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   101556篇
  免费   29443篇
  国内免费   1102篇
耳鼻咽喉   2430篇
儿科学   2661篇
妇产科学   2361篇
基础医学   3005篇
口腔科学   5154篇
临床医学   26312篇
内科学   25554篇
皮肤病学   3411篇
神经病学   12457篇
特种医学   3819篇
外科学   18492篇
综合类   110篇
现状与发展   40篇
一般理论   3篇
预防医学   13677篇
眼科学   2122篇
药学   1369篇
中国医学   46篇
肿瘤学   9078篇
  2024年   741篇
  2023年   5034篇
  2022年   1118篇
  2021年   2775篇
  2020年   5365篇
  2019年   2122篇
  2018年   6996篇
  2017年   7369篇
  2016年   7968篇
  2015年   8074篇
  2014年   10553篇
  2013年   12322篇
  2012年   4021篇
  2011年   3822篇
  2010年   6966篇
  2009年   9232篇
  2008年   3708篇
  2007年   2735篇
  2006年   3840篇
  2005年   2397篇
  2004年   1802篇
  2003年   1430篇
  2002年   1321篇
  2001年   1839篇
  2000年   1162篇
  1999年   1710篇
  1998年   2116篇
  1997年   1935篇
  1996年   1983篇
  1995年   1714篇
  1994年   1105篇
  1993年   934篇
  1992年   742篇
  1991年   654篇
  1990年   510篇
  1989年   524篇
  1988年   508篇
  1987年   379篇
  1986年   363篇
  1985年   305篇
  1984年   254篇
  1983年   302篇
  1982年   229篇
  1981年   203篇
  1980年   121篇
  1978年   120篇
  1977年   118篇
  1976年   86篇
  1974年   72篇
  1972年   73篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
61.
62.
This study evaluated the effects of tobacco Purchase, Use and Possession (PUP) laws on student perceptions of adolescent tobacco use within towns and schools. Twenty‐four towns were randomly assigned into two conditions, the experimental condition (E PUP) involved efforts to increase both PUP law enforcement and reduce minors' access to commercial sources of tobacco, whereas the control condition (C) focused only on efforts to reduce minors' access to commercial sources of tobacco. A hierarchical linear modeling analytical approach was selected due to the multilevel data and nested design. The present study found that over time, youth in the experimental PUP condition observed less youth tobacco usage at school and in their town, and perceived lower rates of tobacco among their peers at school and among friends than youth in the control condition. The findings suggest that PUP law enforcement might be used to strengthen community norms against youth tobacco use.  相似文献   
63.
64.
65.
66.
67.
68.
69.
PURPOSE: The purpose of this study was to measure spectrophotometrically the color stability of pigmented A-2186 silicone maxillofacial elastomer with 10% by volume of titanium white dry earth opacifier before and after exposure to microwave energy over a simulated 1.5-year period of microwave sterilization. Materials AND METHODS: A-2186 silicone elastomer opacified with titanium white dry earth pigment, pigmented with 5 cosmetic dry earth pigment colors [no pigment (control) group (Pc), red (Pr), yellow ochre (Py), burnt sienna (Po), and a mixture of Pr + Py + Po color group (P3)], was used in this study. Each of the 5 experimental groups consisted of 5 specimens. All specimens were placed in a 250 ml glass beaker filled with 150 ml of water (replenished for each microwave exposure). An exposure of 6 minutes was used 18 times (simulating 1.5 years of microwave sterilization with one 6 minute exposure monthly). Reflectance values were measured by spectrophotometer. Three- and two-way analyses of variance with repeated measures were performed for the color difference (DeltaE*) with the factors of group/color/months, and group/months, respectively. Means were compared by Tukey Honest Significant Difference (HSD) multiple range test calculated at the 0.05 level of significance using SPSS. RESULTS: The trained human eye can detect color changes (DeltaE*) greater than 1.0. Most DeltaE* values of the red pigment group at all intervals and the mixed pigment group at 15- and 18- month intervals increased significantly greater than 1.0 (p < 0.001) compared with the control group. Yellow and burnt sienna groups remained the most color stable over time with DeltaE* values below 0.35. CONCLUSIONS: Lack of color stability of red dry earth pigmented A-2186 silicone maxillofacial elastomers was clinically significant after 12-month exposure to microwave energy as compared with yellow, burnt sienna, and opacified A-2186 dry earth pigments.  相似文献   
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