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   255篇
  免费   6篇
  国内免费   3篇
  2016年   4篇
  2015年   3篇
  2014年   6篇
  2013年   3篇
  2012年   6篇
  2011年   5篇
  2010年   10篇
  2009年   7篇
  2008年   10篇
  2007年   12篇
  2006年   4篇
  2005年   3篇
  2004年   3篇
  1998年   3篇
  1997年   3篇
  1996年   4篇
  1995年   5篇
  1993年   4篇
  1992年   4篇
  1989年   2篇
  1987年   9篇
  1986年   2篇
  1984年   2篇
  1983年   5篇
  1982年   2篇
  1981年   4篇
  1980年   6篇
  1979年   5篇
  1978年   2篇
  1977年   7篇
  1975年   4篇
  1974年   5篇
  1973年   2篇
  1971年   3篇
  1965年   3篇
  1964年   3篇
  1959年   12篇
  1958年   10篇
  1957年   8篇
  1956年   7篇
  1955年   7篇
  1954年   5篇
  1953年   2篇
  1952年   3篇
  1951年   5篇
  1950年   4篇
  1949年   4篇
  1948年   4篇
  1947年   2篇
  1946年   2篇
排序方式: 共有264条查询结果,搜索用时 15 毫秒
51.
52.
Lavatera assurgentiflora (Malvaceae) is one of four species of the genus Lavatera native to California and Baja California. Two geographically defined subspecies are recognized: L. a. assurgentiflora on the northern islands and L. a. glabra on the southern islands. We isolated nine polymorphic microsatellite loci that amplify in both subspecies of L. assurgentiflora. Substantial levels of polymorphism were observed at many of the loci. Four loci exhibited more than 10 alleles, polymorphism information content ranged from 0.4 to 0.8, and up to six alleles were found in some individuals, supporting reports that these taxa are hexaploid. All loci also amplified in Lavatera lindsayi from Guadalupe Island, and we anticipate that they will cross‐amplify in other California Lavatera species as well.  相似文献   
53.
Abstract: We studied the behavioral effects of necklace-style radiotransmitters on breeding male western burrowing owls (Athene cunicularia hypugaea) in 2 areas of northwestern Texas, USA, in 2004 and 2005. We tested the hypothesis that transmittered owls would spend time interacting with their necklaces and as a result spend less time in vigilance and resting activities than would nontransmittered owls. Nontransmittered owls (n = 6) spent significantly more time being vigilant (P = 0.007) than did transmittered owls (n = 3) in 2004, who spent significant amounts of time interacting with their necklaces. In 2005, behaviors of transmittered owls (n = 8) were significantly different (P < 0.001) from control individuals (n = 4), but behaviors did not vary consistently by treatment period (prenecklace vs. necklace vs. postnecklace periods). Behavioral activity budgets varied considerably among individuals. Although the owls spent a significant amount of time interacting with their necklaces, they appeared to habituate to the presence of the transmitters within a relatively short period (<1week), and necklaces did not affect survivorship or fitness in the short-term.  相似文献   
54.
ABSTRACT. The microsporidium, Enterocytozoon bieneusi , causes a severe, debilitating, chronic diarrhea in patients with the acquired immunodeficiency syndrome. Specific diagnosis of intestinal microsporidiosis, especially due to Enterocytozoon , is difficult and there is no known therapy that can completely eradicate this parasite. Preliminary studies indicate that a short term (about 6 months) in vitro culture of this parasite yielding low numbers of spores, may be established by inoculating human lung fibroblasts and/or monkey kidney cell cultures with duodenal aspirates and or biopsy from infected patients. The cultures may subsequently be used for the isolation and molecular analysis of parasite DNA.  相似文献   
55.
1. Benthic macroinvertebrates were sampled for 1 year to assess functional and taxonomic differences in invertebrate biomass and production with respect to habitat types, reaches and catchments in Wine Spring Basin, western North Carolina. Quantitative samples were collected from depositional, cobble-riffle and bedrock outcrop habitats at four stream reaches (two headwater sites, one second order, and one third order). Other measures included physical parameters, periphyton and organic matter standing crops. Invertebrate data from the Wine Spring catchment were also compared with data from another catchment (Ball Creek) within the same region. 2. The three habitat types had different current velocities and mean substratum particle sizes; both measures were greatest in bedrock outcrop habitats and lowest in depositional habitats. Organic matter standing crops, invertebrate functional group productivity and biomass also differed significantly with respect to habitat type. Cobble-riffle areas had the lowest standing crops of organic matter, invertebrate productivity and biomass. 3. Both invertebrate communities and organic matter standing crops differed significantly between the two headwater reaches. First- to third-order reaches differed in taxonomic composition at the genus level, yet had similar relative functional group productivity and biomass. 4. Annual mean invertebrate biomass and secondary production were greater in the Wine Spring Basin than in Ball Creek. Sites in both the Wine Spring and Ball Creek catchments, however, exhibited similar functional group distributions per habitat type. 5. Local geomorphology and related physical parameters influenced the structure of invertebrate functional group composition, and the distribution of organic matter standing crops. Furthermore, comparison of community structure in Wine Spring with that in Ball Creek suggested that taxonomic composition was more related to catchment-specific parameters (e.g. thermal regime, evolutionary history) than stream size.  相似文献   
56.
Six new species of the coral genus Acropora arc described from Indonesia. These include a species which is remarkable for tubercular cocnostcal structures similar to those of the confamilial genus Montipora. The new species include three regional endemics (A. togianensis and A. batunai from central east Sulawesi and A. derawanensis from east Kalimantan), one species with broad distribution across the southern island chains (A. sukarnoi) and two species which occur throughout most of the Indonesian archipelago (A. Indonesia and A. hoeksemai). A further two species described from Western Australia and Papua New Guinea in 1994 (A. turaki and A. jacquelineae respectively) are recorded from Indonesia for the first time, as common members of an unusual assemblage type in the Togian Islands. The range of another species described from Lombok in 1994 (A. suharsonoi) is extended into Bali. With A. desalwii, A. lokani and A. indiana , this brings to 12 the number of Acropora species newly recorded as being endemic to the Indonesian archipelago or to Indonesia and one adjoining region (either the Indian Ocean or the western Pacific).  相似文献   
57.
We have developed a new staining procedure that combines the traditional Gram staining for bacteria and the Weber's chromotrope staining method, the standard technique for the detection of microsporidia spores in clinical Specimens. This “Gram-chromotrope” staining technique enhances the staining characteristics of microsporidia spores and facilitates the easy detection and differentiation of spores from other microorganisms that are found in clinical specimens, especially stool samples. This new technique is fast, reliable, and simple to perform, and can be easily adapted for use in clinical laboratories.  相似文献   
58.
59.
60.
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