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   20864篇
  免费   1769篇
  国内免费   1941篇
  2024年   46篇
  2023年   308篇
  2022年   547篇
  2021年   1234篇
  2020年   792篇
  2019年   1052篇
  2018年   990篇
  2017年   734篇
  2016年   1060篇
  2015年   1383篇
  2014年   1686篇
  2013年   1839篇
  2012年   1961篇
  2011年   1804篇
  2010年   1095篇
  2009年   955篇
  2008年   1102篇
  2007年   890篇
  2006年   723篇
  2005年   624篇
  2004年   534篇
  2003年   477篇
  2002年   375篇
  2001年   328篇
  2000年   276篇
  1999年   288篇
  1998年   194篇
  1997年   175篇
  1996年   146篇
  1995年   130篇
  1994年   125篇
  1993年   110篇
  1992年   123篇
  1991年   117篇
  1990年   73篇
  1989年   60篇
  1988年   47篇
  1987年   39篇
  1986年   30篇
  1985年   33篇
  1984年   30篇
  1983年   17篇
  1982年   9篇
  1981年   4篇
  1980年   4篇
  1979年   4篇
  1950年   1篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
951.
952.
953.
954.
To understand the olfactory mechanisms of Holotrichia parallela antennae in detecting volatile compounds in the environment, protein profiles of H. parallela antennae were analyzed using two‐dimensional electrophoresis followed by mass spectrometry and bioinformatics analyses. Approximately 1,100 protein spots in silver staining gel were detected. Quantitative image analysis revealed that in total 47 protein spots showed significant changes in different genders of adult antennae. Thirty‐five differentially expressed proteins were identified by Matrix assisted laser desorption/ionization time of flight mass spectrometry (MALDI‐TOF/TOF) tandem mass spectrometer, among which 65.7% are involved in carbohydrate and energy metabolism, antioxidant system, transport, and amino acid/nucleotide metabolism. Some proteins identified here have not been reported previously in insect antennae. Identified male‐biased proteins included odorant‐binding protein 4, pheromone‐binding protein‐related protein 2, odorant‐binding protein 14, prophenoloxidase‐I, acyl‐CoA dehydrogenase, aldo‐keto reductase‐like, carbamoyl phosphate synthetase, etc. whereas some proteins are female biased, such as antennae‐rich cytochrome P450, aldehyde dehydrogenase, and putative glutamine synthetase. Alterations in the levels of some proteins were further confirmed by real time polymerase chain reaction (RT‐PCR). The proteomic resources displayed here are valuable for the discovery of proteins from H. parallela antennae.  相似文献   
955.
The lycophyte genus Selaginella alone constitutes the family Selaginellaceae, the largest of the lycophyte families. The genus is estimated to contain 700–800 species distributed on all continents except Antarctica, with highest species diversity in tropical and subtropical regions. The monophyly of Selaginella in this broad sense has rarely been doubted, whereas its intrageneric classification has been notoriously contentious. Previous molecular studies were based on very sparse sampling of Selaginella (up to 62 species) and often used DNA sequence data from one genome. In the present study, DNA sequences of one plastid (rbcL) and one nuclear (ITS) locus from 394 accessions representing approximately 200 species of Selaginella worldwide were used to infer a phylogeny using maximum likelihood, Bayesian inference and maximum parsimony methods. The study identifies strongly supported major clades and well resolves relationships among them. Major results include: (i) six deep‐level clades are discovered representing the deep splits of Selaginella; and (ii) 20 major clades representing 20 major evolutionary lineages are identified, which differ from one another in molecular, macro‐morphological, ecological and spore features, and/or geographical distribution.  相似文献   
956.
Impatiens L. is one of the largest angiosperm genera, containing over 1000 species, and is notorious for its taxonomic difficulty. Here, we present, to our knowledge, the most comprehensive phylogenetic analysis of the genus to date based on a total evidence approach. Forty‐six morphological characters, mainly obtained from our own investigations, are combined with sequence data from three genetic regions, including nuclear ribosomal ITS and plastid atpB‐rbcL and trnL‐F. We include 150 Impatiens species representing all clades recovered by previous phylogenetic analyses as well as three outgroups. Maximum‐parsimony and Bayesian inference methods were used to infer phylogenetic relationships. Our analyses concur with previous studies, but in most cases provide stronger support. Impatiens splits into two major clades. For the first time, we report that species with three‐colpate pollen and four carpels form a monophyletic group (clade I). Within clade II, seven well‐supported subclades are recognized. Within this phylogenetic framework, character evolution is reconstructed, and diagnostic morphological characters for different clades and subclades are identified and discussed. Based on both morphological and molecular evidence, a new classification outline is presented, in which Impatiens is divided into two subgenera, subgen. Clavicarpa and subgen. Impatiens; the latter is further subdivided into seven sections.  相似文献   
957.
958.
959.
960.
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