2002 This article is part of the author's D-Phil thesis, written at the University of Oxford and supported by the Ministry of Higher Education of Iran. The author would like to thank the Institute for Studies in Theoretical Physics and Mathematics (IPM), Tehran, Iran, for its financial support whilst working on this article. Mathematics Subject Classification (2000): 03C45 Key words or phrases: Generic structures – Fr?issé-Hrushovski method – Predimension – Simple theories – Stable theories – Stable forking conjecture  相似文献   
993.
The relaxor properties of Fe-doped TlInS2 crystals are investigated. It is shown that Fe-doped TlInS2 compounds exhibit all features inherent in relaxor ferroelectric materials. The temperature range of existence of the microdomain (relaxor) state and the temperature of the transition from this state to a macro-domain state are determined.  相似文献   
994.
The classical economic order quantity (EOQ) model assumes that items produced are of perfect quality and that the unit cost of production is independent of demand. However, in realistic situations, product quality is never perfect, but is directly affected by the reliability of the production process. In this paper, we consider an EOQ model with imperfect production process and the unit production cost is directly related to process reliability and inversely related to the demand rate. In addition, a numerical example is given to illustrate the developed model. Sensitivity analysis is also performed and discussed.  相似文献   
995.
996.
Baidyshev  V. S.  Udodov  V. N.  Popov  A. A.  Potekaev  A. I. 《Russian Physics Journal》2003,46(12):1193-1198
The paper offers a method for calculating phase diagrams of polytype transformations in close-packed crystals based on the generalized axial Ising's model of finite dimensions at non-zero temperatures. Using the Metropolis algorithm, the behavior of systems with polytype transitions is studied under the conditions of changing external shear stress and temperature. The longest polytype period considered here is taken to be 30 close-packed planes.  相似文献   
997.
998.
The use of the integral equation method in electromagnetic-sounding inverse problems is considered. Several approaches to the solution of these inverse problems are proposed.  相似文献   
999.
Indoor radon measurements in dwellings of four Saudi Arabian cities   总被引:1,自引:0,他引:1  
An indoor radon survey of a total of 269 dwellings, with one dosimeter per house, distributed in four Saudi Arabian cities was carried out. The objective of this survey was to carry out indoor radon measurements of two cities in the Eastern Province, Khafji and Hafr Al-Batin and to compare this with two cities in the Western Province, Al-Madina and Taif. The survey provides additional information about indoor radon concentrations in Saudi Arabia. The results of the survey in these cities showed that the overall minimum, maximum and average radon concentration were 7,137 and 30 Bqm−3, respectively. The lowest average radon concentration (20 Bqm−3) was found in Hafr Al-Batin, while the highest average concentration was found in Khafji (40 Bqm−3).  相似文献   
1000.
We prove that the sufficient conditions for the asymptotic stability of impulsive systems obtained by Gurgula and Perestyuk are also necessary conditions.  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