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   945063篇
  免费   96936篇
  国内免费   494篇
  1042493篇
  2018年   9301篇
  2017年   8808篇
  2016年   12400篇
  2015年   15721篇
  2014年   18777篇
  2013年   27050篇
  2012年   30219篇
  2011年   31198篇
  2010年   21331篇
  2009年   19646篇
  2008年   27806篇
  2007年   28928篇
  2006年   27099篇
  2005年   26004篇
  2004年   25730篇
  2003年   24827篇
  2002年   24305篇
  2001年   41342篇
  2000年   40856篇
  1999年   32728篇
  1998年   11863篇
  1997年   12040篇
  1996年   11489篇
  1995年   10648篇
  1994年   10312篇
  1993年   10260篇
  1992年   26551篇
  1991年   26082篇
  1990年   25576篇
  1989年   24885篇
  1988年   22912篇
  1987年   22028篇
  1986年   20414篇
  1985年   20543篇
  1984年   16858篇
  1983年   14669篇
  1982年   11036篇
  1981年   10024篇
  1980年   9332篇
  1979年   15664篇
  1978年   12318篇
  1977年   11148篇
  1976年   10738篇
  1975年   11984篇
  1974年   12917篇
  1973年   12763篇
  1972年   11589篇
  1971年   10411篇
  1970年   9169篇
  1969年   8851篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
61.
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   
62.
63.
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   
64.
Reconstruction of bony structures of the face is always a problem as big as the defect and the function that must be replaced. Everything from simple grafts to sophisticated distant bone flaps has been used. Based on the studies of Cutting et al., Psillakis et al., and Casanova et al., we have developed the full-thickness galeoparietal bone flap, initially for mandibular reconstruction, but of great use for all maxillofacial reconstructions. From July of 1987 to December of 1988, 14 patients have been operated on. The experience with this flap is shown in four patients as follows: primary reconstruction of a mandible as a result of ameloblastoma, secondary reconstruction of a mandible with associated old fractures and malalignment of segments, bilateral malar reconstruction in a patient with Treacher Collins syndrome, and severe sequelae of an already treated Romberg case. Small variations could be made to best accommodate the technique used to the defect we were treating. Some technical details, the experience, the results, and possible sequelae or complications are also discussed.  相似文献   
65.
66.
67.
Besides vobtusine and vobtusine-lactone, deoxyvobtusine was isolated from the leaves of Voacanga grandifolia (Miq. Rolfe. Spectral and chemical evi  相似文献   
68.
69.
70.
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