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   7645篇
  免费   283篇
  国内免费   283篇
  8211篇
  2024年   136篇
  2023年   108篇
  2022年   125篇
  2021年   171篇
  2020年   213篇
  2019年   232篇
  2018年   218篇
  2017年   190篇
  2016年   266篇
  2015年   286篇
  2014年   420篇
  2013年   741篇
  2012年   373篇
  2011年   306篇
  2010年   195篇
  2009年   257篇
  2008年   336篇
  2007年   266篇
  2006年   216篇
  2005年   220篇
  2004年   180篇
  2003年   202篇
  2002年   173篇
  2001年   176篇
  2000年   174篇
  1999年   107篇
  1998年   134篇
  1997年   135篇
  1996年   120篇
  1995年   100篇
  1994年   117篇
  1993年   119篇
  1992年   110篇
  1991年   90篇
  1990年   96篇
  1989年   81篇
  1988年   78篇
  1987年   74篇
  1986年   46篇
  1985年   71篇
  1984年   89篇
  1983年   54篇
  1982年   49篇
  1981年   57篇
  1980年   40篇
  1979年   55篇
  1978年   38篇
  1977年   31篇
  1975年   30篇
  1973年   31篇
排序方式: 共有8211条查询结果,搜索用时 168 毫秒
1.
2.
Systematics and phylogeny of the Aglajidae (Opisthobranchia: Mollusca)   总被引:3,自引:0,他引:3  
The generic limits within the Aglajidae are reviewed and modified, based on the study of 21 species. Navanax Pilsbry, 1895 is reinstated as a genus distinct from Aglaja. The generic placement of several species is altered from previous works. An evaluation of morphological characters suggests that each of six genera has distinctive external morphology. The systematic value of twelve characters is critically reviewed. The evolutionary relationships of the Aglajidae and its genera to other philinacean familes are discussed.  相似文献   
3.
The 17 Ankistrodesmus strains studied do not produce extracellular amylolytic enzymes. 20 out of 28 Scenedesmus strains, however, are able to hydrolyse starch.The groups of strains previously characterized physiologically and biochemically were assigned to established species of the genera Ankistrodesmus (including Monoraphidium) and Scenedesmus.Abbreviation GC Guanine + cytosine  相似文献   
4.
Species identification of slow-growing fungi of the genus Penicillium isolated from ancient permafrost deposits was performed using micro- and macromorphological characteristics as well as the composition of secondary metabolites. The strains producing clavine ergot alkaloids fumigaclavines A and B and festuclavine were assigned to the species P. palitans Westling 1911, whereas the strains forming ochratoxins A and B were identified as P. verrucosum Dierckx 1901.  相似文献   
5.
Summary This paper reviews the biogeography, geographic variation, and habitat characteristics of the Amazilia Hummingbird (Amazilia amazilia). Based on morphological features, habitat preferences, and bioacoustics, I propose that the currently recognized subspeciesA. a. alticola should be regarded as a species distinct fromA. amazilia. Synapomorphic characters found in both taxa indicate membership of the same superspecies, together with the Colombian speciesA. castaneiventris. Considering the distributional focus ofA. alticola in the Andes of southern Ecuador, the English species name Loja Hummingbird is suggested.
Biogeographie, geographische Variation und Habitatwahl der Lesson-Amazilie (Amazilia amazilia Lesson; Aves: Trochilidae), mit Anmerkungen zum Status vonAmazilia alticola Gould
Zusammenfassung Die vorliegende Studie stellt die Ergebnisse von Untersuchungen zur Biogeographie, geographischen Variation, Habitatwahl und Taxonomie der Lesson-Amazilie (Amazilia amazilia) vor. Das Taxon umfaßt gegenwärtig fünf Unterarten, die von W-Ecuador bis SW-Peru verbreitet sind und überwiegend submontane Lebensräume besiedeln. Die Ventralfärbung unterliegt klinaler Variation; weiße Gefiederanteile nehmen von nördlichen zu südlichen Populationen ab, rotbraune Partien dagegen zu. Eigenständige morphologisch-morphometrische Kennzeichen sowie Unterschiede in den Habitatpräferenzen und in der Gesangsstruktur rechtfertigen es, die bisherige UnterartA. a. alticola als Paraspezies (A. alticola, Loja-Amazilie) anzuerkennen. Der Vulgärname weist auf den rezenten Verbreitungsschwerpunkt in den südecuadorianischen Anden hin. Aufgrund der engen Verwandtschaft bildenA. amazilia undA. alticola sowie die in Kolumbien endemische ArtA. castaneiventris eine Superspezies.
  相似文献   
6.
The fate of 15NH inf4 sup+ and 15NOinf3 was followed in control and PO inf4 sup3− enriched 1570 l mesocosms filled with epilimnetic water from an oligotrophic Rocky Mountain lake. Volumetric incorporation of 15NH inf4 sup+ and 15NO inf3 sup− into phytoplankton and bacterioplankton (particulates between 280 and 0.7 μm), and crustacean zooplankton > 80 μm was enhanced by PO inf4 sup3− , but no increase in biomass specific rates of uptake by phytoplankton and bacteria occurred for either form of 15N. Dilution of both 15NH inf4 sup+ and 15NO inf3 sup− by 14NH inf4 sup+ and 14NO inf3 sup− , respectively, was evident indicating regeneration of these nutrients, but regeneration rates were not effected by PO inf4 sup3− enrichment. The results illustrate the strong trophic coupling between N dynamics and PO inf4 sup3− enrichment in this system.  相似文献   
7.
Intraspecific variability of Brachionus plicatilis   总被引:1,自引:1,他引:1  
An extensive study of frontal margins of the lorica of Brachionus plicatilis was undertaken in an attempt to define its variability within this species. Specimens from mass cultures and from the natural environment were examined.  相似文献   
8.
Two new species of Multiclavula are described from Rwanda: M. akagerae , with a thallus consisting of turgescent glomerules, and M. rugaramae , with a thallus composed of flattened, rounded, marginate, and dispersed squamules. They grow on soil in frequently burned savannas or on lateritic soils in eastern Rwanda. The genus Lepidostroma should probably be reduced into synonymy with Multiclavula .  © 2007 The Linnean Society of London, Botanical Journal of the Linnean Society , 2007, 155 , 457–465.  相似文献   
9.
10.
Summary   Blepharodon crabronum from the pre-Cambrian serranias of eastern Bolivia is described and illustrated.  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