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   1650095篇
  免费   159799篇
  国内免费   1534篇
  1811428篇
  2021年   18157篇
  2019年   16261篇
  2018年   18957篇
  2017年   17664篇
  2016年   29065篇
  2015年   43303篇
  2014年   51377篇
  2013年   77751篇
  2012年   45158篇
  2011年   35636篇
  2010年   46584篇
  2009年   47172篇
  2008年   33038篇
  2007年   32160篇
  2006年   35657篇
  2005年   36583篇
  2004年   35821篇
  2003年   33243篇
  2002年   31281篇
  2001年   48562篇
  2000年   46665篇
  1999年   42840篇
  1998年   27328篇
  1997年   27282篇
  1996年   26580篇
  1995年   24778篇
  1994年   24516篇
  1993年   23794篇
  1992年   37514篇
  1991年   36223篇
  1990年   35129篇
  1989年   35382篇
  1988年   32854篇
  1987年   31282篇
  1986年   29786篇
  1985年   31643篇
  1984年   29435篇
  1983年   25919篇
  1982年   24181篇
  1981年   23089篇
  1980年   21535篇
  1979年   26252篇
  1978年   23022篇
  1977年   21873篇
  1976年   20911篇
  1975年   21237篇
  1974年   22205篇
  1973年   22384篇
  1972年   19817篇
  1971年   17854篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
131.
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   
132.
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   
133.
134.
Over the past 10 years the AIDS crisis has produced a large volume of writing. Much of this is documentary. Dozens of studies of AIDS from various clinical and political perspectives have been complemented by just as many published diaries, autobiographies, novels, plays, and poems. A few of these works have risen to the surface not only as extraordinarily valuable testimonies to the changes AIDS has wrought in individual and collective life but also as first-rate literary works, worth reading because beyond their immediate purposes they articulate with extraordinary lucidity and compassion some deep truths about the human--and the modern--condition. Paul Monette's Borrowed Time is among the most distinctive of those. It speaks not only for the community of people with AIDS and those who support them but for a generation.  相似文献   
135.
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   
136.
137.
138.
139.
140.
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