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   781906篇
  免费   95058篇
  国内免费   432篇
  877396篇
  2016年   8525篇
  2015年   12997篇
  2014年   14964篇
  2013年   20817篇
  2012年   23787篇
  2011年   23731篇
  2010年   16085篇
  2009年   15275篇
  2008年   21762篇
  2007年   22362篇
  2006年   20911篇
  2005年   20154篇
  2004年   19991篇
  2003年   19336篇
  2002年   18772篇
  2001年   34301篇
  2000年   34738篇
  1999年   28004篇
  1998年   10732篇
  1997年   11369篇
  1996年   10926篇
  1995年   10328篇
  1994年   10179篇
  1993年   10001篇
  1992年   23590篇
  1991年   22852篇
  1990年   22481篇
  1989年   21808篇
  1988年   20083篇
  1987年   19742篇
  1986年   18116篇
  1985年   18190篇
  1984年   15119篇
  1983年   13200篇
  1982年   10550篇
  1981年   9398篇
  1980年   8952篇
  1979年   14544篇
  1978年   11692篇
  1977年   10565篇
  1976年   9964篇
  1975年   10802篇
  1974年   11629篇
  1973年   11416篇
  1972年   10222篇
  1971年   9484篇
  1970年   8110篇
  1969年   7664篇
  1968年   6842篇
  1967年   6176篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
211.
In this paper the recent population changes of the Wild Boar in different European countries is analysed through the study of hunting statistics. A simultaneous increase in numbers is observed throughout the whole area during the period 1965–1975. From 1975 onwards the population stabilizes itself apart from in peripheral areas like Finland. Potentially favourable factors which play a part in this process are discussed and certain reproductive and dispersive characteristics which favour its invasive behaviour are discussed.  相似文献   
212.
213.
214.
We studied recipient mating ability in the presence of excess F'lac donors. Ninety-five percent of recipients were able to receive F'lac in 30-min matings. Competition between an F'-lac donor and an F'lac traI donor, which mobilized a ColE1 derivative (pML2), showed that each recipient mated with an average of two to three donors in 30 min. Experiments in which the competing donor was added at different times showed that some competition occurred throughout the 30-min mating period, which suggested that aggregate formation was spread over this time.  相似文献   
215.
216.
Administration of purified pertussis toxin to rats induced persistent tachycardia, (observed in conscious rats but not after pithing); as little as 0.05 microgram/100 g produced a significant effect. Pertussis toxin-treatment did not affected the pressor response produced in the pithed rats by the alpha 2-adrenergic agonist methoxamine but markedly diminished the pressor effect of the alpha 2-adrenergic agonists clonidine and azepexole. A role of adenylate cyclase inhibition in the action of postsynaptic vascular alpha 2-adrenergic receptors is suggested.  相似文献   
217.
218.
Mesotocin ([Ile8]-oxytocin), lysipressin ([ Lys8]-vasopressin) and phenypressin ([Phe8]-vasopressin) have been identified in the western gray kangaroo (Macropus fuliginosus) as well as four other macropodids. Lysipressin and phenypressin, which differ by the amino acids in positions 2 (Tyr/Phe) and 8 (Lys/Arg) are likely products of two separate vasopressin-like genes. It is assumed that arginine vasopressin found in most mammals is the product of two identical genes which can be revealed in some species by differential mutations as seen usually in marsupials. The duality can also be revealed by differential mutations in another domain of the precursors, such as the neurophysin (MSEL-neurophysin), as observed in the ox.  相似文献   
219.
Leucostasis, an underestimated cause of death in leukaemia   总被引:1,自引:0,他引:1  
Massive sludging of leukaemic cells in blood vessels is a frequent and often lethal complication of leukaemia. In a retrospective clinicopathological study on the causes of death in 52 patients with acute myeloid leukaemia and myeloproliferative disease, pulmonary leucostasis was found in 40% of the patients. In many of these patients the vessels of the heart, brain and testes were also involved. In search for signs and symptoms specific for leucostasis, the clinical records of the 21 patients with leucostasis (the study group) were compared to those of 20 patients without leucostasis (the control group). Dysfunction of the organs most affected by leucostasis, namely lungs, heart and brain, was found more often in the study group than in the controls, but the combination of unexplained fever with cardiopulmonary and/or central nervous system failure occurred almost exclusively and in half of the patients with leucostasis. Leucostasis occurs predominantly, but not exclusively, in patients with high leucocyte counts, and especially, but again not exclusively, when the leucocyte counts rise sharply.  相似文献   
220.
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