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   411篇
  免费   23篇
  2023年   2篇
  2022年   3篇
  2021年   6篇
  2020年   2篇
  2019年   8篇
  2018年   10篇
  2017年   5篇
  2016年   13篇
  2015年   21篇
  2014年   19篇
  2013年   36篇
  2012年   27篇
  2011年   32篇
  2010年   16篇
  2009年   18篇
  2008年   22篇
  2007年   24篇
  2006年   24篇
  2005年   25篇
  2004年   13篇
  2003年   17篇
  2002年   22篇
  2001年   2篇
  1999年   1篇
  1998年   2篇
  1997年   3篇
  1996年   1篇
  1995年   5篇
  1994年   6篇
  1993年   3篇
  1992年   5篇
  1990年   7篇
  1988年   1篇
  1986年   1篇
  1985年   1篇
  1984年   3篇
  1983年   1篇
  1982年   1篇
  1981年   5篇
  1980年   4篇
  1979年   1篇
  1978年   2篇
  1977年   6篇
  1973年   3篇
  1966年   1篇
  1965年   1篇
  1957年   1篇
  1939年   1篇
  1930年   1篇
排序方式: 共有434条查询结果,搜索用时 15 毫秒
411.
In the Scottish Highlands, Scots pine is at the north-western extreme of its wide natural distribution. Here, the remaining native populations are patchily distributed in highly variable environments, from the more continental, drier eastern Highlands to the milder, wetter Atlantic Ocean coast. As these pinewoods are the remnants of a naturally established forest, they form a valuable system for analysis of genetic and adaptive variation in heterogeneous environments. Using samples from across the Scottish population, we analysed data from nuclear and mitochondrial genes to assess patterns of within and between population genetic variation. Within population diversity levels were high, and significant genetic differentiation among pairs of Scottish populations at relatively small spatial scales was present at several nuclear loci. At these loci, no differentiation had been found among continental populations, even those separated by large geographic distances. Overall, no clear clustering of Scottish samples was found in population structure analysis suggesting that geographically distant populations with high intra-population nucleotide diversity are not strongly isolated or diverged from each other. Scottish populations lacked a mitotype that is widespread in eastern and north-eastern Europe, indicating that pines from that area may not have participated in the most recent colonisation of the British Isles.  相似文献   
412.
413.
Over the past two decades there has been intense study of compounds from vertebrates, microorganisms, plants, mushrooms, marine sponges, worms, etc. as well as insects in terms of their antiviral activity. Insects produce a variety of biologically active peptides. One of them is alloferon. The in vitro and in vivo experiments demonstrate that synthetic alloferon has an immunomodulatory properties. It was reported that alloferon and its analogues (alloferon I and II) have antimicrobial properties, as well. The aim of this study was to evaluate in vitro the effect of alloferon I and II, either alone or in combination with human lymphocytes, on human herpesvirus type 1 (HHV-1) McIntyre strain replication. On the base of results we can conclude that alloferon I and II inhibit the replication of HHV-1 McIntyre strain in HEp-2 cells. Enhanced antiviral activity was observed when infected cells were treated with alloferons and unstimulated or phytohemagglutinin PHA-stimulated lymphocytes simultaneously. After application of alloferons and PHA-stimulated lymphocytes to the HHV-1 infected HEp-2 culture, the mean HHV-1 titer reduction for alloferon and II, when used at the highest dose—400 µg/mL, were 3.69 and 3.27 log10/TCID50/mL, respectively.  相似文献   
414.
This study compared the physiological response to novel situations in sex-separated and sex-mixed groups of horses, as measured by heart rate (HR). The study evaluated the possibility of training horses in a mixed-sex system. The study included 41 Purebred Arabian 2½-year-olds during their first walk on an automated horse walker. Four groups, divided by manner of care and training, consisted of 10 colts and 10 fillies kept in separate stables and trained in separate male or female groups and 12 colts and 9 fillies kept in the same stable and trained together. The study measured HR when horses were at rest before exercise, while moving from stable to walker, during 30 min of exercise on walker, while moving from walker to stable, and at rest after exercise. Mean HR scores recorded from training on the walker were higher in sex-mixed groups. Results obtained while horses were moving from stable to walker, then from walker to stable, were significantly higher in the sex-mixed groups. The study did not recommend training young horses in sex-mixed groups.  相似文献   
415.
416.
417.
Abstract

Annual catches of pelagic organisms, excluding marine mammals, from the Atlantic and Pacific waters surrounding the Americas for the period 1969–1971 averaged 17, 000, 000 metric tons. Catches of the pelagic organisms from the Pacific alone were nearly 14, 000, 000 tons. However, considering the recent drop in the catches of the Peruvian anchovy, the data for 1972 and 1973 when compiled, will show a drastic decline in the catches of pelagic species. Catches from American waters are compared with those from other waters and their relationship to the area and population of the Americas is examined. The potential maximum catch of pelagic organisms currently utilized is projected to 26, 000, 000 tons, whereas if the markets and fishing technology could be developed for non‐conventional species, then it is estimated that the catch could be increased to 42, 000, 000 tons. Rational utilization of the pelagic resources of the Americas necessitates conservational and managerial measures. This in turn calls for international agreements and/or other international arrangements. This paper was presented at the Inter‐American meeting on “Science and Man in the Americas”; in 1973 at Mexico City.  相似文献   
418.
419.
420.
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