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   445624篇
  免费   51504篇
  国内免费   738篇
  497866篇
  2018年   4167篇
  2017年   4008篇
  2016年   5713篇
  2015年   8253篇
  2014年   9605篇
  2013年   12948篇
  2012年   15339篇
  2011年   15797篇
  2010年   10455篇
  2009年   9492篇
  2008年   13845篇
  2007年   14295篇
  2006年   13433篇
  2005年   12808篇
  2004年   12869篇
  2003年   12011篇
  2002年   11670篇
  2001年   18921篇
  2000年   18856篇
  1999年   15078篇
  1998年   5624篇
  1997年   5632篇
  1996年   5358篇
  1995年   5151篇
  1994年   4852篇
  1993年   4852篇
  1992年   12482篇
  1991年   12439篇
  1990年   12202篇
  1989年   11670篇
  1988年   10839篇
  1987年   10217篇
  1986年   9738篇
  1985年   9508篇
  1984年   7883篇
  1983年   6836篇
  1982年   5137篇
  1981年   4631篇
  1980年   4312篇
  1979年   7351篇
  1978年   5966篇
  1977年   5294篇
  1976年   4960篇
  1975年   5774篇
  1974年   6304篇
  1973年   6124篇
  1972年   5461篇
  1971年   5078篇
  1970年   4275篇
  1969年   4205篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
31.
Besides vobtusine and vobtusine-lactone, deoxyvobtusine was isolated from the leaves of Voacanga grandifolia (Miq. Rolfe. Spectral and chemical evi  相似文献   
32.
33.
34.
35.
36.
37.
38.
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   
39.
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   
40.
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