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   292527篇
  免费   36165篇
  国内免费   195篇
  2016年   2931篇
  2015年   4337篇
  2014年   5021篇
  2013年   7202篇
  2012年   8095篇
  2011年   8014篇
  2010年   5525篇
  2009年   5137篇
  2008年   7123篇
  2007年   7302篇
  2006年   6924篇
  2005年   6866篇
  2004年   6669篇
  2003年   6765篇
  2002年   6433篇
  2001年   11082篇
  2000年   11201篇
  1999年   9234篇
  1998年   3587篇
  1997年   3743篇
  1996年   3727篇
  1995年   3476篇
  1994年   3470篇
  1993年   3459篇
  1992年   8191篇
  1991年   7980篇
  1990年   7767篇
  1989年   7702篇
  1988年   7265篇
  1987年   7219篇
  1986年   6683篇
  1985年   6825篇
  1984年   5737篇
  1983年   5140篇
  1982年   4102篇
  1981年   3944篇
  1980年   3585篇
  1979年   5938篇
  1978年   4642篇
  1977年   4440篇
  1976年   4238篇
  1975年   4584篇
  1974年   5046篇
  1973年   4940篇
  1972年   4590篇
  1971年   4141篇
  1970年   3648篇
  1969年   3674篇
  1968年   3274篇
  1967年   2829篇
排序方式: 共有10000条查询结果,搜索用时 156 毫秒
81.
82.
83.
84.
Intraperitoneal stimulation of adoptively sensitized rats with bacterial antigen promotes the localization of lymphoblasts at the site of antigen deposition. Lymphoblast extravasation activity (LEA) is generated only when specifically immune donor lymphocytes and the recipients of these cells share at least on Ag-B haplotype. However, if the specificity criteria for its formation are satisfied, LEA promotes the local development of lymphoblasts of all available specificities and irrespective of their Ag-B genotype. Allogeneic lymphoblasts do not participate actively in the delayed inflammatory reaction even when they are passively recruited into exudates. The results suggest that LEA is a T cell-derived mediator that amplifies the delayed type hypersensitivity reaction by directing recently activated lymphocytes into lesions.  相似文献   
85.
86.
Rosette and single-element strain gauges were implanted on the tibia in 2 dogs and recordings were made during locomotion on a treadmill. At foot contact and during the swing phase of locomotion, bone strains were low and directions of the principal strains were variable. There was a large shift in the directions of the principal strains at the beginning of the stance phase and bone strains were considerably higher. Peak strain occurred midway through the stance phase. At that time, the maximum principal strain (tension) was directed upwards and anteriorly between 30 and 60 degrees with respect to the long axis of the tibia. These bone strain patterns in the dog are similar to those found in sheep while both differ markedly from those found in humans.  相似文献   
87.
88.
89.
90.
To control the environmentally detrimental impact of acid rock drainage, two different countermeasures, layers of acid-buffering materials and sodium dodecyl sulphate addition, were tested for their efficiency in laboratory percolation experiments. In the experiment with a layer of calcium bentonite, only the iron output was reduced. The experiments with layers of concrete grains demonstrated a decrease of the microbial activity as well as a precipitation of heavy-metal ions, whereas the cell numbers did not decrease. Furthermore, finely grained concrete (1–5 mm) formed a water-tight hardpan (self-sealing layer). In the experiment with 1 mM sodium dodecyl sulphate, all the microorganisms were killed and hence metal sulphide dissolution was stopped. With 0.1 mM sodium dodecyl sulphate only a short, transient inhibition of leaching was achieved. The bacteria remained alive. Received: 16 February 1998 / Accepted: 23 February 1998  相似文献   
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