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   616篇
  免费   16篇
  国内免费   1篇
  633篇
  2013年   9篇
  2012年   8篇
  2011年   10篇
  2010年   14篇
  2009年   24篇
  2008年   15篇
  2007年   20篇
  2006年   17篇
  2005年   14篇
  2004年   11篇
  2003年   5篇
  2001年   6篇
  2000年   5篇
  1999年   6篇
  1998年   5篇
  1997年   17篇
  1996年   10篇
  1995年   5篇
  1994年   9篇
  1993年   9篇
  1992年   7篇
  1991年   7篇
  1990年   19篇
  1989年   9篇
  1988年   12篇
  1986年   9篇
  1985年   7篇
  1984年   6篇
  1982年   11篇
  1981年   15篇
  1980年   5篇
  1979年   8篇
  1978年   8篇
  1977年   9篇
  1976年   10篇
  1975年   12篇
  1974年   18篇
  1973年   8篇
  1972年   25篇
  1971年   23篇
  1970年   6篇
  1968年   8篇
  1966年   6篇
  1958年   7篇
  1957年   6篇
  1956年   5篇
  1953年   9篇
  1952年   10篇
  1913年   5篇
  1908年   4篇
排序方式: 共有633条查询结果,搜索用时 0 毫秒
631.
The trophont stage in the life cycle of Ichthyophthirius multifiliis was studied in the electron microscope. Surface ridges contain up to 24 ridge microtubules, disposed as a ribbon. Kinetosomes show the classic morphology of 9 triplets of microtubules. Associated with each kinetosome is a kinetodesmal fibril, originating in proximity to triplets 5, 6, and 7, and having a 30 nm periodicity; 3 to 5 postciliary microtubules, originating between triplets 8 and 9; and up to 3 transverse microtubules, originating at triplet 4, as well as a parasomal sac. Each cell is partially enclosed by a system of 3 “unit” membranes: the outer limiting membrane, and the outer and inner alveolar membranes. The last two membranes define the alveolar sac. Mucocysts, each with a dense core, are present in large numbers. The contractile vacuole system includes the contractile vacuole, associated tubules and vesicles, injection canals, a discharge canal, and a pore. Microtubules abound in the walls of the contractile vacuole, injection and discharge canals, and in the region of the pores, where both ring and radial microtubular arrangements are noted. The ultrastructure suggests that I. multifiliis is more closely related to Tetrahymena pyriformis than to Paramecium aurelia.  相似文献   
632.
An analysis of clutch-size in New World passerine birds   总被引:5,自引:0,他引:5  
GEORGE KULESZA 《Ibis》1990,132(3):407-422
Variation in clutch-size among New World passerine birds was analysed with respect to four variables: body-mass, geographic latitude, the frequency of nest predation, and the structure of the nest. Data were analysed separately by averaging traits at three taxonomic levels: species, genus, and subfamily. Allometric scaling with body-mass did not account for significant variation in clutch-size regardless of the taxonomic level of analysis. Latitudinal effects on clutch-size were highly significant at all taxonomic levels. For species building small-pensile nests and open-cup nests, nest predation had a significant partial effect on clutch-size, with latitude held constant. When nest predation and latitude were held constant, clutch-size was significantly different among species building small-pensile nests, open-cup nests, and domed nests. These results suggest that New World passerine clutch-size is related to at least three variables: latitudinal effects, nest predation, and nest structure.  相似文献   
633.
We developed an automated method for studying the germination kinetics of Bacillus subtilis spores using a microtiter plate (MP) reader. Phosphate buffer supplemented with L-alanine was used to isolate the germination phase as determined by decrease in optical density (OD630). Using a standard 96-well MP, L-alanine triggered germination kinetics were measured by automatic OD measurement every 3 min until the maximum OD630 change (OD630) was determined. When OD630 values were plotted against L-alanine concentration on a double reciprocal plot, a straight line (R2= 0.98) was produced. The addition of D-alanine to the medium demonstrated classical competitive inhibition on double reciprocal plots. A 3-dimensional representation of the untransformed data showed the response surface nature of competitive inhibition. The method automates the tedious task of determining loss of refractility associated with spore germination under defined conditions so that inhibitors to germination can be studied. Since 96 OD630 determinations can be done simultaneously in small volumes (200 μL) extensive data can be generated about inhibitors using relatively small spore crops in a single, short (1.4 h) incubation.  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