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   102627篇
  免费   20824篇
  国内免费   7149篇
  2024年   119篇
  2023年   1002篇
  2022年   1422篇
  2021年   4351篇
  2020年   4763篇
  2019年   6785篇
  2018年   6690篇
  2017年   6295篇
  2016年   7293篇
  2015年   8703篇
  2014年   9536篇
  2013年   10033篇
  2012年   9042篇
  2011年   8061篇
  2010年   7025篇
  2009年   5355篇
  2008年   4850篇
  2007年   4008篇
  2006年   3630篇
  2005年   3035篇
  2004年   2541篇
  2003年   2416篇
  2002年   1899篇
  2001年   1497篇
  2000年   1391篇
  1999年   1216篇
  1998年   735篇
  1997年   627篇
  1996年   655篇
  1995年   585篇
  1994年   555篇
  1993年   420篇
  1992年   582篇
  1991年   430篇
  1990年   392篇
  1989年   343篇
  1988年   271篇
  1987年   244篇
  1986年   238篇
  1985年   212篇
  1984年   172篇
  1983年   157篇
  1982年   123篇
  1981年   91篇
  1980年   78篇
  1979年   90篇
  1976年   63篇
  1974年   70篇
  1973年   67篇
  1972年   61篇
排序方式: 共有10000条查询结果,搜索用时 453 毫秒
51.
52.
53.
54.
Yang  Su-Rong  Sun  Huan-Xin  Hu  Zhen-Zhen  Wang  Si-Heng  Sun  Hui  Xue  Yin-Jia  Ye  Chen-Bo 《Sleep and biological rhythms》2017,15(1):57-65
Sleep and Biological Rhythms - Chronic sleep deprivation (SD) is an overwhelming problem in young students. Firstly, we investigated whether different levels of pre-training SD had effects on...  相似文献   
55.
Applied Microbiology and Biotechnology - The objective of this study was to identify and exploit a robust biocatalyst that can be applied in reductive amination for enantioselective synthesis of...  相似文献   
56.
57.
58.
59.
During the past 40 years, more than 400 Sudden Unexplained Deaths (SUDs) have occurred in Yunnan, southwestern China. Epidemiological and toxicological analyses suggested that a newly discovered mushroom called Trogia venenata was the leading culprit for SUDs. At present, relatively little is known about the genetics and natural history of this mushroom. In this study, we analyzed the sequence variation at four DNA fragments among 232 fruiting bodies of T. venenata collected from seven locations. Our ITS sequence analyses confirmed that all the isolates belonged to the same species. The widespread presence of sequence heterozygosity within many strains at each of three protein-coding genes suggested that the fruiting bodies were diploid, dikaryotic or heterokaryotic. Within individual geographic populations, we found significant deviations of genotype frequencies from Hardy-Weinberg expectations, with the overall observed heterozygosity lower than that expected under random mating, consistent with prevalent inbreeding within local populations. The geographic populations were overall genetically differentiated. Interestingly, while a positive correlation was found between population genetic distance and geographic distance, there was little correlation between genetic distance and barium concentration difference for the geographic populations. Our results suggest frequent inbreeding, geographic structuring, and limited gene flow among geographic populations of T. venenata from southwestern China.  相似文献   
60.
Octopus minor (Sasaki, 1920) is an important economic fishery resource in China. In order to explore the stock information and the phylogeographic status of O. minor, mitochondrial DNA cytochrome c oxidase subunit I (COI, 565?bp) and 16S rRNA (493?bp) genes were amplified from 11 different sampling locations. Genetic diversity evaluated by haplotypic and nucleotidic diversity implied high diversity in Lianjiang, and relatively low diversity in Rongcheng, which suggests that effective measures to protect the O. minor resource in this area are urgently required. Private haplotypes and remarkable higher pairwise ΦST in Yilan are responsible for the deep genetic divergence between Yilan and the 10 other populations. Haplotypes networks and two clusters’ topological structure also support the distinct subgroups (lineages A and lineages B), which apparently possess smaller genetic variation than mean interspecies distance. Taiwan island and its strait may act as a natural barrier that restricts the gene flow from the mainland. Deep genetic divergence between mainland and Taiwanese east coasts suggests different genetic stock, indicating that different management strategies are required.  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