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   921篇
  免费   18篇
  939篇
  2015年   14篇
  2014年   12篇
  2013年   20篇
  2012年   14篇
  2011年   13篇
  2010年   27篇
  2009年   23篇
  2008年   29篇
  2007年   47篇
  2006年   17篇
  2005年   21篇
  2004年   14篇
  2002年   14篇
  1999年   13篇
  1998年   10篇
  1997年   16篇
  1996年   13篇
  1995年   13篇
  1994年   12篇
  1993年   17篇
  1992年   9篇
  1991年   18篇
  1990年   16篇
  1989年   11篇
  1988年   11篇
  1987年   17篇
  1986年   13篇
  1985年   11篇
  1984年   13篇
  1982年   13篇
  1980年   12篇
  1979年   11篇
  1976年   13篇
  1975年   10篇
  1974年   15篇
  1973年   18篇
  1972年   16篇
  1971年   10篇
  1969年   9篇
  1968年   10篇
  1965年   37篇
  1964年   19篇
  1963年   32篇
  1962年   23篇
  1961年   33篇
  1960年   21篇
  1959年   27篇
  1958年   27篇
  1957年   12篇
  1956年   8篇
排序方式: 共有939条查询结果,搜索用时 8 毫秒
931.
932.
Abstract: Estimates of population trend for the interior subspecies of band-tailed pigeon (Patagioenas fasciata fasciata) are not available because no standardized survey method exists for monitoring the interior subspecies. We evaluated 2 potential band-tailed pigeon survey methods (auditory and call-broadcast surveys) from 2002 to 2004 in 5 mountain ranges in southern Arizona, USA, and in mixed-conifer forest throughout the state. Both auditory and call-broadcast surveys produced low numbers of cooing pigeons detected per survey route (x̄ ≤ 0.67) and had relatively high temporal variance in average number of cooing pigeons detected during replicate surveys (CV ≥ 161%). However, compared to auditory surveys, use of call-broadcast increased 1) the percentage of replicate surveys on which ≥1 cooing pigeon was detected by an average of 16%, and 2) the number of cooing pigeons detected per survey route by an average of 29%, with this difference being greatest during the first 45 minutes of the morning survey period. Moreover, probability of detecting a cooing pigeon was 27% greater during call-broadcast (0.80) versus auditory (0.63) surveys. We found that cooing pigeons were most common in mixed-conifer forest in southern Arizona and density of male pigeons in mixed-conifer forest throughout the state averaged 0.004 (SE = 0.001) pigeons/ha. Our results are the first to show that call-broadcast increases the probability of detecting band-tailed pigeons (or any species of Columbidae) during surveys. Call-broadcast surveys may provide a useful method for monitoring populations of the interior subspecies of band-tailed pigeon in areas where other survey methods are inappropriate.  相似文献   
933.
934.
935.
This investigation was conducted to examine the contribution of intrasite variation on the volar forearm to the overall variation in irritation under the conditions of a soap chamber test. Six sites on each forearm of human volunteers were patched with an eight percent aqueous solution of a commercial bar soap, known to be moderately irritating. Clinical evaluations of the sites were made independently by two judges twenty-four hours after the first patch application and six hours following applications conducted over the next four consecutive days. Site to site variability was estimated to be only 3.2% of the total variance component. It is suggested that as with any biologic assay, this variance can be reduced by an increase in the number of panelists.  相似文献   
936.
Effects of allyl sulfides on the growth of predominant gut anaerobes   总被引:1,自引:0,他引:1  
At a small supplied concentration (3–5 mM), diallyl disulfide (DADS) and diallyl monosulfide (DAMS), compounds previously shown to have both tumoricidal and protective effects against carcinogenesis, affected the growth of components of the normal anaerobic gut microflora. Organisms that were affected by DAMS and DADS includedBacteroides ruminicola, Bacteroides succinogenes, Butyrivibrio fibrisolvens, Ruminococcus albus, Ruminococcus flavefaciens, Ruminococcus bromii, andPeptostreptococcus productus. Organisms found unaffected, over the same supplied concentration range, includedBacteroides fragilis, Bacteroides vulgatus, Fusobacterium necrophorum, Fusobacterium nucleatum, andSelenomonas ruminantium. In addition to their direct effects upon host cell physiology, the active components of garlic oil may exert modifying effects on the nature and function of the predominant gut microflora of warm-blooded animals.  相似文献   
937.
Abstract. Female preferences for conspicuous male calls have been documented in many groups. However, relatively few studies have examined the metabolic costs associated with the production of call types preferred by females. We measured the oxygen consumption of calling male Gryllus lineaticeps Stål crickets using closed chamber respirometry. Calling song was recorded concurrently. The average increase in mass-specific oxygen consumption during calling was 2.7 times basal rates of oxygen consumption, and calling males consumed approximately 1.2ml O2g-lh-1. Oxygen consumption increased with increasing chirp rate and pulse duration, but not with increasing chirp duration. Females of this species prefer higher chirp rates, thus some call types that increase the male's attractiveness to females require more metabolic energy to produce.  相似文献   
938.
Chlorophyll content decreased when excised lemon fruits were exposed to light. A quantitative model for the photodestruction of chlorophyll exhibited reasonable agreement with data on in vivo destruction of chlorophyll. Photodestruction of chlorophyll was enhanced by treating fruit with 2′,4′-dichloro-l-cyanoethane-sulphonanilide (R33417). Measurable enhancement of chlorophyll destruction was observed with concentrations of R33417 as low as 10 μg/l. Maximum activity was achieved at approximately 600 μg/1. R33417 treatment enhanced photodestruction of chlorophyll to a greater extent at higher photon flux densities.  相似文献   
939.
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