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   291579篇
  免费   26787篇
  国内免费   279篇
  2021年   2510篇
  2018年   3285篇
  2017年   3188篇
  2016年   4387篇
  2015年   5290篇
  2014年   6369篇
  2013年   8929篇
  2012年   10164篇
  2011年   10951篇
  2010年   7376篇
  2009年   6578篇
  2008年   9378篇
  2007年   9715篇
  2006年   9300篇
  2005年   8877篇
  2004年   8675篇
  2003年   8412篇
  2002年   8148篇
  2001年   12491篇
  2000年   12379篇
  1999年   9700篇
  1998年   3356篇
  1997年   3257篇
  1996年   3142篇
  1995年   2883篇
  1994年   2810篇
  1993年   2732篇
  1992年   7620篇
  1991年   7369篇
  1990年   7436篇
  1989年   7200篇
  1988年   6696篇
  1987年   6318篇
  1986年   5681篇
  1985年   6007篇
  1984年   4892篇
  1983年   4217篇
  1982年   3123篇
  1981年   2959篇
  1980年   2677篇
  1979年   4407篇
  1978年   3444篇
  1977年   3164篇
  1976年   3143篇
  1975年   3483篇
  1974年   3756篇
  1973年   3783篇
  1972年   3246篇
  1971年   2971篇
  1970年   2664篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
102.
103.
104.
105.
106.
107.
Content of dopamine in the striatum; of serotonin, 5-hydroxyindolacetic acid and noradrenaline in the hypothalamus, striatum and midbrain was studied in three groups of minks from population of an animal farm, differing by their reaction to humans (cowardly, calm, aggressive). The reaction to humans was estimated by a system of marks at the attempt to catch the mink with a mitten. Aggressive animals had a lowered level of serotonin in the hypothalamus and striatum, a lesser content of serotonin metabolite--5-hydroxyindolacetic acid in the striatum. Minks of different groups did not differ by noradrenaline content, but dopamine level in the striatum of cowardly minks was higher than in calm and aggressive animals. Conclusion is made that polymorphism of behaviour corresponds to polymorphism of the state of monoaminergic systems.  相似文献   
108.
Celery seeds ( Apium graveolens L.) given a germination induction period (3 days imbibition at 17°C in the light) could be prevented from germinating by up to 14 days subsequent exposure to high temperature (32°C), polyethylene glycol (PEG), abscisic acid (ABA) or dark (22°C). When the seeds were returned to 17°C in the light, germination occurred and, except for the high temperature treatment, was more rapid compared to seeds given a germination induction period only.
Celery seeds incubated for 3 days at 17°C in the light and then air-dried at 20°C germinated slowly when re-sown at 17°C in the light, and achieved only 19% germination after 21 days. Exposing the seeds to high temperature, PEG, ABA or dark for up to 14 days before drying maintained seed viability and subsequent germination was faster. The longer treatment periods gave increased benefit, and PEG was the most effective treatment. It is suggested that the effectiveness of the treatments in inducing dehydration tolerance relates to their ability to inhibit germination possibly via their prevention of cell expansion.  相似文献   
109.
The primary structure of hemagglutinin (HA) gene of Influenza virus A/USSR/90/77 (H1N1) variants after 3 and 11 passages has been determined. In the HA1 coding region of mice-adapted virus (11 passages) there are two amino acid substitutions: Thr 89----Ala and Asn 127----Asp. At the first stage of adaptation (3-rd passage) only a single mutation was detected: Asn 127----Asp. The adaptation is accompanied by the loss of specific carbohydrate attachment sites adjacent to the receptor-binding site located at HA1 subunit with a concomitant variation in antigenicity.  相似文献   
110.
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