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   50597篇
  免费   3885篇
  国内免费   3447篇
  2024年   88篇
  2023年   513篇
  2022年   1260篇
  2021年   2242篇
  2020年   1535篇
  2019年   1947篇
  2018年   2088篇
  2017年   1702篇
  2016年   2218篇
  2015年   2575篇
  2014年   3299篇
  2013年   3590篇
  2012年   4075篇
  2011年   3855篇
  2010年   2724篇
  2009年   2390篇
  2008年   2763篇
  2007年   2507篇
  2006年   2196篇
  2005年   1823篇
  2004年   1710篇
  2003年   1614篇
  2002年   1338篇
  2001年   1120篇
  2000年   948篇
  1999年   689篇
  1998年   407篇
  1997年   348篇
  1996年   324篇
  1995年   349篇
  1994年   315篇
  1993年   242篇
  1992年   336篇
  1991年   309篇
  1990年   253篇
  1989年   247篇
  1988年   174篇
  1987年   215篇
  1986年   192篇
  1985年   168篇
  1984年   120篇
  1983年   115篇
  1982年   100篇
  1981年   91篇
  1980年   71篇
  1979年   84篇
  1978年   83篇
  1977年   72篇
  1976年   65篇
  1973年   77篇
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
41.
The applicability of the nucleophilicity/electrophilicity concept to the explanation of mechanisms of formation and transformation of humic substances was considered. Sequential time changes in the structure and properties of humic substances in phosphatic soil have been revealed. Different elemental composition of humic and fulvic acids at different stages of humus transformation was due to different patterns of electron density distribution in phosphorus-modified fragments of humic molecules. The important role of metals and phosphorus in realization of different pathways of humic substance transformation was demonstrated.  相似文献   
42.
43.
Salmonella enterica serovar Enteritidis (SE) is a foodborne pathogen that can threaten human health through contaminated poultry products. Live poultry, chicken eggs and meat are primary sources of human salmonellosis. To understand the genetic resistance of egg‐type chickens in response to SE inoculation, global gene expression in the spleen of 20‐week‐old White Leghorn was measured using the Agilent 4 × 44 K chicken microarray at 7 and 14 days following SE inoculation (dpi). Results showed that there were 1363 genes significantly differentially expressed between inoculated and non‐inoculated groups at 7 dpi (I7/N7), of which 682 were up‐regulated and 681 were down‐regulated genes. By contrast, 688 differentially expressed genes were observed at 14 dpi (I14/N14), of which 371 were up‐regulated genes and 317 were down‐regulated genes. There were 33 and 28 immune‐related genes significantly differentially expressed in the comparisons of I7/N7 and I14/N14 respectively. Functional annotation revealed that several Gene Ontology (GO) terms related to immunity were significantly enriched between the inoculated and non‐inoculated groups at 14 dpi but not at 7 dpi, despite a similar number of immune‐related genes identified between I7/N7 and I14/N14. The immune response to SE inoculation changes with different time points following SE inoculation. The complicated interaction between the immune system and metabolism contributes to the immune responses to SE inoculation of egg‐type chickens at 14 dpi at the onset of lay. GC, TNFSF8, CD86, CD274, BLB1 and BLB2 play important roles in response to SE inoculation. The results from this study will deepen the current understanding of the genetic response of the egg‐type chicken to SE inoculation at the onset of egg laying.  相似文献   
44.
45.
生态意识及其主要特点   总被引:7,自引:0,他引:7  
一、生态意识产生的时代背景生态意识作为人类思想的先进观念,产生于20世纪后半叶。产业革命以来二百多年,人类依据先进科学技术武装的强大生产力,无限制地向自然进  相似文献   
46.
Analysis of parameters of metabolic function of lungs with respect to lipid metabolism was performed in rats under conditions of acute experimental emotional-nociceptive stress. Study of the stress-sensitivity of lungs in the comparative-age aspect has shown different extent of changes of several parameters of lipid metabolism in pulmonary tissue in animals of different age. The results of the study demonstrate areactivity and high stress-stability of lungs with respect to surface-active properties, free-radical processes, and lipase activity in early postnatal ontogenesis.  相似文献   
47.
48.
49.
50.
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