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   454149篇
  免费   52310篇
  国内免费   741篇
  2018年   4246篇
  2017年   4078篇
  2016年   5854篇
  2015年   8459篇
  2014年   9825篇
  2013年   13309篇
  2012年   15741篇
  2011年   16212篇
  2010年   10749篇
  2009年   9759篇
  2008年   14237篇
  2007年   14720篇
  2006年   13838篇
  2005年   13239篇
  2004年   13337篇
  2003年   12419篇
  2002年   12083篇
  2001年   19011篇
  2000年   18919篇
  1999年   15195篇
  1998年   5750篇
  1997年   5721篇
  1996年   5465篇
  1995年   5234篇
  1994年   4970篇
  1993年   4954篇
  1992年   12558篇
  1991年   12521篇
  1990年   12284篇
  1989年   11751篇
  1988年   10921篇
  1987年   10282篇
  1986年   9811篇
  1985年   9605篇
  1984年   7990篇
  1983年   6928篇
  1982年   5277篇
  1981年   4784篇
  1980年   4461篇
  1979年   7447篇
  1978年   6089篇
  1977年   5403篇
  1976年   5052篇
  1975年   5847篇
  1974年   6412篇
  1973年   6226篇
  1972年   5528篇
  1971年   5122篇
  1970年   4348篇
  1969年   4275篇
排序方式: 共有10000条查询结果,搜索用时 328 毫秒
101.
THE TIMING OF DIVISION IN CHLAMYDOMONAS   总被引:3,自引:2,他引:1  
  相似文献   
102.
The neutrophil-stimulating properties of 38 S. aureus strains and 32 S. epidermidis strains were studied in the reaction of luminol-mediated chemiluminescence. All S. aureus strains and 29 S. epidermidis strains were found to possess neutrophil-stimulating activity, the mean activity index for S. aureus being significantly higher. The stimulating activity of the strains varied within a wide range (the variation coefficient was 120.0 +/- 21.9%) and did not correlate with the content of protein A in bacterial cells and the degree of their hydrophoby. The opsonization of staphylococci with normal human serum enhanced the neutrophil reaction 1.5- to 100-fold and simultaneously leveled out the chemiluminescence indices in experiments with different strains (the variation coefficient was 8.0 +/- 1.5%). The nature of the neutrophil-stimulating effect of staphylococci and its relationship to the exploratory reactions of phagocytes are discussed.  相似文献   
103.
104.
105.
106.
107.
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   
108.
ABSTRACT   The phrase persistent vulnerability reflects the enduring relationship of the rural population in Ceará with a highly variable climate. Persistence underscores the historical and unyielding nature of this vulnerability. Yet contrary to once-catastrophic rates of mortality etched in a public consciousness, no one dies from severe droughts and few people flee them as in the past. Government relief and social transfers have become the institutionalized form of adaptation, giving way to the counterintuitive reality that drought stabilizes the food and income supply for poor people. We analyze how maladaptive risk reduction, which is embedded in clientilistic social relations, undermines resilience, and we examine pathways toward a more sustainable adaptive relationship.  相似文献   
109.
110.
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   
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