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   1535309篇
  免费   138750篇
  国内免费   1594篇
  1675653篇
  2021年   18129篇
  2019年   16316篇
  2018年   18672篇
  2017年   17445篇
  2016年   28907篇
  2015年   43259篇
  2014年   51281篇
  2013年   77769篇
  2012年   42695篇
  2011年   32824篇
  2010年   45948篇
  2009年   46792篇
  2008年   30831篇
  2007年   29424篇
  2006年   33635篇
  2005年   34477篇
  2004年   33728篇
  2003年   31301篇
  2002年   29454篇
  2001年   41332篇
  2000年   38768篇
  1999年   36949篇
  1998年   26509篇
  1997年   26365篇
  1996年   25781篇
  1995年   23799篇
  1994年   23627篇
  1993年   22755篇
  1992年   32399篇
  1991年   30999篇
  1990年   29857篇
  1989年   30588篇
  1988年   28291篇
  1987年   26796篇
  1986年   25360篇
  1985年   27428篇
  1984年   26160篇
  1983年   23078篇
  1982年   22416篇
  1981年   21434篇
  1980年   19993篇
  1979年   22528篇
  1978年   20311篇
  1977年   19565篇
  1976年   18696篇
  1975年   18542篇
  1974年   19536篇
  1973年   19798篇
  1972年   17096篇
  1971年   15701篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
92.
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   
93.
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   
94.
95.
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   
96.
97.
98.
99.
Besides vobtusine and vobtusine-lactone, deoxyvobtusine was isolated from the leaves of Voacanga grandifolia (Miq. Rolfe. Spectral and chemical evi  相似文献   
100.
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