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   1371367篇
  免费   120288篇
  国内免费   1449篇
  2021年   17773篇
  2019年   16182篇
  2018年   17969篇
  2017年   16674篇
  2016年   28179篇
  2015年   42578篇
  2014年   50536篇
  2013年   76983篇
  2012年   36586篇
  2011年   25145篇
  2010年   43875篇
  2009年   45248篇
  2008年   23944篇
  2007年   22173篇
  2006年   27346篇
  2005年   28414篇
  2004年   27761篇
  2003年   25352篇
  2002年   23589篇
  2001年   33673篇
  2000年   30970篇
  1999年   31382篇
  1998年   25490篇
  1997年   25313篇
  1996年   24901篇
  1995年   22995篇
  1994年   22826篇
  1993年   21895篇
  1992年   27750篇
  1991年   26225篇
  1990年   25237篇
  1989年   26061篇
  1988年   24125篇
  1987年   22712篇
  1986年   21657篇
  1985年   23737篇
  1984年   23401篇
  1983年   20677篇
  1982年   20959篇
  1981年   20099篇
  1980年   18702篇
  1979年   19511篇
  1978年   18175篇
  1977年   17539篇
  1976年   16838篇
  1975年   16344篇
  1974年   16961篇
  1973年   17288篇
  1972年   14809篇
  1971年   13552篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
111.
112.
113.
Zooplankton data collected during September 1995 in the NorthWest Atlantic at 4139'N, 4958'W (the location of the siteof the ‘Titanic’ wreck) were analysed. The regioninvestigated was characterized by a very sharp frontal zonebetween the Gulf Stream and the main stream of the LabradorCurrent. The total plankton biomass in the water column wasvery high. The macroplankton biomass values below the 600 mlayer were significantly higher as compared with the similarvalues measured before in other productive boreal regions ofthe Atlantic and Pacific oceans. A lot of dead mesoplanktonanimals occurred in the deep layers. The reason was that thecold-water mesoplankton advected by the Labrador Current diedoff intensively within the deep layers of the frontal zone andwere used as a food resource by the macroplankton carnivoresand scavengers that were very abundant there.  相似文献   
114.
A finite element based method to determine the incremental elastic material properties of planar membranes was developed and evaluated. The method is applicable to tissues that exhibit inhomogeneity, geometric and material nonlinearity, and anisotropy. Markers are placed on the tissue to form a four-node quadrilateral element. The specimen is loaded to an initial reference state, then three incremental loading sets are applied and the nodal displacements recorded. One of these loadings must include shear. These data are used to solve an over-determined system of equations for the tangent stiffness matrix. The method was first verified using analytical data. Next, data obtained from a latex rubber sheet were used to evaluate experimental procedures. Finally, experiments conducted on preconditioned rat skin revealed nonlinear orthotropic behavior. The vector norm comparing the applied and calculated nodal force vectors was used to evaluate the accuracy of the solutions.  相似文献   
115.
Argon laser surgery is an effective treatment for ectasias and congenital port-wine stains; however, its use in children under the age of 13 is controversial. This paper reviews 202 children under the age of 13 who underwent argon laser treatments for congenital port-wine stains, spider angiomas, epidermal nevi, and lentigines. The clinical characteristics of port-wine stains in 170 children are discussed. Good to excellent results (moderate to complete clearing) in port-wine stains were obtained in 60 percent of patients and seemed to correlate best with lack of blanchability on pressure. Hypertrophic scarring was seen in only 7 children, all of whom had undressed wounds; no significant scarring has been seen in any subsequent child who had maintained a dressed wound postoperatively.  相似文献   
116.
117.
118.
119.
    
Ohne Zusammenfassung  相似文献   
120.
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