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   613245篇
  免费   59813篇
  国内免费   1370篇
  2018年   7605篇
  2017年   7372篇
  2016年   11151篇
  2015年   17525篇
  2014年   18779篇
  2013年   23383篇
  2012年   26784篇
  2011年   24603篇
  2010年   16594篇
  2009年   14538篇
  2008年   20076篇
  2007年   20358篇
  2006年   18986篇
  2005年   24352篇
  2004年   23011篇
  2003年   20098篇
  2002年   16372篇
  2001年   21391篇
  2000年   20800篇
  1999年   17608篇
  1998年   6577篇
  1997年   6336篇
  1996年   5950篇
  1995年   5777篇
  1994年   5495篇
  1993年   5356篇
  1992年   14953篇
  1991年   14870篇
  1990年   14549篇
  1989年   13948篇
  1988年   13032篇
  1987年   12213篇
  1986年   11553篇
  1985年   11425篇
  1984年   9269篇
  1983年   7944篇
  1982年   5845篇
  1981年   5331篇
  1980年   4911篇
  1979年   8685篇
  1978年   6923篇
  1977年   6133篇
  1976年   5782篇
  1975年   6766篇
  1974年   7430篇
  1973年   7263篇
  1972年   6462篇
  1971年   6086篇
  1970年   5167篇
  1969年   5083篇
排序方式: 共有10000条查询结果,搜索用时 187 毫秒
41.
42.
Besides vobtusine and vobtusine-lactone, deoxyvobtusine was isolated from the leaves of Voacanga grandifolia (Miq. Rolfe. Spectral and chemical evi  相似文献   
43.
44.
45.
46.
47.
48.
49.
Pythium insidiosum is a pathogenic oomycete known since 1890 that causes pythiosis in mammals. In this report, seven P. insidiosum isolates were recovered from Venezuelan horses and were characterized. The strains were recovered from biopsied tissues and kunkers collected from granulomatous masses located on the hind limb and from a nodular lesion in the left upper eyelid, which decrease the ability of the horses to be used for working purposes. The methods used to identify P. insidiosum isolates were based on the production of sporangia and zoospores, histopathology and PCR assay. To further characterize these strains, portions of the 18S rRNA genes of the seven isolates were sequenced. The sequences showed high homology to previously described P. insidiosum DNA sequences available in GenBank. Similar studies based on the morphological, histological and molecular data identified the etiological agent in samples of granulomatous lesions in these equines as P. insidiosum. In America, the infection has been diagnosed more frequently in equines of Brazil, Colombia, Costa Rica and the United States of America.  相似文献   
50.
Thirteen healthy and fit men [age = 27 +/- 8 (SD) yr, height = 177 +/- 5 cm, mass = 75 +/- 7 kg, body fat = 14 +/- 5%, maximal O2 consumption = 51 +/- 4 ml. kg-1. min-1] participated in an experiment designed to test their thermoregulatory response to a challenging cold exposure after 5 h of demanding mixed exercise during which only water was consumed. Subjects expended 7,314 +/- 741 kJ on cycling, rowing, and treadmill-walking machines, performed 8,403 +/- 1,401 kg. m of mechanical work during resistance exercises, and completed 120 inclined sit-ups. Subjects then assumed a seated position in a 10 degrees C air environment while wearing shorts, T-shirt, rain hat, and neoprene gloves and boots. After 30 min the subjects were showered continuously with cold water ( approximately 920 ml/min at 10 degrees C) on their backs accompanied by a 6 km/h wind for up to 4 h. Blood samples were taken from the nondominant arm every 30 min during the exposure and assayed for energy metabolites, hormones, indexes of hydration, and neurotransmitters. Counterbalanced control trials without prior exercise were also conducted. Blood insulin was higher during the control trial, whereas values of glycerol, nonesterified fatty acids, beta-hydroxybutyrate, lactate, cortisol, free triiodothyronine, and thyroxine were lower. Three subjects lasted the maximum duration of 4.5 h for control and fatigue trials, with final rectal temperatures of 36.43 +/- 0.21 and 36.08 +/- 0.49 degrees C, respectively. Overall, the duration of 172 +/- 68 (SD) min for the fatigue trial was not significantly different from that of the control trial (197 +/- 72 min) and, therefore, was not affected by the preexposure exercise. Although duration was positively correlated to body fatness and shivering intensity, the latter was not correlated to any physical characteristic or the fitness level of the individual.  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