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   677370篇
  免费   82065篇
  国内免费   317篇
  759752篇
  2018年   5837篇
  2016年   7739篇
  2015年   10902篇
  2014年   12694篇
  2013年   18383篇
  2012年   20382篇
  2011年   20774篇
  2010年   14047篇
  2009年   12799篇
  2008年   18288篇
  2007年   19043篇
  2006年   17697篇
  2005年   17156篇
  2004年   16867篇
  2003年   16613篇
  2002年   16172篇
  2001年   30179篇
  2000年   30408篇
  1999年   24255篇
  1998年   8743篇
  1997年   9264篇
  1996年   8792篇
  1995年   8349篇
  1994年   8233篇
  1993年   8310篇
  1992年   20772篇
  1991年   20275篇
  1990年   19698篇
  1989年   19244篇
  1988年   17775篇
  1987年   17159篇
  1986年   15821篇
  1985年   15933篇
  1984年   13290篇
  1983年   11589篇
  1982年   8984篇
  1981年   8028篇
  1980年   7724篇
  1979年   12946篇
  1978年   10142篇
  1977年   9309篇
  1976年   8711篇
  1975年   9546篇
  1974年   10136篇
  1973年   10137篇
  1972年   9215篇
  1971年   8567篇
  1970年   7190篇
  1969年   6966篇
  1968年   6251篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
61.
Argon laser surgery is an effective treatment for ectasias and congenital port-wine stains; however, its use in children under the age of 13 is controversial. This paper reviews 202 children under the age of 13 who underwent argon laser treatments for congenital port-wine stains, spider angiomas, epidermal nevi, and lentigines. The clinical characteristics of port-wine stains in 170 children are discussed. Good to excellent results (moderate to complete clearing) in port-wine stains were obtained in 60 percent of patients and seemed to correlate best with lack of blanchability on pressure. Hypertrophic scarring was seen in only 7 children, all of whom had undressed wounds; no significant scarring has been seen in any subsequent child who had maintained a dressed wound postoperatively.  相似文献   
62.
63.
64.
65.
66.
67.
68.
The Saccharomyces cerevisiae SSU1 gene was isolated based on its ability to complement a mutation causing sensitivity to sulfite, a methionine intermediate. SSU1 encodes a deduced protein of 458 amino acids containing 9 or 10 membrane-spanning domains but has no significant similarity to other proteins in public databases. An Ssu1p-GEP fusion protein was localized to the plasma membrane. Multicopy suppression analysis, undertaken to explore relationships among genes previously implicated in sulfite metabolism, suggests a regulatory pathway in which SSU1 acts downstream of FZF1 and SSU3, which in turn act downstream of GRR1.  相似文献   
69.
An agar-degrading marine bacterium identified as a Microscilla species was isolated from coastal California marine sediment. This organism harbored a single 101-kb circular DNA plasmid designated pSD15. The complete nucleotide sequence of pSD15 was obtained, and sequence analysis indicated a number of genes putatively encoding a variety of enzymes involved in polysaccharide utilization. The most striking feature was the occurrence of five putative agarase genes. Loss of the plasmid, which occurred at a surprisingly high frequency, was associated with loss of agarase activity, supporting the sequence analysis results.  相似文献   
70.
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