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   407048篇
  免费   46209篇
  国内免费   176篇
  453433篇
  2018年   3494篇
  2017年   3482篇
  2016年   4672篇
  2015年   6212篇
  2014年   7232篇
  2013年   10824篇
  2012年   12105篇
  2011年   12244篇
  2010年   8219篇
  2009年   7665篇
  2008年   11132篇
  2007年   11292篇
  2006年   10856篇
  2005年   10267篇
  2004年   10145篇
  2003年   9827篇
  2002年   9582篇
  2001年   18892篇
  2000年   19081篇
  1999年   15505篇
  1998年   5443篇
  1997年   5711篇
  1996年   5532篇
  1995年   5014篇
  1994年   5125篇
  1993年   5002篇
  1992年   12928篇
  1991年   12359篇
  1990年   12288篇
  1989年   12265篇
  1988年   11156篇
  1987年   10618篇
  1986年   9850篇
  1985年   9876篇
  1984年   8009篇
  1983年   6979篇
  1982年   5306篇
  1981年   4681篇
  1980年   4573篇
  1979年   7674篇
  1978年   5943篇
  1977年   5303篇
  1976年   5132篇
  1975年   5552篇
  1974年   5796篇
  1973年   5710篇
  1972年   5182篇
  1971年   4577篇
  1970年   4040篇
  1969年   3742篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
161.
P. A. PRINCE  S. RODWELL  M. JONES  P. ROTHERY 《Ibis》1993,135(2):121-131
We recorded the age of individual wing and tail feathers of Black-browed and Grey-headed Albatrosses Diomedea melanophris and D. chrysostoma of known age and breeding status at Bird Island, South Georgia. Breeders and non-breeders of both species moult their rectrices annually. Non-breeders moult primaries biennially. In the first year of a cycle, the outer three and some inner primaries are moulted descendantly; in the next year the inner primaries are moulted ascendantly, starting from primary seven. There is a general progression to moulting equal numbers of primaries in each half of the cycle by the time breeding starts at about 10 years of age. Grey-headed Albatrosses usually moult fewer primaries than Black-browed Albatrosses, particularly as 3-year-olds, when they undertake substantial plumage change in body moult. Most secondaries in Black-browed Albatrosses have been replaced once by age 4 years. Breeding Black-browed Albatrosses continue the moult pattern established as immatures whether they fail or not, as do failed Grey-headed Albatrosses. Successful Grey-headed Albatrosses, which breed again 16 months later, moult their three innermost primaries after breeding in the remainder of the current year and, after a period when moult is interrupted, renew the remaining primaries the following year. Comparisons between species and between failed and successful birds within species indicate that moult rate is not closely linked to the length of the interval between breeding attempts. Interspecies differences are better explained by breeding latitude, with tropical albatrosses moulting twice as fast as sub-Antarctic species, possibly reflecting food availability outside the breeding season.  相似文献   
162.
163.
164.
165.
The authors have studied in the dog--normal or diabetic insipidus after hypothalamic lesion--submitted to oral ingestion of ethanol the effects of a few antidiuretic drug: chlorpropamid, atromid-S, carbamazepin and carisoprodol. The carisoprodol only can reduce the diuresis and the drinking provoked by ethanol.  相似文献   
166.
167.
168.
169.
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   
170.
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   
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