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   129204篇
  免费   9273篇
  国内免费   32篇
  2023年   664篇
  2022年   589篇
  2021年   1784篇
  2020年   1380篇
  2019年   1487篇
  2018年   2987篇
  2017年   2790篇
  2016年   3979篇
  2015年   5697篇
  2014年   5800篇
  2013年   7865篇
  2012年   9609篇
  2011年   9078篇
  2010年   5795篇
  2009年   4769篇
  2008年   7166篇
  2007年   6985篇
  2006年   6588篇
  2005年   6119篇
  2004年   6021篇
  2003年   5519篇
  2002年   5270篇
  2001年   2256篇
  2000年   2058篇
  1999年   1926篇
  1998年   1403篇
  1997年   1007篇
  1996年   1009篇
  1995年   973篇
  1994年   885篇
  1993年   887篇
  1992年   1171篇
  1991年   1002篇
  1990年   890篇
  1989年   895篇
  1988年   868篇
  1987年   766篇
  1986年   738篇
  1985年   817篇
  1984年   878篇
  1983年   688篇
  1982年   744篇
  1981年   653篇
  1980年   600篇
  1979年   543篇
  1978年   571篇
  1977年   534篇
  1975年   492篇
  1974年   542篇
  1973年   536篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
The phylogeny of the fungus gnat family Mycetophilidae (Diptera) is reconstructed with a focus on the species‐rich and taxonomically difficult subfamilies Gnoristinae and Mycomyinae. The multigene phylogenetic analyses are based on five nuclear (18S, 28S, CAD, MCS, ITS2) and four mitochondrial (12S, 16S, COI, CytB) gene markers. The analyses strongly support the monophyly of Mycetophilidae and the subfamilies Manotinae, Sciophilinae, Leiinae, and Mycomyinae, although Gnoristinae is paraphyletic with respect to Mycetophilinae. All the genera and groups of genera included are supported as monophyletic, except for Acomoptera Vockeroth, Boletina Staeger, Dziedzickia Johannsen, Ectrepesthoneura Enderlein, and Neoempheria Osten Sacken. Ancestral character state reconstructions were applied to two morphological features present in Gnoristinae and Mycomyinae (i.e. presence of setae on wing membrane and wing vein R4) in order to assess their evolution. The wing vein R4 appears as an unstable character, spread throughout different clades. A dated phylogeny of the family Mycetophilidae showed that most of the subfamilies of Mycetophilidae originated and diversified during the Cretaceous. The youngest subfamilies, originated in the Paleogene, appear to be Mycomyinae and Mycetophilinae.  相似文献   
2.
This paper is concerned with gene survival in a population which may increase without density dependence according to a generalization of the Moran model for haploid individuals. A selective advantage to one allele and the possibility of differential reproductive rates are allowed. Simple conditions are given for ultimate homozygosity to be certain and for the possibility of ultimate polymorphism. The results complement and extend those of Heyde (1981, 1982).  相似文献   
3.
The author describes changes in the disintegration of erythrocytes by brilliant cresyl blue in correlation to age, in rats aged 21, 42, 90-105, 340-360 and 690-720 days. The erythrocytes were incubated for 4 hours in an isotonic NaCl solution, in Krebs-Ringer solution and in each of these solutions plus brilliant cresyl blue. Disintegration in plain NaCl solution was found to be the greatest in the case of erythrocytes from 690- to 720-day-old rats. In the same solution plus brilliant cresyl blue, the rate of disintegration was very high in 21-day-old, 42-day-old and 690- to 720-day-old animals; at 90-105 days it was lower and at 340-360 days it was the lowest. Disintegration of erythrocytes in plain Krebs-Ringer solution was the lowest at 21 and 42 days; in the other age groups it was slightly higher. On adding brilliant cresyl blue, the rate of disintegration rose significantly in 21-, 42- and 690- to 720-day-old animals; at 90-105 days and 340-360 days it was no different from disintegration in plain Krebs-Ringer solution. It can be seen from the results that the rate of brilliant cresyl blue-induced erythrocyte disintegration is dependent on the age of the animals from which the erythrocytes are taken.  相似文献   
4.
5.
6.
7.
8.
A formalin-fixed paraffin-embedded (FFPE) sample usually yields highly degraded DNA, which limits the use of techniques requiring high-quality DNA, such as Infinium Methylation microarrays. To overcome this restriction, we have applied an FFPE restoration procedure consisting of DNA repair and ligation processes in a set of paired fresh-frozen (FF) and FFPE samples. We validated the FFPE results in comparison with matched FF samples, enabling us to use FFPE samples on the Infinium HumanMethylation450 Methylation array.  相似文献   
9.
10.
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