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   559852篇
  免费   53430篇
  国内免费   1547篇
  2018年   15883篇
  2017年   14517篇
  2016年   13654篇
  2015年   10175篇
  2014年   11340篇
  2013年   15155篇
  2012年   21426篇
  2011年   29546篇
  2010年   22786篇
  2009年   18031篇
  2008年   24276篇
  2007年   26151篇
  2006年   15086篇
  2005年   14442篇
  2004年   14952篇
  2003年   14032篇
  2002年   13381篇
  2001年   19774篇
  2000年   19571篇
  1999年   15587篇
  1998年   5822篇
  1997年   5807篇
  1996年   5523篇
  1995年   5305篇
  1994年   4961篇
  1993年   4987篇
  1992年   12780篇
  1991年   12709篇
  1990年   12438篇
  1989年   11881篇
  1988年   11051篇
  1987年   10411篇
  1986年   9918篇
  1985年   9696篇
  1984年   8047篇
  1983年   6987篇
  1982年   5249篇
  1981年   4730篇
  1980年   4395篇
  1979年   7528篇
  1978年   6070篇
  1977年   5385篇
  1976年   5060篇
  1975年   5875篇
  1974年   6437篇
  1973年   6237篇
  1972年   5812篇
  1971年   5434篇
  1970年   4394篇
  1969年   4322篇
排序方式: 共有10000条查询结果,搜索用时 250 毫秒
111.
112.
113.
114.
115.
Samples of marine pleuston were collected from the sea-surface along considerable sections of the track of Eye of the Wind during its 2-year circumnavigational expedition 'Operation Drake' from November 1978 to October 1980. One hundred and eleven of the tow samples contained insects of the genus Halobates . They were assigned to four oceanic species: H. micans, H. sericeus, H. germanus and H. splendens; two coastal species: H. maculatus, H. princeps, and one undescribed species. Various development stages of the oceanic species were found. The locations, time of collection and surface temperatures where sea-skaters were collected are tabulated. Distributional boundaries and population densities of the oceanic species collected are discussed.  相似文献   
116.
117.
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   
118.
Burials and mummies of dogs from the Arica, Chile, area are described. It is concluded that these dogs were brought to this area 2500 years ago by shepherds from the highlands and are still present, relatively unchanged.  相似文献   
119.
Vitamin B6, measured as pyridoxal 5′-phosphate (PLP), is a co-enzyme in the transsulfuration pathway of homocysteine metabolism. Since depletion of PLP has been suggested as an independent risk factor for coronary artery disease, PLP is frequently measured to guide patient care. By a change and utilization of an Aquasil C18 column and the addition of an acetonitrile clean-up gradient to the potassium phosphate, with sodium perchlorate and bisulfite buffer between samples we report the modification of a previously described method for analysis of PLP. The result is a more practical, efficient, reliable and robust method for daily clinical use. We also determined and report that it is critical to protect freshly prepared standard PLP samples from light exposure during assay preparation.  相似文献   
120.
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