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   1937175篇
  免费   194530篇
  国内免费   1909篇
  2021年   18735篇
  2018年   20227篇
  2017年   19037篇
  2016年   30219篇
  2015年   44263篇
  2014年   52526篇
  2013年   78804篇
  2012年   57874篇
  2011年   50979篇
  2010年   50666篇
  2009年   49765篇
  2008年   46502篇
  2007年   46107篇
  2006年   47422篇
  2005年   47935篇
  2004年   47122篇
  2003年   44259篇
  2002年   42036篇
  2001年   66890篇
  2000年   65275篇
  1999年   56237篇
  1998年   29694篇
  1997年   29607篇
  1996年   28462篇
  1995年   26645篇
  1994年   26173篇
  1993年   25733篇
  1992年   47740篇
  1991年   45892篇
  1990年   44587篇
  1989年   44546篇
  1988年   41134篇
  1987年   39325篇
  1986年   36917篇
  1985年   38240篇
  1984年   34395篇
  1983年   29933篇
  1982年   26711篇
  1981年   25055篇
  1980年   23434篇
  1979年   31127篇
  1978年   26603篇
  1977年   24819篇
  1976年   23445篇
  1975年   24290篇
  1974年   25786篇
  1973年   25877篇
  1972年   22683篇
  1971年   20894篇
  1970年   18214篇
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
981.
982.
S P Sutton  R Dam  M K Nielsen 《Life sciences》1974,15(12):2097-2108
Levels of 7.8, 18.5 and 26 mole % deuterium oxide were administered sequentially to Coturnix japonica (Japanese quail) via the drinking water. The primary effect observed was on egg frequency, which decreased from a normal level of 0.89 for 7.8 mole % D2O to a low of 0.38 during the administration of 26 mole % D2O. Adverse symptoms, such as hyperexcitability, convulsions, skin ulcerations, comatosity, weight loss, or death, which have been associated with deuterium toxicity in other animals, were not observed in these experiments. The amount of deuterium deposited in the water of the egg was 6.9, 13.98, and 19.83 mole % when 7.8, 18.5 and 26 mole % deuterium respectively was administered. For each period, the deuterium content of egg water rapidly reached a maximum concentration after which the concentration decreased slightly. This dilution effect has not been noted previously in body fluids from other animals.  相似文献   
983.
984.
985.
986.
987.
988.
989.
Drought-stressed flatpea (Lathyrus sylvestris L.) plants from8 to 22 weeks old were analysed for nitrogen, soluble proteinand free amino acids. An increase in nitrogen and free aminoacid concentrations and a decrease in soluble protein levelwere observed in roots of plants up to 16 weeks old. The cumulativeconcentration of free amino acids increased with drought stress.Tissue concentrations of 2, 4-diaminobutyric acid (1.6–2.6%of the dry weight) were highest in leaves. Levels increasedsteadily, nearly doubling, in leaves and stems between weeks10 and 16. Levels in drought-stressed leaves were, on average,11.9% higher than those of controls. Estimated concentrationsof a mixture of 4-aminobutyric acid and an unknown amino acidwere highest in stems, increased in this tissue with age andtended to increase in stems and leaves and decrease in rootsin response to water deficit. Levels of the mixture of homoserineand another unidentified amino acid were not influenced by ageor water status of the plants. Root concentrations of asparagine,arginine, glutamine, aspartate, and another prominent, unidentifiedamino acid increased with plant age and reached a peak at thetime of flowering (14 to 18 weeks). Only the concentration ofthe unknown compound was elevated following drought stress.Concentrations of valine, isoleucine, leucine, phenylalanine,and methionine also increased during this period and were elevatedin drought-stressed plants. Proline levels increased with plantage and drought stress, but proline accounted for only about10% of the total free amino acids in the drought-stressed plants. Key words: 2, 4-Diaminobutyric acid, drought, flatpea  相似文献   
990.
A 3-wk-old lamb died because of neurological disease. The predominant microscopic lesions were in the brain and spinal cord and consisted of nonsuppurative encephalomyelitis with severe gliosis throughout the gray and white matter. Immature and mature schizonts, 15.7 x 10.6 microns (8-30 x 6-18 microns), occurred in capillaries and were structurally similar to those of Sarcocystis tenella.  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