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   78篇
  免费   2篇
  2015年   1篇
  2013年   1篇
  2012年   1篇
  2011年   4篇
  2009年   2篇
  2008年   2篇
  2007年   2篇
  2006年   3篇
  2005年   1篇
  2003年   1篇
  1998年   2篇
  1997年   4篇
  1995年   1篇
  1992年   1篇
  1991年   2篇
  1990年   1篇
  1989年   2篇
  1988年   1篇
  1987年   4篇
  1985年   1篇
  1984年   1篇
  1981年   2篇
  1980年   2篇
  1978年   1篇
  1977年   3篇
  1976年   3篇
  1975年   1篇
  1974年   1篇
  1973年   2篇
  1972年   2篇
  1971年   5篇
  1969年   1篇
  1968年   1篇
  1967年   1篇
  1966年   1篇
  1963年   2篇
  1951年   1篇
  1945年   1篇
  1944年   1篇
  1939年   1篇
  1934年   1篇
  1932年   3篇
  1930年   1篇
  1929年   1篇
  1928年   1篇
  1927年   1篇
  1923年   1篇
  1906年   1篇
排序方式: 共有80条查询结果,搜索用时 671 毫秒
61.
Abstract. Data on the discontinuous ventilation cycle and cost of pedestrian locomotion in female Dasymutilla gloriosa (Sauss.), a desert-dwelling mutillid, are described and compared with equivalent data from other Hymenoptera. The discontinuous ventilation cycle was intermediate between that found in xeric and mesic hymenopterans, with the open phase being about 20% of the cycle. No noticeable flutter phase was observed. Thus D. gloriosa does not attempt to reduce respiratory water loss to the same extent as found in other desert dwelling Hymenoptera. The minimum cost of transport was significantly higher than that obtained for several ant species, indicating that ants are probably more efficient runners than any other Hymenoptera.  相似文献   
62.
63.
64.
Development, growth and nitrogen fixation were monitored over3 years in marsh birdsfoot trefoil (Lotus uliginosus Schkuhr),at an upland site in south-west Scotland Plants exhibited markedseasonality of growth, with production of both aerial shootsand rhizome reaching a peak in September and October Renewedaerial shoot growth in spring was initiated mainly from nodeson rhizomes formed in the previous autumn Nitrogen fixationwas measured in soil cores using the acetylene reduction techniqueFixation commenced in early June, coinciding with increasingsoil temperature, and thereafter rose to a peak in mid-summerThe subsequent decline in fixation was associated with increasingrainfall, decreasing soil temperature, flowering and the onsetof rhizome production Lotus uliginosus Schkuhr, marsh birdsfoot trefoil, seasonality, rhizome production, nitrogen fixation, acetylene reduction  相似文献   
65.
66.
The tribe Vicieae (Adanson) DC. ex Ser. is characterized by an unusual type of stele in which the lateral leaf-traces are present as cortical bundles in the internode below the insertion of their leaf. In most members of the tribe a completely fresh pair of cortical bundles is substituted at each node, but in ten species of Vicia L. there is only partial replacement. The group thus delimited also possesses some distinctive non-anatomical features.
The behaviour of the three leaf-traces at the node also varies throughout the tribe. This variation is shown to be correlated with differences in the shape of the stipules and their size in relation to the rest of the leaf.  相似文献   
67.
Anopheles gambiae sensu stricto Giles (Diptera: Culicidae) is the main malaria vector in sub‐Saharan Africa. Mated females show a circadian rhythm of spontaneous activity under constant environmental conditions that extends across the scotophase (subjective night). The effect of host‐associated cues [i.e. human foot odour supplemented with carbon dioxide (CO2)] on this nocturnal activity pattern is studied in laboratory‐reared A. gambiae s.s. M molecular form. Sixteen mated females (5–10 days old) are held in individual chambers (diameter 3.5 cm, length 4.5 cm) in a wind‐tunnel with a continuous flow (8.0 cm s?1) of clean air. At the onset of hours 3, 6 and 10 of the scotophase, their behaviour is recorded on video for 15 min in clean moving air and then for the next 15 min, with a specific treatment present in the clean airstream: (i) constant CO2 (4.8%) plus human odour; (ii) pulsed CO2 (5 s of every 30 s) plus human odour or (iii) control (clean air). Activities of individual mosquitoes are scored by direct observation of the video records for the incidents of ‘resting’, ‘walking’, ‘jumping’ and ‘flying’ in each of the 15‐min observation periods. There is a significant interaction between hour and treatment on mean changes in female activity level (P = 0.00004). Constant treatment increases the level of activity of A. gambiae females significantly, although only in hour 3 of the scotophase (P < 0.01), whereas pulsed and control treatments show no significant effect throughout the scotophase. Patterns of spontaneous activity in individual A. gambiae females thus appear to be modulated by host‐associated cues, resulting in a more active phase early in the night than might be expected from records of spontaneous activity under constant environmental conditions. Possible ecological and experimental implications of such an increase in activity are discussed in relation to host‐seeking behaviour.  相似文献   
68.
69.
70.
Bone marrow thymocytes in part mediate the bone-preserving effects of estrogen by decreasing their production of osteoclast growth factors such as interleukin-1 and -6 and tumor necrosis factor alpha in the presence of physiological amounts of estradiol. Although several in vitro studies implicate the T-lymphocyte as a candidate mediator of estrogen signaling in the skeleton, whether these cells or any lymphocytes ordinarily express one or both nuclear estrogen receptors was previously unresolved. The purpose of our investigation was therefore to ascertain, by using real-time PCR, immmunoblotting, and cytometric techniques, if any of the nuclear estrogen receptors could be detected in normal peripheral blood mononuclear cells (PBMNC) collected from healthy volunteers. The results of immunoblotting experiments revealed that both estrogen receptor alpha (ESR1) and beta (ESR2) proteins are expressed in nuclei, but not in the cytoplasm of PBMNC harvested from all of the 15 healthy male and female volunteers (aged 23–50 years) we tested. PBMNCs contained mRNA coding for the two major full-length isoforms of ESR2 and the expression of ESR2 protein was localized within a lymphocyte subpopulation by cytometric analysis. Our data provide further evidence that lymphocytes and monocytes are responsive to estrogen and underscore its importance in modulating the immune response, as well as the vascular and skeletal health of men and women.  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