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   5088篇
  免费   130篇
  国内免费   7篇
化学   3013篇
晶体学   125篇
力学   169篇
数学   402篇
物理学   1516篇
  2023年   34篇
  2022年   115篇
  2021年   109篇
  2020年   114篇
  2019年   124篇
  2018年   120篇
  2017年   160篇
  2016年   190篇
  2015年   136篇
  2014年   186篇
  2013年   393篇
  2012年   303篇
  2011年   316篇
  2010年   216篇
  2009年   194篇
  2008年   258篇
  2007年   216篇
  2006年   155篇
  2005年   149篇
  2004年   118篇
  2003年   104篇
  2002年   113篇
  2001年   60篇
  2000年   53篇
  1999年   36篇
  1998年   33篇
  1997年   38篇
  1996年   43篇
  1995年   29篇
  1994年   32篇
  1993年   41篇
  1992年   51篇
  1991年   36篇
  1990年   40篇
  1989年   49篇
  1988年   44篇
  1987年   42篇
  1986年   32篇
  1985年   61篇
  1984年   57篇
  1983年   40篇
  1982年   44篇
  1981年   51篇
  1980年   45篇
  1979年   46篇
  1978年   43篇
  1977年   51篇
  1976年   54篇
  1975年   44篇
  1974年   38篇
排序方式: 共有5225条查询结果,搜索用时 14 毫秒
161.
An efficient, green, and facile method has been developed for the synthesis of benzazole and thiourea analogues from naturally occurring erucin in moderate to good yields. The reaction was carried out in water without using any metal catalyst or base. The present method tolerated the various functional groups on aromatic rings and also applicable for other isothiocyanates.  相似文献   
162.
Image segmentation is required to be studied in detail some particular features (areas of interest) of a digital image. It forms an important and exigent part of image processing and requires an exhaustive and robust search technique for its implementation. In the present work we have studied the working of MRLDE, a newly proposed variant of differential evolution combined with Otsu method, a well known image segmentation method for bi-level thresholding. The proposed variant, termed as Otsu+MRLDE, is tested on a set of 10 images and the results are compared with Otsu method and some other well known metaheuristics.  相似文献   
163.
We have investigated the structural, electronic, magnetic and optical properties of Hg1?xMnxTe in the zinc-blende phase for 0≤x≤1. The calculations were performed by using the full potential linearized augmented plane wave plus local orbitals method within the framework of the density functional theory. The lattice constants of Hg1?xMnxTe at different Mn concentrations exhibit Vegard's law perfectly. For spin-up channel the Mn 3d bands are occupied and mixed with the Te 5p bands whereas for spin-down channel the Mn 3d bands are unoccupied. The values of the p–d exchange splitting energy, ?x(pd) as produced by the Mn 3d states are given. The contribution of the valence band and the conduction band in the process of exchange and splitting is described by the exchange coupling constants N0α and N0β. Due to p–d hybridization the magnetic moment of the Mn atom reduces, which results in small local magnetic moments on the non-magnetic Hg and Te sites. The potential applications of Hg1?xMnxTe in infrared device have been discussed on the basis of its optical properties.  相似文献   
164.
The structural properties of Al isotopes are analysed using the relativistic mean field formalism with NL3 parameter set. The Glauber model technique is implemented to study the reaction dynamics for 23?28Al taking 12C as the target. The enhanced reaction cross section, high value of radius, narrow longitudinal momentum distribution and small proton separation energy of 23Al favours a proton halo structure for this nucleus.  相似文献   
165.
166.
167.
168.
In this paper, we discuss the two-layered Jeffrey-fluid model with mild stenosis in narrow tubes. The blood flow in narrow arteries is treated as a two-fluid model with the suspension of erythrocytes, leukocytes, etc., as a Jeffrey fluid, which is a non-Newtonian fluid, in the core region and plasma, a Newtonian fluid, in the peripheral region. An analytical solution has been obtained for the velocity in the core and peripheral region, volume flow rate, resistance to flow, and wall-shear stress. The effect of Jeffrey-fluid parameters, like the height of stenosis, viscosity, etc., on volume flow rate, resistance to flow (impedance), and wall-shear stress has been discussed graphically. Through the present study, it is found that the wall-shear stress and resistance to flow increases with the increase in height of stenosis and decreases with the increase in the ratio of relaxation time. It is also found that the velocity decreases with an increase in stenosis height in both the core and the peripheral region. A previous result has been also verified.  相似文献   
169.
170.
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