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   344898篇
  免费   3827篇
  国内免费   1684篇
化学   189795篇
晶体学   5266篇
力学   14322篇
综合类   64篇
数学   37126篇
物理学   103836篇
  2020年   2763篇
  2019年   2990篇
  2018年   3944篇
  2017年   3967篇
  2016年   5839篇
  2015年   3804篇
  2014年   5612篇
  2013年   14163篇
  2012年   11695篇
  2011年   14291篇
  2010年   10182篇
  2009年   10063篇
  2008年   13587篇
  2007年   13553篇
  2006年   12904篇
  2005年   11773篇
  2004年   10485篇
  2003年   9441篇
  2002年   9296篇
  2001年   11241篇
  2000年   8404篇
  1999年   6287篇
  1998年   4817篇
  1997年   4872篇
  1996年   4725篇
  1995年   4250篇
  1994年   4291篇
  1993年   4022篇
  1992年   4723篇
  1991年   4844篇
  1990年   4536篇
  1989年   4427篇
  1988年   4341篇
  1987年   4300篇
  1986年   4125篇
  1985年   5349篇
  1984年   5390篇
  1983年   4431篇
  1982年   4660篇
  1981年   4286篇
  1980年   4083篇
  1979年   4500篇
  1978年   4767篇
  1977年   4797篇
  1976年   4753篇
  1975年   4368篇
  1974年   4478篇
  1973年   4529篇
  1972年   3359篇
  1971年   2672篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
171.
In this paper we study a stochastic differential equation with multivalued maximally monotone drift operator. Under certain assumptions on the growth of the multivalued operator we prove a theorem on the existence and uniqueness of the solution of such an equation.Translated fromTeoriya Sluchainykh Protsessov, Vol. 15, pp. 54–59, 1987.  相似文献   
172.
Summary Wet-chemical cleaning procedures of Si(100) wafers are surface analytically characterized and compared. Hydrophobic surfaces show considerably less native oxides in comparison to hydrophilic surfaces.The growth of the oxide is determined as a function of exposure to air by means of XPS measurements. The chemically shifted Si2p XPS signal is utilized for the quantification of the growth kinetics.One hour after cleaning no chemically shifted Si2p XPS peak is discernible on the hydrophobic surfaces. Assuming homogeneous oxide growth, the detection limit of native oxides is estimated to be below 0.05 nm using an emission angle of 18° with respect to the wafer surface. The calculation of the oxide thickness from the chemically shifted and nonchemically shifted Si2p XPS peak intensities is carried out according to Finster and Schulze [1]. For more than a day after cleaning no surface oxides can be identified on the hydrophobic surfaces. The oxide growth kinetics is logarithmic. The very slow oxidation rate cannot be attributed to fluorine residues since no fluorine is seen by XPS. We explain the slow oxidation rate by a homogeneous hydrogen saturated Si(100) wafer surface.
Oberflächenanalytische Charakterisierung oxidfreier Si(100)-Waferoberflächen
  相似文献   
173.
174.
175.
176.
177.
Translated from Ukrainskii Matematicheskii Zhurnal, Vol. 41, No. 8, pp. 1137–1141, August, 1989.  相似文献   
178.
179.
The inference of optical depth and particle size of clouds and aerosols using remotely sensed reflected radiance at solar wavelengths has received much attention recently. The information these measurements provide is path integrated. However, very little is known about the vertical distribution of this weighting. To characterize it, we first solve the radiative transfer equation (RTE) by a Green's function approach, and then investigate the sensitivity of the weighting to vertical inhomogeneities in the extinction by introducing a function that is closely related to the Green's function, herein called the contribution function. This function calculates the contributions to the radiance at the upper boundary of the medium by underlying layers. Three hypothetical clouds of identical optical depth but exhibiting different extinction profiles were used in this study. The contribution function was found very sensitive to the extinction profile. The global reflection and transmission matrices used to construct the Green's function, derived using an eigenmatrix method, resulted in an efficient, stable, and accurate method for calculating the emerging radiances that can be extended to multi-layered media.  相似文献   
180.
A control volume type numerical methodology for the analysis of steady three‐dimensional rotating flows with heat transfer, in both laminar and turbulent conditions, is implemented and experimentally tested. Non‐axisymmetric momentum and heat transfer phenomena are allowed for. Turbulent transport is alternatively represented through three existing versions of the kε model that were adjusted to take into account the turbulence anisotropy promoted by rotation, streamline curvature and thermal buoyancy. Their relative performance is evaluated by comparison of calculated local and global heat balances with those obtained through measurements in a laboratory device. A modified version of the Lam and Bremhorst, low Reynolds number model is seen to give the best results. A preliminary analysis focused on the flow structure and the transfer of heat is reported. Copyright © 2002 John Wiley & Sons, Ltd.  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