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   1839篇
  免费   90篇
  国内免费   85篇
  2014篇
  2024年   3篇
  2023年   23篇
  2022年   14篇
  2021年   42篇
  2020年   38篇
  2019年   49篇
  2018年   45篇
  2017年   45篇
  2016年   41篇
  2015年   54篇
  2014年   66篇
  2013年   145篇
  2012年   46篇
  2011年   75篇
  2010年   47篇
  2009年   83篇
  2008年   115篇
  2007年   92篇
  2006年   97篇
  2005年   90篇
  2004年   83篇
  2003年   81篇
  2002年   66篇
  2001年   55篇
  2000年   62篇
  1999年   47篇
  1998年   39篇
  1997年   27篇
  1996年   32篇
  1995年   34篇
  1994年   15篇
  1993年   27篇
  1992年   21篇
  1991年   16篇
  1990年   20篇
  1989年   28篇
  1988年   25篇
  1987年   18篇
  1986年   25篇
  1985年   14篇
  1984年   8篇
  1983年   6篇
  1982年   11篇
  1981年   4篇
  1980年   4篇
  1979年   12篇
  1978年   3篇
  1977年   6篇
  1976年   6篇
  1975年   3篇
排序方式: 共有2014条查询结果,搜索用时 15 毫秒
41.
A few reports have suggested the possibility that feeding conditions might affect the sexual maturation of free-ranging Japanese monkeys in provisionized troops. In the present study, the sexual maturation of male monkeys at Takasakiyama in 1984, nine years after the start of restriction of artificial feeding, was examined externally and histologically and the results were compared with data obtained in 1971, when artificial foods were abundantly given. Spermatogenesis was not observed in any of the males under 4.5 years old in the present study, whereas it was noted in some premature 3.5-year-old males and in all males over 4.5 years old in the 1971 study. The age of sexual maturation thus rose by one or more years over the 13-year period from 1971 to 1984. The lag in sexual maturation of the males at Takasakiyama in 1984 could have been induced by the restriction of artificial feeding.  相似文献   
42.
A 2‐year study to evaluate the effect of four soil preparation techniques and four species compositions in a pine plantation with an admixture of broad‐leaved trees on the species diversity and structure of ground beetle assemblages (Carabidae) was conducted. The soil preparation techniques were full shallow agricultural plowing (25 cm deep with three variants—plowing, plowing with ridge formation, and plowing with subsoiling) and full deep plowing (50 cm deep). The plantation species compositions were pine 7000/hectare, pine 5500/hectare + broad‐leaved species 1500/hectare, pine 4000/hectare + broad‐leaved species 3000/hectare, and pine 2000/hectare + broad‐leaved species 5000/hectare. Carabidae were sampled monthly with pitfall traps in the plantation from May to November in 2003 and 2004—the fourth and fifth years after afforestation. Only the soil preparation technique affected species diversity. The mean number of carabid species and the Shannon–Wiener index were higher in the case of the full agriculture plowing with subsoiling treatment and the full agriculture plowing with ridge formation than in the full shallow agriculture plowing. The structure of the assemblages was dependent on the soil preparation technique, but not on tree species composition. In general, deep plowing and shallow plowing with subsoiling were conducive to an increase in the proportion of individuals representing late succession species, whereas shallow plowing favored early succession species. The results suggest that for effective plantation of a managed stand, deep plowing or shallow plowing with subsoiling is more beneficial for afforestation of fallow fields than typical shallow agricultural plowing.  相似文献   
43.
Sake is made from steamed rice, malted rice, and water. Sake production begins with the preparation of a small-scale starter (moto); the quality of moto significantly influences the flavor and richness of sake. In the traditional starter, yamahai-moto, the growth of naturally occurring lactic acid bacteria represses the putrefactive micro-organisms, whereas in the modern starter, sokujo-moto, this is achieved by adding lactic acid. In this study, the successive change in bacterial flora of yamahai-moto was analyzed by pyrosequencing 16S ribosomal RNA genes. Lactobacillus was dominant throughout the process (93–98%). Nitrate-reducing bacteria that have been generally assumed to be the first colonizers of yamahai-moto were scarcely found in the early stage, but Lactobacillus acidipiscis dominated. Lactobacillus sakei drastically increased in the middle stage. This is the first report, though one case study, to show how the early stage microbiota in Japanese yamahai-moto is varyingly controlled without nitrate-reducing bacteria using next-generation sequencing.  相似文献   
44.
45.
Brunke AJ  Marshall SA 《ZooKeys》2011,(75):29-68
Staphylinidae (Rove Beetles) from northeastern North America deposited in the University of Guelph Insect Collection (Ontario, Canada) were curated from 2008-2010 by the first author. The identification of this material has resulted in the recognition of thirty-five new provincial or state records, six new Canadian records, one new record for the United States and two new records for eastern Canada. All records are for subfamilies other than Aleocharinae and Pselaphinae, which will be treated in future publications as collaborative projects. Range expansions of ten exotic species to additional provinces and states are reported. The known distributions of each species in northeastern North America are summarized and presented as maps, and those species with a distinctive habitus are illustrated with color photographs. Genitalia and/or secondary sexual characters are illustrated for those species currently only identifiable on the basis of dissected males. The majority of the new records are in groups that have been recently revised, demonstrating the importance of curation and local insect surveys to the understanding of biodiversity, even for taxa and areas considered 'relatively well-known'.  相似文献   
46.
Primary neuroendocrine neoplasm of the liver is extremely rare in both humans and non‐human primates. The present report describes the clinical and pathological findings of an aged Japanese macaque (Macaca fuscata) with hepatic neuroendocrine carcinoma. To our knowledge, this is the first report of hepatic neuroendocrine neoplasm in macaques.  相似文献   
47.
The present study investigated the influence of dominance rank in combination with kinship on age-related differences in social grooming among adult females in a free-ranging group of Japanese monkeys (Macaca fuscata). Eighty-three adult females were divided into six sub-groups according to age-class (younger: 5–9 years old; middle: 10–14 years old; older: 15–22 years old) and dominance rank (high and low rank). The ratio of the number of unrelated females that each female groomed to the total number of available unrelated females and grooming bouts which she gave to unrelated females decreased with increasing age for both high- and low-ranking females, whereas age did not appear to affect corresponding values for related females. On the other hand, compared with low-ranking females, high-ranking females of all age-classes received grooming more often from a larger number of unrelated females. Moreover, older females of low rank received grooming less often from a smaller number of unrelated females than younger females of low rank. These results indicate that with increasing age females are more likely to concentrate on related females when they have grooming interactions with other females. This tendency seems to be more apparent for low-ranking females. Moreover, the present findings also indicate that older high-ranking females could maintain their social attractiveness as high as younger high-ranking females.  相似文献   
48.
目的:旨在探索Ⅰ型日本乙型脑炎病毒传代致弱后基因组突变NS2A-C60A对乙脑病毒生物学特性的影响。方法:首先通过对传代致弱及原始乙脑毒株基因组序列进行测序比对、结构预测分析并利用Western blotting(WB)确定了目标研究位点NS2A-C60A;然后使用反向遗传定点突变技术构建拯救了包含NS2A-C60A单点突变的病毒株;最后利用噬斑形态观察、生长曲线、双萤光素酶分析,WB以及炎性因子检测和动物实验研究了该单点突变对于乙脑病毒生物学特性的影响。结果:首次研究发现Ⅰ型乙脑病毒传代致弱会导致NS1'蛋白表达的显著下降以及可能的相关位点NS2A-C60A,并成功拯救获得了NS2A-C60A单点突变毒株rJEV-C60A,研究发现NS2A-C60A突变对乙脑病毒的生长特性及噬斑形成没有显著影响,但是能够显著降低乙脑病毒NS1'蛋白的表达,并且该位点突变能够轻微阻碍乙脑病毒对细胞炎性因子表达的抑制,动物实验结果显示NS2A-C60A点突变病毒与原毒株具有相似的神经毒力,说明该位点突变不是影响乙脑病毒毒力致弱的关键位点。结论:新发现的NS2A-C60A位点突变能够显著减少乙脑病毒NS1'蛋白的表达,但是对其增殖、诱导炎症及神经毒力等生物学特性没有显著影响。  相似文献   
49.
The Brazilian savanna is the second largest ecosystem in Brazil. It is also one of the most endangered, with only 20% of its habitat remaining unchanged. Agriculture and livestock have been indicated as the main agents of destruction of the Brazilian savanna. Brazilian livestock, for example, is the main reason for cultivation of exotic grasses such as Urochloa spp. (from Africa). Dung beetles are widely used in ecological assessment, mainly because they are recognized as bioindicators of environmental changes. Therefore, efficient sampling is required for any research involving the biodiversity of this group. In order to mitigate the lack of information on efficiency of the attractiveness of baits in the endangered Brazilian savanna and in exotic pasturelands, we sampled dung beetles in four native patches of the Brazilian savanna and in four areas of pastures with Urochloa spp. Dung beetles were captured with pitfall traps baited with carcass, cattle dung, human feces and pig dung, with a total sampling effort of 384 traps. We sampled 7544 individuals belonging to 43 species and 18 genera of dung beetles. Thirty‐eight species were collected in the Brazilian savanna and 24 species in exotic pastureland. In both ecosystems traps baited with human feces sampled greater abundance and species richness of dung beetles when compared with the other three baits used. Our results showed that human feces is a reliable, easy and inexpensive bait to sample greater abundance and species richness of generalist dung beetles in both native and exotic habitats, with clear structural differences.  相似文献   
50.
Japanese encephalitis virus (JEV) is a positive stranded RNA virus that belongs to the flavivirus group. JEV infection damages the central nervous system (CNS) and is one of the main causative agents of acute encephalitis. H-2 restricted virus-specific cytotoxic T lymphocytes (CTL) have been generated specifically against JEV in our laboratory and these CTL have been shown to protect mice against lethal challenge with JEV. Virus replication was found to be inhibited in the brains of animals that were adoptively transferred with JEV specific CTL as revealed by immunohistological staining as well as viral plaque assays. We further show that virus specific CTL could be recovered from such protected mice as long as 45 days after adoptive transfer.  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